JP5150978B2 - High-strength steel with excellent cold forgeability, and excellent strength parts such as screws and bolts or molded parts such as shafts - Google Patents
High-strength steel with excellent cold forgeability, and excellent strength parts such as screws and bolts or molded parts such as shafts Download PDFInfo
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- Metal Rolling (AREA)
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- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Strip Materials And Filament Materials (AREA)
Description
この出願の発明は、冷間圧造性に優れた高強度で且つ高延性を有する鋼、及び当該鋼から製造された高強度を有するねじ及びボルト等の締結部品又は軸類等の成形品に関するものであり、特に、これら鋼及び成形品のそれぞれが具備すべき材質特性及び金属組織等を明確に規定するものである。 The invention of this application relates to high strength and high ductility steel excellent in cold forging, and high-strength screws and bolts, such as screws and bolts manufactured from the steel, or molded articles such as shafts. In particular, it clearly defines the material properties, metal structure, etc. that each of these steels and molded products should have.
従来、鋼線又は鋼棒を冷間圧造、転造及び切削加工等により成形して製造する六角ボルトやその他の比較的高強度の機械構造用部品等は、予め冷間圧造特性を向上させるために、鋼線又は鋼棒を700℃程度の温度で十数時間から一昼夜の長時間加熱に及び、金属組織中のセメンタイトを球状化する、所謂球状化焼なまし処理を施しておくこが必要であり、場合によっては焼入、あるいは焼入・焼戻し等により、材質特性を調整しておくことが必要である。そして、更に冷間圧造成形等により機械構造用部品等に成形した後には、焼入・焼戻し等の調質処理を行なって、強度と靱性を高める必要がある。このように、比較的高強度の機械構造用部品等の製造工程は複雑であり、複数の工程を必要としていた。そのため、熱エネルギーの損失が多く、生産性が低く、また熱処理費用の増加及び納期管理等の点において問題があった。 Conventionally, hexagon bolts and other relatively high-strength mechanical structural parts manufactured by forming steel wire or steel rod by cold forging, rolling, cutting, etc., improve the cold forging characteristics in advance. In addition, it is necessary to apply a so-called spheroidizing annealing process in which a steel wire or a steel rod is heated at a temperature of about 700 ° C. for a long time from a dozen hours to a whole day and night and spheroidizes cementite in the metal structure. In some cases, it is necessary to adjust the material properties by quenching or quenching / tempering. Further, after forming into a machine structural part or the like by cold heading or the like, it is necessary to improve the strength and toughness by performing a tempering treatment such as quenching and tempering. As described above, the manufacturing process of relatively high-strength mechanical structural parts and the like is complicated and requires a plurality of processes. For this reason, there are many heat energy losses, productivity is low, and there are problems in terms of an increase in heat treatment costs and delivery time management.
上記問題点を解決するために、冷間圧造を含む成形をして製品形状にした後には、焼入・焼戻し等の調質処理を施すことなく、最終製品を製造することができる技術が提案されている。例えば、使用する素材として、従来製造されている鋼線又は鋼棒の内、金属組織が焼入・焼戻し組織を有し、その機械的特性値が特定の条件を満たすもの、即ち、降伏強度(YS)と加工硬化指数(n値)との積(YS×n)が、4.0〜11.0kgf/mm2(39.2〜107.9MPa)の範囲内にある鋼線又は鋼棒に限定し、これを素材として用いることにより、これに冷間圧造成形等を施して製品形状に加工した後でも、調質処理を施す必要がないという、冷間圧造特性に優れた調質鋼線又は鋼棒が提案されている(特許文献1)。 In order to solve the above problems, a technology is proposed that can produce a final product without performing tempering treatment such as quenching and tempering after forming into a product shape by forming including cold heading. Has been. For example, as a material to be used, a steel wire or a steel bar that has been manufactured in the past has a metal structure that has a hardened / tempered structure, and its mechanical property value satisfies a specific condition, that is, yield strength ( YS) and a steel wire or steel bar having a product hardening index (n value) (YS × n) in the range of 4.0 to 11.0 kgf / mm 2 (39.2 to 107.9 MPa). By using this as a raw material, it is not necessary to apply a tempering treatment even after it is cold formed and processed into a product shape. Alternatively, a steel bar has been proposed (Patent Document 1).
特許文献1によれば、上記のように降伏強度と加工硬化指数との積が、4.0〜11.0kgf/mm2の範囲内にある鋼線又は鋼棒であれば、特定のVノッチ形状を有する試験片に対して行なった圧縮試験において、当該Vノッチの底面に所定長さ以上の亀裂発生が認められないための限界圧縮率(%)を求め、この限界圧縮率が所定水準値を超えて優れた強度・靱性を有する鋼材の場合には、冷間圧造成形後に調質処理を施す必要がないと提案されている。しかしながら、特許文献1の技術においては、六角ボルト等に冷間圧造するための素材となる鋼線又は鋼棒は、長時間を要する球状化焼なましは不要になるが、冷間圧造をする前の鋼線又は鋼棒に対しては依然として、短時間の焼入・焼戻し処理が必要であることは解消されてない。 According to Patent Document 1, if the product of the yield strength and the work hardening index is in the range of 4.0 to 11.0 kgf / mm 2 as described above, a specific V notch In a compression test performed on a test piece having a shape, a critical compression rate (%) is determined for preventing the occurrence of cracks longer than a predetermined length on the bottom surface of the V-notch, and this critical compression rate is a predetermined standard value. In the case of a steel material having excellent strength and toughness exceeding the above, it is proposed that it is not necessary to perform a tempering treatment after cold forging. However, in the technique of Patent Document 1, the steel wire or the steel rod that is a material for cold forging into a hexagon bolt or the like does not require spheroidizing annealing that requires a long time, but cold forging. The need for a short quenching and tempering treatment for the previous steel wire or bar is still not resolved.
一方、熱間圧延により製造された線材又は棒材の冷間圧造性を向上させるために通常行なわれている当該線材又は棒材に対する球状化焼なましを行なうことなく、冷間加工性に優れた冷間圧造用鋼の製造技術が提案されている(特許文献2)。即ち、鋼中のCをセメンタイト生成温度よりも高温においてFe3C以外の炭化物として生成させることにより、鋼中の固溶C量を実質的に低減させ、変形抵抗、変形能を阻害するセメンタイト、ひいてはパーライトの生成を抑制する一方、初析フェライト量を大幅に増加させ、冷間加工性を大幅に向上させるというものである。具体的には、化学成分組成として、C:0.06〜0.45質量%未満、Si:0.05質量%以下、Mn:0.5〜1.0質量%及びV:0.10〜0.60質量%を含有し、初析フェライトとパーライトとの合計量が、面積率で90%以上であって、しかも初析フェライト量がf(%)=100−125×C(質量%)+22.5×V(質量%)で表わされるfの値以上の面積%(但し、f>100%となるときは、f=100%とする)であり、初析フェライト中にVCが析出している鋼が提案されている。かかる鋼の製造方法として、上記化学成分組成を有する鋼片を、1000から1250℃の加熱をし、仕上温度がAr3点以上、FDTL(℃)=800+190×(C(質量%)+0.5×V(質量%))で表わされるFDTLの値以下の温度で熱間圧延を行ない、圧延終了後、1℃/s以下で冷却するというものである。 On the other hand, it is excellent in cold workability without performing spheroidizing annealing on the wire or bar that is usually performed to improve the cold forging of the wire or bar manufactured by hot rolling. A technology for manufacturing cold forging steel has been proposed (Patent Document 2). That is, by generating C in the steel as a carbide other than Fe 3 C at a temperature higher than the cementite formation temperature, the amount of solid solution C in the steel is substantially reduced, and the cementite that inhibits deformation resistance and deformability, As a result, while suppressing the formation of pearlite, the amount of pro-eutectoid ferrite is greatly increased, and the cold workability is greatly improved. Specifically, as the chemical component composition, C: 0.06 to less than 0.45 mass%, Si: 0.05 mass% or less, Mn: 0.5 to 1.0 mass%, and V: 0.10 The total amount of pro-eutectoid ferrite and pearlite is 90% or more in area ratio, and the pro-eutectoid ferrite amount is f (%) = 100−125 × C (mass%). + 22.5 × V (mass%) The area% is equal to or greater than the value of f (provided that f = 100% when f> 100%), and VC is precipitated in the pro-eutectoid ferrite. Steel has been proposed. As a method for producing such steel, a steel slab having the above chemical composition is heated at 1000 to 1250 ° C., the finishing temperature is Ar3 or higher, FDTL (° C.) = 800 + 190 × (C (mass%) + 0.5 × Hot rolling is performed at a temperature equal to or less than the value of FDTL represented by V (mass%), and cooling is performed at 1 ° C./s or less after the end of rolling.
特許文献2によれば、上記球状化焼なまし処理を省略することはできるが、上記鋼の引張強さは、500MPaまで到達していないので、当該鋼の冷間圧造後の成形品に比較的高強度が要求される場合には、調質処理を必要とする場合がある。また、比較的高価な合金元素であるVの添加を要するので、コスト上昇に繋がる。
さて、機械部品の中でも、ねじ部品に属するおねじ(小ねじ、止めねじ、タッピンねじ)又は木ねじ等のねじ並びにボルトは、従来、所定の化学成分組成を有する鋼片等に所定の熱間加工を施して所定の断面形状の鋼線又は鋼棒を製造し、この鋼線又は鋼棒を球状化焼なまし処理して成形性を向上させた素材とし、所定の冷間圧造及び転造、冷間圧造と切削加工、又は切削加工主体の成形加工によって製品形状に成形される。次いで、製品規格に応じた所定の調質処理を施して機械的性質を向上させ、適宜表面処理を施して製品とする。 Now, among mechanical parts, screws and bolts such as male screws (set screws, set screws, tapping screws) or wood screws belonging to threaded parts are conventionally hot-worked into steel pieces having a predetermined chemical composition. To produce a steel wire or a steel bar having a predetermined cross-sectional shape, a steel wire or a steel bar is subjected to spheroidizing annealing to improve the formability, a predetermined cold forging and rolling, It is formed into a product shape by cold forging and cutting, or by molding mainly of the cutting process. Next, a predetermined tempering treatment according to the product standard is performed to improve mechanical properties, and a surface treatment is appropriately performed to obtain a product.
図11に、鋼片1等からねじ及びボルト等の締結部品又は軸類等の成形品7が製造されるまでの、従来の製造工程の概略フロー図を例示する。ここで、鋼片の化学成分組成は、所望の製品規格に応じた適切なものに規制する。鋼片1を熱間圧延又は熱間鍛造2aにより半製品3に加工し、次いで更に、熱間圧延又は熱間鍛造2bにより鋼線又は鋼棒4に加工する。得られた鋼線又は鋼棒4の強度向上のための焼入・焼戻し等、あるいは、次工程での冷間圧造時の材料の成形性、例えばねじ頭部のリセス成形時の割れ発生を防止するために、材料を軟化させるための球状化焼なまし等の熱処理5を行なう。こうして所要の機械的性質が付与された材料を、冷間圧造及び転造等6によりねじ及びボルト等の締結部品又は軸類等に成形する。なお、各種の軸類を製造する場合は、切削加工25により成形することが多い。従って、この場合には線材又は棒材から成形品7への歩留は極めて低下し、例えば60〜65%程度まで低下する。 FIG. 11 illustrates a schematic flow diagram of a conventional manufacturing process until a molded product 7 such as a fastening part such as a screw and a bolt or a shaft is manufactured from the steel piece 1 or the like. Here, the chemical composition of the steel slab is regulated to an appropriate one according to a desired product standard. The steel slab 1 is processed into a semi-finished product 3 by hot rolling or hot forging 2a, and then further processed into a steel wire or steel bar 4 by hot rolling or hot forging 2b. Quenching and tempering to improve the strength of the steel wire or steel bar 4 obtained, or formability of the material during cold heading in the next process, for example, preventing cracking during recess molding of the screw head For this purpose, a heat treatment 5 such as spheroidizing annealing is performed to soften the material. In this way, the material provided with the required mechanical properties is formed into fastening parts such as screws and bolts or shafts by cold forging and rolling 6 or the like. In addition, when manufacturing various shafts, it is often formed by the cutting process 25. Therefore, in this case, the yield from the wire or bar to the molded product 7 is extremely reduced, for example, about 60 to 65%.
こうして得られた種々の成形品7に対して更に適切な調質処理8を施すことにより所要の機械的性質を付与する。次いで、適宜表面処理9を施して製品10とする。 Necessary mechanical properties are imparted to the various molded articles 7 thus obtained by further appropriate tempering treatment 8. Next, a surface treatment 9 is appropriately performed to obtain a product 10.
上記製造工程における冷間圧造及び転造6は、一般に素材使用量に無駄がなく、成品の寸法精度が良好であり、機械的性質が向上し、また表面粗度が良好であるといった特徴を有する。従って、特に軸類の成形加工において、切削加工工程の主体部分の代わりに冷間圧造工程を適用すれば、その成形加工歩留は飛躍的に向上する。 The cold forging and rolling 6 in the above manufacturing process generally has the characteristics that there is no waste in the amount of material used, the dimensional accuracy of the product is good, the mechanical properties are improved, and the surface roughness is good. . Therefore, particularly in the forming of shafts, if the cold forging process is applied instead of the main part of the cutting process, the forming yield is dramatically improved.
次に、ねじの例として冷間圧造により、小ねじの頭部を成形する場合のヘッダー加工方法を説明する概念図を図12に例示する。これは2段打ちヘッダー(ダブルヘッダー)の例であり、1個のダイス11と2個のパンチ12a、12bとの組合わせにより成形するものである。素材である鋼線を所要長さに切断し、同図(a)に示すように、切断された鋼線(材料)13を第一パンチ(予備据込みパンチ)12aでダイス11の中に押出し、頭部を含めた一次成形をして予備成形品に成形し、次いで同図(b)に示すように、第二パンチ(仕上げ据込みパンチ)12bを押出して、ねじの外形に中間成形すると共に、ダイス11の中の中間成形品16の頭部14に、第二パンチ12bにより十字形状等のリセス(ドライバーにより当該ねじを締め込むための十字形状等の窪み部)を形成させる。同図(c)に、頭部14にリセス15が成形加工された中間成形品17の概略斜視図例を示す。このリセス15の成形加工時には、頭頂部に対して形態が複雑な大変形加工が施される。そのため、この頭頂部の材質特性として、高延性が具備されていない場合には、リセス成形時に当該部分に割れや亀裂が発生する。このリセス割れが発生したねじ及びボルト等の締結部品又は軸類等の成形品は、成品に修復することはできない。 Next, FIG. 12 illustrates a conceptual diagram for explaining a header processing method in the case of forming a head of a small screw by cold heading as an example of a screw. This is an example of a double-stepped header (double header), which is formed by combining one die 11 and two punches 12a and 12b. A steel wire as a raw material is cut to a required length, and the cut steel wire (material) 13 is extruded into a die 11 with a first punch (preliminary upsetting punch) 12a as shown in FIG. Then, primary molding including the head is performed to form a preformed product, and then, as shown in FIG. 4B, a second punch (finish upsetting punch) 12b is extruded to form an outer shape of the screw. At the same time, a recess having a cross shape or the like (a hollow portion having a cross shape or the like for tightening the screw with a screwdriver) is formed on the head 14 of the intermediate molded product 16 in the die 11 by the second punch 12b. FIG. 2C shows an example of a schematic perspective view of an intermediate molded product 17 in which a recess 15 is molded on the head 14. At the time of forming the recess 15, a large deformation process having a complicated shape is applied to the top of the head. For this reason, as a material characteristic of the crown, when high ductility is not provided, cracks or cracks occur in the portion during recess molding. Fastened parts such as screws and bolts or molded parts such as shafts in which the recess cracks have occurred cannot be restored into finished products.
そこで、従来このリセス割れを発生させないようにするために、鋼線を軟化させる、例えば、球状化焼なましによりその引張強さを500MPa程度以下に抑えるといった材料強度の最大値を制限する方法が採られている。しかしながら、このように線材(材料)の強度を制限すると、かかる材料強度の線材からねじ等を成形したのでは、このままでは所望の機械的性質、特に強度を満たすねじ等を製造することはできないので、リセス成形後の転造成形によりねじ部を形成させ、ねじ等の外形を形成させた後、焼入・焼戻し等の調質処理を施して、その機械的性質を所要値まで向上させた後に、製品ラインに送り出し、必要に応じてめっき等の表面処理を施す。 Therefore, in order to prevent the occurrence of recess cracks in the past, there is a method of limiting the maximum material strength such as softening the steel wire, for example, suppressing the tensile strength to about 500 MPa or less by spheroidizing annealing. It is taken. However, if the strength of the wire (material) is limited in this way, if a screw or the like is formed from the wire having such a material strength, a screw or the like that satisfies the desired mechanical properties, particularly strength, cannot be produced as it is. After forming the threaded part by roll forming after recess molding and forming the outer shape of the screw, etc., after applying tempering treatment such as quenching and tempering, and improving its mechanical properties to the required value The product is sent to the product line and surface treatment such as plating is performed as necessary.
ところで、このリセス割れ発生の傾向は、一般に素材の強度ないし硬さが大きく、且つ延性に優れない材料ほど大きくなる。従って、このようなリセスの成形加工を伴う用途に供されてもリセス割れが発生せず、しかもねじ部の転造成形後に焼入・焼戻し処理等の調質処理を施す必要のない小ねじ製品の素材としての鋼線等には、高水準の延性が備わっていることに加えて、所望のねじ等の規格を満たすための高強度が備わっていることが必須の要件である。 By the way, the tendency of the occurrence of the recess crack is generally increased as the strength or hardness of the material is large and the material is not excellent in ductility. Therefore, even if it is used in applications involving such recess forming, recess cracks do not occur, and it is not necessary to apply tempering treatment such as quenching and tempering after the thread rolling In addition to having a high level of ductility, it is an essential requirement that the steel wire or the like as the material has a high strength to satisfy the standard of a desired screw or the like.
そこで、従来リセス割れが発生したり、あるいはこれに類似の欠陥が発生するようなねじ及びボルト等の締結部品又は軸類等の成形品を製造する場合には、上述した冷間圧造において発生するリセス割れないしその類似欠陥が発生しないようにするために、予め図11に示した鋼片1等の化学成分組成としてコスト上昇につながることを容認の上、所定の合金元素の添加をする成分設計をしたり、ねじ及びボルト等の締結部品又は軸類等の成形品7の素材となる鋼線又は鋼棒4の製造条件を制御し、更に、ねじ部を転造又は切削加工により成形した後に、焼入ないし窒化焼入・焼戻し等の調質処理8を施して、強度及び靭性等の向上を図っている。 Therefore, in the case of manufacturing a fastening part such as a screw and a bolt or a molded product such as a shaft that causes a recess crack or a similar defect, it occurs in the cold forging described above. In order to prevent the occurrence of recess cracks or similar defects, it is possible to increase the cost as the chemical composition of the steel slab 1 shown in FIG. After controlling the manufacturing conditions of the steel wire or the steel rod 4 as the material of the molded product 7 such as the fastening parts such as screws and bolts or shafts, and further forming the threaded portion by rolling or cutting. Tempering treatment 8 such as quenching or nitriding quenching / tempering is applied to improve strength and toughness.
また、軸類の製造についても、現在、冷間鍛造工程又はこれと切削工程で製造されているが、現状では軟化焼なましを必要とする場合が多く、その省略要請が強い。 Also, shafts are currently manufactured in the cold forging process or this and the cutting process, but at present there are many cases where softening annealing is required, and there is a strong demand for their omission.
上述したように、素材である鋼線又は鋼棒(線材又は棒材)の段階において球状化焼なまし処理を施し、これを冷間圧造及び転造若しくは切削加工等で成形加工後、更に調質処理を施すとなると、それだけエネルギーコスト等がかかり、また切削加工による歩留低下、ラインの複雑化、製造工程数の増加をきたし、製造納期の短縮化が困難となり、また製造ラインの保全費用も上昇する。ところが、従来技術によれば、特許文献1の技術にみられるように、冷間圧造によりボルト等に成形後、調質処理を施すことなく、目的とする用途に供することができるようにするために、長時間を要する球状化焼なまし処理よりは製造工程上有利な焼入・焼戻し処理を鋼線又は鋼棒に対して施し、得られた線材又は棒材で、材質パラメータ:降伏強度と加工硬化指数との積(YS×n)が、4.0〜11.0kgf/mm2(39.2〜107.9MPa)の範囲内にあるものを用いるという技術が開示されている。しかしながら、特許文献1の技術においても、このように依然として、鋼線又は鋼棒の段階における焼入・焼戻し処理を必要としている。また、上記パラメータ(YS×n)と、リセス割れないしその類似欠陥の不発生との間に、明確な関係があるかどうかについても疑問である。その理由は、上記パラメータ(YS×n)は、降伏強さ・加工硬化バランス性を表わすパラメータであるのに対して、リセス割れないしその類似欠陥の不発生要件は、延性を表わすパラメータにより表わされるものであることを、この出願の発明者等は新たに知見したからである。 As described above, spheroidizing annealing is applied at the stage of the steel wire or steel bar (wire or bar), which is the raw material, and this is further processed after cold forming and rolling or cutting. If quality treatment is applied, energy costs will increase, and the yield will be reduced by cutting, the line will become complicated, the number of manufacturing processes will increase, making it difficult to shorten the production delivery time, and maintenance costs for the production line. Also rises. However, according to the prior art, as seen in the technique of Patent Document 1, after being formed into a bolt or the like by cold heading, it can be used for the intended application without being subjected to a tempering treatment. In addition, the steel wire or bar is subjected to quenching and tempering, which is more advantageous in the manufacturing process than spheroidizing annealing, which takes a long time, and the obtained wire or bar has a material parameter: yield strength and A technique is disclosed in which a product having a work hardening index (YS × n) within a range of 4.0 to 11.0 kgf / mm 2 (39.2 to 107.9 MPa) is used. However, the technique of Patent Document 1 still requires a quenching / tempering process at the stage of the steel wire or the steel bar. It is also questionable whether there is a clear relationship between the parameter (YS × n) and the occurrence of recess cracks or similar defects. The reason is that the parameter (YS × n) is a parameter representing yield strength and work-hardening balance, whereas the non-occurrence requirement for recess cracks or similar defects is represented by a parameter representing ductility. This is because the inventors of this application have newly found out that it is.
更に、リセスにも種々の形状のものがあるので、リセス割れないしその類似欠陥の発生を抑止するための鋼ないし線材又は棒材についても、ねじ等の製品規格の所定強度水準に応じて、種々の水準の強度を有する材料が必要であり、しかも冷間圧造性に優れたものが必要となる。 Furthermore, since there are various types of recesses, steel, wire, or rods for suppressing the occurrence of recess cracks or similar defects are also various depending on the specified strength level of product standards such as screws. A material having a strength of the above level is required, and a material excellent in cold heading is required.
一方、特許文献2の技術により、高強度ねじ等の製造に対して、鋼線又は鋼棒に加工した後の球状化焼なまし処理は不要である冷間圧造性に優れた鋼が得られるが、しかしこれには強度水準に限界があり、例えば引張強さは同文献(実施例、表3)によれば440MPa程度であり、種々の一層高強度水準を要するねじ等の材料としては満足できない。 On the other hand, with the technique of Patent Document 2, a steel excellent in cold heading property that does not require spheroidizing annealing after being processed into a steel wire or a steel rod is obtained for the production of high-strength screws and the like. However, there is a limit to the strength level. For example, the tensile strength is about 440 MPa according to the same document (Example, Table 3), and it is satisfactory as a material such as a screw that requires various higher strength levels. Can not.
そこで、この出願の発明においては、鋼線又は鋼棒に加工した後、これに熱処理を施さずに冷間圧造及び転造若しくは切削加工又は切削主体の加工等によりねじ及びボルト等の締結部品又は軸類等の成形品に成形しても、リセス割れないしその類似欠陥が発生することなく、しかもこの冷間圧造等による成形後のねじ及びボルト等の締結部品又は軸類等の成形品に調質処理を施さなくても、鋼線又は鋼棒の段階で既に所望の高水準強度を有するという線材又は棒材、更に広範囲に当該棒材又は線材を含む鋼を提供し、また、当該線材若しくは棒材又は鋼を利用した高強度のねじ及びボルト等の締結部品又は軸類等の成形品を提供することを課題としている。 Therefore, in the invention of this application, after being processed into a steel wire or a steel bar, a fastening part such as a screw and a bolt or the like by cold forging and rolling or cutting or cutting main processing without being subjected to heat treatment or Even if it is molded into molded parts such as shafts, recess cracks or similar defects do not occur, and it is possible to adjust to molded parts such as screws and bolts or shafts after molding by cold forging. Without any quality treatment, the present invention provides a wire or bar that already has a desired high level strength at the stage of a steel wire or bar, and a steel containing the bar or wire in a wide range. It is an object of the present invention to provide a fastening part such as a high-strength screw and bolt or a molded product such as a shaft using a bar or steel.
なお、これ以後の発明に関する記述においては、鋼線又は鋼棒とは圧延等のままのものを指し、線材又は棒材とは広義の調質処理が施されているか否かを問わず、次工程における成形用材料として供給するために適切な材質特性を有するもの(材料)を指すものとする。 In the following description of the invention, the steel wire or steel bar refers to the one that is still rolled or the like, and the wire or bar is the following regardless of whether or not a tempering treatment is applied in a broad sense. A material (material) having an appropriate material characteristic to be supplied as a molding material in the process shall be indicated.
上記の課題を解決するために、この出願の発明者等は鋭意研究を重ねた。先ず、発明者等は、この発明が提供すべき線材若しくは棒材又は鋼は、化学成分組成、金属組織及び機械的性質は特性的に、如何なる条件を満たしているものであることが必要かについて検討した。その結果、それらは、先ず、化学成分組成に関して
C:セメンタイトが析出しない炭素量以下であること、機械的特性に関して、引張強さが製造目標とする最終製品種別の規格を満たしていること、特にこの発明においては、引張強さが600MPa以上を有することを前提条件とし、その上で、特に決定的に重要な因子は絞りの水準であって、材料の絞りが70%以上であることが必要であることを知見した。また、引張強さが更に高い795MPaであっても、絞りが78%以上を満たすものが得られれば、一層望ましいことを知見した。そして、本発明者等は、かかる機械的性質をその鋼に具備させるためには、金属組織がフェライトのみであり、セメンタイトの体積%が0であって、圧延方向に垂直な断面における平均粒径が1μm以下のフェライト組織であることが必要であることを知見したのである。
また、上記機械的性質を備えた鋼を材料として圧造により成形加工することが容易であること、そしてこうして造られた成形品には材料が有していた機械的性質を持っていることもわかった。従って、上記材料に予め球状化焼なまし処理を施しておく必要はないことも明らかである。
In order to solve the above-mentioned problems, the inventors of this application conducted extensive research. First, the inventors have determined whether the wire, rod, or steel to be provided by the present invention must satisfy the conditions in terms of chemical composition, metallographic structure, and mechanical properties. investigated. As a result, first, regarding the chemical composition, C: the amount of carbon below which cementite does not precipitate, and the mechanical properties, the tensile strength meets the specifications of the final product type targeted for production, especially In this invention, it is a precondition that the tensile strength is 600 MPa or more, and on that basis, a particularly important factor is the level of drawing, and the drawing of the material needs to be 70% or more. I found out. Further, it has been found that even if the tensile strength is 795 MPa, which is even higher, it would be more desirable if a drawing with a drawing satisfying 78% or more was obtained. In order to provide the steel with such mechanical properties, the present inventors have an average particle diameter in a cross section perpendicular to the rolling direction, in which the metal structure is only ferrite and the volume percent of cementite is 0. Is found to be required to have a ferrite structure of 1 μm or less.
It is also clear that steel with the above mechanical properties can be easily molded by forging, and that the molded product thus produced has the mechanical properties that the material had. It was. Therefore, it is clear that it is not necessary to subject the material to spheroidizing annealing in advance.
そして、上述した金属組織及び機械的性質を備えた鋼を製造する効果的な方法の重要条件は、鋼片又は鋼材に対して所定の温度範囲内の温間領域において、所定値以上の総減面率となる圧下を加えるか、又は所定値以上の平均塑性ひずみを導入することであることを知見した。但し、ここで温間圧延、更には温間加工とは、圧延ないし加工温度が350〜800℃の範囲内における圧延を指すものとし、この温度範囲を超える温度での圧延ないし加工を熱間圧延ないし熱間加工という。以下の記載においても同様である。 And the important condition of the effective method for producing the steel having the above-mentioned metal structure and mechanical properties is that the total reduction of a predetermined value or more in the warm region within the predetermined temperature range with respect to the steel slab or the steel material. It has been found that a reduction to an area ratio is applied or an average plastic strain of a predetermined value or more is introduced. However, here, warm rolling, and further warm processing, refers to rolling or rolling within a temperature range of 350 to 800 ° C, and rolling or processing at a temperature exceeding this temperature range is hot rolling. Also called hot working. The same applies to the following description.
この出願の発明は、上記知見に基づき完成されたものである。その要旨は以下の通りである。 The invention of this application has been completed based on the above findings. The summary is as follows.
請求項1に記載の発明に係る冷間圧造用鋼は、下記化学成分組成:
C:0.01質量%未満、
Si:2.0質量%以下、
Mn:3.0質量%以下、
P:0ないし0.2質量%以下、
S:0.03質量%以下、
Al:0.1質量%以下、及び
N:0.02質量%以下を有し、残部がFe及び不可避不純物からなり、セメンタイトの体積分率が0%であるフェライト組織であって、前記フェライト組織は、圧延方向に垂直な断面の平均粒径が1μm以下のフェライト組織であり、引張強さTSが600MPa以上で且つ絞りRAが70%以上の機械的性質を有し、球状化焼なまし処理が施されていないことに特徴を有するものである。
The cold forging steel according to the invention of claim 1 has the following chemical composition:
C: less than 0.01% by mass,
Si: 2.0 mass% or less,
Mn: 3.0% by mass or less,
P: 0 to 0.2% by mass or less,
S: 0.03 mass% or less,
Al: 0.1% by mass or less, and
N: a ferrite structure having 0.02% by mass or less, the balance being Fe and inevitable impurities, and a volume fraction of cementite being 0%, wherein the ferrite structure is an average of a cross section perpendicular to the rolling direction It has a ferrite structure with a grain size of 1 μm or less, has a mechanical property of a tensile strength TS of 600 MPa or more and a drawing RA of 70% or more, and is characterized by no spheroidizing annealing treatment. Is.
請求項2に記載の発明に係るねじ及びボルトの締結部品又は軸類の成形品は、請求項1に記載の冷間圧造用鋼で、圧造を含む加工方法により製造されたものであることに特徴を有するものである。
A screw and bolt fastening part or a shaft molded product according to the invention described in claim 2 is the cold forging steel according to claim 1 and manufactured by a processing method including forging. It has characteristics.
ここで、この鋼を構成するフェライトの形状は、当該鋼が温間圧延温度域の低温領域、例えば500℃で圧延された場合には、等軸粒と伸長粒とが混在する場合がある。この混在状態が存在しても、この発明においては差し支えない。このような場合でも、上記フェライトの平均粒径は、圧延方向に垂直な断面における平均粒径を求めればよい。 Here, the shape of the ferrite constituting the steel may be a mixture of equiaxed grains and elongated grains when the steel is rolled in a low temperature region of the warm rolling temperature range, for example, 500 ° C. Even if this mixed state exists, there is no problem in the present invention. Even in such a case, the average grain size of the ferrite may be obtained by obtaining the average grain size in a cross section perpendicular to the rolling direction.
この出願の発明によれば、従来よりも設備コスト及びランニングコストが低く、簡素化された製造ラインにより工程管理が改善され、特に軸類の成形品においては成形加工歩留の飛躍的向上が可能となり、更に省エネルギーに寄与し得る、高強度で且つ冷間圧造性に優れた鋼及び強度に優れたねじ及びボルト等の締結部品又は軸類等の成形品、並びにこれらの製造方法を提供することができ、工業上極めて有益な効果がもたらされる。 According to the invention of this application, the facility cost and the running cost are lower than before, and the process management is improved by the simplified production line. In particular, in the molded products of shafts, the molding process yield can be dramatically improved. The present invention provides a high-strength and cold-forgeable steel that can further contribute to energy saving, and a molded part such as screws and bolts, such as screws and bolts that are excellent in strength, or shafts, and a method for producing these. This can provide a very beneficial industrial effect.
次に、この発明の実施形態とともに当該実施形態における態様の限定理由について説明する。
[1] この発明に係る冷間圧造用鋼、並びに、この発明に係るねじ及びボルト等の締結部品又は軸類等の成形品
始めに、この発明に係る冷間圧造用鋼、並びに、この発明に係るねじ及びボルト等の締結部品又は軸類等の成形品の実施形態について述べる。
Next, the reason for limitation of the aspect in the embodiment will be described together with the embodiment of the present invention.
[1] Cold forging steel according to the present invention, fasteners such as screws and bolts according to the present invention or molded products such as shafts, cold forging steel according to the present invention, and the present invention Embodiments of fastening parts such as screws and bolts or molded products such as shafts according to the above will be described.
[1−1] この発明に係る冷間圧造用鋼
先ず、この発明に係る冷間圧造用鋼が具備すべき金属組織及び材質特性等の実施形態について述べる。この発明に係る冷間圧造用鋼は、高強度で且つ冷間圧造性に優れた高強度且つ高延性を備えた鋼等であって、金属組織の形態及び機械的性質の特性の両方を前述した通りに定量的に規定することを基本とするものである。以下、具体的に説明する。
[1-1] Cold forging steel according to the present invention First, embodiments of the metal structure and material characteristics, etc. that the cold forging steel according to the present invention should have will be described. The steel for cold forging according to the present invention is a steel having high strength and high ductility that has high strength and excellent cold forging, and has both the form of the metal structure and the characteristics of the mechanical properties. It is based on defining quantitatively as described. This will be specifically described below.
(1)C:セメンタイトが析出しない炭素量以下であること。
この発明に係る鋼等の冷間圧造性を優位に確保するために、特に絞り特性が重要である。一方、強度確保の重要な手段として、C含有量の調整の他に、主相のフェライト粒径の制御により行なうことができる。この観点から、C含有量は0.01質量%以下とすることが望ましい。
(1) C: Less than the amount of carbon in which cementite does not precipitate.
In order to preferentially secure the cold heading properties of steel or the like according to the present invention, drawing characteristics are particularly important. On the other hand, as an important means for ensuring the strength, in addition to the adjustment of the C content, it can be performed by controlling the ferrite grain size of the main phase. In this respect, the C content is preferably 0.01% by mass or less.
(2)〔絞り:70%以上、引張強さ:600MPa以上〕
この出願の発明に係る鋼等は、その用途が比較的強度を要する機械用部品であること、特に高強度を備え、且つ厳しい成形加工に耐えることができる冷間圧造性に優れたものであることを要することから、高強度と高延性との両者をバランスよく備えた鋼等とする必要がある。強度水準を引張強さで600MPa以上に設定し、且つ延性水準を絞りで78%以上に規定する。
優れた延性を確保するためには、一般に伸び又は絞りの値が高いことは重要な因子である。しかし、引張強さが600MPaというかなり強度が高い水準の材料に対して、冷間圧造により変形が複雑で且つ厳しい条件の成形加工が行なわれる場合、例えば、JIS規格のM1.6(ねじの呼び径d:1.6mm)なべ小ねじで、強度区分が6.8以上のものの頭頂面にリセスを冷間圧造する場合に、リセス割れ発生防止に有効な延性水準は、材料の絞りは65%以上が必要である。この場合、リセス割れ発生と材料の伸びとの間には良好な相関関係はなく、その割れ発生を材料の伸びの値で予測することは困難であることを、先ず発明者等は知見した。図1は、そのような例を示すものであり、Si−Mn系炭素鋼素材に対して、温間温度域における多方向への多パス圧延により、総減面率Rが90%以上の試験における試験材の引張試験による引張強さと伸びとの関係を示すグラフにおいて、M1.6なべ小ねじの冷間圧造によるリセス成形時の割れ発生の無し(○印)と有り(×印)の結果例を示す図である。そして、更に材料強度の高いものが必要となり、引張強さで800MPa以上を要する場合(例えば、JIS規格のM1.6なべ小ねじで、強度区分が8.8以上の場合)には、上述したような冷間圧造性を確保するためには、絞りが70%以上であることが望ましい。但し、小ねじのリセス形状は常に一定であるとは限らない。従って、種々形状のリセスを想定し、特に、ねじの頭頂面の面積に対するリセスの占有面積との比が大きいほど、リセス割れが発生し易い点に留意し、要求すべき強度及び絞り水準が必要且つ十分なものとなるように鋼等を設計すべきである。
(2) [drawing: 70% or more, tensile strength: 600 MPa or more]
The steel and the like according to the invention of this application is a machine part that requires relatively strong use, and particularly has high strength and is excellent in cold heading that can withstand severe forming processes. Therefore, it is necessary to use steel having a good balance between high strength and high ductility. The strength level is set to 600 MPa or more in terms of tensile strength, and the ductility level is specified to be 78% or more by drawing.
In order to ensure excellent ductility, a high elongation or drawing value is generally an important factor. However, when a material having a high tensile strength of 600 MPa is deformed by cold forging and is subjected to molding under severe conditions, for example, JIS standard M1.6 (Nominal of screw) (Diameter: 1.6 mm) When a recess is cold-formed on the top of the head of a pan head screw with a strength class of 6.8 or more, the ductility level effective for preventing the occurrence of recess cracking is 65% for material drawing. The above is necessary. In this case, the inventors first found out that there is no good correlation between the occurrence of the recess crack and the elongation of the material, and it is difficult to predict the occurrence of the crack with the value of the elongation of the material. FIG. 1 shows such an example. A test in which the total area reduction ratio R is 90% or more by multi-pass rolling in multiple directions in a warm temperature range for a Si—Mn based carbon steel material. In the graph showing the relationship between tensile strength and elongation by tensile test of test materials in, results of no cracking (○ mark) and presence (× mark) during recess forming by cold heading of M1.6 pan head screw It is a figure which shows an example. Further, when a material with higher material strength is required and a tensile strength of 800 MPa or more is required (for example, when the strength classification is 8.8 or more with a JIS standard M1.6 pan head screw), the above-mentioned is required. In order to ensure such cold heading, it is desirable that the drawing be 70% or more. However, the recess shape of the machine screw is not always constant. Therefore, assuming various shapes of recesses, it should be noted that the greater the ratio of the occupied area of the recess to the area of the top surface of the screw, the easier the cracking occurs, and the required strength and drawing level are required. And steel should be designed to be sufficient.
上記の高強度で且つ冷間圧造性に優れた鋼等、即ち、高強度且つ高延性をバランスよく備えた鋼等は、下記の場合には必要不可欠ともなる。小ねじ等を製造する場合、リセス割れ等の冷間圧造割れ発生を回避するために、比較的軟質な鋼を素材として用い、冷間圧造によるヘッダー加工でリセスを成形し、ねじ部を転造成形した後に、焼入又は浸炭焼入・焼戻し等の調質処理により、ねじの機械的性質を向上させようとしても、ねじの軸径が2.0mm以下の小ねじ等を製造する場合には、焼入後の残留応力又は浸炭焼入の場合の浸炭層の深さと、ねじ径やねじ山の大きさとの関係により、焼入等の熱処理が困難な場合がある。特に、ねじの軸径が1mm以下の場合、又は長尺ものの場合は、焼入・焼戻しに伴う変形により、機械部品として使用することができないこともある。このような微小部材の製造においては、この発明に係る鋼等の供給は極めて有効なものとなる。また、上記の如き焼入・焼戻し等の調質処理を施すことができる場合であっても、この発明に係る鋼等であれば、そのような煩雑な調質処理が不要となるので、コストダウンや生産性の向上等、大きな効果が発揮される。 The above steel having high strength and excellent cold forgeability, that is, steel having high strength and high ductility in a well-balanced manner is indispensable in the following cases. When manufacturing small screws, etc., in order to avoid the occurrence of cold forging cracks such as recess cracks, relatively soft steel is used as the material, the recess is formed by header processing by cold forging, and the threaded portion is rolled. If you want to improve the mechanical properties of the screw by tempering such as quenching or carburizing quenching and tempering after forming, when manufacturing small screws with a screw shaft diameter of 2.0 mm or less Depending on the relationship between the residual stress after quenching or the depth of the carburized layer in the case of carburizing and quenching, and the screw diameter and thread size, heat treatment such as quenching may be difficult. In particular, when the screw shaft diameter is 1 mm or less, or a long screw, it may not be used as a machine part due to deformation accompanying quenching and tempering. In the manufacture of such a micro member, the supply of steel and the like according to the present invention is extremely effective. Further, even if the tempering treatment such as quenching and tempering can be performed as described above, the steel or the like according to the present invention eliminates the need for such a complicated tempering treatment. Great effects such as down and productivity improvement are exhibited.
なお、上記JISに規定されたボルト・小ねじにおいて、強度区分の表記「8.8」は、左側の「8」が呼び引張強さ800MPaの1/100の数値を、右側の「8」が呼び下降伏点又は呼び耐力640MPaと呼び引張強さ800MPaとの比の10倍の数値を表わし、両者を「.」で挟んで表記したものである。 In the bolts and small screws specified in the above JIS, the strength classification “8.8” indicates that the left “8” is 1/100 of the tensile strength of 800 MPa, and the right “8” The numerical value is 10 times the ratio of the nominal lowering yield point or nominal yield strength of 640 MPa and the nominal tensile strength of 800 MPa.
(3)〔第1相:フェライト組織で、圧延方向に垂直な断面組織のフェライト平均粒径が1μm以下とする鋼等〕
この出願の発明に係る鋼等では、当該鋼等の金属組織の形態として、フェライト粒からなる単相組織を有することを必須要件としている。本発明者等は、相変態による強化機構を全く利用せずに鋼等の高強度化を実現する方法として、結晶粒の微細化を図る方法を採ることにした。その際、得られる鋼等の絞りを高水準に確保することが、前記冷間圧造におけるリセス割れ発生防止等の前提条件であることを、本発明者等は今回新たに知見した。そこで、鋼の化学成分組成を種々変化させたSi−Mn系炭素鋼(但し、Feの結晶構造はbccである)に対して、大ひずみ導入の温間多方向の多パス圧延の試験を行なった。この試験結果より、フェライト平均粒径dと引張強さTSとの関係を整理すると、図2が得られる。
(3) [First phase: steel having a ferrite structure with a ferrite average grain size of 1 μm or less in a cross-sectional structure perpendicular to the rolling direction]
In the steel and the like according to the invention of this application, it is an essential requirement to have a single-phase structure composed of ferrite grains as the form of the metal structure of the steel or the like. The present inventors have decided to adopt a method of refining crystal grains as a method of realizing high strength of steel or the like without using any strengthening mechanism by phase transformation. At this time, the present inventors have newly found out that securing the drawing of the obtained steel or the like at a high level is a precondition for preventing the occurrence of recess cracking in the cold heading. Therefore, a test of warm multi-directional multi-pass rolling with a large strain introduced was performed on Si-Mn carbon steel (however, the crystal structure of Fe is bcc) with various chemical composition compositions of steel. It was. From this test result, FIG. 2 is obtained by arranging the relationship between the ferrite average particle diameter d and the tensile strength TS.
図2の結果より、圧延方向に垂直な断面組織の平均粒径が2μm以下のフェライト組織を主相とする鋼であれば、引張強さは600MPa以上が得られており、また、上記平均粒径が(0.7〜1)μm以下のフェライト組織を主相とする鋼であれば、引張強さは800MPa以上が得られている。 From the results shown in FIG. 2, the tensile strength of 600 MPa or more is obtained if the steel has a ferrite structure whose average grain size of the cross-sectional structure perpendicular to the rolling direction is 2 μm or less. If the steel has a ferrite phase with a diameter of (0.7 to 1) μm or less as a main phase, a tensile strength of 800 MPa or more is obtained.
更に、上記において、フェライト粒が一方向に伸長した粒形態が混在していても、圧延方向に垂直な断面組織の平均粒径が2μm以下であれば、引張強さTS=600MPa以上が得られ、また圧延方向に垂直な断面組織の平均粒径が(0.7〜1)μm以下であれば、引張強さTS=800MPa以上が得られることがわかった。 Furthermore, in the above, even if the grain shape in which the ferrite grains are elongated in one direction is mixed, if the average grain size of the cross-sectional structure perpendicular to the rolling direction is 2 μm or less, the tensile strength TS = 600 MPa or more is obtained. It was also found that when the average grain size of the cross-sectional structure perpendicular to the rolling direction is (0.7 to 1) μm or less, a tensile strength TS = 800 MPa or more can be obtained.
次に、Si−Mn系炭素鋼素材に対して、温間温度域における多方向への多パス圧延により、総減面率Rが90%以上の試験により得られた、上述したフェライト粒径を有する試験材の引張試験による引張強さと絞りとの関係をプロットし、一方、これらの試験材に対するM1.6なべ小ねじの冷間圧造によるリセス成形試験を行ない、リセスの割れ発生の有無を試験した。その結果を、図3に示す。図3によれば、引張強さが600MPa以上であっても、絞りRAが65%以上であれば、リセス割れは発生していない。更に、引張強さが800MPa以上のものであるにも関わらず、絞りRAが更に上昇して80%以上の鋼が得られており、この場合にもリセス割れが発生していない。 Next, with respect to the Si-Mn based carbon steel material, the above-described ferrite grain size obtained by a test in which the total area reduction ratio R is 90% or more by multi-pass rolling in multiple directions in the warm temperature range. Plot the relationship between the tensile strength and drawing of the test materials that have the tensile test, while conducting a recess forming test by cold forging M1.6 pan head screws on these test materials to test for the presence of recess cracks. did. The result is shown in FIG. According to FIG. 3, even if the tensile strength is 600 MPa or more, no recess crack occurs if the aperture RA is 65% or more. Furthermore, even though the tensile strength is 800 MPa or more, the drawing RA is further increased to obtain 80% or more of steel, and in this case, there is no recess crack.
前述した通り、リセスには種々形状のものがあるので、リセス割れないしその類似欠陥の発生を抑止するために鋼等が具備すべき必要且つ十分条件は一律ではない。M1.6なべ小ねじのリセス成形は極めて過酷な延性条件を要することを考慮することが必要である。 As described above, since there are various types of recesses, the necessary and sufficient conditions that steel or the like should have in order to suppress the occurrence of recess cracks or similar defects are not uniform. It is necessary to consider that recess molding of M1.6 pan head screws requires extremely severe ductility conditions.
そこで、この出願の発明においては、上記図1、図2及び図3を含めた試験結果及びこれらに対する考察、並びに実用性を総合し、極めて高水準の冷間圧造性が要求されるM1.6なべ小ねじのリセスを含めた種々形状のリセスを、割れ発生無しに成形加工し得るという優れた冷間圧造性を有する鋼等が具備すべき条件は、引張強さが600MPa以上を必要とする成形品を前提条件として、絞りRAが70%以上であることを必須条件とすべきであるとの結論を得た。そして、このような水準の引張強さを具備させる有利な手段は、フェライトの粒径を、圧延方向に垂直な断面組織の平均粒径で、1μm以下になるようにすることが効果的であることを知見した。 Therefore, in the invention of this application, the test results including FIG. 1, FIG. 2 and FIG. 3 above, considerations for these, and practicality are combined, and M1.6, which requires a very high level of cold forging, is required. The conditions that steels having excellent cold forging properties that can be formed into recesses of various shapes including recesses for pan head screws should have a tensile strength of 600 MPa or more. The conclusion was reached that the aperture RA should be 70% or more on the precondition of the molded product. An advantageous means for providing such a level of tensile strength is effective in setting the ferrite grain size to 1 μm or less in terms of the average grain size of the cross-sectional structure perpendicular to the rolling direction. I found out.
(4)[焼入、又は焼入・焼戻し処理不要]
この出願の発明に係る鋼等では、当該鋼等の金属組織の形態として、フェライト粒からなり、引張強さTSが600MPa以上で且つ絞りRAが70%以上を具備しているので、敢えて、焼入、又は焼入・焼戻しにより強度及び延性を改善する必要はない。
(4) [Quenching or quenching / tempering treatment unnecessary]
In the steel and the like according to the invention of this application, as the form of the metal structure of the steel or the like, it is composed of ferrite grains, the tensile strength TS is 600 MPa or more, and the drawing RA is 70% or more. There is no need to improve strength and ductility by quenching or quenching / tempering.
これにより、この発明に係る鋼等のかかる材質特性により、ねじ及びボルト等の締結部品又は軸類等の成形品の製造工程の省略化及び製造コストの低減等、大きな効果が発揮される。 Thereby, such a material characteristic as steel according to the present invention exerts a great effect such as omission of a manufacturing process of a fastening part such as a screw and a bolt or a molded product such as a shaft and reduction of manufacturing cost.
(5)[C以外の化学成分組成]
更に、この出願の発明に係る「鋼」の化学成分組成に関しては、相変態による鋼の強化機構を利用せず、しかも強度を向上させるための合金元素、例えば、Cr、Mo、Cu、Ni、Nb、Ti、V及び/又はB等の合金元素の添加を必須の要件とはしない。但し、このような合金元素を適宜添加しても差し支えない。この発明に係る鋼等は、フェライト単相鋼の広い範囲の化学成分組成の設計をすることができる。そして、この出願の発明に係る鋼等の化学成分組成の内、Cを除く化学成分組成の望ましい範囲は下記の通りである。
(5) [Chemical component composition other than C]
Furthermore, regarding the chemical composition of the “steel” according to the invention of this application, alloy elements for improving the strength, for example, Cr, Mo, Cu, Ni, without using the strengthening mechanism of the steel by phase transformation. The addition of alloy elements such as Nb, Ti, V and / or B is not an essential requirement. However, such alloy elements may be added as appropriate. The steel according to the present invention can be designed with a wide range of chemical composition of ferritic single phase steel. And the desirable range of the chemical component composition excluding C in the chemical component composition of steel or the like according to the invention of this application is as follows.
Si:2.0質量%以下(0質量%を含まず)
Siは、脱酸剤として作用する元素であるから、鋼等に残留する酸化物系非金属介在物の量を低減させて清浄性向上を図り、その延性確保に寄与させ得る。また、Siは、適量の含有量により冷間圧造性の向上に寄与する元素であることも、本発明者等は知見した。特に、Si含有量が0.8〜1.5質量%の範囲内において、その効果が発揮される。しかしながら、Siを過剰に含有させると、却ってその延性を劣化させ、また加工時の変形抵抗が大きくなる。そこで延性劣化を招かないSi含有量として2.0質量%以下に規制する。但し、Siは上述の通り適正含有量において有用な元素であるから、この発明に係る鋼等において、0質量%は含めないものとする。
Si: 2.0% by mass or less (excluding 0% by mass)
Since Si is an element that acts as a deoxidizer, it can reduce the amount of oxide-based non-metallic inclusions remaining in steel and the like, thereby improving cleanliness and contributing to ensuring ductility. In addition, the present inventors have also found that Si is an element that contributes to the improvement of cold heading by an appropriate content. In particular, the effect is exhibited when the Si content is in the range of 0.8 to 1.5 mass%. However, when Si is excessively contained, the ductility is deteriorated on the contrary, and deformation resistance at the time of processing increases. Therefore, the Si content that does not cause ductile deterioration is regulated to 2.0% by mass or less. However, since Si is an element useful in an appropriate content as described above, 0% by mass is not included in the steel according to the present invention.
Mn:3.0質量%以下(0質量%を含まず)
Mnは、強度確保のために有効であり、またSiとの複合脱酸により、鋼中に残留する酸化物系非金属介在物の低減に寄与する。しかしながら、Mnを過剰に含有させると、延性を劣化させる。従って、Mn含有量は上限を3.0質量%に規制する。なお、Mnは上述の通り適正含有量において有用な元素であるから、この発明に係る鋼等において、0質量%は含めないものとし、望ましくは0.01質量%以上とする。
Mn: 3.0% by mass or less (excluding 0% by mass)
Mn is effective for securing the strength, and contributes to the reduction of oxide-based nonmetallic inclusions remaining in the steel by complex deoxidation with Si. However, when Mn is contained excessively, ductility is deteriorated. Therefore, the upper limit of the Mn content is restricted to 3.0% by mass. In addition, since Mn is a useful element in appropriate content as above-mentioned, in the steel etc. which concern on this invention, 0 mass% shall not be included and it shall be 0.01 mass% or more desirably.
P:0.2質量%以下
Pは、延性を劣化させる作用を有する。この発明に係る鋼等おいては、冷間圧造性の指標として極めて重要な絞りRAを劣化させないために、P含有量は上限を0.1質量%に制限することがのぞましい。
P: 0.2% by mass or less P has an effect of deteriorating ductility. In the steel according to the present invention, it is preferable that the upper limit of the P content is limited to 0.1% by mass so as not to deteriorate the drawing RA, which is extremely important as an index of cold heading.
S:0.03質量%以下
Sは、この発明に係る鋼等おいては不純物元素であり、高含有量になると、固溶Sが粒界に偏析し、鋼塊から鋼片への熱間加工において熱間加工性が劣化するので、0.03質量%以下に規制する。また、この発明では不純物元素として扱っているので、少ないほど望ましく、実質的に0質量%であってもよい。
S: 0.03 mass% or less S is an impurity element in the steel and the like according to the present invention, and when the content becomes high, the solid solution S segregates at the grain boundary, and hot from the steel ingot to the steel slab. Since hot workability deteriorates during processing, the content is restricted to 0.03% by mass or less. Further, since it is handled as an impurity element in the present invention, it is desirable that the amount is as small as possible, and it may be substantially 0% by mass.
Al:0.1質量%以下(0質量%を含まず)
Alは、脱酸剤として添加する。また、AlNを生成して粒界に偏析するNをAlで固定して粒界強度を高める作用をする。しかしながら、Al含有量は0.1質量%を超えるとその効果が飽和すると共に、アルミナの凝集介在物等により鋼等の表面性状が劣化するので、上限を0.1質量%とする。なお、下限は、脱酸剤としての効果を発揮させるために、望ましくは0.005質量%とする。
Al: 0.1% by mass or less (excluding 0% by mass)
Al is added as a deoxidizer. Moreover, N which segregates at the grain boundary by producing AlN is fixed with Al, and the grain boundary strength is increased. However, if the Al content exceeds 0.1% by mass, the effect is saturated and the surface properties of the steel and the like deteriorate due to the aggregate inclusions of alumina and the like, so the upper limit is made 0.1% by mass. In addition, in order to exhibit the effect as a deoxidizer, the lower limit is desirably 0.005% by mass.
N:0.02質量%以下
Nは、この発明に係る鋼等おいては、特に添加する必要はなく、溶製プロセスにおいて不可避的に含有される不純物として扱う。Al含有量とのバランスを考慮する必要はあるが、過剰に含有されると、粒界偏析により熱間加工性の劣化を招く。但し、NはAlNとして析出し、結晶粒の微細化にも寄与する。そこで、溶製プロセスの操業性も考慮して、N含有量の上限を0.02質量%に規制することが望ましい。下限値は実操業を考慮すれば規制する必要はない。
N: 0.02% by mass or less N is not particularly required to be added in the steel according to the present invention, and is handled as an impurity inevitably contained in the melting process. Although it is necessary to consider the balance with the Al content, if it is excessively contained, hot workability is deteriorated due to grain boundary segregation. However, N precipitates as AlN and contributes to refinement of crystal grains. Therefore, it is desirable to limit the upper limit of the N content to 0.02% by mass in consideration of the operability of the melting process. The lower limit value does not need to be regulated considering actual operation.
この発明に係る鋼等が冷間圧造性に優れた高強度且つ高延性を安定して発揮し、且つ製造コストを低減するためには、上述した全ての化学成分組成を満たすことが望ましい。そして、Si含有量については、0.8〜1.5質量%の範囲内に調整すると、この発明にかかる鋼等の絞りを一層優れたものにすることができる。 In order for the steel and the like according to the present invention to stably exhibit high strength and high ductility with excellent cold forgeability and to reduce manufacturing costs, it is desirable to satisfy all the above-described chemical component compositions. And about Si content, if it adjusts in the range of 0.8-1.5 mass%, the aperture_diaphragm | restriction of steel etc. concerning this invention can be made more excellent.
なお、この鋼等は、相変態による鋼の強化機構を利用する必要がないので、各種の熱処理を必要とせず、この意味からも、従来の問題点であるエネルギーコストの低減、ラインの複雑化解消、製造工程数増加の解消に極めて有効である。 In addition, this steel does not require the use of a steel strengthening mechanism by phase transformation, so various heat treatments are not necessary. From this point of view, energy costs are reduced, and lines are complicated. It is extremely effective in eliminating the increase in the number of manufacturing processes.
(7)[球状化焼なまし処理不要]
この発明に係る「鋼等」にあっては、いずれも既に、上述した通りの金属組織及び機械的性質を有し、冷間圧造性に優れた高強度でしかも高延性を具備しているので、ねじ及びボルト等の締結部品又は軸類等の成形品に成形加工するに先立って、球状化焼なまし処理を施して軟化させなくても、リセス成形等の厳しい成形加工で割れ発生を伴うことなく当該ねじ及びボルト等の締結部品又は軸類等の成形品を製造することができる。この発明に係る鋼等のかかる材質特性により、ねじ及びボルト等の締結部品又は軸類等の成形品の製造工程の省略及び製造コストの低減等、大きな効果が発揮される。
(7) [Spheroidizing annealing is not required]
In the “steel etc.” according to the present invention, all of them have the metal structure and mechanical properties as described above, and have high strength and high ductility with excellent cold forging. Even if it is not subjected to spheroidizing annealing and softening prior to molding into fasteners such as screws and bolts or molded parts such as shafts, cracks are generated by severe molding such as recess molding. It is possible to manufacture fastening parts such as screws and bolts or molded articles such as shafts without any problems. Such material characteristics of the steel and the like according to the present invention exert a great effect such as omission of a manufacturing process of a fastening part such as a screw and a bolt or a molded product such as a shaft and reduction of manufacturing cost.
(8)[温間圧延:350〜800℃、望ましくは400〜600℃]
更に、製造履歴として350〜800℃の温度範囲内において圧延することにより、微細粒化されたフェライト組織が得られ、その結果材料の引張強さが向上する。しかも、絞りの低下が抑制されて高水準に維持されたものとなる。この温間圧延において、望ましくは圧延温度を低温域の400〜600℃の範囲内に調整すると、フェライト粒の微細化が一層促進されて、引張強さが一層向上する。
(8) [Warm rolling: 350-800 ° C, desirably 400-600 ° C]
Furthermore, by rolling in a temperature range of 350 to 800 ° C. as a production history, a fine-grained ferrite structure is obtained, and as a result, the tensile strength of the material is improved. In addition, the reduction in aperture is suppressed and maintained at a high level. In this warm rolling, when the rolling temperature is desirably adjusted within a low temperature range of 400 to 600 ° C., the refinement of ferrite grains is further promoted, and the tensile strength is further improved.
(9)[平均塑性ひずみ≧0.7]
上記温間圧延により、材料中へ残留する平均組成ひずみが、3次元有限要素法で計算して0.7以上になるように調整されると、材料の引張強さが向上し、絞りが確保されるのに極めて効果的である。
(9) [Average plastic strain ≧ 0.7]
When the above-mentioned warm rolling is adjusted so that the average composition strain remaining in the material is 0.7 or more calculated by the three-dimensional finite element method, the tensile strength of the material is improved and the drawing is secured. It is very effective to be done.
(10)[多方向、多パス圧延]
温間圧延温度域において、その素材に対して多方向に多パスの圧延により平均塑性ひずみが0.7以上となるような圧延が行なわれることにより調製された鋼等が一層望ましい。その理由は、素材に多方向への多パス圧延を行なうに際して、所要の累積圧下率(本願における「総減面率R」(前記(1)式に相当する)を加えれば、アンビル圧縮試験での1パスによる温間大ひずみ圧縮加工における場合と同様の過程を経て、超微細フェライト粒組織を得ることができることを、発明者等は知見しており、この知見に基づき、所要の超微細粒径のフェライトを主相とする引張強さ及び絞りを有する鋼等を得ることができるからである。
(10) [Multi-directional, multi-pass rolling]
In the warm rolling temperature range, steel and the like prepared by rolling the material so that the average plastic strain becomes 0.7 or more by multi-pass rolling in multiple directions are more desirable. The reason for this is that when performing a multi-pass rolling in multiple directions on the material, if the required cumulative rolling reduction ("total surface reduction ratio R" in the present application (corresponding to the above equation (1)) is added, an anvil compression test is performed. The inventors have found that an ultrafine ferrite grain structure can be obtained through a process similar to that in the case of warm large strain compression processing by one pass, and based on this knowledge, the required ultrafine grain is obtained. This is because it is possible to obtain a steel having a tensile strength and a drawing whose main phase is ferrite having a diameter.
[1−2]この出願の発明に係る締結部品又は軸類等の成形品
次に、この発明に係るねじ及びボルト等の締結部品又は軸類等の「成形品」が具備すべき金属組織及び材質特性等の実施形態について述べる。この発明に係る成形品は、高強度を有するものであって、金属組織の形態及び機械的性質の特性の両方を前述した通りに定量的に規定することを基本とするものであり、上述した通りこの成形品の素材は、上記[1−1]で述べたこの発明に係る「鋼等」に包含される「線材又は棒材」である。そして、これを素材として、圧造を含む加工方法により製造されたものである。以下、具体的に説明する。
[1-2] Fastened parts or shafts according to the invention of this application Molded parts such as screws and bolts according to the invention or shafts and other "molded products" Embodiments such as material characteristics will be described. The molded article according to the present invention has high strength, and is based on quantitatively defining both the form of the metal structure and the characteristics of the mechanical properties as described above. The material of the molded product is “wire or rod” included in “steel etc.” according to the present invention described in [1-1]. And it is manufactured by the processing method including forging using this as a raw material. This will be specifically described below.
(1)[圧造を含む加工方法]
強度及び冷間圧造性に優れた線材又は棒材を圧造を含む加工方法により、この発明に係る「成形品」を製造する。この発明に係る成形品は、ねじ等の締結部品とシャフト等の軸類に大別される。締結部品としては、ねじ、ボルト、ナット、リベット、スタッドボルト、ファスナー類、及びその他これらに類する機能を有する機械構造用部品があり、一方、軸類としては、回転動力を伝達するためのシャフトに代表される各種軸からなる機械構造用部品がある。これらの成形品を製造するための圧造を含む加工方法としては、上記成形品の内、締結部品の製造については、所望の種類の締結部品を製造する場合に従来使用されている製造装置を用い、当該製造装置に適した操業方法により、この発明に係る締結部品を製造することができる。その代表的加工方法としては、圧造、転造、切削及び鍛造があり、これらを適宜組み合せて使用することができる。これに対して、軸類の製造については、所望の種類の締結部品を製造するために適した金型等を含む圧造装置と、一部工程につては適宜切削加工装置を使用することもできる。かくして、この発明に係る成形品の加工工程において最も重要な工程は、材料の歩留がよく、生産性よく形状が複雑で厳しい塑性加工が行なわれる圧造による加工工程である。
(1) [Processing method including forging]
A “molded product” according to the present invention is manufactured by a processing method including forging a wire or bar excellent in strength and cold forgeability. The molded products according to the present invention are roughly classified into fastening parts such as screws and shafts such as shafts. Fastening parts include screws, bolts, nuts, rivets, stud bolts, fasteners, and other mechanical structural parts that have similar functions. On the other hand, shafts are used as shafts for transmitting rotational power. There are parts for mechanical structures consisting of various types of shafts. As a processing method including forging for manufacturing these molded products, among the above-mentioned molded products, a manufacturing apparatus conventionally used for manufacturing a desired type of fastening part is used for manufacturing a fastening part. The fastening component according to the present invention can be manufactured by an operation method suitable for the manufacturing apparatus. The typical processing methods include forging, rolling, cutting and forging, and these can be used in appropriate combination. On the other hand, for the manufacture of shafts, a forging device including a die suitable for manufacturing a desired type of fastening part and a cutting device can be used as appropriate for some processes. . Thus, the most important process in the process of processing the molded article according to the present invention is a process by forging in which material yield is high, the shape is high, the shape is complicated, and severe plastic processing is performed.
(2)[調質処理不要]
この発明に係る締結部品又は軸類等の成形品は、上記鋼等に包含される線材又は棒材を素材として、圧造を含む加工法により成形加工される。この発明に係る線材又は棒材は上述した通り、優れた強度を備えているので、ねじ及びボルト等の締結部品又は軸類等の成形品に圧造を含む加工方法により成形加工された後においても、この強度特性は殆どそのままこの成形品に継承される。従って、ねじ及びボルト等の締結部品又は軸類等の成形品に成形加工された後、これらの機械的性質の向上を目的とする調質処理、例えば、強度、硬度、靱性等の向上を図るために焼入・焼戻し等の熱処理は一切施さなくてもよい。
(2) [No tempering treatment required]
A molded product such as a fastening part or a shaft according to the present invention is molded by a processing method including forging using a wire or a bar included in the steel as a raw material. As described above, since the wire or bar according to the present invention has excellent strength, even after being formed and processed by a processing method including forging into a fastening part such as a screw and a bolt or a molded product such as a shaft. This strength characteristic is almost directly inherited by this molded product. Therefore, after being molded into a fastening part such as screws and bolts or a molded product such as shafts, tempering treatment for the purpose of improving these mechanical properties, for example, improving strength, hardness, toughness, etc. Therefore, it is not necessary to perform any heat treatment such as quenching and tempering.
更には、前述したように、M1.6なべ小ねじのように、ねじの軸径が2.0mm以下の小ねじ等を製造する場合であって、焼入後の残留応力又は浸炭焼入の場合の浸炭層の深さと、ねじ径やねじ山の大きさとの関係により、焼入等の熱処理が困難な場合があるので、かかる場合には、調質処理が不要であることは必須要件でもある。前述したように、特に、ねじの軸径が1mm以下の場合、又は長尺ものの場合は、焼入・焼戻しに伴う変形により、機械部品として使用することができないこともある。このような微小部材の製造においては、この発明に係る鋼等の供給は極めて有効なものとなる。かくして、この発明に係るねじ及びボルト等の締結部品又は軸類等の成形品にあっては、調質処理を施すことが不要であることは、この発明の目的の内でも極めて重要部分を構成する特徴である。
なお、勿論、製品固有の規格又は特殊用途等のために、更に機械的性質を向上させる必要がある場合には、適宜調質処理を施すことができ、調質処理が施されている成形品を、この発明に係る成形品から排除するものではない。
Furthermore, as described above, when manufacturing a small screw having a screw shaft diameter of 2.0 mm or less, such as an M1.6 pan head screw, residual stress after quenching or carburizing and quenching In some cases, heat treatment such as quenching may be difficult due to the relationship between the depth of the carburized layer and the screw diameter and thread size. is there. As described above, in particular, when the screw shaft diameter is 1 mm or less or a long screw, it may not be used as a machine part due to deformation accompanying quenching and tempering. In the manufacture of such a micro member, the supply of steel and the like according to the present invention is extremely effective. Thus, in the fastening parts such as screws and bolts or the molded products such as shafts according to the present invention, the fact that it is not necessary to perform the tempering treatment constitutes an extremely important part within the object of the present invention. It is a feature to do.
Of course, if it is necessary to further improve the mechanical properties for product-specific standards or special applications, etc., the tempering treatment can be performed as appropriate, and the molded product is subjected to the tempering treatment. Is not excluded from the molded product according to the present invention.
[2]発明品群の製造方法
次に、この発明に係る高強度で且つ冷間圧造性に優れた鋼(本明細書において「この発明に係る鋼」という)を製造する方法、及びこの発明に係る強度に優れたねじ及びボルト等の締結部品又は軸類等の成形品を製造する方法の実施形態について述べる。
[2] Method for Producing Invention Group Next, a method for producing a steel having high strength and excellent cold forging according to the present invention (referred to as “the steel according to the present invention” in the present specification), and the present invention An embodiment of a method for producing a molded part such as a fastening part such as a screw and a bolt or a shaft excellent in strength according to the above will be described.
[2−1]この発明に係る鋼の製造方法
図4は、この発明に係るねじ等成形品の製造工程の前半部分(線材又は棒材24まで)を示したものである。但し、同図中、線材又は棒材24は、前述した定義の通り、次工程における成形用として適切な材料特性を有するもの(材料)を指す。そして、この線材又は棒材24は、この発明に係る鋼に包含されるものである。この発明に係る鋼の製造方法の望ましい工程を、前記図11に示した従来技術による鋼片からねじ等成形品の製造工程の前半部分(熱処理5まで)と比較すると、従来技術においては半製品3を熱間圧延又は熱間鍛造2bにより鋼線又は鋼棒4を製造し、これを次工程の冷間圧造及び転造等を含む加工工程へ供給するに先だって、球状化焼なまし等何らかの熱処理をすることが必須条件とされているが、この発明においては半製品3を温間圧延23により線材又は棒材24を製造すること、そして得られた線材又は棒材24に対しては全く熱処理を施す必要がなく、これを次工程の冷間圧造及び転造等を含む加工工程へ供給することができる。かかる相違は、この発明においては、上記の通り熱間圧延又は熱間鍛造2bの代わりに、適切な条件下での温間圧延23を行なうからである。以下、詳細に説明する。
[2-1] Steel Manufacturing Method According to the Invention FIG. 4 shows the first half (up to the wire or bar 24) of the manufacturing process of the molded product such as a screw according to the invention. However, in the same figure, the wire or bar 24 refers to a material (material) having material properties suitable for molding in the next step as defined above. And this wire or bar 24 is included in the steel according to the present invention. Comparing the desirable process of the steel manufacturing method according to the present invention with the first half of the manufacturing process of the molded product such as a screw from the steel piece according to the prior art shown in FIG. 3 is manufactured by hot rolling or hot forging 2b to produce a steel wire or steel bar 4, and before supplying it to the processing steps including cold forming and rolling in the next step, spheroidizing annealing, etc. Heat treatment is an indispensable condition, but in the present invention, the semi-finished product 3 is manufactured by warm rolling 23 to produce a wire or bar 24, and the obtained wire or bar 24 is completely different. There is no need to perform heat treatment, and this can be supplied to processing steps including cold forging and rolling in the next step. This difference is because in the present invention, warm rolling 23 under appropriate conditions is performed instead of hot rolling or hot forging 2b as described above. Details will be described below.
この発明に係る鋼の製造方法の基本は、所定の化学成分組成を有する鋼片又は鋼材を圧延素材として所定の温間圧延温度域において、1)所定の減面率の導入、2)所定のカリバーロールの使用による所定の減面率の導入、3)所定の塑性ひずみの導入、又は4)圧延条件パラメータZの規定、をしたカリバー圧延をすることにある。具体的には、その製造方法の必須要件は、温間圧延領域として350〜800℃の範囲内に限定することを共通条件とし、更に、下記[条件1]〜[条件4]の内の一つ又は一つ以上を満たすことである。ここで、
[条件1]とは、所定減面率の導入において、前記(1)式:R={(S0−S)/S0}×100(%)で表わした延開始直前から圧延終了までの材料の総減面率Rが50%以上となるように圧延すること、
[条件2]とは、オーバル形状の孔型を1パス以上用いた場合に限り、圧延素材の総減面率Rが40%以上となるように圧延すること、
[条件3]とは、塑性ひずみの導入において、材料に残留する平均塑性ひずみが、0.7以上となるように調整すること、そして、
[条件4]とは、圧延条件パラメータZの規定について、前記(2)式:Z=log[(ε/t)exp{Q/(8.31(T+273))}]で表わした塑性ひずみ速度ε/tと圧延温度Tとの関数である圧延条件パラメータZの値が11以上となるように圧延をすることである。
The basics of the method for producing steel according to the present invention are as follows: 1) introduction of a predetermined area reduction rate, 2) The purpose is to perform caliber rolling by introducing a predetermined area reduction ratio by using a caliber roll, 3) introducing a predetermined plastic strain, or 4) defining a rolling condition parameter Z. Specifically, the essential requirement of the production method is that the warm rolling region is limited to a range of 350 to 800 ° C., and one of the following [Condition 1] to [Condition 4]. Meeting one or more. here,
[Condition 1] means that, in the introduction of a predetermined area reduction rate, from the immediately before the start of rolling represented by the above formula (1): R = {(S 0 −S) / S 0 } × 100 (%) to the end of rolling. Rolling so that the total area reduction R of the material is 50% or more,
[Condition 2] is that rolling is performed so that the total area reduction ratio R of the rolled material is 40% or more only when an oval hole mold is used for one pass or more.
[Condition 3] means adjusting the average plastic strain remaining in the material to 0.7 or more in the introduction of plastic strain, and
[Condition 4] is a plastic strain rate expressed by the above-mentioned formula (2): Z = log [(ε / t) exp {Q / (8.31 (T + 273))}] regarding the definition of the rolling condition parameter Z. The rolling is performed so that the value of the rolling condition parameter Z, which is a function of ε / t and the rolling temperature T, is 11 or more.
その上で、この発明に係る鋼の製造方法の更に望ましい態様を得るために、適宜、圧延温度範囲を狭く規定すること、圧延済みの鋼に対する熱処理を制限してもよいと規定すること、及びその他の条件を規定することにより、発明品群の製造方法を構成する。以下、詳細に説明する。 In addition, in order to obtain a more desirable mode of the steel manufacturing method according to the present invention, it is appropriately specified that the rolling temperature range is narrowed, the heat treatment on the rolled steel may be restricted, and By defining other conditions, the manufacturing method of the invention group is configured. Details will be described below.
(1)温間圧延温度:350〜800℃について
圧延温度が350〜800℃の範囲内において、所定の臨界ひずみよりも大きなひずみを材料に導入することにより、このひずみによる結晶粒のミクロ的な局所方位差が微細結晶粒の起源となり、加工中あるいは加工後に起きる回復過程において、粒内の転位密度が低下すると同時に結晶粒界が形成されて、微細粒組織を形成することができる。即ち、再結晶温度の下限とみなされていた800℃ないしこれ以下の温度で加工しても、加工と同時に動的な回復ないしは再結晶が起こり、相変態を利用することなく結晶粒の微細化を図ることができる。しかし、加工温度が高過ぎると、不連続再結晶あるいは通常の粒成長により、結晶粒が粗大化する。かくして800℃超えでは2μm以下の微細結晶粒が得られ難い。逆に、加工温度が低過ぎると、所定の臨界ひずみよりも大きなひずみを与えても、回復が十分に起こらないために転位密度の高い加工組織が残存してしまう。かくして圧延温度を350℃未満にすると、やはり2μm以下の微細結晶粒は得られ難くなる。従って、この発明においては温間圧延温度を350〜800℃の範囲内に限定することを必須要件とする。
(1) Warm rolling temperature: about 350 to 800 ° C. When the rolling temperature is in the range of 350 to 800 ° C., a strain larger than a predetermined critical strain is introduced into the material, so that the crystal grains caused by this strain become microscopic. The difference in local orientation becomes the origin of fine crystal grains, and in the recovery process that occurs during or after processing, the dislocation density in the grains decreases and at the same time crystal grain boundaries are formed, so that a fine grain structure can be formed. That is, even when processing at a temperature of 800 ° C. or lower, which was regarded as the lower limit of the recrystallization temperature, dynamic recovery or recrystallization occurs at the same time as the processing, so that the crystal grains can be refined without using phase transformation. Can be achieved. However, if the processing temperature is too high, the crystal grains become coarse due to discontinuous recrystallization or normal grain growth. Thus, when the temperature exceeds 800 ° C., it is difficult to obtain fine crystal grains of 2 μm or less. On the other hand, if the processing temperature is too low, even if a strain larger than a predetermined critical strain is applied, recovery does not occur sufficiently, and a processed structure having a high dislocation density remains. Thus, when the rolling temperature is less than 350 ° C., it is difficult to obtain fine crystal grains of 2 μm or less. Therefore, in this invention, it is an essential requirement to limit the warm rolling temperature within the range of 350 to 800 ° C.
(2)[条件1]:総減面率R≧50%、
[条件2]:オーバル形状カリバーロールを使用した場合に限り、総減面率R≧40%、[条件3]:平均塑性ひずみε≧0.7、
又は、
[条件4]:圧延条件パラメータZ≧11
について
[条件1]、[条件2]又は[条件3]については、圧延温度が350〜800℃の範囲内におけるC<0.45質量%の鋼片又は鋼材のカリバー圧延において、総減面率RがR≧50%であるか、若しくはオーバル型カリバーロールを用いた場合にR≧40%であるか、又は鋼片又は鋼材の平均塑性ひずみεがε≧0.7である場合には、圧延後に得られる鋼等にはサブバウンダリが導入されて、その引張強さTSがTS≧600MPaとなることを、発明者は試験の結果より見出した。そして、同時にそのときには65%以上の絞り(RA≧65%)が得られることもわかった。なお、総減面率R又は平均塑性ひずみεが更に大きくなり、例えば、R≧約83〜95%又はε≧約1.8〜3.0になると、大角粒界が大半を占め、引張強さTSが一層向上し、絞りRAも維持され、ないしは向上する。
(2) [Condition 1]: Total area reduction ratio R ≧ 50%,
[Condition 2]: Only when an oval-shaped caliber roll is used, the total area reduction ratio R ≧ 40%, [Condition 3]: average plastic strain ε ≧ 0.7,
Or
[Condition 4]: Rolling condition parameter Z ≧ 11
About [Condition 1], [Condition 2] or [Condition 3], in the caliber rolling of steel slabs or steel materials with a C <0.45 mass% in the range of 350 to 800 ° C., the total area reduction rate When R is R ≧ 50%, or when using an oval caliber roll, R ≧ 40%, or when the average plastic strain ε of the steel piece or steel material is ε ≧ 0.7, The inventor found from the test results that subboundaries were introduced into the steel obtained after rolling, and the tensile strength TS was TS ≧ 600 MPa. At the same time, it was also found that an aperture of 65% or more (RA ≧ 65%) can be obtained. In addition, when the total area reduction ratio R or the average plastic strain ε is further increased, for example, when R ≧ about 83 to 95% or ε ≧ about 1.8 to 3.0, the large-angle grain boundaries occupy most of the tensile strength. The TS is further improved, and the aperture RA is also maintained or improved.
上記において、カリバー圧延の実操業において材料に導入される塑性ひずみは、一般には材料中で不均一に分布するが、ここではこの不均一分布を平均した塑性ひずみ、即ち平均塑性ひずみεを指標としており、この平均塑性ひずみ量は、3次元有限要素法により計算される平均塑性ひずみをもって表わすことができる。また、カリバーロールとしては公知の通り、角型(スクウェア型又はダイヤモンド型)、丸型及びオーバル型の3種があるが、この発明においては、オーバル型と、角型及び丸型との2種に大別する。そして、オーバル孔型のカリバーロールとは、上型と下型との組合せによって形成される孔の形状が、円形を扁平化した形状を有するものである。 In the above, the plastic strain introduced into the material in the actual operation of caliber rolling is generally unevenly distributed in the material. Here, the plastic strain obtained by averaging this nonuniform distribution, that is, the average plastic strain ε is used as an index. The average plastic strain amount can be expressed by an average plastic strain calculated by a three-dimensional finite element method. Further, as known as caliber rolls, there are three types of square type (square type or diamond type), round type and oval type. In this invention, there are two types of oval type, square type and round type. Broadly divided into The oval hole type caliber roll has a shape in which a hole formed by a combination of an upper mold and a lower mold has a flattened circular shape.
[条件4]については、圧延温度が350〜800℃の範囲内におけるC<0.45質量%の鋼片又は鋼材のカリバー圧延において、本発明者等は、温間強加工(温間における1パスによる大ひずみ加工)によって形成される超微細粒の平均粒径は、加工温度とひずみ速度に依存することに着眼し、圧延条件パラメータとしてZener−Hollomon parameter(=請求項32に記載の(2)式):Z=log[(ε/t)exp{Q/(8.31(T+273))}](但し、ε:平均塑性ひずみ、t:圧延開始から終了までの時間(s)、Q:定数(254000J/mol)、T:圧延温度(℃)、多パス圧延の場合は各パスの圧延温度を平均した温度)を導入し、結晶粒径は、圧延条件パラメータZの増加につれて微細化することを知見した。なお、Zener−Hollomon parameterは、上式に示すように、対数の形で表現した。図5に、圧延条件パラメータZとフェライト平均粒径との関係を例示する。即ち、図5は、Z≧11となるように圧延を制御することにより、フェライト平均粒径が1μm以下の微細粒組織が得られることを示している。
なお、上記圧延条件パラメータZにおいて、平均塑性ひずみεは、3次元有限要素法により計算することができるが、この計算方法の代わりに、操業上比較的簡便に求めることができる材料のひずみ(本明細書において「工業的ひずみ」という)eにより、ある程度代替することができる。工業的ひずみeは、総減面率Rの関数であり、e=−ln(1−R/100)で表わされる。
Regarding [Condition 4], in the caliber rolling of a steel slab or steel material with a C <0.45 mass% at a rolling temperature in the range of 350 to 800 ° C., the present inventors are Focusing on the fact that the average particle size of the ultrafine grains formed by large strain processing by pass) depends on the processing temperature and strain rate, Zener-Holomon parameter (= claim 2 according to claim 32). ) Formula): Z = log [(ε / t) exp {Q / (8.31 (T + 273))}] (where ε: average plastic strain, t: time from the start to the end of rolling (s), Q : Constant (254000 J / mol), T: rolling temperature (° C.), in the case of multi-pass rolling, a temperature obtained by averaging the rolling temperature of each pass), and the crystal grain size becomes finer as the rolling condition parameter Z increases. It was found that the reduction. The Zener-Holomon parameter was expressed in logarithmic form as shown in the above equation. FIG. 5 illustrates the relationship between the rolling condition parameter Z and the ferrite average grain size. That is, FIG. 5 shows that a fine grain structure having an average ferrite grain size of 1 μm or less can be obtained by controlling the rolling so that Z ≧ 11.
In the above rolling condition parameter Z, the average plastic strain ε can be calculated by a three-dimensional finite element method, but instead of this calculation method, the strain of the material (this can be obtained relatively easily in operation) It can be replaced to some extent by e) referred to in the specification as “industrial strain”. The industrial strain e is a function of the total area reduction ratio R, and is represented by e = −ln (1−R / 100).
さて、上記(1)及び(2)項の必須要件に加えて、以下の(3)〜(6)項の条件を付加することにより、この発明に係る鋼の一層望ましい製造方法を実施することができる。 Now, in addition to the essential requirements of the above items (1) and (2), by adding the conditions of the following items (3) to (6), a more desirable method for producing the steel according to the present invention is carried out. Can do.
(3)多方向、多パス圧延
多方向に多パス圧延を行なうとは、カリバー圧延中において、適宜圧延材料を長手方向軸心の周りに実質的に180°未満(0°を含まない)の範囲で回転させることにより行なう。多方向、多パス圧延をすることが望ましい理由は次の通りである。上記温間温度域における多方向に対する多パス圧延により、超微細粒組織の鋼を得るためには、1)所要の臨界塑性ひずみよりも大きな塑性ひずみを材料に導入することが必要であり、しかもこの塑性ひずみは圧延後の材質特性の均質性を確保する観点から、2)材料の中心部の深くまで、できるだけ広範囲に導入することが望ましい。同一総減面率Rの圧延を行なった場合には、多方向、多パス圧延により、平均塑性ひずみεを一層大きくすることが可能となるからであり、しかも一層材料の深部まで塑性ひずみを導入することができるからである。
(3) Multi-directional, multi-pass rolling Multi-directional multi-pass rolling means that during caliber rolling, the rolled material is appropriately less than 180 ° (not including 0 °) around the longitudinal axis. This is done by rotating in a range. The reason why it is desirable to perform multi-directional and multi-pass rolling is as follows. In order to obtain a steel with an ultrafine grain structure by multipass rolling in multiple directions in the warm temperature range, 1) it is necessary to introduce a plastic strain larger than the required critical plastic strain into the material. From the viewpoint of ensuring the homogeneity of the material properties after rolling, it is desirable to introduce this plastic strain as far as possible to 2) deep in the center of the material. This is because, when rolling with the same total area reduction ratio R is performed, the average plastic strain ε can be further increased by multi-directional, multi-pass rolling, and the plastic strain is further introduced deep into the material. Because it can be done.
なお、前記[条件2]におけるオーバル形状カリバーロールの使用により、多方向多パス圧延が容易に導入されて、上記平均塑性ひずみεの増大に寄与する。カリバーロール圧延時には、通常、圧延パス毎に0°超え〜90°未満の範囲内で材料を回転させて、圧下方向を変化させる。その際、オーバル孔型に次いで角孔型で圧延するときは90°、角孔型に次いでオーバル孔型で圧延するときは45°変化させることになる。このようにして、結晶粒の方位を分散させて、大角粒界に囲まれた微細粒を増加させることができる。なお、同一カリバーで連続して2パス圧延する場合(所謂、とも通しの場合)も、当該パス間で材料を90°回転させるので、多方向の多パス圧延に寄与する。 In addition, by using the oval-shaped caliber roll in [Condition 2], multi-directional multi-pass rolling is easily introduced and contributes to the increase in the average plastic strain ε. At the time of caliber roll rolling, the rolling direction is usually changed by rotating the material within a range of 0 ° to less than 90 ° for each rolling pass. At that time, when rolling with the square hole type next to the oval hole type, it is changed by 90 °, and when rolling with the oval hole type after the square hole type, it is changed by 45 °. In this way, the orientation of crystal grains can be dispersed to increase the number of fine grains surrounded by large-angle grain boundaries. It should be noted that even when two-pass rolling is performed continuously with the same caliber (so-called both cases), the material is rotated by 90 ° between the passes, which contributes to multi-directional multi-pass rolling.
なお、上記において、温間圧延の対象とする鋼片としては、所定成分の鋼塊を熱間圧延又は熱間鍛造等によりブルーム又はビレット等の形状に加工したもの、及び連続鋳造等によりブルーム又はビレット等の形状に鋳造された鋳片の内のいずれであってもよい。 In the above, as the steel slab to be subjected to warm rolling, a steel ingot having a predetermined component is processed into a shape such as a bloom or billet by hot rolling or hot forging, and bloom or continuous casting or the like. Any of the slabs cast into a shape such as a billet may be used.
(4)「2A01/2A0≦70/100」について
さて、上記オーバル形状の孔型圧延後の材料の最大短軸長さ(2A01と表記する)を、その圧延前の材料の対辺長さ(2A0と表記する)に対して70%以下、即ち、2A01/2A0≦70/100(%)となるように圧下量を制御することにより、ひずみ量を大きく制御して、微細粒の生成に寄与させる。図6(a)に、オーバル形状18a、18bの孔型による圧延後の材料19の最大短軸長さ2A01を、そして図6(b)に、その圧延前の材料20の対辺長さ2A0を模式的に図示する。なお、同図(a)において、符号21a(斜線部)、21b(斜線部)はオーバル形状カリバーの部分断面を示すものである。このように、2A01/2A0≦70/100(%)となるように制御した圧延を行なうことにより、微細粒を生成させるための臨界ひずみ以上のひずみを材料内部の深部まで与えることが一層容易となり、フェライト粒を広範囲にわたり平均粒径1μm以下にすることを一層有利にできる。
(4) About “2A 01 / 2A 0 ≦ 70/100” Now, the maximum minor axis length (denoted as 2A 01 ) of the material after the above-described oval shape piercing rolling is defined as the opposite side length of the material before the rolling. By controlling the amount of rolling so that it is 70% or less (ie 2A 0 ), that is, 2A 01 / 2A 0 ≦ 70/100 (%), It contributes to the formation of grains. FIG. 6A shows the maximum minor axis length 2A 01 of the material 19 after rolling by the oval shapes 18a and 18b, and FIG. 6B shows the opposite side length 2A of the material 20 before rolling. 0 is schematically illustrated. In FIG. 9A, reference numerals 21a (shaded portions) and 21b (shaded portions) indicate partial cross sections of the oval-shaped caliber. In this way, by performing rolling controlled so as to satisfy 2A 01 / 2A 0 ≦ 70/100 (%), it is possible to further apply a strain higher than the critical strain for generating fine grains to the deep part inside the material. It becomes easier, and it can be made more advantageous to make the ferrite grains have an average grain size of 1 μm or less over a wide range.
(5)一層望ましい圧延温度管理の規定
圧延温度:400〜600℃
圧延待機又は材料冷却:(X+1)パス目圧延の入口材料温度:TX+1,in≦(TX+30)℃について
次に、温間圧延における温度域を一層望ましい範囲内に制御する。前述した通り、温間加工により材料に大ひずみを導入することによって生じた結晶粒のミクロ的な局所方位差が微細結晶粒の起源となり、加工中あるいは加工後に起きる回復過程において、粒内の転位密度が低下すると同時に結晶粒界が形成され、微細粒組織が形成されるが、複雑な圧延条件下においては前述した温間圧延温度350〜800℃の範囲内にあっても、圧延温度が低目であると回復が十分でない場合があり、転位密度の高い加工組織が残存する。これに反して加工温度が高目であると、不連続再結晶あるいは通常の粒成長により結晶粒が粗大化する場合があり、2μm以下の微細結晶粒が得られ難い。そこで、この発明においては、安定して平均粒度を1μm以下に制御するためには、圧延温度を400〜600℃の範囲内に制御することが望ましい。
(5) More desirable rolling temperature control regulation rolling temperature: 400-600 ° C
Rolling standby or material cooling: (X + 1) Inlet material temperature at the first pass rolling: T X + 1, in ≦ (T X +30) ° C. Next, the temperature range in the warm rolling is controlled within a more desirable range. As mentioned above, the microscopic local misorientation of the crystal grains caused by introducing large strains in the material by warm working becomes the origin of the fine grains, and in the recovery process that occurs during or after processing, intra-grain dislocations At the same time as the density decreases, a grain boundary is formed and a fine grain structure is formed. However, under complicated rolling conditions, the rolling temperature is low even in the range of the above-described warm rolling temperature of 350 to 800 ° C. If it is an eye, recovery may not be sufficient, and a processed structure having a high dislocation density remains. On the other hand, if the processing temperature is high, crystal grains may become coarse due to discontinuous recrystallization or normal grain growth, and it is difficult to obtain fine crystal grains of 2 μm or less. Therefore, in the present invention, in order to stably control the average particle size to 1 μm or less, it is desirable to control the rolling temperature within the range of 400 to 600 ° C.
一方、材料の圧延中には、加工発熱が発生する。この発熱量は加工条件により変化するが、圧延中の温度を所望の範囲内に制御することにより、所望粒径の微細粒組織を得るためには、この加工発熱を考慮した温度制御をすることが望ましい。そこで、ある圧延パス(Xパス)目の圧延出口における材料温度(例えば圧延後1秒以内の材料温度)TX,outが、圧延設定温度TXより30℃以上高くなった場合、次の圧延パス(X+1)パス目の圧延入口における材料温度TX+1,inが、TX+1,in≦(TX+30)℃になるまで待機するか、又は材料を冷却して圧延を継続する。但し、最高温度は600℃を超えないようにする。こうすることにより、フェライト粒の平均粒径を更に微細化して、例えば0.5μm以下を狙うことができる。上記温度管理方法は、従来技術による通常の方法で行なえばよい。これに対して、圧延設定温度の下限400℃を保持することは、加工発熱により容易となるので、1パス目圧延開始直前の材料温度が設定温度の範囲内にあれば、温度の挙動監視以外に特別な制御は不要である。 On the other hand, processing heat is generated during rolling of the material. The amount of heat generated varies depending on the processing conditions. In order to obtain a fine grain structure with the desired grain size by controlling the temperature during rolling within a desired range, temperature control in consideration of the processing heat generation should be performed. Is desirable. Therefore, when the material temperature T X, out at the rolling exit of a certain rolling pass (X pass) (for example, the material temperature within 1 second after rolling) becomes 30 ° C. or more higher than the rolling set temperature T X , the next rolling Wait until the material temperature T X + 1, in at the rolling entrance of the pass (X + 1) pass reaches T X + 1, in ≦ (T X +30) ° C., or continue the rolling by cooling the material. . However, the maximum temperature should not exceed 600 ° C. By doing so, the average grain size of the ferrite grains can be further refined, and can be aimed at 0.5 μm or less, for example. The temperature management method may be performed by a normal method according to the conventional technique. On the other hand, maintaining the lower limit 400 ° C. of the rolling set temperature is facilitated by processing heat generation, so if the material temperature just before the start of the first pass rolling is within the set temperature range, other than temperature behavior monitoring No special control is required.
(6)球状化焼なまし処理不要について
次に、上述したこの発明に係る鋼の製造工程により製造された鋼に対しては、球状化焼なまし処理を施す必要はない。その理由は、この発明に係る鋼は前述した通り、高強度であり、しかも絞りが(65〜70)%以上という高水準の延性を有するので、ねじ頭部のリセス成形加工等に要求される冷間圧造性に優れており、リセス割れ等の欠陥も発生しないからである。
(6) Spherical annealing treatment unnecessary Next, it is not necessary to perform spheroidizing annealing on the steel produced by the above-described steel production process according to the present invention. The reason for this is that, as described above, the steel according to the present invention is high in strength and has a high level of ductility of (65 to 70)% or more, so that it is required for the recess forming process of the screw head. It is because it is excellent in cold heading and does not generate defects such as recess cracks.
[2−2]この発明に係るねじ及びボルト等の締結部品又は軸類等の成形品の製造方法
次に、この出願の発明品群の製造方法の内、この発明に係る強度に優れたねじ及びボルト等の締結部品又は軸類等の成形品の製造方法の実施形態について述べる。
[2-2] Manufacturing Method of Fastened Parts such as Screws and Bolts or Molded Products such as Shafts According to the Invention Next, among the manufacturing methods of the invention product group of this application, the screws having excellent strength according to the invention An embodiment of a method for producing a fastening part such as a bolt or a molded product such as a shaft will be described.
(1)基本プロセス
この発明に係るねじ及びボルト等の締結部品又は軸類等の成形品の製造方法の基本プロセスは、始めに、前記[1]項で述べた「この発明に係る高強度で且つ冷間圧造性に優れた鋼」を製造する方法(上記[2−1]項で述べた方法)に準じた方法で、高強度で且つ冷間圧造性に優れた線材又は棒材を製造し、次に、これを素材として圧造を含む加工方法で、強度に優れたねじ及びボルト等の締結部品又は軸類等の成形品を製造するというものであり、その製造方法の望ましい工程の実施形態は、図4に示した通りである。即ち、所定成分の鋼片又は鋳片22を熱間圧延又は熱間鍛造2aにより加工して半製品3に調製し、これを上記[2−1]項で述べた温間圧延23により高強度で且つ冷間圧造性に優れた線材又は棒材24に加工する。この線材又は棒材24に対しては、図11に示した従来技術のように球状化焼なまし等の熱処理5を一切施す必要はなく、これを材料として冷間圧造及び転造等による加工6により、ねじ及びボルト等の締結部品又は軸類等の成形品7を製造する。こうして得られた成形品7に対しては、図9に示した従来技術のように、その機械的性質を所要値まで向上させるために焼入・焼戻し等の調質処理8を施す必要はなく、そのまま製品ラインに送り出し、必要に応じてめっき等の表面処理9を施した後に製品10とする。上記において、圧造を含む加工方法としては、従来技術を採用すればよい。例えば、ねじの製造においては、前記図12を用いて説明したように、ねじ素材の頭部を圧造により成形し、更に圧造(ヘッダー)によりリセスを成形し、次いで転造によりねじ部を成形する。このように、従来技術による圧造を含む加工方法を採用することができるのは、上記線材又は棒材が、前述した通りの冷間圧造性に優れた高強度且つ高延性を備えた材料であるからである。なお、かかるねじ製造工程の一部において、適宜従来技術による切削加工を採用しても差し支えない。また、ねじ以外のボルト等その他の締結部品の製造においても、上記ねじの製造に準じて、従来技術を用いれば差し支えない。一方、軸類の製造においても、適切な金型等の使用による圧造を含む製造工程により締結部品と同様に製造することができる。
(1) Basic process The basic process of the method of manufacturing a molded part such as a fastening part such as a screw and a bolt or a shaft according to the present invention is firstly described in the paragraph [1]. In addition, a method of producing a “steel excellent in cold forging” (method described in the above [2-1] section) is used to produce a wire or bar having high strength and excellent in cold forging. Then, by using this as a raw material, a processing method including forging is used to manufacture a fastening part such as a screw and bolt excellent in strength or a molded product such as a shaft. The form is as shown in FIG. That is, a steel slab or cast slab 22 having a predetermined component is processed into a semi-finished product 3 by hot rolling or hot forging 2a, and this is high strength by the warm rolling 23 described in the section [2-1] above. In addition, it is processed into a wire or bar 24 excellent in cold heading. This wire or bar 24 does not need to be subjected to any heat treatment 5 such as spheroidizing annealing as in the prior art shown in FIG. 6, a fastener 7 such as a screw and a bolt, or a molded product 7 such as a shaft is manufactured. The molded product 7 thus obtained does not need to be subjected to a tempering process 8 such as quenching and tempering in order to improve its mechanical properties to the required value as in the prior art shown in FIG. Then, the product is sent to the product line as it is, and is subjected to a surface treatment 9 such as plating as necessary to obtain a product 10. In the above, a conventional technique may be adopted as a processing method including forging. For example, in the manufacture of a screw, as described with reference to FIG. 12, the head portion of a screw material is formed by forging, a recess is formed by forging (header), and then a thread portion is formed by rolling. . Thus, the processing method including forging according to the prior art can be employed for the above-described wire or bar material having high strength and high ductility with excellent cold forging as described above. Because. It should be noted that in some of the screw manufacturing processes, a conventional cutting process may be employed as appropriate. Also, in the manufacture of other fastening parts such as bolts other than screws, conventional techniques may be used in accordance with the manufacture of the screws. On the other hand, shafts can also be manufactured in the same manner as fastening parts by a manufacturing process including forging by using an appropriate mold or the like.
(2)代替可能プロセス:圧延工程の一部鍛造又は/及びプレス工程による代替
このように、この発明に係るねじ及びボルト等の締結部品又は軸類等の成形品の製造は、上記(1)項の基本プロセスにより行なわれる。その際、同(1)項の基本プロセスに供する高強度で且つ冷間圧造性に優れた線材又は棒材の製造工程においては、その素材をカリバーで温間圧延している。従って、この素材の形状・寸法とこの発明に係るねじ及びボルト等の締結部品又は軸類等の成形品の形状・寸法との関係、あるいは前記鋼片又は鋼材の製造ラインと当該線材又は棒材を製造する温間圧延ラインとの工程運用上の制約等により、温間圧延工程の一部代替として、適宜、鍛造工程又はプレス工程、更にはこれら両工程を併用しても、差し支えない。その理由は、前記[2−1]項、(1)項の圧延温度範囲内(350〜800℃)における加工温度で、このカリバー圧延工程における総減面率Rが同(2)項の下限値(=50%)以上、又はオーバル形状カリバーロールを使用した場合に限り総減面率RがR≧40%で圧延されるならば、当該線材又は棒材が具備すべき化学成分組成、金属組織及び材質特性が得られるので、所望の高強度で且つ冷間圧造性に優れた線材又は棒材が得られるからである。また、設備の配設条件等によっては、かかる製造工程による場合の方が、製造コスト上有利な場合もある。
(2) Substitutable process: Partial forging of rolling process and / or replacement by pressing process As described above, the manufacture of fasteners such as screws and bolts or molded products such as shafts according to the present invention is the above (1). This is done by the basic process of the term. In that case, in the manufacturing process of the wire rod or bar which is provided with the basic process of the same item (1) and is excellent in cold forging, the material is warm-rolled with a caliber. Therefore, the relationship between the shape and size of this material and the shape and size of fastening parts such as screws and bolts or shafts according to the present invention, or the production line of the steel slab or steel material and the wire or bar As a partial replacement of the warm rolling process, the forging process or the pressing process, and further, both of these processes may be used in combination as appropriate, due to restrictions on the process operation with the warm rolling line for manufacturing. The reason for this is the processing temperature within the rolling temperature range (350 to 800 ° C.) of the items [2-1] and (1), and the total area reduction ratio R in this caliber rolling process is the lower limit of the item (2). Value (= 50%) or more, or if the total area reduction ratio R is rolled at R ≧ 40% only when an oval-shaped caliber roll is used, the chemical composition, metal that the wire or rod should have This is because the structure and material characteristics can be obtained, so that a desired high strength wire rod or bar material excellent in cold heading can be obtained. Further, depending on the installation conditions of the equipment, the manufacturing process may be more advantageous in terms of manufacturing cost.
(3)調質処理不要の製造法
この発明においては、ねじ及びボルト等の締結部品又は軸類等の成形品に成形加工された後、これに対して焼入・焼戻し等による調質処理は一切施す必要はない。その理由は、この発明に係るねじ及びボルト等の締結部品又は軸類等の成形品の素材である線材又は棒材は、既に前述した水準の高強度、即ち600MPa以上という引張強さを備えているので、締結部品又は軸類等の成形品に成形加工された後の強度も、実質的に継承される。即ち、各種強度水準のねじ及びボルト等の締結部品又は軸類等の成形品として供することができるからである。なお、前述したように、製品固有の規格等に応じて、更に機械的性質を向上させる必要がある場合には、適宜調質処理を施すことはできる。
(3) Manufacturing method that does not require tempering treatment In this invention, after being processed into a fastening part such as a screw and bolt or a molded product such as a shaft, tempering treatment by quenching and tempering is performed. There is no need to apply it at all. The reason for this is that the wire or bar that is the material of the fastening parts such as screws and bolts or shafts according to this invention or the material of the molded article such as shafts already has the above-mentioned high strength, that is, a tensile strength of 600 MPa or more. Therefore, the strength after being formed into a molded product such as a fastening part or shaft is substantially inherited. That is, it can be used as a fastening part such as screws and bolts of various strength levels or a molded product such as shafts. In addition, as described above, when it is necessary to further improve the mechanical properties in accordance with the product-specific standards, the tempering treatment can be appropriately performed.
以下に、この発明を実施例により更に詳しく説明する。 Hereinafter, the present invention will be described in more detail with reference to examples.
[試験I:実施例1〜実施例5、比較例1]
○試験方法
実施例1〜5を次の通り試験した。表1に示す成分No.1〜5の化学成分組成を有する各鋼を真空溶解炉を用いて溶製し、鋼塊に鋳造し、熱間鍛造により80mm角の棒鋼に成形した。得られた棒鋼の金属組織はいずれもフェライト及びパーライトからなっていた。こうして得られた80mm角の棒鋼から圧延素材を採取し、温間における多方向の多パスカリバー圧延により18mm角の棒材に成形し、水冷して棒材を調製した。この間の圧延方法は、上記80mm角の圧延素材を550℃に加熱した後、圧延温度450〜530℃において、ダイヤモンド型カリバーロールにより19パスの圧延を行なって、24mm角に成形し(この段階で前記図6(b)中の2A0に相当する長さが24mmである)、
次いで、最大短軸長さ(前記図6(a)中の2A01に相当する長さ)が11mmで長軸長さ(前記図6(a)中の2cの長さ)が52mmであるオーバル型カリバーロールによる1パスの圧延を行ない、次いで最後にスクウェア型カリバーロールにより18mm角の棒材を製造した。
[Test I: Examples 1 to 5 and Comparative Example 1]
Test method Examples 1 to 5 were tested as follows. Ingredient No. shown in Table 1 Each steel having a chemical composition of 1 to 5 was melted using a vacuum melting furnace, cast into a steel ingot, and formed into an 80 mm square steel bar by hot forging. The metal structure of the obtained steel bar was composed of ferrite and pearlite. A rolled material was collected from the 80 mm square steel bar thus obtained, formed into a 18 mm square bar by multi-directional multi-pass caliber rolling in the warm, and then cooled with water to prepare a bar. The rolling method during this period is that the 80 mm square rolled material is heated to 550 ° C. and then rolled at a rolling temperature of 450 to 530 ° C. with a diamond-type caliber roll for 19 passes to form a 24 mm square (at this stage). The length corresponding to 2A 0 in FIG. 6B is 24 mm),
Then, the maximum short axis length (length corresponding to 2A 01 in FIG. 6A) is 11 mm and the long axis length (length 2c in FIG. 6A) is 52 mm. One-pass rolling was performed with a type caliber roll, and finally a 18 mm square bar was manufactured with a square type caliber roll.
上記の通り、実施例1〜5においては、合計パス数が21(=19+1+1)で、材料の総減面率(前記(1)式によるR)は95%であった。また、オーバル型カリバーロールによる圧延後材料のC方向断面の最大短軸長さ(2A01=11mm)は、このオーバル型カリバーロールによる圧延直前の材料の角形状C方向断面の対辺長さ(2A0=24mm)に対して、(11/24)×100=46%になる。なお、前記ダイヤモンド型カリバーロールによる19パス中には、圧延材の断面形状をできるだけ正方形に近づけるために適宜行なった、同一カリバーロールに連続2パスずつ通した圧延(所謂とも通し)もカウントされている。また、各パス毎に材料を長さ方向軸芯の周りに回転させて圧下方向を変化させ、多方向の多パス圧延とした。なお、加工発熱も加わって、温間圧延の圧延温度領域でも比較的低温側領域においては、放熱量が比較的小さく、圧延中材料の温度低下に起因する中間加熱の必要性はなかった。 As described above, in Examples 1 to 5, the total number of passes was 21 (= 19 + 1 + 1), and the total surface area reduction ratio (R according to the formula (1)) was 95%. The maximum minor axis length (2A 01 = 11 mm) of the C-direction cross section of the material after rolling with the oval caliber roll is the opposite side length (2A) of the square C-direction cross section of the material immediately before rolling with the oval caliber roll. (11/24) × 100 = 46% with respect to ( 0 = 24 mm). In addition, during 19 passes by the diamond-type caliber roll, rolling (so-called through) that was performed in order to make the cross-sectional shape of the rolled material as close to a square as possible and passed through the same caliber roll for two consecutive passes was also counted. Yes. In addition, for each pass, the material was rotated around the longitudinal axis to change the rolling direction, and multi-directional multi-pass rolling was performed. In addition, due to the processing heat generation, the heat radiation amount is relatively small even in the rolling temperature region of the warm rolling, and there is no need for intermediate heating due to the temperature drop of the material during rolling.
一方、比較例1を次の通り試験した。これは、圧延温度が本発明の範囲外の高温でカリバー圧延を行なったものであって、次の通りである。表1に示した成分No.1の鋼塊から実施例1と同様にして得られた80mm角の棒鋼を用い、圧延温度が880〜920℃の範囲内において、実施例1〜6と同一カリバーロールを用い、同一パス圧延の方法で圧延して、80mm角の棒鋼から18mm角の棒材を製造した。但し、この間圧延温度を確保するために、適宜中間加熱を施した。 On the other hand, Comparative Example 1 was tested as follows. This is the result of performing caliber rolling at a high temperature outside the range of the present invention, and is as follows. Ingredient No. shown in Table 1 Using an 80 mm square steel bar obtained in the same manner as in Example 1 from the steel ingot of 1 and using the same caliber roll as in Examples 1 to 6 within the rolling temperature range of 880 to 920 ° C, It rolled by the method and the 18-mm square bar was manufactured from the 80-mm square steel bar. However, in order to ensure the rolling temperature during this period, intermediate heating was appropriately performed.
以上により得られた実施例1〜5及び比較例1の棒材について、次の確性試験を行なった。
(1)引張試験により、引張強さTS及び絞りRAを測定した。
(2)顕微鏡によるミクロ組織試験により、主相(第1相)の金属組織同定、C方向断面の平均フェライト粒径測定、並びに第2相の金属組織同定及び第2相の分率測定を行なった。なお、第2相の分率(体積%)測定は、試料断面における面積%を測定し、これで評価した。そして、更に、
(3)冷間圧造性評価のために、上記18mm角の棒材からJIS規格M1.6なべ小ねじの成形用素材である1.3mmφの線材を模して、切削加工により1.3mmφの試験片を切削加工により切出し調製して、M1.6なべ小ねじ用のヘッダー成形により頭部に十字形状のリセス成形試験を行なった。リセス成形時の割れ発生の有無は、小ねじ製造時における決定的な合否判定基準の一つである。そこで、リセス割れ発生の有無を10倍の拡大鏡で観察した。図7及び図8のそれぞれに、リセス割れが発生しなかったもの及び発生したものの外観写真を例示する。
The following accuracy tests were performed on the bars of Examples 1 to 5 and Comparative Example 1 obtained as described above.
(1) Tensile strength TS and drawing RA were measured by a tensile test.
(2) The microstructure of the main phase (first phase), the average ferrite particle size measurement of the cross section in the C direction, the identification of the microstructure of the second phase and the fraction measurement of the second phase are performed by microstructural examination using a microscope. It was. In addition, the fraction (volume%) measurement of the 2nd phase measured the area% in a sample cross section, and evaluated this. And furthermore,
(3) For cold heading evaluation, a 1.3 mmφ wire rod, which is a material for forming a JIS standard M1.6 pan-head screw, was simulated from the 18 mm square rod, and the 1.3 mmφ A test piece was cut out and prepared by cutting, and a cross-shaped recess molding test was performed on the head by header molding for M1.6 pan head screws. The presence or absence of cracking at the time of recess molding is one of the decisive criteria for accepting or rejecting at the time of manufacturing the machine screw. Therefore, the presence or absence of recess cracks was observed with a 10 × magnifier. FIG. 7 and FIG. 8 exemplify external appearance photographs of those in which no recess cracks occurred and those in which they occurred.
表2に、上述した実施例1〜5及び比較例1の主な製造条件及び試験結果を示す。 Table 2 shows main manufacturing conditions and test results of Examples 1 to 5 and Comparative Example 1 described above.
○試験結果
以上の結果より、下記事項がわかる。
○ Test results From the above results, the following items can be understood.
[実施例1〜5について]実施例1〜5は、C含有量が0.001〜0.01質量%という低C領域にあり、圧延温度範囲が450〜530℃で温間圧延領域の範囲内における一層望ましい温度領域にあり、更に、総減面率が大なる95%であって、しかもオーバル型カリバーロールを用い、しかもその最大短軸長さのその圧延直前の角形状材料の対辺長さに対する比率2A01/2A0が46%であって、かなり小さい。このように、この発
明に係る鋼の製造方法の中でも、概して極めて望ましい条件に該当している。ここで得られた鋼の金属組織及び機械的性質は、次の通りである。
[Examples 1 to 5] Examples 1 to 5 are in the low C region where the C content is 0.001 to 0.01% by mass, the rolling temperature range is 450 to 530 ° C, and the range of the warm rolling region. The opposite side length of the square-shaped material immediately before rolling, which is in a more desirable temperature range, and has a total area reduction ratio of 95%, which uses an oval type caliber roll, and which has a maximum short axis length. The ratio 2A 01 / 2A 0 to the height is 46%, which is quite small. Thus, the steel manufacturing method according to the present invention generally corresponds to extremely desirable conditions. The metal structure and mechanical properties of the steel obtained here are as follows.
金属組織は平均フェライト粒径が0.7〜0.9μmのフェライト組織であり、フェライト粒径が著しく微細化されている。そのため引張強さTSは635〜795MPaであり、この発明が必要とする強度水準を満たしており、しかもこの発明において冷間圧造性の重要な指標としている絞りRAが78%以上と高く、下限目標値65%を十分に満たしている。 The metal structure is a ferrite structure having an average ferrite particle size of 0.7 to 0.9 μm, and the ferrite particle size is remarkably refined. Therefore, the tensile strength TS is 635 to 795 MPa, satisfies the strength level required by the present invention, and the drawing RA, which is an important index of cold heading in this invention, is as high as 78% or more, and the lower limit target. The value 65% is fully satisfied.
このように、実施例1〜5の鋼の製造条件は、この発明の範囲内の条件の中でも望ましい条件に属するので、金属組織及び機械的性質共に、極めて優れた特性値が得られていることがわかった。 Thus, since the manufacturing conditions of the steels of Examples 1 to 5 belong to desirable conditions among the conditions within the scope of the present invention, extremely excellent characteristic values are obtained for both the metal structure and mechanical properties. I understood.
[比較例1について]上記実施例1〜5に対して、比較例1は、圧延温度が本発明の範囲外に高い領域である880〜920℃での熱間圧延領域であったので、これ以外の製造条件については望ましいものであったにもかかわらず、得られた鋼は、その特性値として平均フェライト粒径が14.5μmと微細化されておらず、そのため引張強さTSが300MPaと満足すべきものではなく、本発明の範囲外の鋼であった。なお、絞りRAは80.0%と優れていたので、冷間圧造性に優れており、リセス割れは発生していない。しかし、比較例1の鋼では、冷間圧造及び転造等によりねじ等に成形された製品は、成形ままではこの発明の目標とする引張強さの下限値600MPaを満たすことができない。 [Comparative Example 1] In contrast to Examples 1 to 5, Comparative Example 1 was a hot rolling region at 880 to 920 ° C, which is a region where the rolling temperature is outside the range of the present invention. In spite of the fact that the production conditions other than those described above were desirable, the obtained steel was not refined as an average ferrite grain size of 14.5 μm as its characteristic value, and therefore the tensile strength TS was 300 MPa. It was not satisfactory and was outside the scope of the present invention. In addition, since the drawing RA was as excellent as 80.0%, it was excellent in cold heading, and no recess crack was generated. However, in the steel of Comparative Example 1, a product formed into a screw or the like by cold heading or rolling cannot satisfy the lower limit 600 MPa of the target tensile strength of the present invention as it is.
以上の試験Iにより、この発明に係る鋼の種々態様の製造方法により、この発明に係る高強度で且つ冷間圧造性に優れた鋼が製造されることが確認された。また、これらの鋼を用いて、この発明に係る強度に優れたねじ及びボルト等の締結部品又は軸類等の成形品が製造されることもわかる。 From the above test I, it was confirmed that the steel having high strength and excellent cold forgeability according to the present invention was manufactured by the manufacturing methods of various aspects of the steel according to the present invention. Moreover, it turns out that molded articles, such as fastening parts, such as a screw and a volt | bolt excellent in the strength which concerns on this invention, or shafts, are manufactured using these steels.
1 鋼片
2a、2b 熱間圧延又は熱間鍛造
3 半製品
4 鋼線又は鋼棒
5 熱処理
6 冷間圧造及び転造
7 ねじ及びボルト等の締結部品又は軸類等の成形品
8 調質処理
9 表面処理
10 製品
11 ダイス
12a 第1パンチ
12b 第2パンチ
13 切断された鋼線(材料)
14 頭部
15 リセス
16 中間成形品
17 リセスが成形された中間成形品
18a、18b:オーバル形状
19:オーバル形状の孔型による圧延後の材料
20:オーバル形状の孔型による圧延前の材料
21a、21b:オーバル形状カリバーの部分断面
22 鋼片又は鋳片
23 温間圧延
24 線材又は棒材
25 切削加工
1 Steel slab 2a, 2b Hot rolling or hot forging 3 Semi-finished product 4 Steel wire or steel bar 5 Heat treatment 6 Cold forging and rolling 7 Fastening parts such as screws and bolts or moldings such as shafts 8 Conditioning treatment 9 Surface treatment 10 Product 11 Die 12a First punch 12b Second punch 13 Cut steel wire (material)
14 Head 15 Recess 16 Intermediate molded product 17 Intermediate molded product 18e, 18b formed with recess: Oval shape 19: Material after rolling with oval shape hole mold 20: Material before rolling with oval shape hole shape 21a, 21b: Partial cross section of oval-shaped caliber 22 Steel slab or slab 23 Warm rolling 24 Wire or bar 25 Cutting
Claims (2)
C:0.01質量%未満、
Si:2.0質量%以下、
Mn:3.0質量%以下、
P:0ないし0.2質量%以下、
S:0.03質量%以下、
Al:0.1質量%以下、及び
N:0.02質量%以下
を有し、残部がFe及び不可避不純物からなり、セメンタイトの体積分率が0%であるフェライト組織であって、前記フェライト組織は、圧延方向に垂直な断面の平均粒径が1μm以下のフェライト組織であり、引張強さTSが600MPa以上で且つ絞りRAが70%以上の機械的性質を有し、球状化焼なまし処理が行なわれていないことを特徴とする冷間圧造用鋼。 The following chemical composition:
C: less than 0.01% by mass,
Si: 2.0 mass% or less,
Mn: 3.0% by mass or less,
P: 0 to 0.2% by mass or less,
S: 0.03 mass% or less,
Al: 0.1% by mass or less, and
N: 0.02 mass% or less
In which the balance is made of Fe and inevitable impurities, and the cementite volume fraction is 0%, and the ferrite structure has a ferrite structure having an average grain size of 1 μm or less in a cross section perpendicular to the rolling direction. A steel for cold heading, which has a mechanical property with a tensile strength TS of 600 MPa or more and a drawing RA of 70% or more and is not subjected to spheroidizing annealing.
In claim 1, wherein the cold heading steel, screws and bolts fastening components or axes such molded articles of which is characterized by being manufactured by a processing method including heading.
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JP2003435980A Division JP4340754B2 (en) | 2003-12-26 | 2003-12-26 | Steel having high strength and excellent cold forgeability, and excellent molded parts such as screws and bolts or shafts having excellent strength, and methods for producing the same. |
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