JP7406762B2 - High strength, high ductility fine martensitic structure steel and manufacturing method thereof - Google Patents
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- 229910000831 Steel Inorganic materials 0.000 title claims description 41
- 239000010959 steel Substances 0.000 title claims description 41
- 229910000734 martensite Inorganic materials 0.000 title claims description 34
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 239000000463 material Substances 0.000 claims description 40
- 238000005096 rolling process Methods 0.000 claims description 14
- 230000009467 reduction Effects 0.000 claims description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 5
- 229910001567 cementite Inorganic materials 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 2
- 239000000126 substance Substances 0.000 claims description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 14
- 229910001566 austenite Inorganic materials 0.000 description 12
- 238000003303 reheating Methods 0.000 description 7
- 229910000859 α-Fe Inorganic materials 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 5
- 229910052742 iron Inorganic materials 0.000 description 5
- 238000000034 method Methods 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000005242 forging Methods 0.000 description 3
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 238000001887 electron backscatter diffraction Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 239000000470 constituent Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 239000011572 manganese Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000029052 metamorphosis Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000011863 silicon-based powder Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
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Description
特許法第３０条第２項適用 平成２９年８月２１日一般社団法人日本鉄鋼協会第１７４回秋季講演大会材料とプロセス研究発表要旨集（ＣＤ版）にて公開Application of Article 30, Paragraph 2 of the Patent Act Published on August 21, 2017 in the Materials and Process Research Presentation Abstracts (CD version) of the 174th Autumn Conference of the Iron and Steel Institute of Japan
特許法第３０条第２項適用 平成２９年９月７日北海道大学札幌キャンパスにおいて開催された一般社団法人日本鉄鋼協会第１７４回秋季講演大会にて発表Application of Article 30, Paragraph 2 of the Patent Act Presented at the 174th Autumn Conference of the Iron and Steel Institute of Japan held on September 7, 2017 at Hokkaido University Sapporo Campus
本発明は、建造物や橋梁等の構造物、自動車の足回り鋼、機械用歯車等部品に使用される鋼として好適な高強度・高延性微細マルテンサイト組織鋼材及びその製造方法に関するものである。 The present invention relates to a high-strength, high-ductility fine martensitic structure steel material suitable for use in parts such as structures such as buildings and bridges, automobile suspension steel, and mechanical gears, and a method for manufacturing the same. .
マルテンサイトは、四つの構成要素でできた複雑な階層構造をとっている。大きさが数１０μｍの旧オーステナイト（γ）粒は大きさ数μｍのパケットが詰まった構造になっており、そのパケットは幅が約１μｍの細長いブロックが詰まってできている。さらに、このブロックはラスによって構成されている。すなわち、旧オーステナイト粒、パケット、ブロック、ラスの四つの構成要素が積み重なってできている。この四つの構成要素の粒界・境界や粒内に数～数１０ｎｍの大きさの炭化物粒子が分散しているという複雑な階層構造をとっている。 Martensite has a complex hierarchical structure made up of four components. Prior austenite (γ) grains with a size of several tens of μm have a structure packed with packets with a size of several μm, and the packets are made up of elongated blocks with a width of about 1 μm. Additionally, this block is made up of laths. In other words, it is made up of four components: prior austenite grains, packets, blocks, and laths. It has a complex hierarchical structure in which carbide particles with a size of several to several tens of nanometers are dispersed within the grain boundaries and boundaries of these four constituent elements.
このような複雑な階層構造をとるマルテンサイト組織を有する鋼材は、建造物や橋梁等、自動車の足回り鋼、機械用歯車等部品に使用される場合、強度・延性が十分とは言えず、さらなる改良を行うことが望まれていた。 Steel materials with a martensitic structure that has such a complex hierarchical structure cannot be said to have sufficient strength and ductility when used in parts such as buildings and bridges, automobile undercarriage steel, and mechanical gears. Further improvements were desired.
本発明は、このような従来技術の問題に鑑みてなされたもので、建造物や橋梁等、自動車の足回り鋼、機械用歯車等部品に使用した場合でも、十分な機械的強度、延性を有する高強度・高延性微細マルテンサイト組織鋼材及びその製造方法を提供することを課題とする。 The present invention was made in view of the problems of the prior art, and it provides sufficient mechanical strength and ductility even when used in parts such as buildings and bridges, automobile suspension steel, mechanical gears, etc. An object of the present invention is to provide a high-strength, high-ductility fine martensitic structure steel material and a method for producing the same.
本発明によれば、上記課題を解決するため、下記の技術的手段ないし技術的手法が提供される。
〔１〕Ｃ：０．０７５～０．３ｗｔ％、Ｍｎ：３～１０ｗｔ％、Ｓｉ：０～２．５ｗｔ％を含有するとともに、残部がＦｅ及び不可避的不純物からなり、旧γ粒径が２．０μｍ以下であり、シングルブロック構造である等軸マルテンサイトである組織を有する高強度・高延性微細マルテンサイト組織鋼材。
〔２〕上記第１の発明において、引張強さが１２００ＭＰａ以上、全伸びが１０％以上であることを特徴とする高強度・高延性微細マルテンサイト組織鋼材。
〔３〕上記第１又は第２の発明の高強度・高延性鋼材の製造方法であって、前記化学成分の素材に３００～６００℃の温度範囲で圧下率５０％以上の圧延加工を行い、微細フェライト－セメンタイトの組織とし、次いで７００～９５０℃の温度範囲で１秒～３時間保持後、水冷又は空冷を行い、シングルブロック構造をもつ等軸微細マルテンサイトである組織を有する高強度・高延性鋼材を製造することを特徴とする高強度・高延性微細マルテンサイト組織鋼材の製造方法。
According to the present invention, in order to solve the above problems, the following technical means or techniques are provided.
[1] Contains C: 0.075 to 0.3 wt%, Mn: 3 to 10 wt%, Si: 0 to 2.5 wt%, the balance is Fe and unavoidable impurities, and the prior γ grain size is 2. A high-strength, high-ductility fine martensitic microstructure steel material having a microstructure of equiaxed martensite with a single block structure and having a diameter of .0 μm or less.
[2] The high-strength, high-ductility fine martensitic structure steel material according to the first invention, characterized in that it has a tensile strength of 1200 MPa or more and a total elongation of 10% or more.
[3] A method for producing a high-strength, high-ductility steel material according to the first or second invention, which comprises rolling the material having the chemical composition at a reduction rate of 50% or more in a temperature range of 300 to 600°C; A fine ferrite-cementite structure is formed, then held at a temperature range of 700 to 950°C for 1 second to 3 hours, and then water or air cooled to produce a high-strength, high-strength material with a structure of equiaxed fine martensite with a single block structure. A method for producing a high-strength, high-ductility fine martensitic structure steel material, which is characterized by producing a ductile steel material.
本発明によれば、上記構成を採用したので、建造物や橋梁等、自動車の足回り鋼、機械用歯車等部品に使用した場合でも、十分な機械的強度、延性を有するという優れた効果を得ることができる。 According to the present invention, since the above structure is adopted, even when used in parts such as buildings and bridges, automobile undercarriage steel, mechanical gears, etc., the excellent effect of having sufficient mechanical strength and ductility can be achieved. Obtainable.
以下、本発明を実施の形態により詳細に説明する。 Hereinafter, the present invention will be explained in detail using embodiments.
本発明の高強度・高延性微細マルテンサイト組織鋼材は、Ｃ：０．０７５～０．３ｗｔ％、Ｍｎ：３～１０ｗｔ％、Ｓｉ：０～２．５ｗｔ％を含有するとともに、残部がＦｅ及び不可避的不純物からなり、旧γ粒径が２．０μｍ以下であり、シングルブロックをもつ等軸マルテンサイトである組織を有することを特徴とする。 The high strength and high ductility fine martensitic structure steel material of the present invention contains C: 0.075 to 0.3 wt%, Mn: 3 to 10 wt%, Si: 0 to 2.5 wt%, and the balance is Fe and It is characterized by consisting of unavoidable impurities, having a prior γ grain size of 2.0 μm or less, and having an equiaxed martensite structure with a single block.
本発明の鋼材において、Ｃは０．０７５～０．３ｗｔ％とする。Ｃは焼入性とは引張強度を確保するために必要であるが、０．０７５ｗｔ％未満では、マルテンサイトを生成せず鋼材の引張強度を十分に満たさないおそれがあり、０．３ｗｔ％を超えると、鋼材の延性・靱性の低下及び溶接性の低下となる。 In the steel material of the present invention, C is 0.075 to 0.3 wt%. C is necessary to ensure hardenability and tensile strength, but if it is less than 0.075 wt%, martensite will not be generated and the tensile strength of the steel material may not be fully satisfied. If it exceeds this, the ductility and toughness of the steel material will decrease, as well as the weldability.
また、Ｓｉは０～２．５ｗｔ％とする。Ｓｉは、材質を大きく硬質化する置換型元素であり、鋼の強度を有効な元素である。しかしながら、Ｓｉ含有量が過度に高くなると熱間加工時の加熱中にＳｉスケールが多く発生しスケール除去に余分のコストがかかることや、スケールによる表面疵が発生し易くなる。したがって、Ｓｉの上限は２．５ｗｔ％とする。 Further, Si is set at 0 to 2.5 wt%. Si is a substitutional element that greatly hardens the material, and is an element that is effective in increasing the strength of steel. However, if the Si content is excessively high, a large amount of Si scale will be generated during heating during hot working, resulting in extra cost for scale removal and surface flaws due to scale. Therefore, the upper limit of Si is set to 2.5 wt%.
また、Ｍｎは３～１０ｗｔ％とする。Ｍｎは、オーステナイト生成元素であり、焼入れ性を向上させ、微細γ粒からマルテンサイトを生成させる。しかし、Ｍｎが高濃度になると凝固時の鋼中Ｍｎの偏析が過大となり材料内部の均一性を害する。また、素材の調製工程における熱間加工工程において表面割れが発生し易くなる。したがって、Ｍｎの上限は１０ｗｔ％とする。 Further, Mn is set at 3 to 10 wt%. Mn is an austenite-forming element, improves hardenability, and generates martensite from fine γ grains. However, when the concentration of Mn becomes high, the segregation of Mn in the steel during solidification becomes excessive, impairing the uniformity inside the material. Furthermore, surface cracks are likely to occur during the hot working step in the material preparation step. Therefore, the upper limit of Mn is set to 10 wt%.
本発明の鋼材の微細組織は、旧γ粒径が２．０μｍ以下、より好ましくは１．０μｍであり、シングルブロックをもつ等軸マルテンサイトである。前述のように、通常マルテンサイトは、旧オーステナイト、パケット、ブロック、ラスの階層構造をもち、ひとつの旧オーステナイト（γ）粒は、複数のパケットを持ち、パケット内部には様々な方位（バアリアント）をもつブロックが変態生成する。ブロック境界は大角粒界である。ところがγ粒径を微細化していくと、図１に示すようにシングルパケットマルチブロック、さらに微細化するとシングルブロック（シングルバリアント）マルテンサイトが生成する可能性がある。つまり、旧オーステナイトを微細化してゆくと、その内部に生成し得るブロックの数が減ってゆく。最終的には、一つのブロックしか生成できなくなる。あたかも、見かけ上一つの旧オーステナイトが一つのフェライト粒に変化したようになる。しかし、一般にγ粒径を微細化すると焼入性が低下し、マルテンサイトとならない。ところが、本発明では、Ｍｎを適量添加するとともに、熱間圧延により組織をあらかじめ超微細フェライト－セメンタイトとすることにより、旧γ粒径を２．０μｍ以下とし、さらにＭｎを適量添加することにより、シングルブロック構造をもつ等軸マルテンサイトである組織とすることを可能にした。ここで超微細とは、旧オーステナイト粒径２μｍ以下のことをいう。シングルブロック構造とは、オーステナイト粒から１つのブロックのみが存在している構造をいう。隣接するブロックとは、母相であるオーステナイトが異なるものになる。これは、組織のＥＢＳＤ（電子線後方散乱回折）観察結果をバリアント解析法によって確認できる。 The microstructure of the steel material of the present invention has a prior γ grain size of 2.0 μm or less, more preferably 1.0 μm, and is equiaxed martensite with a single block. As mentioned above, martensite usually has a hierarchical structure of prior austenite, packets, blocks, and laths, and one prior austenite (γ) grain has multiple packets, and inside the packet there are various orientations (variants). A block with a metamorphosis is generated. Block boundaries are large-angle grain boundaries. However, when the γ grain size is made finer, single-packet multi-block may be produced as shown in FIG. 1, and when it is further made finer, single-block (single variant) martensite may be produced. In other words, as the former austenite becomes finer, the number of blocks that can be generated inside it decreases. In the end, only one block can be generated. It appears as if one old austenite has changed into one ferrite grain. However, in general, when the γ grain size is made finer, the hardenability decreases and martensite cannot be formed. However, in the present invention, by adding an appropriate amount of Mn and making the structure into ultrafine ferrite-cementite in advance by hot rolling, the prior γ grain size is set to 2.0 μm or less, and by further adding an appropriate amount of Mn, This made it possible to create an equiaxed martensite structure with a single block structure. Here, the term "ultrafine" refers to a prior austenite grain size of 2 μm or less. The single block structure refers to a structure in which only one block exists from austenite grains. Adjacent blocks have different austenite matrix. This can be confirmed by variant analysis of tissue EBSD (electron backscatter diffraction) observation results.
本発明の高強度・高延性微細マルテンサイト組織鋼材は、引張強さが１２００ＭＰａ以上、全伸びが１０％以上である。 The high strength and high ductility fine martensitic structure steel material of the present invention has a tensile strength of 1200 MPa or more and a total elongation of 10% or more.
次に、本発明の高強度・高延性微細マルテンサイト組織鋼材の製造方法について説明する。 Next, a method for manufacturing the high strength, high ductility fine martensitic structure steel material of the present invention will be explained.
まず、Ｆｅ粉末、Ｃ粉末、Ｓｉ粉末、Ｍｎ粉末をそれぞれＣ：０．０７５～０．３ｗｔ％、Ｍｎ：３～１０ｗｔ％、Ｓｉ：０～２．５ｗｔ％、残りＦｅとなるように調整し、素材とする。そして、この素材に熱間圧延を施す。 First, Fe powder, C powder, Si powder, and Mn powder were adjusted so that C: 0.075 to 0.3 wt%, Mn: 3 to 10 wt%, Si: 0 to 2.5 wt%, and the remainder was Fe. , material. This material is then hot rolled.
温間圧延は、工業的に行われている厚鋼板製造ラインにおける平ロール圧延、極厚鋼板製造ラインにおける鍛造、棒鋼又は鋼線材製造ラインにおける溝ロール圧延、及び条鋼又は形鋼ラインにおける形ロール圧延の内のいずれであってもよい。これらいずれかの加工方式により、素材に対して塑性ひずみを与える。この温間圧延は、３００～６００℃の温度範囲で圧下率５０～９０％の圧延加工を行い、超微細フェライト－セメンタイトの組織とする。温間圧延の温度が３００℃未満であると、セメンタイトが生成せず、一方６００℃を超えるとオーステナイトが逆変態生成してしまう。圧下率が５０％未満であると、初期組織の加工硬化状態となり、微細フェライトと微細セメンタイトが十分に発達しない。 Warm rolling includes flat roll rolling on industrial thick steel plate production lines, forging on extra-thick steel plate production lines, groove roll rolling on steel bar or steel wire production lines, and shaped roll rolling on long bar or shape steel production lines. It may be any of the following. Plastic strain is applied to the material by any of these processing methods. This warm rolling is performed at a temperature range of 300 to 600° C. with a rolling reduction of 50 to 90%, resulting in an ultrafine ferrite-cementite structure. If the warm rolling temperature is less than 300°C, cementite will not be produced, while if it exceeds 600°C, austenite will be produced through reverse transformation. If the rolling reduction is less than 50%, the initial structure will be in a work-hardened state, and fine ferrite and fine cementite will not develop sufficiently.
温間圧延の後、７３０～９５０℃の温度範囲で１秒～３時間保持し、再加熱を行う。再加熱の後、水冷、あるいは空冷を行い、シングルバリアントをもつ等軸マルテンサイトである組織を有する高強度・高延性鋼材を製造する。再加熱温度が７３０℃未満であると、フェライト＋セメンタイト組織が完全に逆変態せず、フェライトとオーステナイトの２相組織となり、マルテンサイト組織を得ることができない。９５０℃を超えると逆変態オーステナイト組織が粗大となり、微細マルテンサイトを得ることができない。 After warm rolling, it is held at a temperature range of 730 to 950°C for 1 second to 3 hours and reheated. After reheating, water or air cooling is performed to produce a high-strength, high-ductility steel material with an equiaxed martensite structure with a single variant. If the reheating temperature is less than 730°C, the ferrite+cementite structure will not undergo complete reverse transformation, resulting in a two-phase structure of ferrite and austenite, making it impossible to obtain a martensitic structure. If the temperature exceeds 950°C, the reversely transformed austenite structure becomes coarse and fine martensite cannot be obtained.
以下、本発明を実施例により更に具体的に説明する。
＜実施例１＞
溶解用主原料としてＦｅ、Ｃ、Ｓｉ、Ｍｎを０．１ｗｔ％、Ｃ－２ｗｔ％Ｓｉ－５ｗｔ％Ｍｎ、残りＦｅを準備した。この溶解用主原料に高周波真空誘導加熱炉を用いて、溶製し、縦１００ｍｍ×横１００×高さ３００ｍｍの鋼塊を鋳造し、本発明の高強度・高延性鋼材の素材とした。この素材を１２００℃で熱間鍛造し、断面３８角の角棒とした。
EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.
<Example 1>
As main raw materials for dissolution, 0.1 wt% of Fe, C, Si, and Mn, C-2 wt% Si-5 wt% Mn, and the remainder Fe were prepared. This main raw material for melting was melted using a high frequency vacuum induction heating furnace, and a steel ingot measuring 100 mm in length x 100 mm in width x 300 mm in height was cast, and was used as a material for the high strength and high ductility steel material of the present invention. This material was hot forged at 1200°C to form a square bar with a cross section of 38 squares.
次に、この素材を５５０℃で１時間加熱の後、圧下率９０％で温間溝ロール圧延を行い、組織をあらかじめ超微細フェライト－セメンタイトとした。得られた組織のフェライト粒径は約０．５μｍであった。 Next, this material was heated at 550° C. for 1 hour and then warm groove rolled at a rolling reduction rate of 90% to form an ultrafine ferrite-cementite structure in advance. The ferrite grain size of the obtained structure was about 0.5 μm.
次に、旧γ粒径を大きく変化させるため、再加熱温度を７００、７５０、８００、１２００℃として、１時間保持後水冷を行い、バリアント解析により旧粒径を算出した。また、引張試験を行い、力学的特性を評価した。 Next, in order to greatly change the prior γ grain size, the reheating temperature was set to 700, 750, 800, and 1200° C., and after holding for 1 hour, water cooling was performed, and the prior grain size was calculated by variant analysis. In addition, a tensile test was conducted to evaluate the mechanical properties.
図２に再加熱温度７５０℃と１２００℃で得られたマルテンサイト組織のＥＢＳＤ－ＩＰＦ（電子線後方散乱回折－結晶方位）像を示す。図２の黒線は、バリアント解析で決定したγ粒界を示す。図３は、図２の正極点図を表す。図３（ａ）より黒線で囲まれた領域は、全ブロックがＫ－Ｓの関係を持ち、複数のパケット・ブロックからなる旧γ粒径約１８０μｍマルテンサイトとわかった。図３（ｂ）は、図２（ｂ）の黒線で囲まれた領域（正極点図の中心★印）と周囲の粒の方位関係をプロットした結果であるが、Ｋ－Ｓの関係がみられなかった。したがって黒線で囲まれた領域は独立した旧γ粒であるとわかった。旧γ粒径は約２．０μｍまで微細化すると、シングルバリアントをもつ等軸マルテンサイトが得られた。図４は公称応力－公称ひずみ曲線を示すが、シングルバリアントマルテンサイトは、高強度・高延性であった。 FIG. 2 shows EBSD-IPF (electron backscatter diffraction-crystal orientation) images of martensitic structures obtained at reheating temperatures of 750° C. and 1200° C. The black lines in FIG. 2 indicate the γ grain boundaries determined by variant analysis. FIG. 3 represents the positive pole figure of FIG. From FIG. 3(a), it was found that the area surrounded by the black line is martensite with a prior γ grain size of approximately 180 μm, which is composed of a plurality of packet blocks and has a KS relationship in all blocks. Figure 3(b) is the result of plotting the orientation relationship between the area surrounded by the black line in Figure 2(b) (the center ★ mark of the positive pole figure) and the surrounding grains. I couldn't see it. Therefore, the region surrounded by the black line was found to be an independent prior γ grain. When the prior γ grain size was refined to about 2.0 μm, equiaxed martensite with a single variant was obtained. Figure 4 shows the nominal stress-nominal strain curve, and single variant martensite had high strength and high ductility.
＜実施例２＞
溶解用主原料としてＦｅ、Ｃ、Ｓｉ、Ｍｎを０．１５ｗｔ％Ｃ－２ｗｔ％Ｓｉ－５ｗｔ％Ｍｎ、残りＦｅを準備したこと以外は、実施例１と同様にして、熱間鍛造し、断面３８角の角棒とした。
<Example 2>
Hot forging was carried out in the same manner as in Example 1, except that 0.15wt%C-2wt%Si-5wt%Mn of Fe, C, Si, and Mn were prepared as the main raw materials for melting, and the remainder was Fe. It was made into a 38 square bar.
次に、この素材を５５０℃で１時間加熱の後、圧下率９０％で温間溝ロール圧延を行い、組織をあらかじめ超微細フェライト－セメンタイトとした。得られた組織のフェライト粒径は、実施例と同様に約０．５μｍであった。 Next, this material was heated at 550° C. for 1 hour and then warm groove rolled at a rolling reduction rate of 90% to form an ultrafine ferrite-cementite structure in advance. The ferrite grain size of the obtained structure was about 0.5 μm, similar to the example.
次に、旧γ粒径を大きく変化させるため、再加熱温度を７５０℃として、１時間保持後水冷を行い、バリアント解析により旧粒径を算出した。また、引張試験を行い、力学的特性を評価した。 Next, in order to greatly change the prior γ grain size, the reheating temperature was set to 750° C., and after holding for 1 hour, water cooling was performed, and the prior grain size was calculated by variant analysis. In addition, a tensile test was conducted to evaluate the mechanical properties.
＜実施例３＞
溶解用主原料としてＦｅ、Ｃ、Ｓｉ、Ｍｎを０．２ｗｔ％Ｃ－２ｗｔ％Ｓｉ－５ｗｔ％Ｍｎ、残りＦｅを準備したこと以外は、実施例１と同様にして、熱間鍛造し、断面３８角の角棒とした。
<Example 3>
Hot forging was carried out in the same manner as in Example 1, except that 0.2wt%C-2wt%Si-5wt%Mn of Fe, C, Si, and Mn were prepared as the main raw materials for melting, and the remainder was Fe. It was made into a 38 square bar.
次に、この素材を５５０℃で１時間加熱の後、圧下率９０％で温間溝ロール圧延を行い、組織をあらかじめ超微細フェライト－セメンタイトとした。得られた組織のフェライト粒径は、実施例と同様に約０．５μｍであった。 Next, this material was heated at 550° C. for 1 hour and then warm groove rolled at a rolling reduction rate of 90% to form an ultrafine ferrite-cementite structure in advance. The ferrite grain size of the obtained structure was about 0.5 μm, similar to the example.
次に、旧γ粒径を大きく変化させるため、再加熱温度を７５０℃として、１時間保持後水冷を行い、バリアント解析により旧粒径を算出した。また、引張試験を行い、力学的特性を評価した。 Next, in order to greatly change the prior γ grain size, the reheating temperature was set to 750° C., and after holding for 1 hour, water cooling was performed, and the prior grain size was calculated by variant analysis. In addition, a tensile test was conducted to evaluate the mechanical properties.
力学的特性を評価した結果、実施例２の鋼材では、引張強さが１４５０Ｍｐａであり、全伸びが１２％であった。また、実施例３の鋼材では、引張強さが１６００Ｍｐａであり、全伸びが１０％であった。 As a result of evaluating the mechanical properties, the steel material of Example 2 had a tensile strength of 1450 Mpa and a total elongation of 12%. Further, the steel material of Example 3 had a tensile strength of 1600 Mpa and a total elongation of 10%.
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| WO2007058364A1 (en) | 2005-11-21 | 2007-05-24 | National Institute For Materials Science | Steel for warm working, method of warm working of the steel, and steel material and steel part obtained by the same |
| JP2013173970A (en) | 2012-02-24 | 2013-09-05 | National Institute For Materials Science | High hardness steel of ultrafine martensite, and method of producing the same |
| JP2015017292A (en) | 2013-07-09 | 2015-01-29 | 独立行政法人物質・材料研究機構 | Martensite steel and production method thereof |
| WO2015102050A1 (en) | 2014-01-06 | 2015-07-09 | 新日鐵住金株式会社 | Steel material and process for producing same |
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| WO2007058364A1 (en) | 2005-11-21 | 2007-05-24 | National Institute For Materials Science | Steel for warm working, method of warm working of the steel, and steel material and steel part obtained by the same |
| JP2013173970A (en) | 2012-02-24 | 2013-09-05 | National Institute For Materials Science | High hardness steel of ultrafine martensite, and method of producing the same |
| JP2015017292A (en) | 2013-07-09 | 2015-01-29 | 独立行政法人物質・材料研究機構 | Martensite steel and production method thereof |
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