JP5821260B2 - High-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property, and method for producing the same - Google Patents
High-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property, and method for producing the same Download PDFInfo
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- 238000007710 freezing Methods 0.000 title claims description 26
- 230000008014 freezing Effects 0.000 title claims description 25
- 229910001335 Galvanized steel Inorganic materials 0.000 title claims description 24
- 239000008397 galvanized steel Substances 0.000 title claims description 24
- 238000004519 manufacturing process Methods 0.000 title claims description 9
- 229910001566 austenite Inorganic materials 0.000 claims description 48
- 229910000734 martensite Inorganic materials 0.000 claims description 42
- 238000001816 cooling Methods 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 18
- 238000005246 galvanizing Methods 0.000 claims description 15
- 230000000717 retained effect Effects 0.000 claims description 15
- 229910000859 α-Fe Inorganic materials 0.000 claims description 14
- 238000007747 plating Methods 0.000 claims description 11
- 238000000137 annealing Methods 0.000 claims description 10
- 229910001568 polygonal ferrite Inorganic materials 0.000 claims description 10
- 238000000034 method Methods 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 9
- 238000005275 alloying Methods 0.000 claims description 8
- 238000005097 cold rolling Methods 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 229910052759 nickel Inorganic materials 0.000 claims description 7
- 229910052758 niobium Inorganic materials 0.000 claims description 7
- 229910052720 vanadium Inorganic materials 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 229910000831 Steel Inorganic materials 0.000 description 27
- 239000010959 steel Substances 0.000 description 27
- 230000000694 effects Effects 0.000 description 14
- 238000005096 rolling process Methods 0.000 description 14
- 230000009466 transformation Effects 0.000 description 9
- 229910001563 bainite Inorganic materials 0.000 description 8
- 238000002791 soaking Methods 0.000 description 7
- 230000007423 decrease Effects 0.000 description 6
- 238000005098 hot rolling Methods 0.000 description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- 238000005554 pickling Methods 0.000 description 5
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- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
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- 238000005728 strengthening Methods 0.000 description 3
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- 229910045601 alloy Inorganic materials 0.000 description 2
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- 238000007796 conventional method Methods 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
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- 238000009864 tensile test Methods 0.000 description 2
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Description
本発明は、自動車用鋼板としての用途に好適な成形性及び形状凍結性に優れる高強度溶融亜鉛めっき鋼板、並びにその製造方法に関する。 The present invention relates to a high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property suitable for use as a steel sheet for automobiles, and a method for producing the same.
近年、地球環境の保全の見地から自動車の燃費向上が重要な課題となっている。このため、車体材料の高強度化により薄肉化を図り、車体そのものの軽量化により燃費向上を図る動きが活発になってきている。自動車部品のようにプレス加工や曲げ加工により製品に成型される鋼板には高強度を保ちつつ加工に耐えうる成形性が要求される。特許文献１では焼戻しマルテンサイトおよび残留オーステナイトを活用することで高強度と高加工性の両立を実現している。ところが、一般に鋼板の強度が高くなるにつれ、加工後のスプリングバックは大きくなり、形状凍結成性が低下するという問題がある。特許文献１では形状凍結性については検討されておらず改善の余地が見られる。一方で、特許文献２ではフェライト、ベイナイトとＣ濃度の低いオーステナイトからなる組織を活用することで、YRが低く、形状凍結性に優れる鋼板が得られている。しかし伸びフランジ性については評価しておらず、十分な加工性を有するとは云い難い。特許文献３では焼戻しマルテンサイト、ベイナイト、残留オーステナイトを活用することで高強度と高延性を両立させているが、形状凍結性に関しては言及されていない。また、伸びフランジ性は絶対値としては必ずしも高くなく、改善の余地がある。 In recent years, improving the fuel efficiency of automobiles has become an important issue from the viewpoint of conservation of the global environment. For this reason, efforts are being made to reduce the thickness by increasing the strength of the vehicle body material and to improve the fuel efficiency by reducing the weight of the vehicle body itself. Steel sheets that are formed into products by pressing or bending, such as automobile parts, are required to have formability that can withstand processing while maintaining high strength. In Patent Document 1, both high strength and high workability are realized by utilizing tempered martensite and retained austenite. However, generally, as the strength of the steel sheet increases, the spring back after processing increases, and there is a problem that the shape freezing property decreases. In Patent Document 1, the shape freezing property is not studied and there is room for improvement. On the other hand, Patent Document 2 uses a structure composed of ferrite, bainite, and austenite having a low C concentration to obtain a steel sheet having a low YR and excellent shape freezeability. However, stretch flangeability has not been evaluated, and it is difficult to say that it has sufficient workability. In Patent Document 3, high strength and high ductility are made compatible by utilizing tempered martensite, bainite, and retained austenite, but no mention is made regarding shape freezeability. Further, the stretch flangeability is not necessarily high in absolute value, and there is room for improvement.
本発明は、上記した従来技術が抱える問題を有利に解決し、自動車部品用素材として好適な、引張強さ(TS)：1180MPa以上、全伸び(EL)：14％以上、穴拡げ率(λ)：30％以上かつ降伏比(YR)：70％以下である成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板、並びにその製造方法を提供することを目的とする。なお、降伏比(YR)は、引張強さ(TS)に対する降伏強さ(YS)の比で、YR(％)=(YS/TS)×100で表される。 The present invention advantageously solves the above-mentioned problems of the prior art and is suitable as a material for automobile parts. Tensile strength (TS): 1180 MPa or more, total elongation (EL): 14% or more, hole expansion rate (λ ): 30% or more and yield ratio (YR): 70% or less It is an object to provide a high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property, and a method for producing the same. The yield ratio (YR) is the ratio of the yield strength (YS) to the tensile strength (TS) and is expressed as YR (%) = (YS / TS) × 100.
本発明者らは、上記した課題を達成し、成形性および形状凍結性に優れる高強度溶融亜鉛めっき鋼板を製造するため、鋼板の成分組成およびミクロ組織の観点から鋭意研究を重ねた結果、以下のことを見出した。 In order to achieve the above-mentioned problems and to produce a high-strength hot-dip galvanized steel sheet that is excellent in formability and shape freezing property, the present inventors have conducted earnest research from the viewpoint of the component composition and microstructure of the steel sheet. I found out.
合金元素を適当に調整した上で、面積率で0〜5％のポリゴナルフェライト、5％以上のベイニティックフェライト、5〜20％のマルテンサイト、30〜60％の焼戻しマルテンサイトと、5〜20％の残留オーステナイトを含む組織とし、かつ旧オーステナイトの平均粒径を15μm以下とすることで高強度と高成形性および高形状凍結性の両立が可能となる。 After appropriately adjusting the alloy elements, the area ratio is 0-5% polygonal ferrite, 5% or more bainitic ferrite, 5-20% martensite, 30-60% tempered martensite, 5 When the structure contains -20% retained austenite and the average particle size of prior austenite is 15 μm or less, both high strength, high formability, and high shape freezing property can be achieved.
焼戻しマルテンサイト主体組織にマルテンサイトが分散することで形状凍結性が向上する理由については必ずしも明確ではないが、めっき後またはめっき合金化後冷却の際に焼戻しマルテンサイトに接しているオーステナイトがマルテンサイト変態して焼戻しマルテンサイト中に可動転位が導入されることでYRが減少するためであることなどが考えられる。また、旧オーステナイト粒を微細にすることでλが向上する理由についても明確ではないが、旧オーステナイト粒が微細になることで焼鈍後組織の平均粒径が小さくなり、伸びフランジ加工時に亀裂の伝播経路が多くなり亀裂の連結が抑制されるためであると推察される。 The reason why the shape freezing property is improved by dispersing martensite in the tempered martensite main structure is not necessarily clear, but austenite in contact with the tempered martensite after cooling after plating or plating alloying is martensite. This may be because YR is reduced by introducing mobile dislocations in the tempered martensite after transformation. The reason why λ is improved by making the prior austenite grains fine is not clear, but the fine grain of the prior austenite grains decreases the average grain size of the microstructure after annealing, and crack propagation during stretch flange processing This is probably because the number of paths increases and the crack connection is suppressed.
こうしたミクロ組織は、焼鈍時に、500℃〜Ac1点までを5℃/ｓ以上の平均加熱速度で、Ac3点−20〜1000℃まで加熱し10〜1000秒保持した後、750℃から15℃/ｓ以上の平均冷却速度でMs点−80℃〜Ms点−30℃の温度域まで冷却した後、350〜500℃に加熱し、10〜600秒保持することによって得られる。 During annealing, these microstructures were heated from 500 ° C. to Ac 1 point at an average heating rate of 5 ° C./s or more to Ac 3 point −20 to 1000 ° C. and held for 10 to 1000 seconds, and then from 750 ° C. to 15 ° C. After cooling to a temperature range of Ms point −80 ° C. to Ms point −30 ° C. at an average cooling rate of at least ° C./s, it is obtained by heating to 350 to 500 ° C. and holding for 10 to 600 seconds.
本発明は、このような知見に基づきなされたもので、以下の発明を提供する。 The present invention has been made based on such findings, and provides the following inventions.
（１）質量％で、C：0.10〜0.35％、Si：0.5〜3.0％、Mn：1.5〜4.0％、P：0.100％以下、S：0.02％以下、Al：0.010〜0.5％を含み、残部がFeおよび不可避的不純物からなる成分組成を有し、かつミクロ組織は、面積率で0〜5％のポリゴナルフェライト、5％以上のベイニティックフェライト、5〜20％のマルテンサイト、30〜60％の焼き戻しマルテンサイトと、5〜20％の残留オーステナイトを含み、かつ旧オーステナイトの平均粒径が15μｍ以下であることを特徴とする成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板。 (1) In mass%, C: 0.10 to 0.35%, Si: 0.5 to 3.0%, Mn: 1.5 to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.010 to 0.5%, the balance Has a composition composed of Fe and inevitable impurities, and the microstructure is 0-5% polygonal ferrite, 5% bainitic ferrite, 5-20% martensite, 30-30 High-strength hot-dip galvanizing with excellent formability and shape-freezing properties, comprising 60% tempered martensite and 5-20% retained austenite, and the average grain size of prior austenite is 15 μm or less steel sheet.
（２）さらに、質量％で、Cr：0.005〜2.00％、Mo：0.005〜2.00％、V：0.005〜2.00％、Ni：0.005〜2.00％、Cu：0.005〜2.00％から選ばれる少なくとも一種の元素を含有することを特徴とする（１）に記載の成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板。 (2) Further, at least one element selected from Cr: 0.005-2.00%, Mo: 0.005-2.00%, V: 0.005-2.00%, Ni: 0.005-2.00%, Cu: 0.005-2.00% in mass%. The high-strength hot-dip galvanized steel sheet having excellent formability and shape freezing property as described in (1).
（３）さらに、質量％で、Ti：0.01〜0.20％、Nb：0.01〜0.20％から選ばれる少なくとも一種の元素を含有することを特徴とする（１）または（２）に記載の成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板。 (3) The moldability according to (1) or (2), further comprising at least one element selected from Ti: 0.01 to 0.20% and Nb: 0.01 to 0.20% by mass%. High-strength hot-dip galvanized steel sheet with excellent shape freezing properties.
（４）さらに、質量％で、B：0.0005〜0.0050％を含有することを特徴とする（１）から（３）のいずれかに記載の成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板。 (4) The high-strength hot-dip galvanizing excellent in formability and shape freezing property according to any one of (1) to (3), further comprising B: 0.0005 to 0.0050% by mass% steel sheet.
（５）さらに、質量％で、Ca：0.001〜0.005％、REM：0.001〜0.005％から選ばれる少なくとも一種の元素を含有することを特徴とする（１）から（４）のいずれかに記載の成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板。 (5) The composition according to any one of (1) to (4), further comprising at least one element selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005% by mass%. High-strength hot-dip galvanized steel sheet with excellent formability and shape freezing properties.
（６）亜鉛めっきが合金化亜鉛めっきであることを特徴とする（１）から（５）のいずれかに記載の成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板。 (6) The high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property according to any one of (1) to (5), wherein the galvanizing is alloyed galvanizing.
（７） （１）から（５）のいずれかに記載の成分組成を有するスラブを、熱間圧延し、またはさらに冷間圧延し、その後連続焼鈍を施すに際し、500℃〜Ac1点までを5℃/ｓ以上の平均加熱速度で、Ac3点−20℃〜1000℃の温度域に加熱し10〜1000秒保持した後、750℃から15℃/ｓ以上の平均冷却速度でMs点−80℃〜Ms点−30℃の温度域まで冷却した後、350℃〜500℃に加熱し10〜600秒保持した後、溶融亜鉛めっきを施し、またはさらにめっき合金化処理を行うことを特徴とする成形性及び形状凍結性に優れた高強度溶融亜鉛めっき鋼板の製造方法。 (7) When the slab having the component composition according to any one of (1) to (5) is hot-rolled or further cold-rolled, and then subjected to continuous annealing, 500 ° C. to Ac 1 point. Ac 3 point at an average heating rate of 5 ° C / s or more-After heating to a temperature range of 20 ° C to 1000 ° C and holding for 10 to 1000 seconds, Ms point at an average cooling rate of 750 ° C to 15 ° C / s or more- After cooling to a temperature range of 80 ° C to Ms point -30 ° C, after heating to 350 ° C to 500 ° C and holding for 10 to 600 seconds, hot dip galvanizing is performed, or further plating alloying treatment is performed. A method for producing a high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing.
本発明によれば、引張強さ(TS)：1180MPa以上、全伸び(EL)：14％以上、穴拡げ率(λ)：30％以上かつ降伏比(YR)：70％以下である成形性および形状凍結性に優れた高強度溶融亜鉛めっき鋼板を得ることができる。 According to the present invention, the tensile strength (TS) is 1180 MPa or more, the total elongation (EL) is 14% or more, the hole expansion rate (λ) is 30% or more, and the yield ratio (YR) is 70% or less. In addition, a high-strength hot-dip galvanized steel sheet excellent in shape freezing property can be obtained.
以下に、本発明の詳細を説明する。なお、成分元素の含有量を表す「％」は、特に断らない限り「質量％」を意味する。 Details of the present invention will be described below. Note that “%” representing the content of component elements means “% by mass” unless otherwise specified.
１）成分組成
C：0.10〜0.35％
Cは、マルテンサイトや焼戻しマルテンサイトなどの低温変態相を生成させてTSを上昇させるために必要な元素である。C量が0.10％未満では、焼戻しマルテンサイトを面積率で30％以上かつマルテンサイトを5％以上確保することは難しい。一方、C量が0.35％を超えると、ELやスポット溶接性が劣化する。したがって、C量は0.10〜0.35％、好ましくは0.15〜0.3％とする。
1) Component composition
C: 0.10 to 0.35%
C is an element necessary for increasing TS by generating a low temperature transformation phase such as martensite and tempered martensite. If the amount of C is less than 0.10%, it is difficult to secure tempered martensite in an area ratio of 30% or more and martensite of 5% or more. On the other hand, when the C content exceeds 0.35%, EL and spot weldability deteriorate. Therefore, the C content is 0.10 to 0.35%, preferably 0.15 to 0.3%.
Si：0.5〜3.0％
Siは、鋼を固溶強化してTS-ELバランスを向上させたり、残留オーステナイトを生成させるのに有効な元素である。こうした効果を得るには、Si量を0.5％以上にする必要がある。一方、Siが3.0％を超えると、ELの低下や表面性状、溶接性の劣化を招く。したがって、Si量は0.5〜3.0％、好ましくは0.9〜2.0％とする。
Si: 0.5-3.0%
Si is an element effective for improving the TS-EL balance by solid solution strengthening of steel and generating retained austenite. In order to obtain such effects, the Si amount needs to be 0.5% or more. On the other hand, if Si exceeds 3.0%, the EL is lowered and the surface properties and weldability are deteriorated. Therefore, the Si content is 0.5 to 3.0%, preferably 0.9 to 2.0%.
Mn：1.5〜4.0％
Mnは、鋼の強化に有効であり、マルテンサイトなどの低温変態相の生成を促進する元素である。こうした効果を得るには、Mn量を1.5％以上にする必要がある。一方、Mn量が4.0％を超えると、ELの劣化が著しくなり、加工性が低下する。したがって、Mn量は1.5〜4.0％、好ましくは2.0〜3.5％とする。
Mn: 1.5-4.0%
Mn is an element that is effective in strengthening steel and promotes the generation of low-temperature transformation phases such as martensite. In order to obtain such an effect, the Mn content needs to be 1.5% or more. On the other hand, if the amount of Mn exceeds 4.0%, the EL deteriorates significantly and the workability decreases. Therefore, the Mn content is 1.5 to 4.0%, preferably 2.0 to 3.5%.
P：0.100％以下
Pは、粒界偏析により鋼を劣化させ、溶接性を劣化させるため、その量は極力低減することが望ましい。しかし、製造コストの面などからP量は0.100％以下とする。
P: 0.100% or less
P deteriorates steel by grain boundary segregation and deteriorates weldability. Therefore, it is desirable to reduce the amount of P as much as possible. However, the amount of P is 0.100% or less from the viewpoint of manufacturing cost.
S：0.02％以下
Sは、MnSなどの介在物として存在して、溶接性を劣化させるため、その量は極力低減することが好ましい。しかし、製造コストの面からS量は0.02％以下とする。
S: 0.02% or less
Since S exists as inclusions such as MnS and degrades weldability, the amount is preferably reduced as much as possible. However, the amount of S is 0.02% or less from the viewpoint of manufacturing cost.
Al：0.010〜0.5％
Alは、脱酸剤として作用し、脱酸工程で添加することが好ましい。こうした効果を得るには、Al量を0.010％以上にする必要がある。一方、Al量が0.5％を超えると、連続鋳造時のスラブ割れの危険性が高まる。したがって、Al量は0.010〜0.5％とする。
Al: 0.010 to 0.5%
Al acts as a deoxidizer and is preferably added in the deoxidation step. In order to obtain such an effect, the Al content needs to be 0.010% or more. On the other hand, if the Al content exceeds 0.5%, the risk of slab cracking during continuous casting increases. Therefore, the Al content is 0.010 to 0.5%.
残部はFeおよび不可避的不純物であるが、必要に応じて以下の元素の1種以上を適宜含有させることができる。 The balance is Fe and inevitable impurities, but one or more of the following elements can be appropriately contained as necessary.
Cr：0.005〜2.00％、Mo：0.005〜2.00％、V：0.005〜2.00％、Ni：0.005〜2.00％、Cu：0.005〜2.00％から選ばれる少なくとも1種
Cr、Mo、V、Ni、Cuはマルテンサイトなどの低温変態相の生成に有効な元素である。こうした効果を得るには、Cr、Mo、V、Ni、Cuから選ばれる少なくとも1種の元素の含有量を0.005％にする必要がある。一方、Cr、Mo、V、Ni、Cuのそれぞれの含有量が2.00％を超えると、その効果が飽和し、コストアップを招く。したがって、Cr、Mo、V、Ni、Cuの含有量はそれぞれ0.005〜2.00％とする。
Cr: 0.005-2.00%, Mo: 0.005-2.00%, V: 0.005-2.00%, Ni: 0.005-2.00%, Cu: 0.005-2.00%
Cr, Mo, V, Ni, and Cu are effective elements for generating a low-temperature transformation phase such as martensite. In order to obtain such an effect, the content of at least one element selected from Cr, Mo, V, Ni, and Cu needs to be 0.005%. On the other hand, if the content of each of Cr, Mo, V, Ni, and Cu exceeds 2.00%, the effect is saturated and the cost is increased. Therefore, the contents of Cr, Mo, V, Ni, and Cu are each 0.005 to 2.00%.
また、さらにTi：0.01〜0.20％、Nb：0.01〜0.20％から選ばれる少なくとも1種を含有することができる。 Further, at least one selected from Ti: 0.01 to 0.20% and Nb: 0.01 to 0.20% can be contained.
TiおよびNbは、炭窒化物を形成し、鋼を析出強化により高強度化するのに有効な元素である。こうした効果を得るにはTiおよびNbの含有量を0.01％以上にする必要がある。一方、TiおよびNbの含有量が0.20％を超えると、高強度化の効果は飽和し、ELが低下する。したがって、TiおよびNbの含有量は0.01〜0.20％とする。 Ti and Nb are effective elements for forming carbonitrides and increasing the strength of steel by precipitation strengthening. In order to obtain such effects, the Ti and Nb contents must be 0.01% or more. On the other hand, when the content of Ti and Nb exceeds 0.20%, the effect of increasing the strength is saturated and the EL decreases. Therefore, the content of Ti and Nb is set to 0.01 to 0.20%.
また、さらにB：0.0005〜0.0050％を含有することができる。 Further, B: 0.0005 to 0.0050% can be contained.
Bは、オーステナイト粒界からのフェライト生成を抑制し、低温変態相を生成するのに有効な元素である。こうした効果を得るには、B量を0.0005％以上にする必要がある。一方、B量が0.0050％を超えると、その効果が飽和し、コストアップを招く。したがって、B量は0.0005〜0.0050％とする。 B is an element effective in suppressing the formation of ferrite from the austenite grain boundary and generating a low-temperature transformation phase. In order to obtain such an effect, the B amount needs to be 0.0005% or more. On the other hand, when the amount of B exceeds 0.0050%, the effect is saturated and the cost is increased. Therefore, the B amount is 0.0005 to 0.0050%.
また、さらにCa：0.001〜0.005％、REM：0.001〜0.005％から選ばれる少なくとも1種を含有することができる。 Further, it may further contain at least one selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005%.
Ca、REMは、いずれも硫化物の形態制御により加工性を改善させるのに有効な元素である。こうした効果を得るには、Ca、REMから選ばれる少なくとも1種の元素の含有量を0.001％以上とする必要がある。一方、Ca、REMのそれぞれの含有量が0.005％を超えると、鋼の清浄度に悪影響を及ぼし、所望の特性が得られないおそれがある。したがって、Ca、REMの含有量は0.001〜0.005％とする。 Ca and REM are both effective elements for improving workability by controlling the morphology of sulfides. In order to obtain such an effect, the content of at least one element selected from Ca and REM needs to be 0.001% or more. On the other hand, if the content of each of Ca and REM exceeds 0.005%, the cleanliness of the steel is adversely affected and desired characteristics may not be obtained. Therefore, the content of Ca and REM is set to 0.001 to 0.005%.
２）ミクロ組織
ポリゴナルフェライトの面積率：0〜5％
ポリゴナルフェライトの面積率が5％を超えると、TS1180MPa以上と穴拡げ率30％以上の両立が困難になる。したがって、ポリゴナルフェライトの面積率は0〜5％とする。
2) Microstructure Area ratio of polygonal ferrite: 0 to 5%
If the area ratio of polygonal ferrite exceeds 5%, it becomes difficult to achieve both TS1180MPa or more and hole expansion ratio of 30% or more. Therefore, the area ratio of polygonal ferrite is set to 0 to 5%.
ベイニティックフェライトの面積率：5％以上
ベイナイト変態はオーステナイトにCを濃化させ、オーステナイトを安定化することでEL上昇に有効な残留オーステナイトを確保するのに有効である。この効果を得るには、ベイニティックフェライトの面積率を5％以上にする必要がある。従って、ベイニティックフェライトの面積率を5％以上にする。
Bainitic ferrite area ratio: 5% or more The bainite transformation is effective in securing retained austenite effective for increasing EL by concentrating C in austenite and stabilizing austenite. In order to obtain this effect, the area ratio of bainitic ferrite needs to be 5% or more. Therefore, the area ratio of bainitic ferrite is set to 5% or more.
マルテンサイトの面積率：5〜20％
マルテンサイトはTSの向上に有効である。また、YRを低下させるのに有効である。
こうした効果を得るにはマルテンサイトの面積率が5％以上必要である。一方、20％を超えるとELや穴拡げ率の低下が顕著になる。したがって、マルテンサイトの面積率は5〜20％とする。
Martensite area ratio: 5-20%
Martensite is effective in improving TS. It is also effective in reducing YR.
In order to obtain such an effect, the area ratio of martensite is required to be 5% or more. On the other hand, when it exceeds 20%, the decrease in EL and hole expansion rate becomes remarkable. Therefore, the area ratio of martensite is 5 to 20%.
焼戻しマルテンサイトの面積率：30〜60％
焼戻しマルテンサイトの面積率が30％未満になると、TS1180MPa以上と穴拡げ率30％以上の両立が困難になる。一方、その面積率が60％を超えると、YRの上昇が顕著になり形状凍結性が低下する。したがって、焼戻しマルテンサイトの面積率は30〜60％とする。
Tempered martensite area ratio: 30-60%
If the area ratio of tempered martensite is less than 30%, it becomes difficult to achieve both TS1180MPa or more and hole expansion ratio of 30% or more. On the other hand, if the area ratio exceeds 60%, the increase in YR becomes remarkable and the shape freezing property decreases. Therefore, the area ratio of tempered martensite is 30 to 60%.
残留オーステナイトの面積率：5〜20％
残留オーステナイトは、ELの向上に有効である。このような効果を得るには、残留オーステナイトの面積率を5％以上にする必要がある。しかしながら、その面積率が20％を超えると、穴拡げ率の低下が顕著になる。したがって、残留オーステナイトの面積率は5〜20％とする。
Residual austenite area ratio: 5-20%
Residual austenite is effective in improving EL. In order to obtain such an effect, the area ratio of retained austenite needs to be 5% or more. However, when the area ratio exceeds 20%, the hole expansion rate is significantly reduced. Therefore, the area ratio of retained austenite is 5 to 20%.
旧オーステナイトの平均粒径15μｍ以下
旧オーステナイト粒の微細化はλの向上に有効である。このような効果を得るには旧オーステナイトの平均粒径を15μｍ以下にする必要がある。したがって、旧オーステナイトの平均粒径は15μｍ以下とする。
The average grain size of prior austenite is 15 μm or less Refinement of prior austenite grains is effective in improving λ. In order to obtain such an effect, it is necessary to make the average grain size of prior austenite 15 μm or less. Therefore, the average particle size of the prior austenite is set to 15 μm or less.
なお、ポリゴナルフェライト、ベイニティックフェライト、マルテンサイト、焼戻しマルテンサイト、残留オーステナイト以外の相としてパーライトを含む場合もあるが、上記のミクロ組織の条件を満たしていれば、本発明の目的は達成される。 In addition, pearlite may be included as a phase other than polygonal ferrite, bainitic ferrite, martensite, tempered martensite, and retained austenite, but the object of the present invention is achieved as long as the above microstructure conditions are satisfied. Is done.
ここで、ポリゴナルフェライト、ベイニティックフェライト、マルテンサイト、焼戻しマルテンサイトの面積率とは、観察面積に占める各相の面積の割合のことで、ポリゴナルフェライト、マルテンサイト、ベイニティックフェライト、焼戻しマルテンサイトの面積率は以下に示す方法で求めた。鋼板の板厚断面を研磨後、3％ナイタールで腐食し、板厚1/4位置をSEM（走査型電子顕微鏡）で1500倍の倍率で3視野撮影し、これをMedia Cybernetics社製のImage-Proを用いて各視野の対象組織を塗り別け、その視野に占める対象組織の面積率を求め、各視野の面積率の平均を対象組織の面積率とした。また、残留オーステナイトの面積率については、鋼板を板厚1/4位置まで研磨後、化学研磨によりさらに0.1ｍｍ研磨した面について、X線回折装置でMoのKα線を用いて、fcc鉄の（200）、（220）、（311）面とbcc鉄の（200）、（211）、（220）面の積分強度を測定し、これから残留オーステナイトの割合を求め、この割合を残留オーステナイトの面積率とした。また、旧オーステナイトの平均粒径については、鋼板の板厚断面を研磨後、3％ナイタールで腐食し、板厚1/4位置をSEM（走査型電子顕微鏡）で1500倍の倍率で観察し、視野の旧オーステナイト粒界に囲まれる組織の面積の合計をその個数で割って平均面積を求め、その1／2乗を平均粒径とした。 Here, the area ratio of polygonal ferrite, bainitic ferrite, martensite, and tempered martensite is the ratio of the area of each phase in the observed area. Polygonal ferrite, martensite, bainitic ferrite, The area ratio of tempered martensite was determined by the method shown below. After the plate thickness section of the steel plate was polished, it was corroded with 3% nital, and the 1/4 position of the plate thickness was photographed with SEM (scanning electron microscope) at a magnification of 1500 times, and this was image-produced by Media Cybernetics. The target tissue of each visual field was painted using Pro, the area ratio of the target tissue in the visual field was determined, and the average of the area ratios of each visual field was defined as the area ratio of the target tissue. As for the area ratio of retained austenite, the surface of the steel plate was polished to a thickness of 1/4 position and then further polished by 0.1 mm by chemical polishing. Measure the integrated strength of the (200), (220), (311) plane and the (200), (211), (220) plane of bcc iron, determine the percentage of retained austenite from this, and use this ratio as the area ratio of retained austenite It was. The average grain size of the prior austenite was corroded with 3% nital after polishing the thickness section of the steel sheet, and the 1/4 position of the thickness was observed with a scanning electron microscope (SEM) at a magnification of 1500 times. The total area of the structures surrounded by the prior austenite grain boundaries in the field of view was divided by the number to determine the average area, and the 1/2 power was taken as the average grain size.
３）製造条件
本発明の高強度溶融亜鉛めっき鋼板は、上記の成分組成を有するスラブに、熱間圧延、酸洗を施し、またはさらに冷間圧延を施し、その後、連続焼鈍で、500℃〜Ac1点までを5℃/ｓ以上の平均加熱速度で、Ac3点−20℃〜1000℃の温度域に加熱し10〜1000秒保持した後、750℃から15℃/ｓ以上の平均冷却速度でMs点−80℃〜Ms点−30℃の温度域まで冷却した後、350℃〜500℃に加熱し10〜600秒保持した後、溶融亜鉛めっきを施し、またはさらにめっき合金化処理を行い製造する。以下、詳しく説明する。
3) Manufacturing conditions The high-strength hot-dip galvanized steel sheet of the present invention is hot-rolled, pickled, or further cold-rolled to a slab having the above component composition, and then subjected to continuous annealing at 500 ° C to Heat up to Ac 1 point at an average heating rate of 5 ° C / s or higher and hold at Ac 3 point –20 ° C to 1000 ° C for 10 to 1000 seconds, then average cooling from 750 ° C to 15 ° C / s or higher After cooling to a temperature range of Ms point -80 ° C to Ms point -30 ° C at a speed, heat to 350 ° C to 500 ° C and hold for 10 to 600 seconds, then apply hot dip galvanizing or further alloying treatment To make. This will be described in detail below.
上記成分組成を有する鋼を溶製してスラブとし、スラブを熱間圧延した後、冷却し巻取る。熱間圧延後の巻取り温度が650℃を超えると、黒シミが生成し、めっき性が低下する。一方、熱間圧延後の巻取り温度が400℃未満では熱延板の形状が悪化する。したがって、熱間圧延後の巻取り温度は400〜650℃とすることが好ましい。 Steel having the above composition is melted to form a slab, the slab is hot-rolled, and then cooled and wound. When the coiling temperature after hot rolling exceeds 650 ° C., black spots are generated and the plating property is lowered. On the other hand, when the coiling temperature after hot rolling is less than 400 ° C., the shape of the hot rolled sheet deteriorates. Therefore, the coiling temperature after hot rolling is preferably 400 to 650 ° C.
次に、熱延板を酸洗し、熱延板表層のスケールを除去することが好ましい。酸洗工程は特に限定されず、常法でよい。必要に応じて、酸洗後の熱延板を冷間圧延する。冷間圧延工程は特に限定されず、常法でよい。酸洗後の熱延板又は冷間圧延後の冷延板を以下の条件で連続焼鈍する。 Next, the hot-rolled sheet is preferably pickled to remove the scale of the hot-rolled sheet surface layer. The pickling step is not particularly limited, and may be a conventional method. If necessary, the hot-rolled sheet after pickling is cold-rolled. A cold rolling process is not specifically limited, A conventional method may be sufficient. The hot-rolled sheet after pickling or the cold-rolled sheet after cold rolling is continuously annealed under the following conditions.
500℃〜Ac1点までの平均加熱速度：5℃/ｓ以上
500℃〜Ac1点までの平均加熱速度が5℃/ｓ未満では再結晶によりオーステナイトが粗大化して、本発明のミクロ組織が得られない。したがって、500℃〜Ac1点までの平均加熱速度を5℃/ｓ以上とする。
Average heating rate from 500 ℃ to Ac 1 point: 5 ℃ / s or more
If the average heating rate from 500 ° C. to Ac 1 point is less than 5 ° C./s, the austenite is coarsened by recrystallization, and the microstructure of the present invention cannot be obtained. Therefore, the average heating rate from 500 ° C. to Ac 1 point is set to 5 ° C./s or more.
Ac3点−20℃〜1000℃の温度域に加熱し10〜1000秒均熱保持
均熱保持温度がAc3点−20℃未満ではオーステナイトの生成が不十分となり、本発明のミクロ組織が得られない。一方、均熱保持温度が1000℃を超えると、オーステナイトが粗大化し、焼鈍後の構成相が粗大化して靱性などを低下させる。したがって、均熱保持温度はAc3点−20℃〜1000℃とする。均熱保持時間が10秒未満ではオーステナイトの生成が不十分となり、本発明のミクロ組織が得られない。また、均熱保持時間が1000秒を超えるとコストアップを招く。したがって、均熱保持時間は10〜1000秒とする。
Heating in the temperature range of Ac 3 point -20 ° C to 1000 ° C and keeping soaking for 10 to 1000 seconds If the soaking temperature is less than Ac 3 point -20 ° C, austenite formation is insufficient and the microstructure of the present invention is obtained. I can't. On the other hand, when the soaking temperature exceeds 1000 ° C., austenite becomes coarse, and the constituent phase after annealing becomes coarse to reduce toughness and the like. Therefore, the soaking temperature is set to Ac 3 point −20 ° C. to 1000 ° C. If the soaking time is less than 10 seconds, austenite is not sufficiently generated, and the microstructure of the present invention cannot be obtained. In addition, if the soaking time exceeds 1000 seconds, the cost increases. Therefore, the soaking time is 10 to 1000 seconds.
750℃から15℃/ｓ以上の平均冷却速度でMs点−80℃〜Ms点−30℃の温度域まで冷却
750℃からMs点−80℃〜Ms点−30℃の温度域までの平均冷却速度が15℃/s未満では冷却中に多量のフェライトが生成し、本発明のミクロ組織が得られない。したがって平均冷却速度を15℃/s以上とする。
Cooling from 750 ° C to an average cooling rate of 15 ° C / s or higher to a temperature range of Ms point –80 ° C to Ms point –30 ° C
If the average cooling rate from 750 ° C. to the temperature range from Ms point −80 ° C. to Ms point −30 ° C. is less than 15 ° C./s, a large amount of ferrite is generated during cooling, and the microstructure of the present invention cannot be obtained. Accordingly, the average cooling rate is set to 15 ° C./s or more.
冷却停止温度：Ms点−80℃〜Ms点−30℃
冷却到達温度まで冷却すると、オーステナイトの一部がマルテンサイトに変態し、その後の再加熱時やめっき合金化処理時に、マルテンサイトは焼戻しマルテンサイトに、未変態オーステナイトは残留オーステナイトあるいはマルテンサイトやベイナイトになる。このとき、冷却到達温度がMs点−30℃を超えると焼戻しマルテンサイト量が不十分となり、Ms点−80℃未満では未変態オーステナイトが著しく減少し、また焼戻しマルテンサイトが増加するため本発明のミクロ組織が得られない。したがって、冷却到達温度はMs点−80℃〜Ms点−30℃とする。
Cooling stop temperature: Ms point –80 ° C to Ms point –30 ° C
When cooled to the cooling temperature, a part of austenite is transformed into martensite, and during subsequent reheating or plating alloying process, martensite becomes tempered martensite and untransformed austenite becomes residual austenite or martensite or bainite. Become. At this time, when the temperature reached by cooling exceeds the Ms point −30 ° C., the amount of tempered martensite becomes insufficient. When the Ms point is less than −80 ° C., untransformed austenite is remarkably reduced, and tempered martensite is increased. A microstructure cannot be obtained. Accordingly, the cooling arrival temperature is set to Ms point −80 ° C. to Ms point −30 ° C.
再加熱温度：350〜500℃
冷却到達温度まで冷却後、350〜500℃の温度域に再加熱すると、冷却時に生成したマルテンサイトが焼き戻され、焼戻しマルテンサイトとなり、また、未変態オーステナイトにC濃化が進行し、残留オーステナイトとして安定化する。また、ベイナイト変態が進行し、ベイニティックフェライトよりCが拡散して未変態オーステナイトをさらに安定化させる。再加熱温度350℃未満では進行するベイナイト変態が炭化物を含むベイナイトとなるため未変態オーステナイトにあまりCが濃化せず、残留オーステナイトとしての安定性が不十分になる。一方、500℃を超えると未変態オーステナイトが炭化物を生成あるいはパーライト変態しやすくなり、本発明のミクロ組織が得られない。したがって、再加熱温度は350〜500℃とする。好ましくは380〜480℃である。
Reheating temperature: 350-500 ° C
After cooling to the temperature at which cooling is achieved, when reheated to a temperature range of 350 to 500 ° C., the martensite generated during cooling is tempered to become tempered martensite, and C enrichment proceeds to untransformed austenite, resulting in residual austenite. As stabilized. In addition, bainite transformation proceeds, C diffuses from bainitic ferrite and further stabilizes untransformed austenite. If the reheating temperature is less than 350 ° C., the bainite transformation that progresses becomes bainite containing carbide, so that C does not concentrate much in the untransformed austenite, and the stability as retained austenite becomes insufficient. On the other hand, if it exceeds 500 ° C., untransformed austenite tends to form carbides or pearlite, and the microstructure of the present invention cannot be obtained. Therefore, the reheating temperature is set to 350 to 500 ° C. Preferably it is 380-480 degreeC.
再加熱温度での保持時間：10〜600秒
保持時間が10秒未満では、ベイナイトの生成が不十分になり、また、600秒を超えると未変態オーステナイトが炭化物を生成あるいはパーライト変態しやすくなり、本発明のミクロ組織が得られない。したがって保持時間は10〜600秒とする。
Holding time at reheating temperature: 10 to 600 seconds If the holding time is less than 10 seconds, the formation of bainite becomes insufficient, and if it exceeds 600 seconds, untransformed austenite tends to generate carbide or pearlite, The microstructure of the present invention cannot be obtained. Therefore, the holding time is 10 to 600 seconds.
溶融亜鉛めっき処理は、上記により得られた鋼板を440℃以上500℃以下の亜鉛めっき浴中に浸漬し、その後、ガスワイピングなどによってめっき付着量を調整して行うことが好ましい。さらに亜鉛めっきを合金化する際は460℃以上550℃以下の温度域に1秒以上40秒以下保持して合金化することが好ましい。亜鉛めっきはAl量が0.08〜0.18％である亜鉛めっき浴を用いることが好ましい。 The hot dip galvanizing treatment is preferably performed by immersing the steel plate obtained as described above in a galvanizing bath at 440 ° C. or higher and 500 ° C. or lower, and then adjusting the plating adhesion amount by gas wiping or the like. Further, when alloying the galvanizing, it is preferable to keep the alloy in the temperature range of 460 ° C. to 550 ° C. for 1 second to 40 seconds. For galvanization, it is preferable to use a galvanizing bath having an Al content of 0.08 to 0.18%.
溶融亜鉛めっき合金化処理を施した後の鋼板には、形状矯正や表面粗度の調整などを目的に調質圧延を行うことができる。また、樹脂や油脂コーティングなどの各種塗装処理を施すこともできる。 The steel sheet after the hot dip galvanizing alloying treatment can be subjected to temper rolling for the purpose of shape correction, adjustment of surface roughness, and the like. Moreover, various coating processes, such as resin and oil-fat coating, can also be given.
その他の製造方法の条件は、特に限定しないが、以下の条件で行うのが好ましい。 The conditions for other production methods are not particularly limited, but the following conditions are preferable.
スラブは、マクロ偏析を防止するため、連続鋳造法で製造するのが好ましいが、造塊法、薄スラブ鋳造法により製造することもできる。スラブを熱間圧延するには、スラブをいったん室温まで冷却し、その後再加熱して熱間圧延を行ってもよいし、スラブを室温まで冷却せずに加熱炉に装入して熱間圧延を行うこともできる。あるいはわずかの保熱を行った後に直ちに熱間圧延する省エネルギープロセスも適用できる。スラブを加熱する場合は、炭化物を溶解させたり、圧延荷重の増大を防止するため、1100℃以上に加熱することが好ましい。また、スケールロスの増大を防止するため、スラブの加熱温度は1300℃以下とすることが好ましい。 The slab is preferably produced by a continuous casting method in order to prevent macro segregation, but can also be produced by an ingot-making method or a thin slab casting method. To hot-roll the slab, the slab may be cooled to room temperature and then re-heated for hot rolling, or the slab may be charged in a heating furnace without being cooled to room temperature. Can also be done. Alternatively, an energy saving process in which hot rolling is performed immediately after performing a slight heat retention can also be applied. When heating the slab, it is preferable to heat to 1100 ° C. or higher in order to dissolve carbides and prevent an increase in rolling load. In order to prevent an increase in scale loss, the heating temperature of the slab is preferably 1300 ° C. or lower.
スラブを熱間圧延する時は、スラブの加熱温度を低くしても圧延時のトラブルを防止する観点から、粗圧延後の粗バーを加熱することもできる。また、粗バー同士を接合し、仕上げ圧延を連続的に行う、いわゆる連続圧延プロセスを適用できる。仕上げ圧延は、異方性を増大させ、冷間圧延・焼鈍後の加工性を低下させる場合があるので、Ar3変態点以上の仕上げ温度で行うことが好ましい。また、圧延荷重の低減や形状・材質の均一化のために、仕上げ圧延の全パスあるいは一部のパスで摩擦係数が0.10〜0.25となる潤滑圧延を行うことが好ましい。 When hot rolling a slab, the rough bar after rough rolling can be heated from the viewpoint of preventing troubles during rolling even if the heating temperature of the slab is lowered. Moreover, what is called a continuous rolling process which joins rough bars and performs finish rolling continuously can be applied. Since finish rolling may increase anisotropy and reduce workability after cold rolling / annealing, it is preferably performed at a finishing temperature equal to or higher than the Ar 3 transformation point. Further, in order to reduce the rolling load and make the shape and material uniform, it is preferable to perform lubrication rolling with a friction coefficient of 0.10 to 0.25 in all passes or a part of the finish rolling.
巻取り後の鋼板は、スケールを酸洗などにより除去した後、熱延板を上記の条件で焼鈍するか、あるいは熱延板を冷間圧延した後上記の条件で焼鈍し、溶融亜鉛めっきが施される。冷間圧延を施す場合は、冷間圧下率を40％以上とすることが好ましい。また、冷間圧延時の圧延負荷を低減するために、巻取り後の鋼板に熱延板焼鈍を施すこともできる。 The steel sheet after winding is removed by pickling or the like, and then the hot-rolled sheet is annealed under the above-mentioned conditions, or the hot-rolled sheet is cold-rolled and then annealed under the above-mentioned conditions. Applied. When performing cold rolling, it is preferable that the cold rolling reduction be 40% or more. Moreover, in order to reduce the rolling load at the time of cold rolling, the steel plate after winding can also be hot-rolled sheet annealed.
表１に示す成分組成の鋼を転炉により溶製し、連続鋳造により鋼スラブとした（表１中、Ｎは不可避的不純物である）。これらの鋼スラブを1200℃に加熱後粗圧延、仕上圧延し、巻取り温度400〜650℃の範囲で巻取り、板厚2.3mmの熱延板とした。次いで、一部バッチ処理により到達温度600℃、熱処理時間5時間の条件で軟質化を施し、酸洗後、板厚1.4mmに冷間圧延し冷延鋼板を製造し焼鈍に供した。また一部、板厚2.3mmまで熱間圧延した鋼板を酸洗したものをそのまま焼鈍に供した。焼鈍は連続溶融亜鉛めっきラインにより、表2、3に示す条件で行い、460℃のめっき浴中に浸漬し、付着量35〜45g/m2のめっきを形成させ、冷却速度10℃/ｓで冷却し溶融亜鉛めっき鋼板1〜29を作製した。また一部、めっき後さらに525℃でめっき合金化処理を行い、冷却速度10℃/ｓで冷却し、合金化溶融亜鉛めっき鋼板を作製した。そして、得られためっき鋼板について、上記の方法でポリゴナルフェライト、ベイニティックフェライト、マルテンサイト、焼戻しマルテンサイトの面積率、残留オーステナイトの面積率および旧オーステナイトの平均粒径を測定した。また、圧延方向と直角方向にJIS５号引張試験片を採取し、歪速度10-3で引張試験を行った。さらに、150mm×150mmの試験片を採取し、JFST 1001(日本鉄鋼連盟規格、2008年)に準拠して穴拡げ試験を3回行って平均の穴拡げ率(％)を求め、伸びフランジ性を評価した。結果を表4、5に示す。 Steel having the component composition shown in Table 1 was melted by a converter and made into a steel slab by continuous casting (in Table 1, N is an unavoidable impurity). These steel slabs were heated to 1200 ° C., followed by rough rolling and finish rolling, and the steel slab was wound at a winding temperature of 400 to 650 ° C. to obtain a hot-rolled sheet having a thickness of 2.3 mm. Next, softening was performed by partial batch processing under the conditions of an ultimate temperature of 600 ° C. and a heat treatment time of 5 hours, pickling, and cold rolling to a thickness of 1.4 mm to produce a cold-rolled steel plate, which was subjected to annealing. A part of the steel sheet hot-rolled to a thickness of 2.3 mm and pickled was subjected to annealing as it was. Annealing is performed by a continuous hot dip galvanizing line under the conditions shown in Tables 2 and 3 and immersed in a plating bath at 460 ° C. to form a plating with an adhesion amount of 35 to 45 g / m 2 at a cooling rate of 10 ° C./s. It cooled and produced the hot-dip galvanized steel plates 1-29. Further, after partially plating, a plating alloying treatment was further performed at 525 ° C., and cooling was performed at a cooling rate of 10 ° C./s to prepare an alloyed hot-dip galvanized steel sheet. And about the obtained plated steel plate, the area ratio of polygonal ferrite, bainitic ferrite, martensite, tempered martensite, the area ratio of retained austenite, and the average particle diameter of prior austenite were measured by the above-described methods. In addition, a JIS No. 5 tensile test piece was taken in a direction perpendicular to the rolling direction, and a tensile test was performed at a strain rate of 10 −3 . In addition, a 150mm x 150mm test piece was taken and the hole expansion test was performed three times in accordance with JFST 1001 (Japan Iron and Steel Federation Standard, 2008) to obtain the average hole expansion rate (%), and stretch flangeability was determined. evaluated. The results are shown in Tables 4 and 5.
本発明ではYRが70％以下となり、高い形状凍結性を有することが確認された。また、TSが1180MPa以上、ELが14％以上、λが30％以上となり、高い強度と成形性を有することが確認された。したがって、本発明例によれば、形状凍結性に優れた溶融亜鉛めっき鋼板が得られ、自動車の軽量化に寄与し、自動車車体の高性能化に大きく寄与するという優れた効果を奏する。 In the present invention, YR was 70% or less, and it was confirmed to have high shape freezing property. In addition, TS was 1180 MPa or more, EL was 14% or more, and λ was 30% or more, and it was confirmed that it had high strength and moldability. Therefore, according to the example of the present invention, a hot-dip galvanized steel sheet having excellent shape freezing property is obtained, which contributes to reducing the weight of the automobile and greatly improving the performance of the automobile body.
本発明によれば、引張強さ(TS)：1180MPa以上、全伸び(EL)：14％以上、穴拡げ率(λ)：30％以上かつ降伏比(YR)：70％以下である成形性および形状凍結性に優れた高強度溶融亜鉛めっき鋼板を得ることができる。本発明の高強度溶融亜鉛めっき鋼板を自動車用部品用途に使用すると、自動車の軽量化に寄与し、自動車車体の高性能化に大きく寄与することができる。 According to the present invention, the tensile strength (TS) is 1180 MPa or more, the total elongation (EL) is 14% or more, the hole expansion rate (λ) is 30% or more, and the yield ratio (YR) is 70% or less. In addition, a high-strength hot-dip galvanized steel sheet excellent in shape freezing property can be obtained. When the high-strength hot-dip galvanized steel sheet of the present invention is used for automotive parts, it contributes to reducing the weight of an automobile and greatly contributes to improving the performance of an automobile body.
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