JP4464748B2 - High-strength steel sheet, high-strength hot-dip galvanized steel sheet, high-strength alloyed hot-dip galvanized steel sheet excellent in shape freezing property and stretch flangeability, and methods for producing them - Google Patents
High-strength steel sheet, high-strength hot-dip galvanized steel sheet, high-strength alloyed hot-dip galvanized steel sheet excellent in shape freezing property and stretch flangeability, and methods for producing them Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 92
- 239000010959 steel Substances 0.000 title claims description 92
- 238000007710 freezing Methods 0.000 title claims description 63
- 230000008014 freezing Effects 0.000 title claims description 61
- 238000000034 method Methods 0.000 title claims description 20
- 229910001335 Galvanized steel Inorganic materials 0.000 title claims description 9
- 239000008397 galvanized steel Substances 0.000 title claims description 9
- 150000001875 compounds Chemical class 0.000 claims description 39
- 238000005096 rolling process Methods 0.000 claims description 31
- 239000002245 particle Substances 0.000 claims description 30
- 238000005098 hot rolling Methods 0.000 claims description 26
- 238000004519 manufacturing process Methods 0.000 claims description 19
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 15
- 230000009467 reduction Effects 0.000 claims description 15
- 238000001816 cooling Methods 0.000 claims description 13
- 238000005246 galvanizing Methods 0.000 claims description 13
- 229910001563 bainite Inorganic materials 0.000 claims description 11
- 229910052742 iron Inorganic materials 0.000 claims description 9
- 229910000859 α-Fe Inorganic materials 0.000 claims description 8
- 239000000203 mixture Substances 0.000 claims description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims description 6
- 229910052726 zirconium Inorganic materials 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 2
- 238000004804 winding Methods 0.000 claims description 2
- 230000000694 effects Effects 0.000 description 23
- 238000005452 bending Methods 0.000 description 21
- 239000013078 crystal Substances 0.000 description 13
- 229910001567 cementite Inorganic materials 0.000 description 10
- 238000012360 testing method Methods 0.000 description 10
- 238000010438 heat treatment Methods 0.000 description 8
- 238000005275 alloying Methods 0.000 description 7
- 238000000137 annealing Methods 0.000 description 6
- 238000005097 cold rolling Methods 0.000 description 6
- 230000007547 defect Effects 0.000 description 6
- 238000007747 plating Methods 0.000 description 6
- 239000002244 precipitate Substances 0.000 description 6
- 238000012545 processing Methods 0.000 description 6
- 239000011701 zinc Substances 0.000 description 6
- 238000005259 measurement Methods 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000005266 casting Methods 0.000 description 4
- 229910052804 chromium Inorganic materials 0.000 description 4
- 239000010960 cold rolled steel Substances 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 229910052749 magnesium Inorganic materials 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 229910052758 niobium Inorganic materials 0.000 description 4
- 238000003825 pressing Methods 0.000 description 4
- 150000003568 thioethers Chemical class 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- 229910052725 zinc Inorganic materials 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 238000005498 polishing Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 239000010409 thin film Substances 0.000 description 3
- 230000037303 wrinkles Effects 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 238000003723 Smelting Methods 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000007598 dipping method Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 239000006260 foam Substances 0.000 description 2
- -1 iron carbides Chemical class 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000005554 pickling Methods 0.000 description 2
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- 238000005204 segregation Methods 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- JBQYATWDVHIOAR-UHFFFAOYSA-N tellanylidenegermanium Chemical compound [Te]=[Ge] JBQYATWDVHIOAR-UHFFFAOYSA-N 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 229910052721 tungsten Inorganic materials 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- 230000000007 visual effect Effects 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910000905 alloy phase Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- DXHPZXWIPWDXHJ-UHFFFAOYSA-N carbon monosulfide Chemical class [S+]#[C-] DXHPZXWIPWDXHJ-UHFFFAOYSA-N 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
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- 238000009713 electroplating Methods 0.000 description 1
- 239000010408 film Substances 0.000 description 1
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- 229910052739 hydrogen Inorganic materials 0.000 description 1
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- 230000006872 improvement Effects 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
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Description
本発明は、形状凍結性と伸びフランジ成形性に優れた高強度鋼板、高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板と、それらの製造方法に関するもので、自動車部品等が主たる用途である。 The present invention relates to a high-strength steel sheet, high-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet excellent in shape freezing property and stretch flangeability, and methods for producing them. It is.
本発明の鋼板は、熱延鋼板と冷延鋼板の双方を含有する。溶融亜鉛めっきとは、純亜鉛のほか、Ｆｅ、Ａｌ、Ｍｇ、Ｃｒ、Ｃｕ等を含有してもよい。 The steel plate of the present invention contains both a hot rolled steel plate and a cold rolled steel plate. In addition to pure zinc, the hot dip galvanizing may contain Fe, Al, Mg, Cr, Cu and the like.
自動車からの炭酸ガスの排出量を抑えるために、高強度鋼板を使用して自動車車体の軽量化が進められている。また、搭乗者の安全性確保のためにも、自動車車体には、軟鋼板の他に高強度鋼板が多く使用されるようになってきている。さらに、自動車車体の軽量化を今後進めていくために、従来以上に高強度鋼板の使用強度レベルを高めたいという新たな要請が非常に高まりつつある。 In order to reduce carbon dioxide emissions from automobiles, the weight of automobile bodies is being reduced using high-strength steel sheets. In addition, in order to ensure the safety of passengers, high strength steel plates are often used in automobile bodies in addition to mild steel plates. Furthermore, in order to reduce the weight of automobile bodies in the future, new demands for increasing the strength level of use of high-strength steel sheets are increasing.
しかしながら、高強度鋼板に成形を加えると、加工後の形状は、その高強度ゆえに、加工冶具の形状から離れて加工前の形状の方向にもどりやすくなるというスプリング・バック現象や、成形中の曲げ−曲げ戻しからの弾性回復により側壁部の平面が曲率を持った面になってしまうという壁そり現象が起こり、狙いとする加工部品の形状が得られないという寸法精度不良が生じる。 However, when forming a high-strength steel sheet, the shape after processing tends to move away from the shape of the processing jig and return to the direction of the shape before processing because of its high strength. -A wall warp phenomenon in which the flat surface of the side wall becomes a curved surface due to the elastic recovery from the bending back, resulting in a dimensional accuracy defect that the shape of the target processed part cannot be obtained.
したがって、従来の自動車の車体では、主として５９０ＭＰａ以下の高強度鋼板が使用されてきた。すなわち、自動車車体にとっては、５９０ＭＰａ以上の高強度鋼板を使用して車体の軽量化を進めていく必要があるにもかかわらず、スプリング・バックや壁そりが起こりにくく、寸法精度が良好、すなわち、形状凍結性の良い高強度鋼板が存在しないのが実状である。 Therefore, high-strength steel sheets of 590 MPa or less have been mainly used in conventional automobile bodies. That is, for a car body, although it is necessary to reduce the weight of the car body using a high-strength steel plate of 590 MPa or more, spring back and wall warpage hardly occur, and dimensional accuracy is good. The fact is that there is no high-strength steel sheet with good shape freezing properties.
本発明者らの一部は、特許文献１および特許文献２にて、鋼板の集合組織に着目した形状凍結性に優れた高強度鋼板について開示している。また、特許文献３には、形状凍結性の良好な鋼板として、ｒ値の面内異方性Δｒの絶対値が０．２以下である熱延鋼板が開示されている。
Some of the present inventors have disclosed a high-strength steel sheet excellent in shape freezing property focusing on the texture of the steel sheet in
しかし、この発明は、低降伏比化することによって形状凍結性を向上させることを特徴としており、本発明で述べているような思想に基づいた形状凍結性の向上を目的とした集合組織制御に関しては、記載されていない。 However, this invention is characterized by improving the shape freezing property by lowering the yield ratio, and regarding texture control for the purpose of improving the shape freezing property based on the idea described in the present invention. Is not described.
一方、特許文献４には、ＴｉとＭｏとを添加した成形性に優れた鋼板について開示されているが、形状凍結性を改善する技術ではない。
On the other hand,
以上のように、形状凍結性を改善するための試みは行われてはいるが、その改善代は十分とは言えず、さらに良好な形状凍結性を有する高強度鋼板が待望されている。 As described above, attempts to improve the shape freezing property have been made, but the improvement allowance cannot be said to be sufficient, and a high-strength steel sheet having a better shape freezing property is desired.
引張強度が５９０ＭＰａ超の高強度鋼板に加工を施すと、鋼板の強度に依存しながら、大きなスプリング・バックや壁そりなどの形状不良が発生し、加工成形部品の形状凍結性が悪いのが現状である。本発明は、この問題を抜本的に解決し、同時に延性、伸びフランジ成形性、溶接性にも優れた高強度鋼板とその製造方法を提供するものである。 When processing high-strength steel sheets with a tensile strength of over 590 MPa, depending on the strength of the steel sheets, shape defects such as large spring backs and wall sleds occur, and the shape freezing property of processed molded parts is poor. It is. The present invention fundamentally solves this problem and provides a high-strength steel sheet excellent in ductility, stretch flange formability, and weldability, and a method for producing the same.
従来の知見によれば、スプリング・バックや壁そり等の形状不良を抑えるための方策としては、鋼板の変形応力を低くすることがとりあえず重要であると考えられていた。そして、変形応力を低くするためには、引張強さの低い鋼板を使用せざるを得なかった。しかし、これは、高強度鋼板のスプリング・バック量を低く抑えるための根本的な解決にはならない。 According to the conventional knowledge, it has been considered to be important for the time being to reduce the deformation stress of the steel sheet as a measure for suppressing shape defects such as spring back and wall warp. And in order to make a deformation stress low, the steel plate with low tensile strength had to be used. However, this is not a fundamental solution for keeping the springback amount of high-strength steel sheets low.
そこで、本発明者らは、曲げ加工性を向上させてスプリング・バックや壁そりの発生を根本的に解決するために、新たに鋼板の集合組織と強化方法の曲げ加工性への影響に着目して、その作用効果を詳細に調査、研究した。その結果、降伏強度が高く形状凍結性が劣位であると位置付けられていた析出強化と所定の集合組織とを組み合わせることによって、これまで以上に形状凍結性の優れた高強度鋼板を得るに至った。 Therefore, in order to improve the bending workability and fundamentally solve the occurrence of springback and wall warpage, the present inventors have newly focused on the influence of the texture of the steel sheet and the strengthening method on the bending workability. The effect was investigated and studied in detail. As a result, a combination of precipitation strengthening, which had been positioned as having high yield strength and inferior shape freezing properties, and a predetermined texture resulted in obtaining a high strength steel sheet with better shape freezing properties than ever before. .
すなわち、｛１００｝＜０１１＞〜｛２２３｝＜１１０＞方位群の強度を高め、圧延方向のｒ値および圧延方向と直角方向のｒ値のうち少なくとも１つをできるだけ低い値とした上で、微細析出物を分散させることによって、形状凍結性が飛躍的に向上することを明らかにしたものである。 That is, after increasing the strength of the {100} <011> to {223} <110> orientation group and setting at least one of the r value in the rolling direction and the r value in the direction perpendicular to the rolling direction as low as possible, It is clarified that the shape freezing property is remarkably improved by dispersing fine precipitates.
このような効果が得られる理由は必ずしも明らかでないが、以下のように考えられる。 The reason why such an effect is obtained is not necessarily clear, but is considered as follows.
すなわち、このような集合組織とすることによって、曲げ主体の成形においてはすべり系が限定されるため基本的に動的回復が生じやすく、結果として変形抵抗が小さくなる。微細な析出物は、すべり系をさらに限定的なものとする効果を奏し、形状凍結性をより一層良好にする。 In other words, by using such a texture, basically, since the slip system is limited in the bending-based molding, dynamic recovery is likely to occur, resulting in a low deformation resistance. Fine precipitates have the effect of further limiting the slip system and further improve the shape freezeability.
また、曲げ曲げ戻しなどの反転負荷が生ずる場合には、微細析出物にパイルアップした転位が、反転負荷にバックストレスとして働き、変形抵抗を下げるので、この場合にも、形状凍結性は向上する。したがって、本発明の鋼板は、フォーム成形の他、ドローベンド、フォームドローなど種々の成形法に対して効果がある。 In addition, when an inversion load such as bending and bending back occurs, dislocations piled up on fine precipitates act as back stress on the inversion load and lower the deformation resistance. In this case as well, the shape freezing property is improved. . Therefore, the steel sheet of the present invention is effective for various forming methods such as draw bending and foam drawing in addition to foam forming.
また、延性および伸びフランジ性と形状凍結性との両立のためには、フェライト相またはベイナイト相を最大相とすることも重要である。 In order to achieve both ductility and stretch flangeability and shape freezing properties, it is also important to make the ferrite phase or bainite phase the maximum phase.
本発明は、前述の知見に基づいて構成されており、その要旨とするところは以下の通りである。 The present invention is configured based on the above-described knowledge, and the gist thereof is as follows.
（１）質量％で、
Ｃ ：０．０２％以上、０．１５％以下、
Ｓｉ：０．５％超、１．６％以下、
Ｍｎ：０．０１％以上、３．０％以下、
Ｐ ：０．０２％以下、
Ｓ ：０．０１％以下、
Ａｌ：２．０％以下、
Ｎ ：０．０１％以下、
Ｏ ：０．０１％以下、
Ｔｉ：０．０５４％以上、０．４％以下、
Ｂ：０．０００２％以上、０．００７０％以下を含有し、さらに、
Ｎｂ：０．４％以下、Ｍｏ：１．０％以下の１種または２種を含有し、
残部は鉄および不可避的不純物よりなり、フェライトまたはベイナイトを面積率で最大相とし、１／２板厚における板面の｛００１｝＜１１０＞〜｛２２３｝＜１１０＞方位群のＸ線ランダム強度比の平均値が６．０以上で、かつ、これらの方位群の中で｛１１２｝＜１１０＞方位および｛００１｝＜１１０＞方位のうちいずれか一方または両方のＸ線ランダム強度比が８．０以上であり、加えて、圧延方向のｒ値および圧延方向と直角方向のｒ値のうち少なくとも１つが０．８以下で、かつ、径が１５ｎｍ以下の化合物粒子の個数が全化合物粒子の個数の６０％以上であることを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度鋼板。
(1) In mass%,
C: 0.02% or more, 0.15% or less,
Si: more than 0.5%, 1.6% or less,
Mn: 0.01% or more, 3.0% or less,
P: 0.02% or less,
S: 0.01% or less,
Al: 2.0% or less,
N: 0.01% or less,
O: 0.01% or less ,
Ti: 0.054% or more, 0.4% or less ,
B: 0.0002% or more and 0.0070% or less,
Nb: 0.4% or less, Mo: 1.0% or less of 1 type or 2 types ,
The balance consists of iron and unavoidable impurities, with ferrite or bainite as the maximum phase in area ratio, and X-ray random strength of {001} <110> to {223} <110> orientation groups on the plate surface at 1/2 plate thickness The average value of the ratio is 6.0 or more, and among these orientation groups, the X-ray random intensity ratio of either or both of the {112} <110> orientation and the {001} <110> orientation is 8 In addition, at least one of the r value in the rolling direction and the r value in the direction perpendicular to the rolling direction is 0.8 or less and the number of compound particles having a diameter of 15 nm or less is the total number of compound particles. A high-strength steel sheet excellent in shape freezeability and stretch flangeability, characterized by being 60% or more of the number.
（３）質量％で、さらに、Ｂ：０．０００２〜０．００７０％を含有することを特徴とする前記（１）または（２）記載の形状凍結性と伸びフランジ成形性に優れた高強度鋼板。 (3) High strength excellent in shape freezing property and stretch flange formability as described in (1) or (2) above, further comprising B: 0.0002 to 0.0070% by mass% steel sheet.
（２）質量％で、さらに、Ｖ：０．４％以下、Ｚｒ：０．２％以下、Ｃｒ：２％以下の１種または２種以上を含有することを特徴とする前記（１）に記載の形状凍結性と伸びフランジ成形性に優れた高強度鋼板。 (2) In the above (1), the composition further contains one or more of V: 0.4% or less, Zr: 0.2% or less, and Cr: 2% or less. High-strength steel sheet with excellent shape freezing and stretch flange formability.
（３）質量％で、さらに、Ｒｅｍ：０．００１％以上、０．１％以下を含有することを特徴とする前記（１）または（２）に記載の形状凍結性と伸びフランジ成形性に優れた高強度鋼板。 (3) By mass%, it further contains Rem: 0.001% or more and 0.1% or less, in the shape freezing property and stretch flange formability described in the above (1) or (2) Excellent high-strength steel sheet.
（４）前記（１）〜（３）のいずれかに記載の高強度鋼板の表面に溶融亜鉛めっきを有することを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度溶融亜鉛めっき鋼板。 (4) the (1) to a high-strength galvanized steel sheet having excellent shape fixability and stretch flangeability which is characterized by having a surface galvanized high strength steel sheet according to any one of (3) .
（５）前記（１）〜（３）のいずれかに記載の高強度鋼板の表面に合金化溶融亜鉛めっきを有することを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度合金化溶融亜鉛めっき鋼板。 (5) High strength alloying excellent in shape freezing property and stretch flange formability, characterized by having alloyed hot dip galvanizing on the surface of the high strength steel plate according to any one of (1) to (3) . Hot dip galvanized steel sheet.
（６）前記（１）〜（３）のいずれかに記載の形状凍結性と伸びフランジ成形性に優れた高強度鋼板を製造する方法であって、前記（１）〜（３）のいずれかに記載の成分組成からなる鋼片を熱間圧延するに当たり、１１５０℃以上に加熱し、８８０℃未満での圧下率の合計が３０％以上となるように熱間圧延し、８８０℃未満で熱間圧延を終了し、熱間圧延終了温度から７００℃以下までを３０℃／ｓ以上の平均冷却速度で冷却した後、５８０〜６８０℃で巻き取ることを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度鋼板の製造方法。 (6) the (1) to (3) a method for producing a high strength steel sheet excellent in shape fixability and stretch flangeability according to any one of any one of (1) to (3) When hot-rolling a steel slab having the composition described in 1. above, it is heated to 1150 ° C. or higher, hot-rolled so that the total rolling reduction at less than 880 ° C. is 30% or more, and heated at less than 880 ° C. The shape freezing property and stretch flange forming are characterized in that the hot rolling is finished and the temperature from the hot rolling finish temperature to 700 ° C. or lower is cooled at an average cooling rate of 30 ° C./s or more and then wound at 580 to 680 ° C. A method for producing high-strength steel sheets with excellent properties.
（７）前記（１）〜（３）のいずれかに記載の形状凍結性と伸びフランジ成形性に優れた高強度鋼板を製造する方法であって、前記（１）〜（３）のいずれかに記載の成分組成からなる鋼片を熱間圧延するに当たり、１１５０℃以上に加熱し、８８０℃未満での圧下率の合計が３０％以上となるように熱間圧延し、８８０℃未満で熱間圧延を終了し、平均冷却速度１５℃／ｓ以上で冷却し、６５０〜７２０℃の範囲で５ｓ以上空冷した後、６６０℃以下で巻き取ることを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度鋼板の製造方法。 (7) the (1) to (3) a method for producing a high strength steel sheet excellent in shape fixability and stretch flangeability according to any one of any one of (1) to (3) When hot-rolling a steel slab having the composition described in 1. above, it is heated to 1150 ° C. or higher, hot-rolled so that the total rolling reduction at less than 880 ° C. is 30% or more, and heated at less than 880 ° C. Finished hot rolling, cooled at an average cooling rate of 15 ° C./s or more, air-cooled in the range of 650 to 720 ° C. for 5 s or more, and then wound up at 660 ° C. or less. For producing high-strength steel sheets with excellent resistance.
（８）前記（６）または（７）に記載の高強度鋼板を６０％未満の圧下率で冷間圧延し、その後、５００〜８００℃の温度範囲に加熱し、冷却することを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度鋼板の製造方法。 (8) The high- strength steel sheet according to (6) or (7) is cold-rolled at a rolling reduction of less than 60%, and then heated to a temperature range of 500 to 800 ° C. and cooled. A method for producing high-strength steel sheets with excellent shape freezing properties and stretch flangeability.
（９）前記（６）または（７）に記載の高強度鋼板の製造方法により製造した鋼板、または、該鋼板を６０％未満の圧下率で冷間圧延した鋼板を５００〜８００℃の温度範囲に加熱し、その後、溶融亜鉛めっきを施すことを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度溶融亜鉛めっき鋼板の製造方法。 (9) A temperature range of 500 to 800 ° C. of a steel plate produced by the method for producing a high- strength steel plate according to (6) or (7) , or a steel plate cold-rolled with a reduction rate of less than 60%. A method for producing a high-strength hot-dip galvanized steel sheet having excellent shape freezing property and stretch flange formability, characterized by heating to galvanizing and then hot-dip galvanizing.
（１０）前記（９）に記載の溶融亜鉛めっきに引き続き、４５０〜６００℃の範囲で合金化処理を施すことを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。 (10) High-strength galvannealed alloy with excellent shape freezing property and stretch flange formability, characterized by being alloyed in the range of 450 to 600 ° C. following hot dip galvanizing described in (9 ) above Manufacturing method of plated steel sheet.
本発明によれば、薄鋼板の析出物と集合組織を同時に制御することにより、形状凍結性が著しく向上し、また、穴拡げ性にも優れる薄鋼板を提供できるようになった。特に、従来は形状不良の問題から高強度鋼板の適用が難しかった部品にも、高強度鋼板が使用できるようになる。スプリング・バック量および壁そり量が少なく、形状凍結性と穴拡げ性に優れた高強度鋼板が適用できるようになると、自動車車体の軽量化をより一層推進することができる。 According to the present invention, by simultaneously controlling the precipitate and texture of the thin steel plate, the shape freezing property is remarkably improved, and a thin steel plate having excellent hole expansibility can be provided. In particular, a high-strength steel plate can be used even for parts that have conventionally been difficult to apply a high-strength steel plate due to the problem of shape defects. If a high-strength steel sheet having a small amount of spring back and wall warpage and having excellent shape freezing property and hole expandability can be applied, it is possible to further reduce the weight of the automobile body.
以下に、本発明の内容を詳細に説明する。 The contents of the present invention will be described in detail below.
１／２板厚における板面の｛００１｝＜１１０＞〜｛２２３｝＜１１０＞方位群のＸ線ランダム強度比の平均値：
本発明で重要な特性値である。板厚中心位置での板面のＸ線回折を行い、ランダム試料を用いて規格化し、各方位の極密度（ランダム強度比）を求めたときの、｛００１｝＜１１０＞〜｛２２３｝＜１１０＞方位群の平均値が６．０以上でなくてはならない。これが６．０未満では形状凍結性が劣悪となる。
Average value of X-ray random intensity ratio of {001} <110> to {223} <110> orientation group on the plate surface at 1/2 plate thickness:
This is an important characteristic value in the present invention. {001} <110> to {223} <when X-ray diffraction of the plate surface at the plate thickness center position is performed, normalized using a random sample, and the pole density (random intensity ratio) in each direction is obtained. The average value of 110> direction group must be 6.0 or more. If this is less than 6.0, the shape freezing property becomes poor.
この方位群に含まれる主な方位は、｛１００｝＜０１１＞、｛１１６｝＜１１０＞、｛１１４｝＜１１０＞、｛１１３｝＜１１０＞、｛１１２｝＜１１０＞、｛３３５｝＜１１０＞および｛２２３｝＜１１０＞である。 The main orientations included in this orientation group are {100} <011>, {116} <110>, {114} <110>, {113} <110>, {112} <110>, {335} < 110> and {223} <110>.
これら各方位のＸ線ランダム強度比（極密度）は、｛１１０｝、｛１００｝、｛２１１｝、｛３１０｝の各極点図のうち複数の極点図（好ましくは３つ以上）を用いて級数展開法で計算した３次元集合組織から求めればよい。 The X-ray random intensity ratio (pole density) in each of these directions is obtained by using a plurality of pole figures (preferably three or more) among the pole figures of {110}, {100}, {211}, and {310}. What is necessary is just to obtain | require from the three-dimensional texture calculated by the series expansion method.
すなわち、上記各結晶方位のＸ線ランダム強度比には、３次元集合組織のφ２＝４５゜断面における（００１）［１−１０］、（１１６）［１−１０］、（１１４）［１−１０］、（１１３）［１−１０］、（１１２）［１−１０］、（３３５）［１−１０］、（２２３）［１−１０］の強度をそのまま用いればよい。 That is, the X-ray random intensity ratio of each crystal orientation described above includes (001) [1-10], (116) [1-10], (114) [1-] in the φ2 = 45 ° cross section of the three-dimensional texture. 10], (113) [1-10], (112) [1-10], (335) [1-10], (223) [1-10] strengths may be used as they are.
｛００１｝＜０１１＞〜｛２２３｝＜１１０＞方位群の平均値とは、上記の各方位の相加平均である。上記の全ての方位の強度を得ることができない場合には、｛１００｝＜１１０＞、｛１１６｝＜１１０＞、｛１１４｝＜１１０＞、｛１１２｝＜１１０＞、｛２２３｝＜１１０＞の各方位の相加平均で代替してもよい。 The average value of {001} <011> to {223} <110> azimuth group is an arithmetic average of the above azimuths. When the strengths of all the above directions cannot be obtained, {100} <110>, {116} <110>, {114} <110>, {112} <110>, {223} <110> Alternatively, an arithmetic average of each direction may be substituted.
これらの方位群の中で、｛００１｝＜１１０＞と｛１１２｝＜１１０＞方位は、壁そりの低減に極めて効果的な方位である、したがって、これらの方位群の中で、｛００１｝＜１１０＞または｛１１２｝＜１１０＞方位のＸ線ランダム強度比が最大かつ８．０以上になると、形状凍結性はさらに向上するので好ましい。 Among these orientation groups, the {001} <110> and {112} <110> orientations are extremely effective orientations for reducing wall warpage. Therefore, among these orientation groups, {001} It is preferable that the X-ray random intensity ratio in the <110> or {112} <110> orientation is maximum and 8.0 or more because the shape freezing property is further improved.
さらに、１／２板厚における板面の｛５５４｝＜２２５＞、｛１１１｝＜１１２＞および｛１１１｝＜１１０＞の３つの結晶方位のＸ線ランダム強度比の平均値は３．５以下であることが好ましい。これが３．５超であると、｛１００｝＜０１１＞〜｛２２３｝＜１１０＞方位群の強度が適正であっても、良好な形状凍結性を得ることが困難となる。 Furthermore, the average value of the X-ray random intensity ratio of the three crystal orientations of {554} <225>, {111} <112> and {111} <110> on the plate surface at 1/2 plate thickness is 3.5 or less. It is preferable that If this exceeds 3.5, it will be difficult to obtain good shape freezing properties even if the strength of the {100} <011> to {223} <110> orientation groups is appropriate.
｛５５４｝＜２２５＞、｛１１１｝＜１１２＞および｛１１１｝＜１１０＞のＸ線ランダム強度比も、上記の方法に従って計算した３次元集合組織から求めればよい。 The X-ray random intensity ratio of {554} <225>, {111} <112>, and {111} <110> may be obtained from the three-dimensional texture calculated according to the above method.
より望ましくは、｛００１｝＜０１１＞〜｛２２３｝＜１１０＞方位群のＸ線ランダム強度比の平均値が８．０以上、｛００１｝＜０１１＞または｛１１２｝＜１１０＞方位のＸ線ランダム強度比が１０．０以上、｛５５４｝＜２２５＞、｛１１１｝＜１１２＞および｛１１１｝＜１１０＞のＸ線ランダム強度比の相加平均値が２．５未満である。 More preferably, the average value of the X-ray random intensity ratios in the {001} <011> to {223} <110> orientation groups is 8.0 or more, and the {001} <011> or {112} <110> orientation X The linear random intensity ratio is 10.0 or more, and the arithmetic average value of the X-ray random intensity ratios of {554} <225>, {111} <112> and {111} <110> is less than 2.5.
Ｘ線回折に供する試料は、機械研磨などによって鋼板を所定の板厚まで減厚し、次いで、化学研磨や電解研磨などによって歪みを除去すると同時に、板厚１／２面が測定面となるように作製する。 The sample to be subjected to X-ray diffraction is thinned to a predetermined plate thickness by mechanical polishing or the like, and then the distortion is removed by chemical polishing or electrolytic polishing, and at the same time, the 1/2 plate thickness becomes the measurement surface. To make.
鋼板の板厚中心層に偏析帯や欠陥などが存在し、測定上不都合が生ずる場合には、板厚の３／８〜５／８の範囲で適当な面が測定面となるように、上述の方法に従って試料を調整して測定すればよい。 When there is a segregation zone or a defect in the thickness center layer of the steel sheet, which causes inconvenience in measurement, the above-described surface is set so that an appropriate surface becomes the measurement surface in the range of 3/8 to 5/8 of the plate thickness. The sample may be adjusted according to the above method.
当然のことであるが、上述のＸ線強度の限定が板厚１／２近傍だけでなく、なるべく多くの厚みについて満たされることで、より一層形状凍結性が良好になる。なお、｛ｈｋｌ｝＜ｕｖｗ＞で表される結晶方位とは、板面の法線方向が＜ｈｋｌ＞に平行で、圧延方向が＜ｕｖｗ＞と平行であることを示している。 As a matter of course, the above-described limitation of the X-ray intensity is satisfied not only in the vicinity of the plate thickness ½ but also as much as possible, so that the shape freezing property is further improved. The crystal orientation represented by {hkl} <uvw> indicates that the normal direction of the plate surface is parallel to <hkl> and the rolling direction is parallel to <uvw>.
圧延方向のｒ値（ｒＬ）および圧延方向と直角方向のｒ値（ｒＣ）：
本発明において重要である。すなわち、本発明者らが鋭意検討の結果、上述した種々の結晶方位の極密度が適正であることと同時に、ｒＬおよびｒＣのうち少なくとも１つが０．８以下であることが良好な形状凍結性を得るために必須であることが判明した。より好ましくは０．６以下である。
R value (rL) in the rolling direction and r value (rC) in the direction perpendicular to the rolling direction:
Important in the present invention. That is, as a result of intensive studies by the present inventors, the shape density of the above-mentioned various crystal orientations is appropriate and at the same time, at least one of rL and rC is 0.8 or less. Turned out to be essential to obtain. More preferably, it is 0.6 or less.
ｒＬおよびｒＣの下限は、特に定めることなく本発明の効果を得ることができるが、ｒ値は、ＪＩＳ５号引張試験片を用いた引張試験により評価する。引張歪みは、通常１５％であるが、均一伸びが１５％を下回る場合には、均一伸びの範囲で、できるだけ１５％に近い歪みで評価すればよい。 The lower limit of rL and rC is not particularly defined, and the effect of the present invention can be obtained. The r value is evaluated by a tensile test using a JIS No. 5 tensile test piece. The tensile strain is usually 15%, but if the uniform elongation is less than 15%, the strain may be evaluated as close to 15% as possible within the range of uniform elongation.
なお、曲げ加工を施す方向は加工部品によって異なるので、特に限定するものではないが、ｒ値が小さい方向に対して垂直もしくは垂直に近い方向に折り曲げる加工を主とすることが好ましい。 The direction in which the bending process is performed differs depending on the processed part, and is not particularly limited. However, it is preferable that the bending process is mainly performed in a direction perpendicular to or close to the perpendicular to the direction in which the r value is small.
ところで、一般に、集合組織とｒ値とは相関があることが知られているが、本発明においては、既述の結晶方位の極密度に関する限定とｒ値に関する限定とは互いに同義ではなく、両方の限定が同時に満たされなくては、良好な形状凍結性を得ることはできない。 Incidentally, it is generally known that there is a correlation between the texture and the r value. However, in the present invention, the above-mentioned limitation on the polar density of the crystal orientation and the limitation on the r value are not synonymous with each other. Unless the above limitations are satisfied at the same time, good shape freezing property cannot be obtained.
組織：
延性、伸びフランジ成形性および形状凍結性の観点から、組織はフェライトまたはベイナイト相を最大相とする。ただし、フェライトとベイナイトの各々の集合組織を比べると、ベイナイト部分で、形状凍結に有利な｛００１｝＜０１１＞〜｛２２３｝＜１１０＞方位の集合組織が発達しやすい。
Organization:
From the viewpoints of ductility, stretch flangeability, and shape freezing, the structure has a ferrite or bainite phase as the maximum phase. However, when the textures of ferrite and bainite are compared, the texture of {001} <011> to {223} <110> orientation, which is advantageous for shape freezing, easily develops in the bainite portion.
この理由は明らかではないが、ベイナイト組織が、熱延中に形成される形状凍結性に優位なオーステナイト集合組織を受け継ぎやすいためと考えられる。したがって、ベイナイトの占積率が大きい方がより望ましい。 The reason for this is not clear, but it is considered that the bainite structure easily inherits the austenite texture that is formed during hot rolling and has an excellent shape freezing property. Therefore, it is more desirable that the bainite space factor is large.
この観点からは、ベイナイトの面積率は５０％超であることが望ましい。フェライトまたはベイナイトの面積率は、板厚中央部を光学顕微鏡により１００〜１０００倍で５視野以上観察し、その平均値より求めることとする。板厚中心部に偏析層などが存在する場合には回避して観察する。板厚中心部とは板厚の３／８〜５／８を示す。 From this point of view, the area ratio of bainite is desirably more than 50%. The area ratio of ferrite or bainite is determined from an average value obtained by observing the central part of the plate thickness with an optical microscope at 100 to 1000 times at least 5 views. If a segregation layer or the like is present in the center of the plate thickness, observe it while avoiding it. The plate thickness center portion indicates a plate thickness of 3/8 to 5/8.
化合物粒子：
本発明において非常に重要である。すなわち、上述したとおり、微細化合物粒子が多数存在することで、集合組織の効果をより顕著なものとする。また、延性や伸びフランジ成形性の観点からも有利に作用する。
Compound particles:
This is very important in the present invention. That is, as described above, the presence of many fine compound particles makes the texture effect more remarkable. Moreover, it acts advantageously also from a viewpoint of ductility and stretch flange formability.
径が１５ｎｍ以下の化合物粒子の個数が全化合物粒子の個数の６０％以上を占める必要がある。径が１５ｎｍ超では、このような効果が小さいので、これを上限とする。好ましくは１０ｎｍ以下、さらに好ましくは５ｎｍ以下である。 The number of compound particles having a diameter of 15 nm or less needs to occupy 60% or more of the total number of compound particles. If the diameter exceeds 15 nm, such an effect is small, so this is the upper limit. Preferably it is 10 nm or less, More preferably, it is 5 nm or less.
径とは、粒子の最長径を示す。すなわち、観察した粒子が円形であれば直径を、楕円形であれば長径を、四角形であれば対角線の長さを表す。 The diameter indicates the longest diameter of the particle. That is, when the observed particle is circular, the diameter is represented, when the particle is elliptical, the major axis is represented, and when the observed particle is quadrilateral, the length of the diagonal line is represented.
このような微細粒子は、Ｔｉ系の炭化物、窒化物、炭窒化物を主体とするが、酸化物や硫化物、さらにはＴｉ以外の化合物であっても構わない。 Such fine particles are mainly composed of Ti-based carbides, nitrides, and carbonitrides, but may be oxides, sulfides, or compounds other than Ti.
なお、化合物粒子の全てが１５ｎｍ以下である必要はなく、全化合物粒子個数のうち、６０％以上、より好ましくは８５％以上とする。これが６０％未満では、集合組織が好適に発達していても形状凍結性への効果は限定的である。 All the compound particles need not be 15 nm or less, and the total number of compound particles is 60% or more, more preferably 85% or more. If this is less than 60%, the effect on the shape freezing property is limited even if the texture is suitably developed.
化合物粒子の観察用試料には、板厚の３／８〜５／８の範囲から採取した薄膜を用い、透過型電子顕微鏡（電解放射型電子銃であればなお好ましい）にて、１０万倍以上の倍率で、５平方μｍ以上の面積について観察する。 As a sample for observing the compound particles, a thin film collected from the range of 3/8 to 5/8 of the plate thickness was used, and 100,000 times with a transmission electron microscope (preferably an electrolytic emission electron gun). With the above magnification, an area of 5 μm or more is observed.
視野の選択は無作為に行い、５視野以上を観察する。このとき、結晶粒界に存在する微細化合物は観察が困難であるので対象とせず、結晶粒内のみを対象とする。化合物の見落としを避けるため、焦点を故意にずらす、デフォーカス法を用いることが好ましい。 Select a field of view at random, and observe at least 5 fields of view. At this time, the fine compound existing in the crystal grain boundary is difficult to observe, so it is not an object, and only the inside of the crystal grain is an object. In order to avoid overlooking the compound, it is preferable to use a defocus method in which the focus is intentionally shifted.
薄膜の厚さによっては、同じ面積を観察しても観察される化合物の数が異なるのは当然のことであるが、ここでは、微細化合物の大きさとそれらが全体に占める存在割合を対象とするので、透過型電子顕微鏡で鮮明に観察できる範囲で十分に厚いことが好ましい。 Obviously, depending on the thickness of the thin film, the number of compounds observed is different even when the same area is observed, but here, the size of the fine compounds and the abundance ratio of them are considered. Therefore, it is preferable that the thickness is sufficiently thick as long as it can be clearly observed with a transmission electron microscope.
上記の条件で観察される粒子数が、ここでの全粒子数である。微細化合物粒子の密度は特に限定しないが、上記の電子顕微鏡による観察で、１平方μｍあたり１０個以上存在する。好ましくは１００個以上である。 The number of particles observed under the above conditions is the total number of particles here. The density of the fine compound particles is not particularly limited, but is 10 or more per square μm as observed with the electron microscope. Preferably it is 100 or more.
また、粒界におけるセメンタイト等の鉄系炭化物の占有率が０．１超または鉄炭化物の最大粒子径が１μｍ超になると、粒界で、これらの鉄炭化物が連結し伸びフランジ性が著しく劣化する。したがって、粒界における鉄炭化物の占有率を０．１以下、かつ、この鉄炭化物の最大粒子径を１μｍ以下にすることが好ましい。鉄炭化物の占有率および最大粒子径は、小さいほど望ましいことから、下限は特に規定しない。 Further, when the occupation ratio of cementitious carbide such as cementite at the grain boundary exceeds 0.1 or the maximum particle diameter of the iron carbide exceeds 1 μm, these iron carbides are connected at the grain boundary, and the stretch flangeability is remarkably deteriorated. . Therefore, it is preferable that the occupation ratio of the iron carbide in the grain boundary is 0.1 or less and the maximum particle diameter of the iron carbide is 1 μm or less. Since the iron carbide occupancy and the maximum particle size are preferably as small as possible, the lower limit is not particularly defined.
鉄炭化物による粒界の占有率（−）は、鉄材の断面サンプルにおいて、ある領域での粒界の総長さＬと、鉄炭化物によって占有されている粒界の長さとの総和ｄの比ｄ／Ｌで与えられる。 The grain boundary occupancy (-) by iron carbide is the ratio d / of the sum d of the total length L of grain boundaries in a certain region and the length of grain boundaries occupied by iron carbide in a cross-sectional sample of iron material. L is given.
測定は、２００倍以上の倍率の光学顕微鏡観察写真において、画像処理によってＬおよびｄを直接求めてもよい。より簡便な方法としては、上記写真上に描いたｎ本の直線と粒界との交点の数Ｎと、Ｎ個の交点の中で、その交点の位置に鉄炭化物が存在した場合の数Ｍを用いてＭ／Ｎで求めてもよい。 In the measurement, L and d may be directly obtained by image processing in an optical microscope observation photograph having a magnification of 200 times or more. As a simpler method, the number N of intersections between the n straight lines drawn on the photograph and the grain boundary, and the number M when iron carbide exists at the position of the intersections among the N intersections. You may obtain | require by M / N using.
この時採用する直線の数Ｎを３以上とすることで、十分な精度が確保できる。また、写真の倍率は、この１本の直線と粒界の交点の数が１０以上になるように選択することで、十分な精度を確保できる。 Sufficient accuracy can be ensured by setting the number N of straight lines to be 3 or more. Moreover, sufficient accuracy can be ensured by selecting the magnification of the photograph so that the number of intersections of the single straight line and the grain boundary is 10 or more.
次に、成分範囲の限定条件について述べる。なお、％は質量％を意味する。 Next, the limiting conditions of the component range will be described. In addition,% means the mass%.
Ｃの下限を０．０２％としたのは、これを下回ると、５９０ＭＰａ以上の引張強度を得ることが困難であるだけなく、微細化合物を十分に得ることができなくなるためである。一方、０．１５％超になると伸びフランジ成形性が劣化するので、上限を０．１５％に設定する。 The reason why the lower limit of C is set to 0.02% is that when the lower limit is not reached, it is difficult to obtain a tensile strength of 590 MPa or more, and a fine compound cannot be obtained sufficiently. On the other hand, if it exceeds 0.15%, stretch flange formability deteriorates, so the upper limit is set to 0.15%.
Ｓｉは本発明において重要である。すなわち、Ｓｉを０．５％超添加することで、化合物が微細となり、結果として、形状凍結性が向上することを新たにつきとめた。したがって、下限を０．５％超とする。 Si is important in the present invention. That is, it was newly found that the compound becomes finer by adding more than 0.5% of Si, and as a result, the shape freezing property is improved. Therefore, the lower limit is made over 0.5%.
一方、１．６％超となると加工性が劣化したり、表面疵やめっき性の問題などが発生したりするので、１．６％を上限とする。０．５％超〜１．２％がより好ましい範囲である。また、溶融亜鉛めっきを施す際には、０．５％超〜０．８％未満の添加とすることが好ましい。 On the other hand, if it exceeds 1.6%, the workability deteriorates or problems such as surface defects and plating properties occur, so 1.6% is made the upper limit. More than 0.5% to 1.2% is a more preferable range. Moreover, when performing hot dip galvanization, it is preferable to add more than 0.5% to less than 0.8%.
Ｍｎも鋼板の機械的強度を高めるのに有効な元素であるが、３．０％超となると、延性、伸びフランジ成形性が劣化するので、３．０％を上限とする。一方、実用鋼で、Ｍｎを０．０１％未満とするのは、コスト高となり、材質上のメリットもないので、０．０１％を下限とする。 Mn is also an element effective for increasing the mechanical strength of the steel sheet. However, if it exceeds 3.0%, ductility and stretch flange formability deteriorate, so 3.0% is made the upper limit. On the other hand, in practical steel, if Mn is less than 0.01%, the cost is high and there is no merit in material, so 0.01% is made the lower limit.
ＰとＳは、それぞれ、０．０２％以下、０．０１％以下とする。これは、加工性の劣化や熱間圧延、または冷間圧延時の割れを防ぎ、溶接性を確保するためである。 P and S are 0.02% or less and 0.01% or less, respectively. This is to prevent weldability deterioration and cracking during hot rolling or cold rolling to ensure weldability.
Ａｌは、脱酸やフェライト生成促進を通して延性を向上せしめる一方、多すぎると、加工性や溶接性が劣化したり、表面性状が劣悪となるので、上限を２．０％とする。 Al improves ductility through deoxidation and promotion of ferrite formation. On the other hand, if it is too much, workability and weldability deteriorate and surface properties become poor, so the upper limit is made 2.0%.
ＮとＯは、微細化合物を得るのに役立つが、あまり多いと、粗大な化合物を増加させ、形状凍結性が劣化するので、それぞれ、０．０１％以下、０．０１％以下とする。 N and O are useful for obtaining a fine compound. However, if too much is added, a coarse compound is increased and the shape freezing property is deteriorated, so the content is made 0.01% or less and 0.01% or less, respectively.
Ｔｉは、本発明において重要な元素である。Ｔｉは、炭化物、窒化物、炭窒化物または硫化物や炭硫化物、炭窒硫化物などの化合物として微細析出し、強度上昇に効果があるとともに、セメンタイトを初めとする鉄炭化物を低減させることから、形状凍結性と伸びフランジ性を改善する。 Ti is an important element in the present invention. Ti precipitates finely as carbides, nitrides, carbonitrides or compounds such as sulfides, carbon sulfides, carbonitride sulfides, and is effective in increasing strength, while reducing iron carbides including cementite. Therefore, shape freezing property and stretch flangeability are improved.
また、Ｔｉは、上述した形状凍結性に好ましい集合組織を発達させる効果を有する。したがって、所望される強度に応じて、０．０５％以上添加する。ただし、過度に添加しても格段の効果はなく、むしろ、加工性や表面性状を劣化させるので、０．４％を上限とした。なお、本件発明では、Ｔｉの下限を、後述の実施例の値に基づいて、０．０５４％とした。 Further, Ti has an effect of developing a texture preferable for the shape freezing property described above. Therefore, 0.05% or more is added depending on the desired strength. However, even if added excessively, there is no remarkable effect. Rather, the workability and surface properties are deteriorated, so 0.4% was made the upper limit. In the present invention, the lower limit of Ti is set to 0.054% based on the values of examples described later.
ＮｂおよびＭｏも、Ｔｉと同様に、炭化物、窒化物、炭窒化物または硫化物や炭硫化物、炭窒硫化物などとして微細析出し、強度上昇に効果があるとともに、セメンタイトを初めとする鉄炭化物を低減させることから、形状凍結性と伸びフランジ性を改善する。また、形状凍結性に好ましい集合組織を発達させる効果を有する。 Nb and Mo, like Ti, are finely precipitated as carbides, nitrides, carbonitrides or sulfides, carbonitrides, carbonitrides, and the like, and are effective in increasing strength, and iron such as cementite. Since the carbides are reduced, the shape freezing property and stretch flangeability are improved. It also has the effect of developing a texture that is favorable for shape freezing.
したがって、所望される強度に応じて、Ｎｂを０．４％以下、Ｍｏを１．０％以下添加する。ただし、過度に添加しても格段の効果はなく、むしろ加工性や表面性状を劣化させるので、ＮｂおよびＭｏそれぞれの上限を、０．４％、１．０％とした。なお、ＮｂやＭｏは、Ｔｉ系化合物の中に存在する場合も有る。 Therefore, Nb is added at 0.4% or less and Mo is added at 1.0% or less depending on the desired strength. However, even if added excessively, there is no remarkable effect, but rather the workability and surface properties are deteriorated, so the upper limits of Nb and Mo were set to 0.4% and 1.0%, respectively. Nb and Mo may exist in the Ti-based compound.
Ｂは、化合物の微細化に寄与することを通じて、形状凍結性を向上せしめるので、必要に応じて添加する。０．０００２％未満では効果が小さく、一方、多量の添加は鋼板の延性を劣化させるので、０．００７０％以下とする。 B improves the shape-freezing property by contributing to the refinement of the compound, and is added as necessary. If the content is less than 0.0002%, the effect is small. On the other hand, addition of a large amount deteriorates the ductility of the steel sheet, so the content is made 0.0070% or less.
Ｖ、Ｚｒ、Ｗ、Ｃｒ、Ｃｕ、Ｎｉ、および、Ｓｎは、機械的強度を高める他、耐水素脆性や加工性、形状凍結性の向上など、材質を改善する効果があるので、必要に応じて添加する。しかし、過度の添加は逆に加工性を劣化させるので、Ｖ、Ｚｒ、Ｗ、Ｃｒ、Ｃｕ、Ｎｉ、および、Ｓｎの上限を、それぞれ、０．４％、０．２％、０．３％、２％、２％、２％、および、０．２％とする。 V, Zr, W, Cr, Cu, Ni, and Sn increase the mechanical strength and have the effect of improving the material such as hydrogen embrittlement resistance, workability, and shape freezing properties. Add. However, since excessive addition adversely degrades workability, the upper limits of V, Zr, W, Cr, Cu, Ni, and Sn are set to 0.4%, 0.2%, and 0.3%, respectively. 2%, 2%, 2%, and 0.2%.
Ｃａ、Ｍｇ、および、Ｒｅｍは、硫化物の形態を制御することで微細化合物を形成し、形状凍結性と伸びフランジ成形性を改善するので、必要に応じて、それぞれ、０．０００５％以上、０．０００１％以上、および、０．００１％以上添加することが望ましい。過度に添加しても、格段の効果はなくコスト高となるので、Ｃａ、Ｍｇ、および、Ｒｅｍのそれぞれ上限を、０．０１％、０．０３％、および、０．１％と設定した。 Ca, Mg, and Rem form a fine compound by controlling the form of sulfide, and improve shape freezing property and stretch flange formability. Therefore, if necessary, 0.0005% or more, It is desirable to add 0.0001% or more and 0.001% or more. Even if added excessively, there is no remarkable effect and the cost is high, so the upper limits of Ca, Mg, and Rem were set to 0.01%, 0.03%, and 0.1%, respectively.
なお、本発明では特に限定しないが、Ｏは微細化合物粒子の形成に役立つので、０．０００５％以上添加しても構わない。 Although not particularly limited in the present invention, O is useful for forming fine compound particles, so 0.0005% or more may be added.
溶融亜鉛めっき皮膜の化学成分は特に限定するものではなく、亜鉛（Ｚｎ）の他、Ａｌ、Ｍｇ、Ｃｒ、Ｎｉ、Ｃｕ、Ｍｎ、Ｆｅなどを含有しても構わない。合金化溶融亜鉛めっきの場合には、亜鉛（Ｚｎ）と鉄（Ｆｅ）との合金相が主であるが、その他の化合物を含有しても構わない。 The chemical component of the hot dip galvanized film is not particularly limited, and may contain Al, Mg, Cr, Ni, Cu, Mn, Fe, etc. in addition to zinc (Zn). In the case of alloyed hot dip galvanizing, an alloy phase of zinc (Zn) and iron (Fe) is mainly used, but other compounds may be contained.
なお、本発明の鋼板の表面には、上記の溶融亜鉛めっきや合金化溶融亜鉛めっきのほか、種々のめっきや被覆が施されていても構わない。めっきの種類は特に限定するものではなく、電気めっき、溶融めっき、蒸着めっき等のいずれでも、本発明の効果が得られる。 In addition to the above hot dip galvanizing and alloying hot dip galvanizing, various platings and coatings may be applied to the surface of the steel sheet of the present invention. The type of plating is not particularly limited, and the effects of the present invention can be obtained by any of electroplating, hot dipping, vapor deposition plating and the like.
次に、製造方法について説明する。 Next, a manufacturing method will be described.
熱間圧延に先行する製造方法は特に限定するものではない。すなわち、高炉，転炉や電炉等による溶製に引き続き各種の２次製錬を行い、次いで、通常の連続鋳造、インゴット法による鋳造の他、薄スラブ鋳造などの方法で鋳造すればよい。連続鋳造の場合には、一度低温まで冷却したのち、再度加熱してから熱間圧延してもよいし、鋳造スラブを連続的に熱延してもよい。原料にはスクラップを使用しても構わない。 The production method preceding hot rolling is not particularly limited. That is, various secondary smelting may be performed following smelting in a blast furnace, converter, electric furnace, etc., and then cast by a method such as thin slab casting in addition to normal continuous casting and casting by an ingot method. In the case of continuous casting, after cooling to a low temperature once, it may be heated again and then hot rolled, or the cast slab may be continuously hot rolled. Scrap may be used as a raw material.
本発明の形状凍結性に優れた鋼板は、上記成分組成の鋼を鋳造した後、熱間圧延後冷却まま、熱間圧延後熱処理、熱間圧延後冷却・酸洗し冷延した後に焼鈍、または、熱延鋼板もしくは冷延鋼板にめっきを施し、もしくは、溶融めっきラインにて熱処理を施したまま、さらには、これらの鋼板に別途表面処理を施すことによっても得られる。 The steel sheet excellent in shape freezing property of the present invention, after casting the steel of the above component composition, as it is cooled after hot rolling, heat treatment after hot rolling, cooling after cold rolling, pickling and annealing after cold rolling, Alternatively, it can be obtained by plating a hot-rolled steel sheet or a cold-rolled steel sheet, or by subjecting these steel sheets to a separate surface treatment while being heat-treated in a hot dipping line.
熱延の加熱温度は１１５０℃以上とする。加熱温度が１１５０℃未満では、ＴｉやＮｂの化合物が十分に再固溶しないことから、十分な引張強度が得られないばかりでなく、集合組織を先鋭化させる効果が低減するとともに、粗大化合物によって穴拡げ性が劣化する。 The heating temperature for hot rolling is 1150 ° C. or higher. When the heating temperature is less than 1150 ° C., the Ti and Nb compounds are not sufficiently re-dissolved, so that not only a sufficient tensile strength cannot be obtained, but also the effect of sharpening the texture is reduced, and the coarse compound Hole expandability deteriorates.
上限は特に限定しないが、加熱温度を１３５０℃超にしても効果が飽和するばかりで、コスト上、設備上、デメリットが大きいことから、１３５０℃が実質的な上限である。 The upper limit is not particularly limited, but even if the heating temperature exceeds 1350 ° C., the effect is saturated, and the disadvantage is large in terms of cost and equipment, so 1350 ° C. is a practical upper limit.
前記（１）の発明で規定する各結晶方位のＸ線強度比レベルを達成するためには、８８０℃未満で合計３０％以上の圧延を行う。この圧延が行われないと、圧延されたオーステナイトの集合組織が十分に発達せず、そのために、次に、如何様な冷却を施しても、最終的に得られる熱延鋼板の板面に、前記（１）の発明で規定する極密度が得られない。したがって、８８０℃未満での圧下率合計の下限値を３０％とした。 In order to achieve the X-ray intensity ratio level of each crystal orientation defined in the invention of (1) above, a total of 30% or more rolling is performed at less than 880 ° C. If this rolling is not performed, the texture of the rolled austenite does not develop sufficiently, and therefore, whatever the cooling is applied to the plate surface of the hot-rolled steel sheet finally obtained, The pole density specified in the invention of (1) cannot be obtained. Therefore, the lower limit of the total rolling reduction at less than 880 ° C. is set to 30%.
合計圧下率は高いほどより先鋭な集合組織形成が期待されるので、４０％以上とすることが好ましいが、この圧下率合計が９７．５％を越えると、圧延機の剛性を過剰に高める必要があり、経済上のデメリットを生じるので、望ましくは９７．５％以下とする。 As the total rolling reduction is higher, sharper texture formation is expected. Therefore, it is preferable to set it to 40% or more. However, if the total rolling reduction exceeds 97.5%, it is necessary to excessively increase the rigidity of the rolling mill. There is an economic demerit, so 97.5% or less is desirable.
熱間圧延終了温度は、８８０℃以上では集合組織全体がランダム化することから形状凍結性が劣化するので、８８０℃未満を上限とする。さらには、８５０℃未満がより好ましい。なお、下限は特に指定しないが、Ａr3変態温度未満では圧延荷重が変動しやすく、板厚精度が劣化するので、Ａr3変態点以上で仕上げることが好ましい。 When the hot rolling end temperature is 880 ° C. or higher, the entire texture is randomized, and the shape freezing property deteriorates. Therefore, the upper limit is less than 880 ° C. Furthermore, less than 850 degreeC is more preferable. Although the lower limit is not particularly specified, the rolling load is likely to fluctuate below the Ar 3 transformation temperature and the plate thickness accuracy is deteriorated. Therefore, it is preferable to finish at the Ar 3 transformation point or higher.
８８０℃未満の熱間圧延時の熱間圧延ロールと鋼板との摩擦係数が０．２を越えている場合には、鋼板表面近傍における板面に、｛１１０｝面を主とする結晶方位が発達し、形状凍結性が劣化するので、より良好な形状凍結性を指向する場合には、Ａr3変態温度以上（Ａr3＋１００）℃以下の熱間圧延時における少なくとも１パスについて、熱間圧延ロールと鋼板との摩擦係数を０．２以下とすることが望ましい。 When the friction coefficient between the hot rolling roll and the steel plate at the time of hot rolling at less than 880 ° C. exceeds 0.2, the crystal orientation mainly consisting of {110} plane is present on the plate surface near the steel plate surface. Since it develops and shape freezeability deteriorates, when aiming for better shape freezeability, at least one pass during hot rolling at an Ar 3 transformation temperature or higher (Ar 3 +100) ° C. or lower is hot rolled. It is desirable that the coefficient of friction between the roll and the steel plate be 0.2 or less.
この摩擦係数は、低ければ低いほど好ましく、下限は定めないが、さらに良好な形状凍結性が要求される場合には、Ａr3変態温度以上（Ａr3＋１００）℃以下の熱間圧延の全パスについて、摩擦係数を０．１５以下とすることが望ましい。摩擦係数の測定方法は、特に規定しないが一般によく知られているように、先進率と圧延荷重から求めるのが望ましい。 The lower the coefficient of friction, the better. The lower limit is not defined, but if a better shape freezing property is required, all passes of hot rolling above the Ar 3 transformation temperature and below (Ar 3 +100) ° C. It is desirable that the coefficient of friction be 0.15 or less. The method for measuring the friction coefficient is not particularly defined, but it is desirable to obtain it from the advanced rate and the rolling load, as is generally well known.
熱間圧延終了後は、以下に示す２つの方法のいずれかに従って冷却し、その後、巻き取る。 After the hot rolling is finished, it is cooled according to one of the following two methods and then wound up.
第１の方法について説明する。熱間圧延終了温度から７００℃以下までを３０℃／ｓ以上の平均冷却速度で冷却することによって、先鋭な集合組織を形成し、同時に、巻取中の微細化合物の形成を促す。３０℃／ｓ未満では、このような効果が小さくなるので、３０℃／ｓを下限とする。 The first method will be described. By cooling from the hot rolling end temperature to 700 ° C. or less at an average cooling rate of 30 ° C./s or more, a sharp texture is formed, and at the same time, formation of a fine compound during winding is promoted. If it is less than 30 ° C./s, such an effect becomes small, so 30 ° C./s is made the lower limit.
巻取温度を５８０〜６８０℃の範囲とするのも、同様の理由からである。６８０℃超では粗大化合物が出現するため、形状凍結性および伸びフランジ成形性と引張強度とのバランスが劣化する。一方、５８０℃未満では、微細化合物を十分に得ることが困難となるため、５８０℃を下限とする。 The coiling temperature is set to a range of 580 to 680 ° C. for the same reason. When the temperature exceeds 680 ° C., a coarse compound appears, and the balance between shape freezing property and stretch flange formability and tensile strength deteriorates. On the other hand, if it is less than 580 ° C., it is difficult to obtain a fine compound sufficiently, so 580 ° C. is the lower limit.
次に、第２の方法について説明する。熱間圧延終了温度から続く空冷開始温度までの平均冷却速度を１５℃／ｓ以上とする。１５℃／ｓ未満では、粗大化合物の量が多くなり、形状凍結性や伸びフランジ成形性を劣化させる。引き続き６５０〜７２０℃までの温度範囲内で５ｓ間以上空冷する。これによって、微細化合物の生成と形状凍結性に好ましい集合組織形成を促進する効果がある。 Next, the second method will be described. The average cooling rate from the hot rolling end temperature to the subsequent air cooling start temperature is set to 15 ° C./s or more. If it is less than 15 degreeC / s, the quantity of a coarse compound will increase and shape freezing property and stretch flange formability will deteriorate. Subsequently, it is air-cooled for 5 seconds or more within a temperature range of 650 to 720 ° C. This has the effect of promoting the formation of a texture that is favorable for the production of fine compounds and the shape freezing property.
その後の巻取り温度は６６０℃以下とする。６６０℃を超えると粗大析出物が生成し形状凍結性が劣化する。下限は限定しないが常温未満ではコストアップし、特段の効果もないので常温以上とする。 Thereafter, the coiling temperature is 660 ° C. or lower. When it exceeds 660 degreeC, a coarse precipitate will produce | generate and shape freezing property will deteriorate. The lower limit is not limited, but if it is less than room temperature, the cost will increase and there will be no special effect.
熱間圧延においては、粗圧延後にシートバーを接合し、連続的に仕上げ圧延をしてもよい。その際に、粗バーを一旦コイル状に巻き、必要に応じて、保温機能を有するカバーに格納し、再度巻き戻してから接合を行ってもよい。 In hot rolling, a sheet bar may be joined after rough rolling, and finish rolling may be performed continuously. At that time, the coarse bar may be wound once in a coil shape, stored in a cover having a heat retaining function, if necessary, and rewound again before joining.
熱延鋼板には、必要に応じて、スキンパス圧延を施してもよい。スキンパス圧延には、加工成形時に発生するストレッチャーストレインの防止や形状矯正の効果があることは言うまでもない。 The hot-rolled steel sheet may be subjected to skin pass rolling as necessary. Needless to say, the skin pass rolling has the effect of preventing stretcher strain generated during processing and shape correction.
このようにして得られた熱延鋼板を冷間圧延し、焼鈍して最終的な薄鋼板とする際には、冷間圧延の全圧下率を６０％未満とする。６０％以上では、一般的な冷間圧延−再結晶集合組織である板面に平行な結晶面のＸ線回折積分面強度比において、｛１１１｝面や｛５５４｝面成分が高くなり、本発明の特徴である前記（１）の発明で規定する結晶方位を満たさなくなるためである。 When the hot-rolled steel sheet thus obtained is cold-rolled and annealed to obtain a final thin steel sheet, the total rolling reduction of the cold-rolling is set to less than 60%. If it is 60% or more, the {111} plane and {554} plane components become high in the X-ray diffraction integral plane intensity ratio of the crystal plane parallel to the plate surface, which is a general cold rolling-recrystallization texture. This is because the crystal orientation defined in the invention of (1), which is a feature of the invention, is not satisfied.
形状凍結性を高めるためには、冷間圧下率を４０％以下に制限することが望ましい。冷間圧延率の下限は特に定めることなく本発明の効果を得ることができるが、結晶方位の強度を適当な範囲に制御するためには、３％以上とすることが好ましい。 In order to enhance the shape freezing property, it is desirable to limit the cold reduction rate to 40% or less. The lower limit of the cold rolling rate is not particularly defined, and the effects of the present invention can be obtained. However, in order to control the strength of the crystal orientation within an appropriate range, it is preferably 3% or more.
このような範囲で冷間加工された冷延鋼板を焼鈍する際には、焼鈍温度が５００℃未満の場合には加工組織が残留し成形性を著しく劣化させるので、焼鈍温度の下限を５００℃とする。一方、焼鈍温度が８００℃超になると、ＴｉＣおよびＮｂＣが粗大化して穴拡げ性が劣化するとともに、形状凍結性も低下する。したがって、焼鈍温度は５００〜８００℃とする。 When annealing a cold-rolled steel sheet that has been cold worked in such a range, if the annealing temperature is less than 500 ° C, the processed structure remains and the formability deteriorates significantly, so the lower limit of the annealing temperature is 500 ° C. And On the other hand, when the annealing temperature exceeds 800 ° C., TiC and NbC are coarsened and the hole expansibility deteriorates, and the shape freezing property also decreases. Accordingly, the annealing temperature is set to 500 to 800 ° C.
冷延鋼板には、必要に応じてスキンパス圧延を施してもよい。 The cold-rolled steel sheet may be subjected to skin pass rolling as necessary.
熱延後および圧下率６０％未満の冷延後に、溶融亜鉛めっきを施しても構わない。このとき、最高到達温度を５００〜８００℃とする。５００℃未満では、溶融亜鉛めっき浴に浸漬する際の侵入板温が溶融亜鉛浴温度を大きく下回り、亜鉛を溶融状態に保つことが困難となるので、５００℃を下限とする。また、８００℃超では化合物粒子が粗大化して形状凍結性と穴拡げ性が低下するので、８００℃を上限とする。 After hot rolling and after cold rolling with a rolling reduction of less than 60%, hot dip galvanizing may be performed. At this time, the maximum temperature reached is 500 to 800 ° C. If it is less than 500 ° C., the intrusion plate temperature when immersed in the hot dip galvanizing bath is much lower than the hot dip zinc bath temperature, and it becomes difficult to keep zinc in a molten state. Further, if it exceeds 800 ° C., the compound particles become coarse and the shape freezing property and the hole expansibility decrease, so 800 ° C. is the upper limit.
溶融亜鉛めっき後には、必要に応じて、合金化処理を施しても構わない。合金化処理とは、Ｚｎと鋼板のＦｅとを反応せしめＦｅとＺｎとの化合物を形成させるための熱処理である。 After hot dip galvanization, an alloying treatment may be performed as necessary. The alloying treatment is a heat treatment for reacting Zn with Fe of a steel plate to form a compound of Fe and Zn.
合金化処理温度が４５０℃未満では、反応に要する時間が過大になるので、４５０℃を下限とする。一方、６００℃超では、合金化反応が進行しすぎて合金層が脆くなり、成形加工によってパウダリング等のトラブルを誘発するので、６００℃を上限とする。好ましい範囲は４８０〜５６０℃である。 If the alloying treatment temperature is less than 450 ° C, the time required for the reaction becomes excessive, so 450 ° C is set as the lower limit. On the other hand, if it exceeds 600 ° C., the alloying reaction proceeds too much and the alloy layer becomes brittle, and troubles such as powdering are induced by the forming process. A preferred range is 480-560 ° C.
なお、本発明に係る鋼板は、曲げ加工だけでなく、曲げ、張り出し、絞り等、曲げ加工を主体とする複合成形にも適用できる。 Note that the steel sheet according to the present invention can be applied not only to bending, but also to composite forming mainly composed of bending, such as bending, overhanging and drawing.
（実施例１）
本発明の実施例を挙げながら、本発明の技術的内容について説明する。
Example 1
The technical contents of the present invention will be described with reference to examples of the present invention.
まず、表１に示す成分組成を有するＡからＫまでの鋼を用いて検討した結果について説明する。これらの鋼は、鋳造後１２５０℃に加熱され、その後、表２に示す条件で熱間圧延が施され、最終的には１．４ｍｍ厚の熱延鋼板とした。酸洗後、スキンパスを０．５％施した。 First, the results of studies using steels A to K having the component compositions shown in Table 1 will be described. These steels were heated to 1250 ° C. after casting, and then hot-rolled under the conditions shown in Table 2 to finally form hot rolled steel sheets having a thickness of 1.4 mm. After pickling, 0.5% skin pass was applied.
この板から、５０ｍｍ幅，２７０ｍｍ長さの試験片を作成し、ポンチ幅７８ｍｍ、ポンチ肩Ｒ５、ダイ肩Ｒ５の金型を用いてハット曲げ試験を行った。 A test piece having a width of 50 mm and a length of 270 mm was prepared from this plate, and a hat bending test was performed using a die having a punch width of 78 mm, a punch shoulder R5, and a die shoulder R5.
曲げ試験を行った試験片は、三次元形状測定装置にて板幅中心部の形状を測定し、図１に示したように、点（ａ）と点（ｂ）の接線と点（ｃ）と点（ｄ）の接線の交点の角度から９０°を引いた値の左右での平均値をスプリング・バック量、点（ｃ）と点（ｅ）間の曲率の逆数を左右で平均化した値を壁そり量、左右の点（ｅ）間の長さからポンチ幅を引いた値を寸法精度として形状凍結性を評価した。 The test piece subjected to the bending test was measured for the shape of the central part of the plate width with a three-dimensional shape measuring device, and as shown in FIG. 1, the tangent line of point (a) and point (b) and point (c) The average value on the left and right of the value obtained by subtracting 90 ° from the angle of the intersection of the tangent line and point (d) is averaged on the left and right, and the inverse of the curvature between point (c) and point (e) The shape freezing property was evaluated using the value obtained by subtracting the punch width from the wall warp amount and the length between the left and right points (e) as the dimensional accuracy.
なお、曲げ方向は、曲げの稜線に対して垂直方向が、圧延方向と平行な場合にはＬ曲げ、曲げ稜線が圧延方向と平行な場合にはＣ曲げと称した。 The bending direction was referred to as L bending when the perpendicular direction to the bending ridge line was parallel to the rolling direction, and C bending when the bending ridge line was parallel to the rolling direction.
ところで、図２および図３に示すように、スプリング・バック量や壁そり量は、ＢＨＦ（しわ押さえ力）によっても変化する。本発明の効果は、いずれのＢＨＦで評価を行っても、その傾向は変わらないが、実機で実部品をプレスする際には、あまり高いＢＨＦはかけられないことから、今回はＢＨＦ２９ｋＮで各鋼種のハット曲げ試験を行った。 By the way, as shown in FIGS. 2 and 3, the amount of spring back and the amount of wall warp also change depending on the BHF (wrinkle pressing force). The effect of the present invention does not change even if the evaluation is performed with any BHF, but when pressing actual parts with an actual machine, a very high BHF cannot be applied. The hat bending test was performed.
Ｘ線の測定は、鋼板の代表値として、板厚の７／１６厚の位置で板面に平行なサンプルを調整し、実施した。 The X-ray measurement was performed by adjusting a sample parallel to the plate surface at a position of 7/16 thickness as a representative value of the steel plate.
穴拡げ試験は、１辺１００ｍｍの試験片の中央に径１０ｍｍの打ち抜き穴を加工し、その初期穴を頂角６０°の円錐ポンチにて押し広げ、割れが鋼板を貫通した時点での穴径ｄの初期穴径１０ｍｍに対する穴広げ率λ（次式）で評価した。
λ＝｛（ｄ−１０）／１０｝×１００（％）
In the hole expansion test, a punched hole with a diameter of 10 mm is processed in the center of a test piece with a side of 100 mm, the initial hole is expanded with a conical punch with an apex angle of 60 °, and the hole diameter when the crack penetrates the steel plate. Evaluation was made with a hole expansion ratio λ (the following formula) for an initial hole diameter of 10 mm.
λ = {(d−10) / 10} × 100 (%)
化合物粒子の観察用試料には、板厚の３／８〜５／８の範囲から採取した薄膜を用い、電解放射型電子銃搭載の透過型電子顕微鏡にて、１５万倍で１０平方μｍ以上の面積について観察する。このとき視野の選択は無作為に行い、１０視野以上とした。観察された粒子数を全粒子数とした。ただし、結晶粒界上の化合物粒子は無視した。全粒子数に対して径が１５ｎｍ以下である粒子数の割合を求めた。 As a sample for observing the compound particles, a thin film collected from a range of 3/8 to 5/8 of the plate thickness was used, and a transmission electron microscope equipped with an electrolytic emission electron gun was used at 150,000 times and 10 square μm or more. Observe the area. At this time, the visual field was selected at random, and 10 visual fields or more were selected. The number of particles observed was taken as the total number of particles. However, the compound particles on the grain boundaries were ignored. The ratio of the number of particles having a diameter of 15 nm or less with respect to the total number of particles was determined.
表３に、ＪＩＳ５号試験片にて測定した引張特性、Ｘ線ランダム強度比、スプリング・バック量、壁そり量および穴拡げ率を示す。なお、本発明の条件を満たしている鋼板の組織は、いずれも、フェライトまたはベイナイトが主相であった。 Table 3 shows the tensile properties, X-ray random strength ratio, spring-back amount, wall warp amount, and hole expansion rate measured with a JIS No. 5 test piece. In addition, as for the structure | tissue of the steel plate which satisfy | fills the conditions of this invention, all were ferrite or bainite.
本発明例は発明外のものに比べて、スプリング・バック量、壁そり量が小さくなり、結果として寸法精度が向上していることがわかる。本発明のものはいずれのケースも伸びフランジ性も良好である。即ち、本発明で限定される成分、各結晶方位の極密度、ｒ値、化合物粒子の条件を満たして初めて良好な形状凍結性と高伸びフランジ性鋼板を得ることが可能になるのである。 It can be seen that the example of the present invention has a smaller amount of spring back and wall warp than those outside the invention, resulting in improved dimensional accuracy. The cases of the present invention have good stretch flangeability in any case. That is, it is possible to obtain a steel sheet with good shape freezing property and high stretch flangeability only after satisfying the conditions of the components limited in the present invention, the polar density of each crystal orientation, the r value, and the compound particles.
（実施例２）
実施例１に示した、Ｂ−１、Ｃ−１およびＩ−１を７００℃および８５０℃に加熱し、４０ｓ間保持した後、４６０℃まで１０℃／ｓの速度で冷却した後、溶融Ｚｎめっき浴（Ａｌ量＝０．０９％）に浸漬し、さらに、５３０℃，４０ｓ間の合金化処理を施した。スキンパス圧延率は０．５％とした。
(Example 2)
B-1, C-1 and I-1 shown in Example 1 were heated to 700 ° C. and 850 ° C., held for 40 s, cooled to 460 ° C. at a rate of 10 ° C./s, and then molten Zn It was immersed in a plating bath (Al content = 0.09%) and further subjected to alloying treatment at 530 ° C. for 40 s. The skin pass rolling rate was 0.5%.
表４から明らかな通り、加熱温度を本発明の範囲である７００℃とした場合には、８５０℃の場合に比較して良好な特性を示した。 As is apparent from Table 4, when the heating temperature was 700 ° C., which is the range of the present invention, better characteristics were shown compared to the case of 850 ° C.
（実施例３）
実施例１に示した、Ｂ−１、Ｃ−１およびＩ−１の熱延板を圧下率３０％で冷間圧延後、７００℃および８５０℃に加熱し、６０ｓ間保持した後、５℃／ｓにて２０ｓ間冷却した後、３５０℃にて２５０ｓ間保持した後、室温まで冷却し、スキンパスを０．３％施した。
(Example 3)
The hot rolled sheets of B-1, C-1 and I-1 shown in Example 1 were cold-rolled at a reduction rate of 30%, heated to 700 ° C. and 850 ° C., held for 60 s, and then 5 ° C. After being cooled for 20 s at / s and held at 350 ° C. for 250 s, it was cooled to room temperature and a skin pass was applied at 0.3%.
表５から明らかな通り、加熱温度を本発明の範囲である７００℃とした場合には、８５０℃の場合に比較して良好な特性を示した。 As is apparent from Table 5, when the heating temperature was set to 700 ° C., which is the range of the present invention, better characteristics were shown compared to the case of 850 ° C.
本発明によれば、前述したように、自動車車体の軽量化をより一層推進することができる。したがって、本発明は、工業的に極めて高い利用可能性を有する発明である。 According to the present invention, as described above, it is possible to further promote weight reduction of the automobile body. Therefore, the present invention is an invention having very high industrial applicability.
Claims (10)
Ｃ ：０．０２％以上、０．１５％以下、
Ｓｉ：０．５％超、１．６％以下、
Ｍｎ：０．０１％以上、３．０％以下、
Ｐ ：０．０２％以下、
Ｓ ：０．０１％以下、
Ａｌ：２．０％以下、
Ｎ ：０．０１％以下、
Ｏ ：０．０１％以下、
Ｔｉ：０．０５４％以上、０．４％以下、
Ｂ：０．０００２％以上、０．００７０％以下を含有し、さらに、
Ｎｂ：０．４％以下、Ｍｏ：１．０％以下の１種または２種を含有し、
残部は鉄および不可避的不純物よりなり、フェライトまたはベイナイトを面積率で最大相とし、１／２板厚における板面の｛００１｝＜１１０＞〜｛２２３｝＜１１０＞方位群のＸ線ランダム強度比の平均値が６．０以上で、かつ、これらの方位群の中で｛１１２｝＜１１０＞方位および｛００１｝＜１１０＞方位のうちいずれか一方または両方のＸ線ランダム強度比が８．０以上であり、加えて、圧延方向のｒ値および圧延方向と直角方向のｒ値のうち少なくとも１つが０．８以下で、かつ、径が１５ｎｍ以下の化合物粒子の個数が全化合物粒子の個数の６０％以上であることを特徴とする形状凍結性と伸びフランジ成形性に優れた高強度鋼板。 % By mass
C: 0.02% or more, 0.15% or less,
Si: more than 0.5%, 1.6% or less,
Mn: 0.01% or more, 3.0% or less,
P: 0.02% or less,
S: 0.01% or less,
Al: 2.0% or less,
N: 0.01% or less,
O: 0.01% or less ,
Ti: 0.054% or more, 0.4% or less ,
B: 0.0002% or more and 0.0070% or less,
Nb: 0.4% or less, Mo: 1.0% or less of 1 type or 2 types ,
The balance consists of iron and unavoidable impurities, with ferrite or bainite as the maximum phase in area ratio, and X-ray random strength of {001} <110> to {223} <110> orientation groups on the plate surface at 1/2 plate thickness The average value of the ratio is 6.0 or more, and among these orientation groups, the X-ray random intensity ratio of either or both of the {112} <110> orientation and the {001} <110> orientation is 8 In addition, at least one of the r value in the rolling direction and the r value in the direction perpendicular to the rolling direction is 0.8 or less and the number of compound particles having a diameter of 15 nm or less is the total number of compound particles. A high-strength steel sheet excellent in shape freezeability and stretch flangeability, characterized by being 60% or more of the number.
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| WO2013161231A1 (en) | 2012-04-24 | 2013-10-31 | Ｊｆｅスチール株式会社 | High-strength steel sheet and process for producing same |
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| JP4740099B2 (en) * | 2006-03-20 | 2011-08-03 | 新日本製鐵株式会社 | High-strength cold-rolled steel sheet and manufacturing method thereof |
| JP4646881B2 (en) * | 2006-09-15 | 2011-03-09 | 株式会社神戸製鋼所 | Hot-rolled steel sheet with excellent stretch flangeability |
| JP5906753B2 (en) | 2011-02-24 | 2016-04-20 | Ｊｆｅスチール株式会社 | Alloy hot-dip galvanized steel sheet |
| JP5408383B2 (en) | 2011-03-28 | 2014-02-05 | 新日鐵住金株式会社 | Cold-rolled steel sheet and manufacturing method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2013161231A1 (en) | 2012-04-24 | 2013-10-31 | Ｊｆｅスチール株式会社 | High-strength steel sheet and process for producing same |
| KR20150002775A (en) | 2012-04-24 | 2015-01-07 | 제이에프이 스틸 가부시키가이샤 | High-strength steel sheet and process for producing same |
| US9738960B2 (en) | 2012-04-24 | 2017-08-22 | Jfe Steel Corporation | High strength steel sheet |
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