JP4167587B2 - High-strength steel sheet excellent in hydrogen embrittlement resistance and method for producing the same - Google Patents
High-strength steel sheet excellent in hydrogen embrittlement resistance and method for producing the same Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 134
- 239000010959 steel Substances 0.000 title claims description 134
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 56
- 239000001257 hydrogen Substances 0.000 title claims description 56
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims description 54
- 238000004519 manufacturing process Methods 0.000 title claims description 37
- 238000001816 cooling Methods 0.000 claims description 69
- 239000002131 composite material Substances 0.000 claims description 40
- 239000002244 precipitate Substances 0.000 claims description 39
- 229910052719 titanium Inorganic materials 0.000 claims description 39
- 229910052720 vanadium Inorganic materials 0.000 claims description 38
- 229910052758 niobium Inorganic materials 0.000 claims description 36
- 229910052804 chromium Inorganic materials 0.000 claims description 32
- 229910052750 molybdenum Inorganic materials 0.000 claims description 32
- 150000004767 nitrides Chemical class 0.000 claims description 27
- 150000003568 thioethers Chemical class 0.000 claims description 27
- 239000002245 particle Substances 0.000 claims description 26
- 229910000734 martensite Inorganic materials 0.000 claims description 12
- 229910001563 bainite Inorganic materials 0.000 claims description 6
- 238000009826 distribution Methods 0.000 claims description 6
- 239000000047 product Substances 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 238000005266 casting Methods 0.000 claims 4
- 230000003111 delayed effect Effects 0.000 description 47
- 238000010438 heat treatment Methods 0.000 description 41
- 238000005098 hot rolling Methods 0.000 description 28
- 238000000137 annealing Methods 0.000 description 23
- 230000000694 effects Effects 0.000 description 16
- 238000005096 rolling process Methods 0.000 description 13
- 239000000126 substance Substances 0.000 description 13
- 230000001965 increasing effect Effects 0.000 description 12
- 230000009467 reduction Effects 0.000 description 12
- 239000010960 cold rolled steel Substances 0.000 description 10
- 238000001556 precipitation Methods 0.000 description 10
- 230000007423 decrease Effects 0.000 description 9
- 238000005554 pickling Methods 0.000 description 9
- 238000000034 method Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- 238000012545 processing Methods 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 239000013078 crystal Substances 0.000 description 6
- 238000003466 welding Methods 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 5
- 230000006866 deterioration Effects 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 238000005097 cold rolling Methods 0.000 description 4
- 230000000717 retained effect Effects 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- 238000005452 bending Methods 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 229910001562 pearlite Inorganic materials 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 238000004804 winding Methods 0.000 description 3
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 229910001567 cementite Inorganic materials 0.000 description 2
- 230000006378 damage Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 238000003303 reheating Methods 0.000 description 2
- 230000003014 reinforcing effect Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 229910052727 yttrium Inorganic materials 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- -1 oxides Chemical class 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 239000012779 reinforcing material Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 229910000658 steel phase Inorganic materials 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000012916 structural analysis Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Description
本発明は、自動車、建材、家電製品などに適する耐水素脆化に優れた高強度薄鋼板及びその製造方法に関する。 The present invention relates to a high-strength thin steel sheet excellent in hydrogen embrittlement resistance suitable for automobiles, building materials, home appliances, and the like, and a method for producing the same.
従来、ボルト、ＰＣ鋼線やラインパイプといった用途には高強度鋼が多く使われており、９８０ＭＰａ以上の強度になると、鋼中への水素の侵入により遅れ破壊が発生することが知られている。これに対し、（１）薄鋼板は板厚が薄いため水素が侵入しても短時間で放出されること、（２）加工性の点で９８０ＭPa以上の鋼板の利用がほとんどなかったことなどから、遅れ破壊に対する問題意識は低かったと言える。
しかし、最近では自動車の軽量化や衝突安全性の向上の必要性から、９８０ＭＰａ以上の超高強度薄鋼板にプレス成形、パイプ成形、曲げ加工、端面加工、穴拡げ加工などを施して、バンパーやインパクトビーム等の補強材やシートレール等に使用に供する場合が急速に増えてきている。したがって、耐遅れ破壊性を備えた超高強度薄鋼板の開発が急務である。
Conventionally, high-strength steel is often used for applications such as bolts, PC steel wires, and line pipes, and it is known that when the strength exceeds 980 MPa, delayed fracture occurs due to the penetration of hydrogen into the steel. . On the other hand, (1) the thin steel plate is thin, so even if hydrogen enters, it is released in a short time, and (2) there is almost no use of a steel plate of 980 MPa or more in terms of workability. It can be said that the awareness of problems with delayed destruction was low.
However, recently, due to the necessity of reducing the weight of automobiles and improving collision safety, press forming, pipe forming, bending, end face processing, hole expansion processing, etc. are applied to ultra-high strength thin steel sheets of 980 MPa or more, and bumpers and The number of cases where it is used for reinforcing materials such as impact beams and seat rails is rapidly increasing. Therefore, there is an urgent need to develop ultra high strength thin steel sheets with delayed fracture resistance.
これまで、耐遅れ破壊を向上させる技術はほとんどがボルトや条鋼、厚板といった製品のままでかつ耐力または降伏応力以下で使用されることの多い鋼材に対して開発されてきた。
例えば条鋼・ボルト用鋼においては、焼き戻しマルテンサイトを中心に開発が行われ、非特許文献１に、Ｃｒ，ＭｏやＶといった焼き戻し軟化抵抗性を示す添加元素が耐遅れ破壊性向上に有効であることが報告されている。これは合金炭化物を析出させて、これを水素のトラップサイトに活用することで遅れ破壊形態を粒界から粒内破壊へと移行させる技術である。しかし、これらの鋼はＣ量０．４％以上で合金元素も多く含むことから、薄鋼板で要求される加工性や溶接性が劣悪で、さらに、合金炭化物析出には数時間以上という析出熱処理が必要なため、製造性にも問題がある。
Until now, most technologies for improving delayed fracture resistance have been developed for steel materials that are often used as products such as bolts, strips, and thick plates, and are used below the yield strength or yield stress.
For example, in steel for steel bars and bolts, development has been conducted mainly on tempered martensite. In Non-Patent Document 1, additive elements exhibiting temper softening resistance such as Cr, Mo and V are effective for improving delayed fracture resistance. It has been reported that. This is a technique for precipitating alloy carbides and utilizing them as hydrogen trap sites to shift the delayed fracture mode from grain boundaries to intragranular fracture. However, these steels have a C content of 0.4% or more and contain a large amount of alloy elements, so the workability and weldability required for thin steel sheets are inferior, and the precipitation of alloy carbide takes several hours or more. Therefore, there is a problem in manufacturability.
また特許文献１では、Ｔｉ，Ｍｇを主体とする酸化物が水素性欠陥を防ぐことに効果があるとされている。しかしこれは対象が厚鋼板であり、特に大入熱の溶接後の遅れ破壊については考慮されているものの、薄鋼板に要求される加工度の高い成形加工を受けたり、端面加工に伴うバリ発生等の遅れ破壊現象に及ぼす影響については一切考慮されていない。さらには、薄鋼板の基本的特性である加工性についての考慮もいっさい無い。 In Patent Document 1, an oxide mainly composed of Ti and Mg is considered to be effective in preventing hydrogen defects. However, this is for thick steel plates, especially considering delayed fracture after welding with high heat input, but undergoes high forming work required for thin steel plates and generates burrs due to end face processing. No consideration is given to the effects on delayed fracture phenomena. Furthermore, no consideration is given to workability, which is a basic characteristic of thin steel sheets.
一方、薄鋼板の遅れ破壊に関しては、例えば非特許文献２に、残留オーステナイト量の加工誘起変態に起因した遅れ破壊の助長について報告されている。これは薄鋼板の成型加工を考慮したものであるが、耐遅れ破壊性を劣化させない残留オーステナイト量の規制について述べられている。すなわち、特定の組織を持つ高強度薄鋼板に関するものであり、根本的な耐遅れ破壊向上対策とは言えない。 On the other hand, regarding delayed fracture of thin steel sheets, for example, Non-Patent Document 2 reports on the promotion of delayed fracture due to work-induced transformation of the amount of retained austenite. This is in consideration of the forming process of a thin steel sheet, but the regulation of the amount of retained austenite which does not deteriorate the delayed fracture resistance is described. That is, it relates to a high-strength thin steel sheet having a specific structure, and is not a fundamental countermeasure for improving delayed fracture resistance.
特に自動車に使用される部材に関しては、スポット溶接により他の部材と接合される場合が多い。スポット溶接部においては、鋼板が一度溶解し再び凝固するため、溶接部近傍では引張の残留応力が働き、水素脆化に対しより厳しい状況となる。しかもスポット溶接部では鋼板が一度溶解するため、熱処理工程において析出させたトラップサイトも溶解してしまい、遅れ破壊感受性が増大する。
上記のように、特に薄鋼板の使用環境や現状設備による製造性を考慮し、使用前に加工等を行った鋼板の遅れ破壊、ならびに鋼板使用時のスポット溶接後の遅れ破壊特性に対策を講じた開発事例はほとんどない。
本発明は水素性欠陥を防止し、耐遅れ破壊性に優れた鋼板とその製造方法について提供することを目的とする。
As mentioned above, taking into consideration the use environment of thin steel sheets and manufacturability with current equipment, measures are taken for delayed fracture of steel sheets processed before use, and delayed fracture characteristics after spot welding when using steel sheets. There are few development cases.
An object of this invention is to provide the steel plate which prevented the hydrogen defect, and was excellent in delayed fracture resistance, and its manufacturing method.
本発明者らは、以上のような背景から、薄鋼板における使用環境および現状設備での製造方法、ならびにスポット溶接部における耐水素脆化特性を十分に考慮して、根本的に耐遅れ破壊性を向上させる方法を見出すに至った。すなわち薄鋼板の成型性を劣化させることなく、Ｎｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、複合晶出物および複合析出物を形成させ、かつ現状の製造設備（熱間圧延、連続焼鈍、箱焼鈍など）を用いて、成形加工後の耐遅れ破壊性を向上させることが可能なことを見出した。詳細は以下の通りである。
本発明者等は、種々検討を行った結果、引張り強度を９８０ＭＰａ以上の領域で、水素脆化を改善する手法として、ミクロ組織および成分範囲を限定することで、９８０ＭＰａ以上の強度を保ちつつ耐水素脆化特性の向上を図ることが可能なことを見出した。
From the background as described above, the present inventors have fundamentally considered delayed fracture resistance in consideration of the use environment in thin steel sheets and the manufacturing method in the current equipment, and the hydrogen embrittlement resistance in spot welds. I came to find a way to improve. In other words, Nb, V, Cr, Ti, and Mo oxides, sulfides, nitrides, composite crystals and composite precipitates can be formed without degrading the formability of the thin steel sheet, and the current production equipment (heat It has been found that delayed fracture resistance after forming can be improved by using hot rolling, continuous annealing, box annealing, and the like. Details are as follows.
As a result of various investigations, the present inventors, as a technique for improving hydrogen embrittlement in a region where the tensile strength is 980 MPa or more, limit the microstructure and the component range, thereby maintaining the strength of 980 MPa or more. It has been found that the hydrogen embrittlement characteristics can be improved.
本発明は、上記知見に基づいて完成したもので、その要旨は以下の通りである。
（１）質量％で、
Ｃ ：０．０１〜０．３０％、 Ｓｉ：２．０％以下、
Ｍｎ：０．０１〜３％、 Ｐ ：０．１％以下、
Ｓ ：０．０５％以下、 Ａｌ：０．００５〜４％、
Ｎ ：０．０１％以下
を含有し、更に、
Ｃｒ：１．１％以上と、
Ｎｂ，Ｖ，Ｔｉ，Ｍｏの元素群中から１種又は２種以上を合計で０．００１％以上とを含有し、かつ、
ＣｒとＮｂ，Ｖ，Ｔｉ，Ｍｏの１種又は２種以上との合計が３％以下
であり、残部がＦｅおよび不可避的不純物からなり、ミクロ組織がベイナイトまたはマルテンサイトを面積率で最大の相として、粒内のＮｂ、Ｖ，Ｃｒ，Ｔｉ，Ｍｏの酸化物、硫化物、窒化物、複合晶出物、複合析出物のいずれか１種以上を、
平均粒子径ｄ：０．００１〜５．０μｍ
密度ρ：１平方ｍｍあたり１００〜１×１０13個
分布：平均粒子径からの標準偏差σと平均粒子径ｄの比が、σ／ｄ≦１．０
を満たす分布形態を有し、引張強度が９８０ＭＰａ以上であることを特徴とする耐水素脆化に優れた高強度薄鋼板。
（２）さらに、鋼中に質量％で、
Ｗ ：０．００５〜５％
を含有することを特徴とする前記（１）に記載の耐水素脆化に優れた高強度薄鋼板。
（３）さらに、鋼中に質量％で、
Ｃｕ：０．００５〜５％、 Ｎｉ：０．００５〜５％
の１種または２種を含有することを特徴とする前記（１）または（２）に記載の耐水素脆化に優れた高強度薄鋼板。
（４）さらに、鋼中に質量％で、
Ｂ ：０．０００２〜０．１％
を含有することを特徴とする前記（１）〜（３）の何れか１項に記載の耐水素脆化に優れた高強度薄鋼板。
（５）さらに、鋼中に質量％で、
ＲＥＭ：０．０００５〜０．０１％、 Ｙ ：０．０００５〜０．０１％、
Ｃａ：０．０００５〜０．０１％、 Ｍｇ：０．０００５〜０．０１％
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）〜（４）の何れか１項に記載の耐水素脆化に優れた高強度薄鋼板。
The present invention has been completed based on the above findings, and the gist thereof is as follows.
(1) In mass%,
C: 0.01 to 0.30%, Si: 2.0% or less,
Mn: 0.01 to 3%, P: 0.1% or less,
S: 0.05% or less, Al: 0.005-4%,
N: 0.01% or less , and
Cr: 1.1% or more,
Nb, V, Ti, and containing a from among the element group of Mo 1 or two or more in total 0.001% or more and,
The total of Cr and one or more of Nb, V, Ti, and Mo is 3% or less
The remainder is composed of Fe and inevitable impurities, and the microstructure is bainite or martensite with the largest area ratio, and the oxides, sulfides, nitrides of Nb, V, Cr, Ti, Mo in the grains Any one or more of the composite crystallized product and the composite precipitate,
Average particle diameter d: 0.001 to 5.0 μm
Density ρ: 100 to 1 × 10 13 per square mm Distribution: Ratio of standard deviation σ from average particle diameter to average particle diameter d is σ / d ≦ 1.0
A high-strength thin steel sheet excellent in hydrogen embrittlement resistance, characterized by having a distribution form satisfying the above and a tensile strength of 980 MPa or more.
(2) Furthermore, in steel,
W: 0.005 to 5%
The high-strength thin steel sheet excellent in hydrogen embrittlement resistance as described in (1) above.
(3) In addition, in steel,
Cu: 0.005 to 5%, Ni: 0.005 to 5%
The high-strength thin steel sheet excellent in hydrogen embrittlement resistance according to the above (1) or (2), characterized by containing one or two of the following.
(4) Furthermore, in mass% in steel,
B: 0.0002 to 0.1%
The high-strength thin steel sheet excellent in hydrogen embrittlement resistance according to any one of the above (1) to (3), comprising:
(5) Furthermore, in steel,
REM: 0.0005 to 0.01%, Y: 0.0005 to 0.01%,
Ca: 0.0005 to 0.01%, Mg: 0.0005 to 0.01%
The high strength thin steel sheet excellent in hydrogen embrittlement resistance according to any one of the above (1) to (4), characterized by containing one or more of the following.
（６） 前記（１）〜（５）のいずれか１項に記載の鋼板を製造する方法であって、（１）〜（５）のいずれか１項に記載の成分からなる鋳造スラブを鋳造まま、あるいは、一旦冷却した後に再度加熱し、Ａｒ3 点以上の仕上温度で熱間圧延を施し、その後２５〜７００℃の温度域に０．１〜１０００℃／秒の冷却速度で冷却後巻き取り、引き続いて４００〜７００℃の温度範囲で１〜１０００００秒保持後室温まで冷却した熱延鋼板を酸洗後冷延し、その後焼鈍時の最高温度を６００〜９５０℃で焼鈍した後に０．１〜１０００℃／秒の冷却速度で２５〜５００℃の温度域に冷却し、引き続いて同温度域で１〜１００００秒保持を行うことを特徴とする耐水素脆化に優れた高強度薄鋼板の製造方法。
（７）前記（６）に記載の製造方法により製造した鋼板を、さらに４００〜７００℃の温度域で１分〜１０時間保持を行うことを特徴とする耐水素脆化に優れた高強度薄鋼板の製造方法。
(6) A method for producing the steel sheet according to any one of (1) to (5) above, wherein a cast slab made of the component according to any one of (1) to (5) is cast. As it is, or after being cooled, it is heated again, hot rolled at a finishing temperature of Ar3 point or higher, and then cooled to a temperature range of 25 to 700 ° C at a cooling rate of 0.1 to 1000 ° C / second and wound up. Subsequently, the hot-rolled steel sheet, which was kept at a temperature range of 400 to 700 ° C. for 1 to 100000 seconds and then cooled to room temperature, was cold-rolled after pickling, and then annealed at a maximum temperature of 600 to 950 ° C. A high-strength thin steel sheet excellent in hydrogen embrittlement resistance, which is cooled to a temperature range of 25 to 500 ° C. at a cooling rate of ˜1000 ° C./second, and subsequently held for 1 to 10000 seconds in the same temperature range. Production method.
(7) A high strength thin film excellent in hydrogen embrittlement resistance, characterized in that the steel plate produced by the production method according to (6) is further held in a temperature range of 400 to 700 ° C. for 1 minute to 10 hours. A method of manufacturing a steel sheet.
（８）前記（１）〜（５）のいずれか１項に記載の鋼板を製造する方法であって、（１）〜（５）のいずれか１項に記載の成分からなる鋳造スラブを鋳造まま、あるいは、一旦冷却した後に再度加熱し、Ａｒ3 点以上の仕上温度で熱間圧延を施し、その後２５〜７００℃の温度域に０．１〜１０００℃／秒の冷却速度で冷却後巻き取り、引き続いて４００〜７００℃の温度範囲で１〜１０００００秒保持後室温まで冷却した熱延鋼板を酸洗後冷延し、引き続いて４００〜７００℃の温度域で１分〜１０時間保持を行うことを特徴とする耐水素脆化に優れた高強度薄鋼板の製造方法。
（９）前記（１）〜（５）のいずれか１項に記載の鋼板を製造する方法であって、（１）〜（５）のいずれか１項に記載の成分からなる鋳造スラブを鋳造まま、あるいは、一旦冷却した後に再度加熱し、Ａｒ3 点以上の仕上温度で熱間圧延を施し、その後２５〜５００℃の温度域に０．１〜１０００℃／秒の冷却速度で冷却後巻き取り、引き続いて同温度範囲で１〜１０００００秒保持後室温まで冷却した熱延鋼板を酸洗後冷延し、引き続いて４００〜７００℃の温度域で１分〜１０時間保持を行うことを特徴とする耐水素脆化に優れた高強度薄鋼板の製造方法。
（１０） 前記（１）〜（５）のいずれか１項に記載の鋼板を製造する方法であって、 （１）〜（５）のいずれか１項に記載の成分からなる鋳造スラブを鋳造まま、あるいは、一旦冷却した後に再度加熱し、Ａｒ3 点以上の仕上温度で熱間圧延を施し、その後巻取温度まで０．１〜１０００℃／秒の冷却速度で冷却後２５〜７００℃で巻き取り、引き続いて４００〜７００℃の温度範囲で１〜１０００００秒保持後、室温まで冷却した熱延鋼板を酸洗後冷延し、その後焼鈍時の最高温度を６００〜９５０℃で焼鈍した後に０．１〜１０００℃／秒の冷却速度で０〜３５０℃の温度域に冷却し、引き続いて１００〜７００℃の温度域で１〜１００００秒保持を行うことを特徴とする耐水素脆化に優れた高強度薄鋼板の製造方法。
(8) A method for producing the steel sheet according to any one of (1) to (5) above, wherein a cast slab made of the component according to any one of (1) to (5) is cast. As it is, or after being cooled, it is heated again, hot rolled at a finishing temperature of Ar3 point or higher, and then cooled to a temperature range of 25 to 700 ° C at a cooling rate of 0.1 to 1000 ° C / second and wound up. Subsequently, the hot-rolled steel sheet that has been kept at a temperature range of 400 to 700 ° C. for 1 to 100000 seconds and then cooled to room temperature is cold-rolled after pickling, and subsequently kept at a temperature range of 400 to 700 ° C. for 1 minute to 10 hours. A method for producing a high-strength thin steel sheet excellent in hydrogen embrittlement resistance.
(9) A method for producing the steel sheet according to any one of (1) to (5) above, wherein a cast slab comprising the component according to any one of (1) to (5) is cast. As it is, or once cooled and then heated again, hot rolled at a finishing temperature not lower than the Ar3 point, and then cooled to a temperature range of 25 to 500 ° C. and cooled at a cooling rate of 0.1 to 1000 ° C./second and wound up. The hot-rolled steel sheet, which is subsequently held in the same temperature range for 1 to 100000 seconds and then cooled to room temperature, is cold-rolled after pickling, and subsequently maintained in the temperature range of 400 to 700 ° C. for 1 minute to 10 hours. The manufacturing method of the high strength thin steel plate excellent in hydrogen embrittlement resistance.
(10) A method for producing the steel sheet according to any one of (1) to (5), wherein a cast slab made of the component according to any one of (1) to (5) is cast. As it is, or after cooling once, it is heated again, hot rolled at a finishing temperature of Ar3 point or higher, and then cooled to a coiling temperature at a cooling rate of 0.1 to 1000 ° C./second and then wound at 25 to 700 ° C. Then, after holding for 1 to 100,000 seconds in the temperature range of 400 to 700 ° C., the hot-rolled steel sheet cooled to room temperature is pickled and cold-rolled, and then annealed at a maximum temperature of 600 to 950 ° C. and then 0. .Excellent hydrogen embrittlement resistance, characterized by cooling to a temperature range of 0 to 350 ° C. at a cooling rate of 1 to 1000 ° C./second and subsequently holding for 1 to 10,000 seconds in a temperature range of 100 to 700 ° C. A method for producing high strength thin steel sheets.
本発明による薄鋼板では、Ｎｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏ添加により、Ｎｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、複合晶出物および複合析出物を微細に生成することで、水素のトラップサイトを分散させ、自動車のバンパーやドアインパクトビームなどの補強部材として最適な強度と、加工後の耐遅れ破壊性を向上させることができる。 In the thin steel sheet according to the present invention, by adding Nb, V, Cr, Ti and Mo, oxides, sulfides, nitrides, composite crystallized substances and composite precipitates of Nb, V, Cr, Ti and Mo are finely generated. By doing so, it is possible to disperse the hydrogen trap sites and improve the optimum strength as a reinforcing member such as an automobile bumper or door impact beam, and the delayed fracture resistance after processing.
焼き戻しマルテンサイト鋼において遅れ破壊は、旧オーステナイト粒界等に水素が集積することによってボイド等が発生し、その部分が起点となって破壊を生じると考えられている。そこで、水素のトラップサイトを均等かつ微細に分散させて、その部分に水素をトラップさせると、拡散性水素濃度が下がり、遅れ破壊の感受性が下がる。前出の特許文献１にあるように、ＭｇおよびＴｉを複合添加した厚鋼板における酸化物の分散形態制御で、水素起因の耐遅れ破壊性が向上することが分かっている。
しかし、一般的に薄鋼板においては使用前に成形加工を受けるため、高い残留応力の発生や、加工端面におけるバリ等の存在が必然的に耐遅れ破壊性も劣化するため、これに伴う耐遅れ破壊特性の劣化を補足できない。このように、薄鋼板の使用形態を考慮した遅れ破壊特性に関する研究は少なく、ＭｇやＴｉの酸化物形態制御のみでは解決できない。
In tempered martensitic steel, delayed fracture is considered to be caused by the accumulation of hydrogen at the prior austenite grain boundaries and the like, resulting in the formation of voids and the like as the starting point. Therefore, if the hydrogen trap sites are dispersed evenly and finely and hydrogen is trapped there, the concentration of diffusible hydrogen is lowered and the susceptibility to delayed fracture is lowered. As described in the above-mentioned Patent Document 1, it has been found that delayed fracture resistance due to hydrogen is improved by controlling the oxide dispersion form in a thick steel plate to which Mg and Ti are added in combination.
However, since thin steel sheets are generally subjected to forming before use, the occurrence of high residual stress and the presence of burrs on the processed end faces inevitably deteriorate delayed fracture resistance. It cannot supplement the deterioration of fracture characteristics. Thus, there are few studies on delayed fracture characteristics in consideration of the usage pattern of thin steel sheets, and it cannot be solved only by controlling the oxide morphology of Mg or Ti.
そこで本発明者らは上述の背景を踏まえて、薄鋼板の使用環境、すなわち成形加工後においても耐遅れ破壊性を確保・向上させるため、種々の晶出物、析出物に加えて、鋼板の強度、組織の影響をそれぞれ検討した。その結果、薄鋼板の使用環境下で、高い残留応力下や端面のバリ発生があっても、耐遅れ破壊性を向上・確保するための技術を見出した。 In view of the above-mentioned background, the present inventors therefore ensured and improved delayed fracture resistance even after forming, in addition to various crystallized substances and precipitates. The effects of strength and organization were examined. As a result, we have found a technique for improving and ensuring delayed fracture resistance even under high residual stress and end face burrs in the environment where thin steel sheets are used.
すなわち、
（１）Ｎｂ，Ｖ，Ｃｒ，Ｔｉ，Ｍｏの酸化物、硫化物、窒化物、複合晶出物、複合析出 物の粒内の分散形態制御、
（２）鋼板のミクロ組織中の残留オーステナイト量、
をそれぞれ制御することで、有効に水素のトラップサイトであるＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、複合晶出物および複合析出物を効果的に分散させ、加工後の耐遅れ破壊性の確保する事ができる。このためには、製造条件を制御する事によって、種々の元素の酸化物、硫化物、窒化物、複合晶出物および複合析出物が水素のトラップサイトになり得る形態制御を行った。
これは薄鋼板の加工により導入される転位や残留応力場とトラップサイトとなる粒子との相互作用が、厚鋼板での熱間圧延や溶接後冷却時に導入される転位や残留応力とのそれとは異なることや、薄鋼板と厚鋼板の熱処理方法の違いに起因すると考えられる。
That is,
(1) Nb, V, Cr, Ti, Mo oxides, sulfides, nitrides, composite crystallization products, and dispersion control within the grains of composite precipitates,
(2) The amount of retained austenite in the microstructure of the steel sheet,
By effectively controlling each of these, oxides, sulfides, nitrides, composite crystals and composite precipitates of Nb, V, Cr, Ti and Mo which are hydrogen trap sites are effectively dispersed and processed. Later delayed fracture resistance can be secured. For this purpose, by controlling the production conditions, a form control was performed in which oxides, sulfides, nitrides, composite crystals and composite precipitates of various elements could become hydrogen trap sites.
This is because the interaction between dislocations and residual stress fields introduced by processing thin steel sheets and particles that become trap sites is different from those introduced during hot rolling and cooling after welding on thick steel sheets. It is thought that it originates in a difference and the difference in the heat processing method of a thin steel plate and a thick steel plate.
詳細な限定については、以下のように限定する。
平均粒子径：平均粒子径は、０．００１〜５．０μｍに限定した。これは平均粒子径が５．０μｍを超えると、薄鋼板の機械的性質の劣化となる上製造も困難となり、加えて粗大粒子はトラップサイトとしての作用がなくなり、また破壊の起点となり得るためである。また平均粒子径が０．００１μｍ未満では水素のトラップサイトとしての効果が小さくなるからである。
About detailed limitation, it limits as follows.
Average particle diameter: The average particle diameter was limited to 0.001 to 5.0 μm. This is because when the average particle diameter exceeds 5.0 μm, the mechanical properties of the thin steel sheet deteriorate and the manufacturing becomes difficult, and in addition, the coarse particles can no longer act as trap sites and can be the starting point of destruction. is there. Further, when the average particle diameter is less than 0.001 μm, the effect as a hydrogen trap site is reduced.
密度：粒子の存在密度は、１００〜１×１０13個／ｍｍ2 とした。粒子密度が低いことは、トラップサイト数が少ないことを意味し、加工後の耐遅れ破壊性を確保できないため、下限を１００個／ｍｍ2 とした。また高密度の場合には、延性や成形加工性が劣化することおよび耐遅れ破壊性向上効果も飽和することから、１×１０13個／ｍｍ2 を上限とした。 Density: the density of the particles was set to 100 to 1 × 10 13 pieces / mm 2. Low particle density means that the number of trap sites is small, and delayed fracture resistance after processing cannot be secured, so the lower limit was set to 100 particles / mm 2 . In the case of high density, the ductility and molding processability deteriorate and the effect of improving delayed fracture resistance is saturated, so 1 × 10 13 pieces / mm 2 was set as the upper limit.
分布：粒子の分布を、平均粒子径からの標準偏差σ［μｍ］と平均粒子径ｄ［μｍ］の比が、σ／ｄ≦１．０を満たすこととした。σ／ｄ＞１．０とは、粒子分布が広範囲にわたることを意味し、耐遅れ破壊向上効果が同じ平均粒径に比べて小さくなり、延性劣化や破壊の起点数の増加にもつながることから、上限を決めて１．０以下とした。 Distribution: The ratio of the standard deviation σ [μm] from the average particle size to the average particle size d [μm] is determined to satisfy σ / d ≦ 1.0. σ / d> 1.0 means that the particle distribution covers a wide range, and the effect of improving delayed fracture resistance is smaller than that of the same average particle size, which leads to ductile deterioration and an increase in the number of fracture starting points. The upper limit was determined to be 1.0 or less.
ここで、Ｎｂ，Ｖ，Ｃｒ，Ｔｉ，Ｍｏの酸化物、硫化物、窒化物、複合晶出物、複合析出物を含む粒子の測定について述べる。平均粒子径の測定は、薄膜または抽出レプリカのサンプルを用いて、走査型または透過型電子顕微鏡にて、５０００〜５０００００倍の倍率で観察を行い、最低３０視野を測定することで得られる値とする。平均粒子径は、画像解析による円相当経にて評価する。平均粒子径は前記の方法により測定した粒子径を単純平均した値とし、標準偏差はこれらの粒子径から求めた値とする。 Here, measurement of particles including oxides, sulfides, nitrides, composite crystallized substances, and composite precipitates of Nb, V, Cr, Ti, and Mo will be described. Measurement of the average particle diameter is a value obtained by observing at least 5000 visual fields with a scanning or transmission electron microscope at a magnification of 5,000 to 500,000 using a sample of a thin film or an extraction replica. To do. The average particle diameter is evaluated by the equivalent circle by image analysis. The average particle size is a value obtained by simply averaging the particle sizes measured by the above method, and the standard deviation is a value obtained from these particle sizes.
また密度を求める際には、複合析出または晶出物は１ヶとして数える。組成分析は、ＥＤＸおよびＥＬＬＳを用い、構造解析はDiffraction pattern を解析することで行った。 複合晶出物とは、主にＭｇ，Ａｌ，Ｔｉ等を含有した単独あるいは複合酸化物であり、各複合化合物とは、Ｔｉ，Ｎｂ，Ｖ，Ｃｒ，Ｍｏ，Ｍｇなどを含有した化合物（炭化物、窒化物、酸化物や硫化物など）である。 Moreover, when calculating | requiring a density, a composite precipitation or a crystallized substance is counted as one piece. The composition analysis was performed by using EDX and ELLS, and the structural analysis was performed by analyzing the Diffraction pattern. A composite crystallized substance is a single or composite oxide mainly containing Mg, Al, Ti or the like, and each composite compound is a compound (carbide) containing Ti, Nb, V, Cr, Mo, Mg or the like. Nitrides, oxides, sulfides, etc.).
次にミクロ組織について説明する。
面積率最大の相をベイナイト又はマルテンサイトとする理由は、９８０ＭＰａ以上の引張強度を得るためには、硬質相であるベイナイト又はマルテンサイトを素地とすることが好ましく、これらの面積率は３０％以上１００％以下であることが好ましい。ただし、ここで言う面積率１００％とは、当然鋼材中には不可避的不純物や介在物が存在し、厳密には１００％とならないが、光学顕微鏡での観察ではこれらの不可避的不純物や介在物が認識できないレベルの大きさで存在することから、１００％であるとした。
Next, the microstructure will be described.
The reason why the phase with the largest area ratio is bainite or martensite is that, in order to obtain a tensile strength of 980 MPa or more, it is preferable to use bainite or martensite which is a hard phase as a base material, and these area ratios are 30% or more. It is preferable that it is 100% or less. However, the area ratio of 100% mentioned here naturally has unavoidable impurities and inclusions in the steel, and is not strictly 100%. However, these unavoidable impurities and inclusions are not observed by observation with an optical microscope. Is 100% because it exists at a level that cannot be recognized.
以下に本発明を更に詳細に説明する。
まず、本発明における鋼の化学成分の限定理由について説明する。
Ｃは、鋼板の強度を上昇できる元素である。特にマルテンサイトやオーステナイトなどの硬質相を生成し高強度化には必須の元素であり、９８０ＭＰａ以上の強度を得るためには０．０１％以上が必要であるが、逆に多く含有すると、脆性破壊の起点となるセメンタイトを増加させるため水素脆性を生じ易くなる。従って上限を０．３％とした。
The present invention is described in further detail below.
First, the reasons for limiting the chemical components of steel in the present invention will be described.
C is an element that can increase the strength of the steel sheet. In particular, it is an essential element for forming a hard phase such as martensite and austenite and increasing the strength, and 0.01% or more is necessary to obtain a strength of 980 MPa or more. Hydrogen embrittlement is likely to occur because the cementite that is the starting point of fracture is increased. Therefore, the upper limit is set to 0.3%.
Ｓｉは、材質を大きく硬質化する置換型固溶体強化元素であり、鋼板の強度を上昇させることに有効なうえ、セメンタイト析出を抑制する元素であるが、２．０％を超えると熱間圧延でのスケール除去にコストがかかり経済的に不利なため、２．０％を上限とする。下限は特に定めないが、極低下は製造コストの高騰を招くことから、０．００５以上の添加とすることが望ましい。 Si is a substitutional solid solution strengthening element that hardens the material greatly, and is effective in increasing the strength of the steel sheet, and is an element that suppresses cementite precipitation. Since it is costly to remove the scale and is economically disadvantageous, 2.0% is made the upper limit. Although the lower limit is not particularly defined, it is desirable to add 0.005 or more because the extreme decrease leads to an increase in manufacturing cost.
Ｍｎは、鋼板の強度上昇に有効な元素である。しかし、０．０１％未満ではこの効果が得られないので、下限値を０．０１％とした。逆に多いとＰ、Ｓとの共偏析を助長するだけでなく、加工性が劣化する場合があるため３．０％を上限値とする。 Mn is an element effective for increasing the strength of the steel sheet. However, since this effect cannot be obtained if the content is less than 0.01%, the lower limit is set to 0.01%. On the contrary, if the amount is large, not only co-segregation with P and S is promoted, but also workability may be deteriorated, so 3.0% is made the upper limit.
Ｐは、粒界偏析による粒界破壊の助長をする元素であり、低い方が望ましいが、極低化は製造コスト上好ましくない。また耐食性を劣化させる元素であるため、上限を０．１％とする。 P is an element that promotes grain boundary fracture due to grain boundary segregation, and a lower value is desirable, but extremely low is not preferable in terms of manufacturing cost. Moreover, since it is an element which degrades corrosion resistance, the upper limit is made 0.1%.
Ｓは、腐食環境下での水素吸収を助長する元素であり、低い方が望ましいが、極低下は製造コスト上好ましくない。特に加工性を高めるためには低い方が望ましく、上限を０．０５％とする。 S is an element that promotes hydrogen absorption in a corrosive environment, and a lower value is desirable. However, extreme reduction is not preferable in terms of manufacturing cost. In particular, in order to improve workability, a lower value is desirable, and the upper limit is set to 0.05%.
Ａｌは、脱酸のために０．００５％以上を添加するが、添加量が増加するとアルミナ等の介在物が増加して加工性が劣化するため、４．０％を上限とする。 Al is added in an amount of 0.005% or more for deoxidation. However, if the addition amount increases, inclusions such as alumina increase and workability deteriorates, so 4.0% is made the upper limit.
Ｎは、加工性劣化や溶接時のブローホール発生にも寄与するため少ない方が良い。０．０１％を超えると加工性が劣化してくるので、０．０１％を上限とする。 N is better because it contributes to workability deterioration and blowhole generation during welding. If it exceeds 0.01%, workability deteriorates, so 0.01% is made the upper limit.
Ｃｒは、鋼板の強度上昇に有効な元素である上、Ｃｒを含有する析出物および晶出物は水素トラップサイトとなるため非常に重要な元素である。Ｃｒ量の下限値は、本発明の実施例の表１の鋼種番号Ｄ，Ｆ及びＧの１．１％に基づいて、１．１％とした。しかし、Ｎｂ，Ｖ，Ｃｒ，Ｔｉ，Ｍｏを合計で３％超含有すると加工性低下が生じるため、上限値を３％とした。 Cr is an element that is effective in increasing the strength of the steel sheet, and is a very important element because precipitates and crystallized substances containing Cr serve as hydrogen trap sites. The lower limit value of the Cr amount was 1.1% based on 1.1% of steel type numbers D, F and G in Table 1 of the examples of the present invention. However, if Nb, V, Cr, Ti, and Mo are contained in excess of 3% in total, the workability deteriorates, so the upper limit was made 3% .
Ｎｂは、鋼板の強度上昇及び細粒化に有効な元素である上、Ｎｂを含有する析出物および晶出物は水素トラップサイトとなるため非常に重要な元素である。しかし、Ｎｂ単独又は後述のＶ，Ｔｉ，Ｍｏの１種又は２種以上との合計で０．００１％未満ではこれらの効果が得られないため、下限値を０．００１％とした。逆にＮｂ，Ｖ，Ｃｒ，Ｔｉ，Ｍｏを合計で３％超含有すると、炭窒化物の析出が多くなり加工性および耐遅れ破壊性低下が生じるため、上限値を３％とした。 Nb is an element that is effective for increasing the strength and refining of the steel sheet, and is a very important element because precipitates and crystallized substances containing Nb serve as hydrogen trap sites. However, since these effects cannot be obtained if Nb alone or a total of one or more of V 1 , Ti 2 and Mo described below is less than 0.001%, the lower limit is set to 0.001%. On the contrary, if Nb, V, Cr, Ti, and Mo are contained in excess of 3% in total, the precipitation of carbonitride increases and the workability and delayed fracture resistance decrease, so the upper limit was made 3% .
Ｖは、鋼板の強度上昇及び粒径の微細化に有効である上、Ｖを含有する析出物および晶出物は水素トラップサイトとなるため非常に重要な元素である。しかし、Ｖ単独又はＮｂ，後述のＴｉ，Ｍｏの１種又は２種以上との合計で０．００１％未満ではこの効果が得られないために、下限値を０．００１％とした。逆にＮｂ，Ｖ，Ｃｒ，Ｔｉ，Ｍｏを合計で３％超含有すると炭窒化物の析出が顕著になり、延性低下が著しくなる。このため上限値を３％とした。 V is an extremely important element because it is effective for increasing the strength of the steel sheet and making the grain size finer, and precipitates and crystallized substances containing V become hydrogen trap sites. However, if the total of V alone or Nb, and one or more of Ti 2 and Mo described later is less than 0.001%, this effect cannot be obtained, so the lower limit was made 0.001%. On the other hand, when Nb, V, Cr, Ti, and Mo are contained in excess of 3% in total, the precipitation of carbonitrides becomes remarkable, and the ductility decreases remarkably. For this reason, the upper limit is set to 3% .
Ｔｉは、Ｔｉを含有する析出物および晶出物は水素トラップサイトとなるため非常に重要な元素である。しかし、Ｔｉ単独又はＮｂ，Ｖ、後述のＭｏの１種又は２種以上との合計で０．００１％未満では析出物および晶出物の個数が低下するために、下限値を０．００１％とした。逆にＮｂ，Ｖ，Ｃｒ，Ｔｉ，Ｍｏの合計が３％超では、粗大析出または晶出物が多量に生成するために加工性および耐遅れ破壊性が低下する。このため上限値を３％とした。 Ti is a very important element because precipitates and crystallized substances containing Ti become hydrogen trap sites. However, if the total of Ti alone, Nb, V, or one or more of Mo described later is less than 0.001%, the number of precipitates and crystallized substances decreases, so the lower limit is 0.001%. It was. On the other hand, if the total of Nb, V, Cr, Ti, and Mo exceeds 3%, a large amount of coarse precipitates or crystallized products are generated, so that workability and delayed fracture resistance are deteriorated. For this reason, the upper limit is set to 3% .
Ｍｏは、鋼板の焼入れ性を高め連続焼鈍設備で安定してマルテンサイトを得るために有効な元素であるだけでなく、粒界を強化して水素脆性の発生を抑制する効果がある。さらにＭｏを含有する析出物および晶出物は水素トラップサイトとなるため非常に重要な元素である。しかし、Ｍｏ単独又はＮｂ，Ｖ，Ｔｉの１種又は２種以上との合計で０．００１％未満ではこれらの効果が得られないため、下限値を０．００１％とした。またＮｂ，Ｖ，Ｃｒ，Ｔｉ，Ｍｏの合計が３％超ではこれらの効果が飽和するため、上限値を３％とした。 Mo is not only an effective element for improving the hardenability of the steel sheet and obtaining martensite stably in a continuous annealing facility, but also has an effect of strengthening grain boundaries and suppressing the occurrence of hydrogen embrittlement. Further, Mo-containing precipitates and crystallized substances are very important elements because they become hydrogen trap sites. However, since these effects cannot be obtained when Mo alone or a total of one or more of Nb, V and Ti is less than 0.001%, the lower limit is set to 0.001%. Further , when the total of Nb, V, Cr, Ti, and Mo exceeds 3%, these effects are saturated, so the upper limit is set to 3% .
Ｗは、鋼板の強度上昇に有効である上、Ｗを含有する析出物および晶出物は水素トラップサイトとなるため非常に重要な元素である。しかし、０．００５％未満ではこれらの効果が得られないため、下限値を０．００５％とした。逆に５％超含有すると加工性低下が生じるため、上限値を５％とした。 W is an extremely important element because it is effective for increasing the strength of the steel sheet, and precipitates and crystallized substances containing W become hydrogen trap sites. However, since these effects cannot be obtained at less than 0.005%, the lower limit is set to 0.005%. On the other hand, if the content exceeds 5%, the workability deteriorates, so the upper limit was made 5%.
Ｃｕは、強化に有効である上、自信の微細析出は遅れ破壊の向上にも寄与するため、０．００５％以上の添加とした。また過剰添加は加工性の劣化を招くことから、上限を５．０％とした。 Cu is effective for strengthening, and the fine precipitation of confidence contributes to the improvement of delayed fracture, so 0.005% or more was added. Moreover, since excessive addition causes deterioration of workability, the upper limit was made 5.0%.
Ｎｉは、Ｎｉ硫化物が水素侵入を抑制し遅れ破壊特性を向上させる効果や、鋼板の焼入れ性を高めることにより鋼板の強度を確保する効果がある。しかし０．００５％未満ではこれらの効果が得られないため、下限値を０．００５％とした。逆に５％超では加工性が悪くなるため、上限値を５％とした。 Ni has the effect that Ni sulfide suppresses hydrogen penetration and improves delayed fracture characteristics, and the effect of ensuring the strength of the steel sheet by enhancing the hardenability of the steel sheet. However, if less than 0.005%, these effects cannot be obtained, so the lower limit was set to 0.005%. On the other hand, if it exceeds 5%, workability deteriorates, so the upper limit was set to 5%.
Ｂは、鋼板の強度上昇に有効な元素である。しかし、０．０００２％未満ではこれらの効果が得られないため、下限値を０．０００２％とした。逆に０．１％超含有すると熱間加工性が劣化するため、上限値を０．１％とした。 B is an element effective for increasing the strength of the steel sheet. However, since these effects cannot be obtained if the content is less than 0.0002%, the lower limit is set to 0.0002%. On the other hand, if the content exceeds 0.1%, the hot workability deteriorates, so the upper limit was made 0.1%.
Ｍｇは、自身の化合物が耐遅れ破壊向上に効果的なだけでなく、他元素との複合析出物または複合昇出物を生成させ、かつそれらの形態を耐遅れ破壊性向上に寄与するよう制御するために必要な元素であることから、０．０００５％以上とした。しかし、０．０１％超では粗大酸化物および硫化物を生成して、形態制御に効果的でなくなる上、薄鋼板の基本的要求特性である加工性を低下させるため、上限を０．０１％とした。 Mg is not only effective in improving delayed fracture resistance of its own compound, but also controls the formation of composite precipitates or composite ascendants with other elements and contributes to the improvement of delayed fracture resistance. Since it is an element necessary for this, the content is set to 0.0005% or more. However, if it exceeds 0.01%, coarse oxides and sulfides are produced, which is not effective for shape control, and lowers the workability, which is a basic required characteristic of a thin steel sheet, so the upper limit is 0.01%. It was.
ＲＥＭ，Ｃａ，Ｙは、介在物の形態制御に有効で、耐遅れ破壊性に寄与することから、０．０００５％以上の添加とした。一方、過剰添加は熱間加工性を劣化させるため、それぞれ０．０１％以下の添加とした。ここでＲＥＭは Rera Earth Metal の略でＬａから始まるランタノイド系元素の総称である。 REM, Ca, and Y are effective for controlling the form of inclusions and contribute to delayed fracture resistance, so 0.0005% or more was added. On the other hand, since excessive addition deteriorates hot workability, the addition was made 0.01% or less. Here, REM is an abbreviation for Rera Earth Metal and is a general term for lanthanoid elements starting from La.
次に製造方法について説明する。
先ず、前記（６）に係る発明について説明する。
製造方法は一般に行われている熱延鋼板、冷延鋼板の製造設備で構わない。熱延後冷延・焼鈍して本発明の鋼板を製造する場合には、所定の成分に調整されたスラブを直接もしくは一旦冷却した後再加熱して熱延を行う。このときの再加熱温度は１１００℃以上１３００℃以下とすることが望ましい。これは再加熱温度が高温になると粗粒化や厚い酸化スケールが形成される。一方、低温加熱では圧延抵抗が高くなってしまうため、上記の温度範囲が望ましい。
Next, a manufacturing method will be described.
First, the invention according to (6) will be described.
The manufacturing method may be a generally used hot-rolled steel plate or cold-rolled steel plate manufacturing facility. When the steel sheet of the present invention is manufactured by cold rolling and annealing after hot rolling, the slab adjusted to a predetermined component is directly or once cooled and then reheated for hot rolling. In this case, the reheating temperature is desirably 1100 ° C. or higher and 1300 ° C. or lower. As the reheating temperature becomes higher, coarse grains and thick oxide scales are formed. On the other hand, since the rolling resistance is increased by low-temperature heating, the above temperature range is desirable.
次に熱間圧延では、フェライト粒にひずみが過度に加わり加工性が低下するのを防ぐために熱間圧延をＡｒ3 以上で行い、逆に高温すぎても焼鈍後の再結晶粒径およびＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、複合晶出物および複合析出物が必要以上に粗大化するため、９５０℃以下が望ましい。 Next, in hot rolling, hot rolling is performed at Ar3 or higher in order to prevent distortion from being excessively applied to ferrite grains and deterioration of workability. Conversely, even if the temperature is too high, the recrystallized grain size after annealing and Nb, V , Cr, Ti and Mo oxides, sulfides, nitrides, composite crystals and composite precipitates are coarsened more than necessary, and therefore, 950 ° C. or lower is desirable.
熱間圧延後２５〜７００℃の巻取温度域まで０．１〜１０００℃／秒の冷却速度で冷却する。
冷却停止温度を２５℃より低くすることは操業上困難であるため下限を２５℃とし、冷却停止温度の上限が７００℃より高いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物が粗大化することによりトラップ能が低下したり、９８０ＭＰａ以上の強度が得られなくなることから、前記の範囲に規定する。
また、冷却速度が０．１℃／秒より遅いと、フェライトやパーライトの生成を促進して強度低下を招く懸念があることから、冷却速度の下限を０．１℃／秒とした。一方、冷却速度が１０００℃／秒を超えることは操業上困難なため、これを上限とした。
熱間圧延後の冷却温度域は、トラップサイトとなるＮｂ、Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物の析出しやすい５００〜７００℃が好ましく、またその温度域への冷却速度は、上記トラップサイトとなる析出物の析出を促進させるために、２０℃／秒以上の冷却速度が好ましい。
After hot rolling, it is cooled to a coiling temperature range of 25 to 700 ° C. at a cooling rate of 0.1 to 1000 ° C./second.
Since it is difficult to operate the cooling stop temperature below 25 ° C., the lower limit is set to 25 ° C. When the upper limit of the cooling stop temperature is higher than 700 ° C., oxides, sulfides of Nb, V, Cr, Ti and Mo, When the nitride and the composite precipitate are coarsened, the trapping ability is reduced, and the strength of 980 MPa or more cannot be obtained.
Further, if the cooling rate is slower than 0.1 ° C./second, there is a concern that the formation of ferrite and pearlite is promoted and the strength is lowered, so the lower limit of the cooling rate is set to 0.1 ° C./second. On the other hand, since it is difficult in operation that the cooling rate exceeds 1000 ° C./second, this is set as the upper limit.
The cooling temperature range after hot rolling is preferably 500 to 700 ° C., at which oxides, sulfides, nitrides, and composite precipitates of Nb, V, Cr, Ti and Mo that become trap sites are likely to precipitate. The cooling rate to the temperature range is preferably a cooling rate of 20 ° C./second or more in order to promote the precipitation of the precipitate that becomes the trap site.
巻き取り温度については、高温にすれば再結晶や粒成長が促進され、加工性の向上が望まれるが、熱間圧延時に発生するスケールの生成も促進され酸洗性が低下するので、７００℃以下とする。下限は操業上２５℃以上とし、さらに１００℃以上とすることが好ましい。 Regarding the coiling temperature, recrystallization and grain growth are promoted at a high temperature, and improvement in workability is desired. However, since the generation of scale generated during hot rolling is promoted and the pickling property is lowered, 700 ° C. The following. The lower limit is 25 ° C. or higher for operation, and preferably 100 ° C. or higher.
前記の冷却、巻取りに引き続いて、４００〜７００℃の温度範囲で１〜１０００００秒保持後室温まで冷却する。保持温度が４００℃より低いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物の析出が遅くなる、もしくは析出しなくなることから下限を４００℃とし、７００℃より高いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物が粗大化することによるトラップ能の低下や、鋼材強度の低下を招くことから上限を７００℃とした。 Subsequent to the cooling and winding, the temperature is maintained at 400 to 700 ° C. for 1 to 100000 seconds and then cooled to room temperature. If the holding temperature is lower than 400 ° C., the precipitation of oxides, sulfides, nitrides, and composite precipitates of Nb, V, Cr, Ti, and Mo becomes slow or no longer precipitate. When the temperature is higher than ℃, the upper limit is 700 because Nb, V, Cr, Ti and Mo oxides, sulfides, nitrides, and composite precipitates are coarsened, leading to a decrease in trapping capability and a decrease in steel strength. C.
又、前記温度範囲での保持時間が１秒より短いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物の析出量が不十分であり、また１０００００秒より長いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物が粗大化することによるトラップ能の低下や、鋼材強度の低下を招くことから、前記の範囲に規定する。
このときの温度範囲および保持時間は、トラップサイトとなるＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物が、請求項１で規定した平均粒子径、密度の範囲中で、より小さい平均粒子径、より高い密度を満たすことにより、トラップ能が上昇することから、５００〜７００℃の温度範囲で、１０分〜１０時間保持することが好ましい。保持後は厚い酸化スケールの形成を防ぐため、室温まで冷却する。
Further, if the holding time in the temperature range is shorter than 1 second, the amount of oxides, sulfides, nitrides and composite precipitates of Nb, V, Cr, Ti and Mo is insufficient, and 100,000 seconds. If it is longer, the oxides, sulfides, nitrides, and composite precipitates of Nb, V, Cr, Ti, and Mo are coarsened, leading to a decrease in trapping capability and a decrease in steel material strength. Stipulate.
The temperature range and holding time at this time are the average particle size and density defined in claim 1 for the oxides, sulfides, nitrides, and composite precipitates of Nb, V, Cr, Ti and Mo that become trap sites. In this range, the trapping ability is increased by satisfying a smaller average particle size and a higher density. Therefore, it is preferable to maintain the temperature in the temperature range of 500 to 700 ° C. for 10 minutes to 10 hours. After holding, cool to room temperature to prevent the formation of thick oxide scale.
酸洗後の冷間圧延は、圧下率が低いと鋼板の形状矯正が難しくなるため下限値を３０％とすることが好ましい。また、８０％を超える圧下率で圧延すると、鋼板のエッジ部に割れの発生及び形状の乱れのため、上限値を８０％とすることが好ましい。 In cold rolling after pickling, if the rolling reduction is low, it becomes difficult to correct the shape of the steel sheet, so the lower limit is preferably 30%. In addition, when rolling at a rolling reduction exceeding 80%, it is preferable to set the upper limit value to 80% because of the occurrence of cracks in the edge portion of the steel sheet and disorder of the shape.
連続焼鈍温度は低すぎると未再結晶の状態になり硬質化し、逆に高すぎると粒が粗大化しプレス時に肌荒れを起こす場合があるという問題点があるので、６００℃以上９５０℃以下とする。 If the continuous annealing temperature is too low, it becomes a non-recrystallized state and becomes hard, and conversely if too high, there is a problem that the grains become coarse and rough skin may occur during pressing.
焼鈍後、０．１〜１０００℃／秒の冷却速度で２５〜５００℃の温度域に冷却し、引き続いて同温度域で１〜１００００秒保持を行う。冷却速度が０．１℃／秒より遅いとフェライトやパーライトの生成を促進して強度低下を招く懸念があることから、冷却速度の下限を０．１℃／秒とした。一方、冷却速度が１０００℃／秒超の場合には最終的な鋼板中のマルテンサイト相などの硬質相が多量になってしまうことや、操業上困難なため、前記の範囲に規定する。
また、冷却停止温度を２５℃より低くすることは操業上困難であるため下限を２５℃とし、５００℃より高いと結晶粒の粗大化を招き９８０ＭＰａ以上の強度を得られないことから、前記の範囲に規定する。
After annealing, it is cooled to a temperature range of 25 to 500 ° C. at a cooling rate of 0.1 to 1000 ° C./second, and subsequently held for 1 to 10,000 seconds in the same temperature range. If the cooling rate is slower than 0.1 ° C./second, the lower limit of the cooling rate is set to 0.1 ° C./second because there is a concern that the formation of ferrite and pearlite is promoted and the strength is lowered. On the other hand, when the cooling rate is more than 1000 ° C./second, the amount of hard phase such as martensite phase in the final steel sheet becomes large and it is difficult to operate.
Further, since it is difficult to operate at a cooling stop temperature lower than 25 ° C., the lower limit is set to 25 ° C. If the temperature is higher than 500 ° C., the crystal grains become coarse and a strength of 980 MPa or more cannot be obtained. Specified in the range.
冷却停止温度での保持時間を１秒より短くすることは製造ラインの性能からまたはコストから困難であり、１００００秒より長くすることは結晶粒の粗大かを招き９８０ＭＰａ以上の強度を得られないことから、前記の範囲に規定する。
また必要に応じて、前記の保持後、４００〜７００℃の温度域で１分から１０時間保持して、その後冷却しても良い（前記（７）に係る発明）。この熱処理により、合金炭化物または窒化物（例えばＶ，Ｃｒ，Ｍｏ，Ｔｉ，Ｎｂ含有の炭窒化物）を析出させ、これらが新たな水素のトラップサイトとして働き、より耐遅れ破壊性が高まる。条件が、低温短時間になると十分な析出が起こらず、高温長時間になると析出物が粗大化してトラップサイトとして機能しなくなることから、本範囲とした。
It is difficult to make the holding time at the cooling stop temperature shorter than 1 second from the performance of the production line or from the cost, and making it longer than 10000 seconds invites the coarseness of the crystal grains, and the strength of 980 MPa or more cannot be obtained. To the above range.
Moreover, after the said holding | maintenance as needed, you may hold | maintain for 1 to 10 hours in the temperature range of 400-700 degreeC, and you may cool after that (invention concerning said (7)). By this heat treatment, alloy carbides or nitrides (for example, carbonitrides containing V, Cr, Mo, Ti, and Nb) are precipitated, and these act as new hydrogen trap sites, thereby further improving delayed fracture resistance. If the conditions are low temperature for a short time, sufficient precipitation does not occur, and if the temperature is high for a long time, the precipitate becomes coarse and does not function as a trap site.
また、熱間圧延後２５〜７００℃の温度域に０．１〜１０００℃／秒の冷却速度で冷却後巻取り、引き続いて４００〜７００℃の温度範囲で１〜１０００００秒保持後室温まで冷却した熱延鋼板を酸洗後冷延し、４００〜７００℃の温度域で１分〜１０時間保持してもよい（前記（８）に係る発明）。 Also, after hot rolling, it is wound after cooling at a cooling rate of 0.1 to 1000 ° C./second in a temperature range of 25 to 700 ° C., and subsequently kept at a temperature range of 400 to 700 ° C. for 1 to 100,000 seconds and then cooled to room temperature. The obtained hot-rolled steel sheet may be cold-rolled after pickling and held in a temperature range of 400 to 700 ° C. for 1 minute to 10 hours (the invention according to (8)).
熱間圧延後の冷却停止温度を２５℃より低くすることは操業上困難であるため下限を２５℃とし、上限が７００℃より高いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物の析出が困難となることから、前記の範囲に規定する。
また、冷却速度が０．１℃／秒より遅いと、フェライトやパーライトの生成を促進して強度低下を招く懸念があることから、冷却速度の下限を０．１℃／秒とした。一方、冷却速度が１０００℃／秒超の場合には最終的な鋼板中のマルテンサイト相などの硬質相が多量になってしまうことや、操業上困難なため、これを上限とした。
Lowering the cooling stop temperature after hot rolling below 25 ° C is difficult in operation, so the lower limit is 25 ° C. If the upper limit is higher than 700 ° C, oxides and sulfides of Nb, V, Cr, Ti and Mo Therefore, it is difficult to deposit nitrides and composite precipitates, so the above range is specified.
Further, if the cooling rate is slower than 0.1 ° C./second, there is a concern that the formation of ferrite and pearlite is promoted and the strength is lowered, so the lower limit of the cooling rate is set to 0.1 ° C./second. On the other hand, when the cooling rate is higher than 1000 ° C./second, the hard steel phase such as martensite phase in the final steel sheet becomes large and operation is difficult.
前記の冷却に引き続いて行う保持温度が４００℃より低いと、Ｎｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物の析出が遅くなる、もしくは析出しなくなることから下限を４００℃とし、７００℃より高いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物が粗大化することによるトラップ能の低下や、鋼材強度の低下を招くことから、上限を７００℃とした。 When the holding temperature performed subsequent to the cooling is lower than 400 ° C., the precipitation of oxides, sulfides, nitrides, and composite precipitates of Nb, V, Cr, Ti, and Mo is slow or no longer precipitates. If the lower limit is set to 400 ° C., and the temperature is higher than 700 ° C., the trap ability is reduced due to the coarsening of oxides, sulfides, nitrides, and composite precipitates of Nb, V, Cr, Ti and Mo, and the strength of the steel material. The upper limit was set to 700 ° C. because it caused a decrease.
又、前記温度範囲での保持時間が１秒より短いと、Ｎｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物の析出量が不十分であり、また１０００００秒より長いとＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物、および複合析出物が粗大化することによるトラップ能の低下や、鋼材強度の低下を招くことから、前記の範囲に規定する。
前記の保持後、室温まで冷却した熱延鋼板を酸洗後冷延し、４００〜７００℃の温度域で１分〜１０時間保持するのは、前記（６）に係る発明の冷延−焼鈍後に同じ熱処理をする方法と同じ理由によるものである。
If the holding time in the temperature range is shorter than 1 second, the amount of oxides, sulfides, nitrides and composite precipitates of Nb, V, Cr, Ti and Mo is insufficient, and 100,000 If it is longer than 2 seconds, the trapping ability is reduced due to coarsening of oxides, sulfides, nitrides, and composite precipitates of Nb, V, Cr, Ti and Mo, and the strength of the steel material is reduced. Specified in the range.
After the holding, the hot-rolled steel sheet cooled to room temperature is pickled and then cold-rolled, and held in the temperature range of 400 to 700 ° C. for 1 minute to 10 hours. The cold rolling-annealing of the invention according to (6) above This is due to the same reason as the method of performing the same heat treatment later.
また、熱間圧延時にＡｒ3 点以上の仕上温度で熱間圧延を施し、その後２５〜５００℃の温度域に０．１〜１０００℃／秒の冷却速度で冷却後巻き取り、引き続いて２５〜５００℃で１〜１０００００秒保持後室温まで冷却した熱延鋼板を酸洗後冷延し、引き続いて４００〜７００℃の温度域で１分〜１０時間保持を行うことで、より高い水素トラップ能が得られる（前記（９）に係る発明）。
これは熱間圧延時の冷却中および２５〜５００℃での温度保持中に、ベイナイトまたはマルテンサイトが主相となり、冷間圧延後の焼鈍時に微細にＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物および複合析出物が析出し、高い水素トラップ能が得られ、さらに遅れ破壊特性改善される。巻取り温度を２５〜５００℃に規定するのも蒸気と同じ理由によるものである。その他の条件の規定理由は前記（６）〜（８）の発明と同様である。
Further, during hot rolling, hot rolling is performed at a finishing temperature of the Ar3 point or higher, and then winding is performed after cooling at a cooling rate of 0.1 to 1000 ° C./second in a temperature range of 25 to 500 ° C., followed by 25 to 500 ° C. A hot rolled steel sheet cooled to room temperature for 1 to 100000 seconds at 0 ° C. is pickled and then cold-rolled, and then kept for 1 minute to 10 hours in a temperature range of 400 to 700 ° C. Obtained (invention according to (9) above).
This is because bainite or martensite becomes the main phase during cooling during hot rolling and during temperature holding at 25 to 500 ° C., and finely oxidized Nb, V, Cr, Ti and Mo during annealing after cold rolling. Deposits, sulfides, nitrides, and composite precipitates are obtained, and a high hydrogen trapping ability is obtained, and the delayed fracture characteristics are further improved. The reason for setting the coiling temperature to 25 to 500 ° C. is the same as that for steam. The reasons for defining other conditions are the same as in the inventions of (6) to (8).
また、熱間圧延時にＡｒ3 点以上の仕上温度で熱間圧延を施し、その後２５〜７００℃の温度域に０．１〜１０００℃／秒の冷却速度で冷却後巻き取り、引き続いて４００〜７００℃で１〜１０００００秒保持後室温まで冷却した熱延鋼板を酸洗後冷延し、その後焼鈍時の最高温度を６００〜９５０℃で焼鈍した後に０．１〜１０００℃／秒の冷却速度で０〜３５０℃の温度域に冷却し、引き続いて１００〜７００℃の温度域で１〜１００００秒保持を行うことで、高い水素トラップ能が得られる（前記（１０）に係る発明）。
これは冷間圧延後の焼鈍時に最高加熱温度から０〜３５０℃の温度域に冷却する事で、ベイナイトまたはマルテンサイトが主相となり、その後の１００〜７００℃での保持により微細にＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物および複合析出物が析出し、高い水素トラップ能が得られ遅れ破壊特性改善されるからである。焼鈍時の最高加熱温度からの冷却速度および冷却停止温度は、５０〜２００℃／秒及び２５〜１００℃程度が好ましく、またその後の加熱速度は５〜２０℃／程度が好ましい。この時の加熱温度及び保持時間は必要とする強度及び耐遅れ破壊特性によって異なるが、上記範囲内である事が好ましい。
その他の条件については前記（６）に係る発明と同様である。
Further, during hot rolling, hot rolling is performed at a finishing temperature equal to or higher than the Ar3 point, and after that, winding is performed after cooling at a cooling rate of 0.1 to 1000 ° C./second in a temperature range of 25 to 700 ° C., and subsequently 400 to 700 ° C. Hot-rolled steel sheet cooled to room temperature after being held at C for 1 to 100000 seconds is pickled and then cold-rolled, and then annealed at a maximum temperature of 600 to 950 C for annealing at a cooling rate of 0.1 to 1000 C / sec. High hydrogen trap ability is obtained by cooling to a temperature range of 0 to 350 ° C. and subsequently holding in a temperature range of 100 to 700 ° C. for 1 to 10,000 seconds (the invention according to (10) above).
This is because the bainite or martensite becomes the main phase by cooling from the maximum heating temperature to a temperature range of 0 to 350 ° C. during annealing after cold rolling, and then the Nb, V is finely retained by holding at 100 to 700 ° C. This is because oxides, sulfides, nitrides, and composite precipitates of Cr, Ti, and Mo are precipitated, and a high hydrogen trapping ability is obtained and delayed fracture characteristics are improved. The cooling rate and the cooling stop temperature from the highest heating temperature during annealing are preferably about 50 to 200 ° C./second and about 25 to 100 ° C., and the subsequent heating rate is preferably about 5 to 20 ° C./about. The heating temperature and holding time at this time vary depending on the required strength and delayed fracture resistance, but are preferably within the above ranges.
Other conditions are the same as in the invention according to (6).
本発明において最も重要な技術は、薄鋼板の製造設備は条鋼や厚鋼板における製造設備と異なることや、使用に際し加工および溶接を行うという観点から、耐水素脆化特性向上のために析出させるトラップサイトを、熱間圧延中、連続焼鈍および箱焼鈍において析出させることにあり、これを実現するために前述の成分範囲、熱間圧延およびその後の熱処理条件範囲を制限した。この時のトラップサイトとなるＮｂ，Ｖ，Ｃｒ，ＴｉおよびＭｏの酸化物、硫化物、窒化物および複合析出物は、４００〜７００℃の温度範囲で１分〜１０時間の保持により析出させる事が好ましい（前記（６）〜（８）、（１０）に係る発明）。 The most important technique in the present invention is that the manufacturing equipment for thin steel sheets is different from that for steel strips and thick steel sheets, and trapping is performed for improving hydrogen embrittlement resistance from the viewpoint of processing and welding during use. The site is to be precipitated in the continuous annealing and the box annealing during the hot rolling, and in order to realize this, the aforementioned component range, hot rolling and the subsequent heat treatment condition range are limited. The oxides, sulfides, nitrides and composite precipitates of Nb, V, Cr, Ti and Mo that become trap sites at this time should be precipitated by holding for 1 minute to 10 hours in a temperature range of 400 to 700 ° C. Is preferable (the inventions according to (6) to (8) and (10) above).
次に本発明を実施例に基づいて説明する。
表１に示す成分の鋼を溶製し、常法に従い連続鋳造でスラブとした。符号Ｄ〜Ｇが本発明に従った成分の鋼で符号Ｕ，Ｖは成分が逸脱するものである。これらの鋼を加熱炉中で１１６０〜１２５０℃の温度で加熱し、表３に示す９通りの条件で熱間圧延、連続焼鈍および箱焼鈍を行った。
ここで条件１〜６，８，９は本発明に従った製造条件であり、一方条件７は巻取り温度が低い条件で４００〜７００℃での保持を行っていない事から、本発明より逸脱する製造条件である。次いで再結晶焼鈍を行い、表２−１〜表２−４に鋼板の材質特性を示す。
以下に条件１〜９の製造条件を詳細に述べる。
Next, this invention is demonstrated based on an Example.
Steels having the components shown in Table 1 were melted and slabs were obtained by continuous casting according to a conventional method. Sign steel components code D~G is in accordance with the present invention U, V are those components deviates. These steels were heated in a heating furnace at a temperature of 1160 to 1250 ° C. and subjected to hot rolling, continuous annealing and box annealing under the nine conditions shown in Table 3.
Here, conditions 1 to 6, 8, and 9 are production conditions according to the present invention, while condition 7 deviates from the present invention because holding at 400 to 700 ° C. is not performed under conditions where the coiling temperature is low. Manufacturing conditions. Next, recrystallization annealing is performed, and Table 2-1 to Table 2-4 show the material properties of the steel sheets.
The manufacturing conditions of conditions 1-9 are described in detail below.
条件１では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で５０℃まで冷却し５０℃で巻き取り、室温（２０℃）まで冷却し、酸洗後圧下率５０％の冷間圧延をした。その後表３のＣ欄に示すように、２０℃／間の加熱速度で６００℃まで加熱し５時間保持を行った後、２０℃／時間で２００℃まで炉冷した。その後０．５％の調質圧延をして冷延鋼板となした。 In condition 1, as shown in column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 50 ° C at a cooling rate of 60 ° C / second, and wound at 50 ° C. The sample was taken, cooled to room temperature (20 ° C.), and cold-rolled at a reduction rate of 50% after pickling. Thereafter, as shown in column C of Table 3, after heating to 600 ° C. at a heating rate of 20 ° C./hour and holding for 5 hours, the furnace was cooled to 200 ° C. at 20 ° C./hour. Thereafter, 0.5% temper rolling was performed to obtain a cold-rolled steel sheet.
条件２では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で６００℃まで冷却し６００℃で巻き取った。引き続き６００℃で１時間保持し、室温（２０℃）まで冷却した。その熱延鋼板を酸洗後、圧下率５０％の冷間圧延を行い、表３のＢ欄に示す連続焼鈍条件のように、５℃／秒の加熱速度で８５０℃まで加熱し、９０秒保持した後、６０℃／秒の冷却速度で２５０℃まで冷却し同温度域で６００秒保持し再結晶焼鈍を行い、その後０．５％の調質圧延をして冷延鋼板となした。 In condition 2, as shown in the column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 600 ° C at a cooling rate of 60 ° C / second, and wound at 600 ° C. I took it. Subsequently, the temperature was maintained at 600 ° C. for 1 hour and cooled to room temperature (20 ° C.). The hot-rolled steel sheet is pickled, cold-rolled at a reduction rate of 50%, and heated to 850 ° C. at a heating rate of 5 ° C./second as in the continuous annealing conditions shown in column B of Table 3, for 90 seconds. After being held, it was cooled to 250 ° C. at a cooling rate of 60 ° C./second, held at the same temperature range for 600 seconds, recrystallized and annealed, and then subjected to 0.5% temper rolling to obtain a cold-rolled steel sheet.
条件３では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で６００℃まで冷却し６００℃で巻き取った。引き続き６００℃で１時間保持し、室温（２０℃）まで冷却した。その熱延鋼板を酸洗後、圧下率５０％の冷間圧延を行い、表３のＢ欄に示す連続焼鈍条件のように、５℃／秒の加熱速度で８５０℃まで加熱し、９０秒保持した後、６０℃／秒の冷却速度で２５０℃まで冷却し同温度域で６００秒保持し再結晶焼鈍を行い、その後表３のＣ欄に示すように、２０℃／時間の加熱速度で６００℃まで加熱し１時間保持を行った後、２０℃／時間で２００℃まで炉冷した。その後０．５％の調質圧延をして冷延鋼板となした。 In condition 3, as shown in the column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 600 ° C at a cooling rate of 60 ° C / second, and wound at 600 ° C. I took it. Subsequently, the temperature was maintained at 600 ° C. for 1 hour and cooled to room temperature (20 ° C.). The hot-rolled steel sheet is pickled, cold-rolled at a reduction rate of 50%, and heated to 850 ° C. at a heating rate of 5 ° C./second as in the continuous annealing conditions shown in column B of Table 3, for 90 seconds. After being held, cooled to 250 ° C. at a cooling rate of 60 ° C./second, held for 600 seconds in the same temperature range and recrystallized and annealed, and then at a heating rate of 20 ° C./hour, as shown in column C of Table 3. After heating to 600 ° C. and holding for 1 hour, the furnace was cooled to 200 ° C. at 20 ° C./hour. Thereafter, 0.5% temper rolling was performed to obtain a cold-rolled steel sheet.
条件４では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で４００℃まで冷却し４００℃で巻き取った。引き続き４００℃で１時間保持し、室温（２０℃）まで冷却し、酸洗後圧下率５０％の冷延をした。その後表３のＣ欄に示すように、２０℃／時間の加熱速度で６００℃まで加熱し５時間保持を行った後、２０℃／時間で２００℃まで炉冷した。その後０．５％の調質圧延をして冷延鋼板となした。 In condition 4, as shown in column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 400 ° C at a cooling rate of 60 ° C / second, and wound at 400 ° C. I took it. Subsequently, it was kept at 400 ° C. for 1 hour, cooled to room temperature (20 ° C.), and cold-rolled at a reduction rate of 50% after pickling. Thereafter, as shown in column C of Table 3, after heating to 600 ° C. at a heating rate of 20 ° C./hour and holding for 5 hours, the furnace was cooled to 200 ° C. at 20 ° C./hour. Thereafter, 0.5% temper rolling was performed to obtain a cold-rolled steel sheet.
条件５では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で５０℃まで冷却し５０℃で巻き取った。引き続き室温（２０℃）まで冷却した。その熱延鋼板を酸洗後、圧下率５０％の冷間圧延を行い、表３のＢ欄に示す連続焼鈍条件のように、５℃／秒の加熱速度で８５０℃まで加熱し、９０秒保持した後、６０℃／秒の冷却速度で２５０℃まで冷却し同温度域で６００秒保持し再結晶焼鈍を行い、その後表３のＣ欄に示すように、２０℃／時間の加熱速度で６００℃まで加熱し５時間保持を行った後、２０℃／時間で２００℃まで炉冷した。その後０．５％の調質圧延をして冷延鋼板となした。 In condition 5, as shown in column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 50 ° C at a cooling rate of 60 ° C / second, and wound at 50 ° C. I took it. Subsequently, it was cooled to room temperature (20 ° C.). The hot-rolled steel sheet is pickled, cold-rolled at a reduction rate of 50%, and heated to 850 ° C. at a heating rate of 5 ° C./second as in the continuous annealing conditions shown in column B of Table 3, for 90 seconds. After being held, cooled to 250 ° C. at a cooling rate of 60 ° C./second, held for 600 seconds in the same temperature range and recrystallized and annealed, and then at a heating rate of 20 ° C./hour, as shown in column C of Table 3. After heating to 600 ° C. and holding for 5 hours, the furnace was cooled to 200 ° C. at 20 ° C./hour. Thereafter, 0.5% temper rolling was performed to obtain a cold-rolled steel sheet.
条件６では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で６００℃まで冷却し６００℃で巻き取った。その後表３のＣ欄に示すように、２０℃／時間の加熱速度で６００℃まで加熱し１時間保持を行った後、２０℃／時間で２００℃まで炉冷した。その熱延鋼板を酸洗後、圧下率５０％の冷間圧延を行い、表３のＢ欄に示す連続焼鈍条件のように、５℃／秒の加熱速度で８５０℃まで加熱し、９０秒保持した後、６０℃／秒の冷却速度で２５０℃まで冷却し同温度域で６００秒保持し再結晶焼鈍を行い、その後０．５％の調質圧延をして冷延鋼板となした。 In condition 6, as shown in column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 600 ° C at a cooling rate of 60 ° C / second, and wound at 600 ° C. I took it. Thereafter, as shown in column C of Table 3, after heating to 600 ° C. at a heating rate of 20 ° C./hour and holding for 1 hour, the furnace was cooled to 200 ° C. at 20 ° C./hour. The hot-rolled steel sheet is pickled, cold-rolled at a reduction rate of 50%, and heated to 850 ° C. at a heating rate of 5 ° C./second as in the continuous annealing conditions shown in column B of Table 3, for 90 seconds. After being held, it was cooled to 250 ° C. at a cooling rate of 60 ° C./second, held at the same temperature range for 600 seconds, recrystallized and annealed, and then subjected to 0.5% temper rolling to obtain a cold-rolled steel sheet.
条件７では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で３００℃まで冷却し３００℃で巻き取った。引き続き３００℃で１時間保持し、室温（２０℃）まで冷却した。その熱延鋼板を酸洗後、圧下率５０％の冷間圧延を行い、表３のＢ欄に示す連続焼鈍条件のように、５℃／秒の加熱速度で５５０℃まで加熱し、９０秒保持した後、６０℃／秒の冷却速度で２５０℃まで冷却し同温度域で６００秒保持し再結晶焼鈍を行い、その後０．５％の調質圧延をして冷延鋼板となした。 In condition 7, as shown in column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 300 ° C at a cooling rate of 60 ° C / second, and wound at 300 ° C. I took it. Subsequently, the temperature was maintained at 300 ° C. for 1 hour and cooled to room temperature (20 ° C.). The hot-rolled steel sheet is pickled, cold-rolled at a reduction rate of 50%, and heated to 550 ° C. at a heating rate of 5 ° C./second as in the continuous annealing conditions shown in column B of Table 3, for 90 seconds. After being held, it was cooled to 250 ° C. at a cooling rate of 60 ° C./second, held at the same temperature range for 600 seconds, recrystallized and annealed, and then subjected to 0.5% temper rolling to obtain a cold-rolled steel sheet.
条件８では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で３５０℃まで冷却し３５０℃で巻き取った。引き続き３５０℃で１時間保持し、室温（２０℃）まで冷却し、酸洗後圧下率５０％の冷延をした。その後表３のＣ欄に示すように、２０℃／時間の加熱速度で５５０℃まで加熱し５時間保持を行った後、２０℃／時間で２００℃まで炉冷した。その後０．５％の調質圧延をして冷延鋼板となした。 In condition 8, as shown in column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 350 ° C at a cooling rate of 60 ° C / second, and wound at 350 ° C. I took it. Subsequently, it was kept at 350 ° C. for 1 hour, cooled to room temperature (20 ° C.), and cold-rolled at a reduction rate of 50% after pickling. Thereafter, as shown in column C of Table 3, after heating to 550 ° C. at a heating rate of 20 ° C./hour and holding for 5 hours, the furnace was cooled to 200 ° C. at 20 ° C./hour. Thereafter, 0.5% temper rolling was performed to obtain a cold-rolled steel sheet.
条件９では表３のＡ欄に示すように、１２００℃でスラブを加熱後、熱間圧延を８８０℃の仕上げ温度で行い、６０℃／秒の冷却速度で６００℃まで冷却し６００℃で巻き取った。引き続き６００℃で１時間保持し、室温（２０℃）まで冷却した。その熱延鋼板を酸洗後、圧下率５０％の冷間圧延を行い、表３のＢ欄に示す連続焼鈍条件のように、５℃／秒の加熱速度で８５０℃まで加熱し、９０秒保持した後、６０℃／秒の冷却速度で２５℃まで冷却し、その後５℃／秒の加熱速度で３００℃まで加熱し同温度域で６００秒保持し、その後０．５％の調質圧延をして冷延鋼板となした。 In condition 9, as shown in the column A of Table 3, after heating the slab at 1200 ° C, hot rolling is performed at a finishing temperature of 880 ° C, cooled to 600 ° C at a cooling rate of 60 ° C / second, and wound at 600 ° C. I took it. Subsequently, the temperature was maintained at 600 ° C. for 1 hour and cooled to room temperature (20 ° C.). The hot-rolled steel sheet is pickled, cold-rolled at a reduction rate of 50%, and heated to 850 ° C. at a heating rate of 5 ° C./second as in the continuous annealing conditions shown in column B of Table 3, for 90 seconds. After being held, it is cooled to 25 ° C. at a cooling rate of 60 ° C./second, then heated to 300 ° C. at a heating rate of 5 ° C./second and held at the same temperature range for 600 seconds, and then temper rolling at 0.5% To obtain a cold-rolled steel sheet.
表２−１〜表２−４に、鋼板の耐遅れ破壊特性の評価を示した。評価方法は１００mm×３０mmの短冊試験片を曲げ加工し、表面に耐水性の歪みゲージを装着した後で０．５mol/l 硫酸中に漬け、電流によって電解して水素を侵入させ、２時間後の割れの発生を評価した。曲げ加工の半径は１０mmとし、与える応力はそれぞれ５８８．４ＭＰａ（６０kgf/mm2 ）と８８２．６ＭＰａ（９０kgf/mm2 ）とした。
さらに、スポット溶接部の遅れ破壊特性評価のために、上記のサイズの試験片を１０Ｒにて曲げ加工後、端部同士をスポット溶接した試験片を、０．５mol/l の硫酸中に漬け、電流によって電解して水素を侵入させ、２時間後の割れの発生も併せて評価した。
Tables 2-1 to 2-4 show the evaluation of delayed fracture resistance of steel sheets. The evaluation method is that a strip test piece of 100 mm x 30 mm is bent, and after mounting a water-resistant strain gauge on the surface, it is immersed in 0.5 mol / l sulfuric acid, electrolyzed by current and allowed to invade hydrogen, and after 2 hours The occurrence of cracks was evaluated. The bending radius was 10 mm, and the applied stress was 588.4 MPa (60 kgf / mm 2 ) and 882.6 MPa (90 kgf / mm 2 ), respectively.
Further, in order to evaluate the delayed fracture characteristics of the spot welded portion, after bending the test piece of the above size at 10R, the test piece in which the end portions are spot welded is immersed in 0.5 mol / l sulfuric acid, Electrolysis was carried out by electric current to infiltrate hydrogen, and the occurrence of cracks after 2 hours was also evaluated.
表２−１〜表２−４、表３に示すように、本発明鋼であるＤ〜Ｇの鋼種で熱処理条件を１〜６、８、９としたものは、自動車の補強部品に適用するに充分な引張り強度と延性を示しており、上記の遅れ破壊試験において割れが発生しなかったことから耐遅れ破壊性に優れている。
これらに対して比較鋼であるＵ，Ｖ鋼またはＤ〜Ｇ鋼において熱処理条件を７としたものは、成分と熱処理条件のいずれかが本発明範囲から逸脱している。
したがって、種々の添加元素を添加した上でトラップサイトとなる酸化物、硫化物、窒化物および複合析出物を有効に作用するように、４００〜７００℃において保持することが耐遅れ破壊特性に有効であることは明らかである。
Table 2-1 Table 2-4, as shown in Table 3, the heat treatment conditions in D~G steels are invention steels those with 1 to 6, 8, and 9, applied to a reinforcing component of the motor vehicle Has sufficient tensile strength and ductility, and is excellent in delayed fracture resistance because cracks did not occur in the delayed fracture test.
In contrast, in U, V steel, or D to G steel, which are comparative steels, the heat treatment conditions are set to 7, either of the components or the heat treatment conditions deviate from the scope of the present invention.
Therefore, it is effective for delayed fracture resistance to keep at 400-700 ° C so that oxides, sulfides, nitrides and composite precipitates acting as trap sites can act effectively after adding various additive elements. Obviously.
Claims (10)
Ｃ ：０．０１〜０．３０％、
Ｓｉ：２．０％以下、
Ｍｎ：０．０１〜３％、
Ｐ ：０．１％以下、
Ｓ ：０．０５％以下、
Ａｌ：０．００５〜４％、
Ｎ ：０．０１％以下
を含有し、更に、
Ｃｒ：１．１％以上と、
Ｎｂ，Ｖ，Ｔｉ，Ｍｏの元素群中から１種又は２種以上を合計で０．００１％以上とを含有し、かつ、
ＣｒとＮｂ，Ｖ，Ｔｉ，Ｍｏの１種又は２種以上との合計が３％以下
であり、残部がＦｅおよび不可避的不純物からなり、ミクロ組織がベイナイトまたはマルテンサイトを面積率で最大の相として、粒内のＮｂ、Ｖ，Ｃｒ，Ｔｉ，Ｍｏの酸化物、硫化物、窒化物、複合晶出物、複合析出物のいずれか１種以上を、
平均粒子径ｄ：０．００１〜５．０μｍ
密度ρ：１平方ｍｍあたり１００〜１×１０13個
分布：平均粒子径からの標準偏差σと平均粒子径ｄの比が、σ／ｄ≦１．０
を満たす分布形態を有し、引張強度が９８０ＭＰａ以上であることを特徴とする耐水素脆化に優れた高強度薄鋼板。 % By mass
C: 0.01 to 0.30%
Si: 2.0% or less,
Mn: 0.01 to 3%
P: 0.1% or less,
S: 0.05% or less,
Al: 0.005 to 4%,
N: 0.01% or less , and
Cr: 1.1% or more,
Containing one or more of Nb, V 1 , Ti 2 , and Mo in a total of 0.001 % or more , and
The total of Cr and one or more of Nb, V, Ti, and Mo is 3% or less
, And the balance being Fe and unavoidable impurities, as a maximum phase microstructure of bainite or martensite at an area ratio, Nb in the grains, V, Cr, Ti, oxides of Mo, sulfides, nitrides Any one or more of the composite crystallized product and the composite precipitate,
Average particle diameter d: 0.001 to 5.0 μm
Density ρ: 100 to 1 × 10 13 per square mm Distribution: Ratio of standard deviation σ from average particle diameter to average particle diameter d is σ / d ≦ 1.0
A high-strength thin steel sheet excellent in hydrogen embrittlement resistance, characterized by having a distribution form satisfying the above and a tensile strength of 980 MPa or more.
Ｗ ：０．００５〜５％
を含有することを特徴とする請求項１に記載の耐水素脆化に優れた高強度薄鋼板。 Furthermore, in steel,
W: 0.005 to 5%
The high-strength thin steel sheet excellent in hydrogen embrittlement resistance according to claim 1, comprising:
Ｃｕ：０．００５〜５％、
Ｎｉ：０．００５〜５％
の１種または２種を含有することを特徴とする請求項１または２に記載の耐水素脆化に優れた高強度薄鋼板。 Furthermore, in steel,
Cu: 0.005 to 5%,
Ni: 0.005 to 5%
The high-strength thin steel sheet excellent in hydrogen embrittlement resistance according to claim 1 or 2, characterized by containing one or two of the following.
Ｂ ：０．０００２〜０．１％
を含有することを特徴とする請求項１〜３の何れか１項に記載の耐水素脆化に優れた高強度薄鋼板。 Furthermore, in steel,
B: 0.0002 to 0.1%
The high-strength thin steel sheet excellent in hydrogen embrittlement resistance according to any one of claims 1 to 3.
ＲＥＭ：０．０００５〜０．０１％、
Ｙ ：０．０００５〜０．０１％、
Ｃａ：０．０００５〜０．０１％、
Ｍｇ：０．０００５〜０．０１％
の１種または２種以上を含有することを特徴とする請求項１〜４の何れか１項に記載の耐水素脆化に優れた高強度薄鋼板。 Furthermore, in steel,
REM: 0.0005 to 0.01%,
Y: 0.0005 to 0.01%
Ca: 0.0005 to 0.01%,
Mg: 0.0005 to 0.01%
The high-strength thin steel sheet excellent in hydrogen embrittlement resistance according to any one of claims 1 to 4, characterized by containing one or more of the following.
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| JPH101740A (en) * | 1996-06-12 | 1998-01-06 | Kobe Steel Ltd | Ultrahigh strength steel sheet excellent in delayed fracture resistance, and its production |
| JP3890748B2 (en) * | 1998-06-19 | 2007-03-07 | Ｊｆｅスチール株式会社 | High strength steel plate with excellent stretch flangeability and delayed fracture resistance |
| JP2000080440A (en) * | 1998-08-31 | 2000-03-21 | Kawasaki Steel Corp | High strength cold rolled steel sheet and its manufacture |
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| CN111527224A (en) * | 2017-12-27 | 2020-08-11 | 杰富意钢铁株式会社 | High-strength steel sheet and method for producing same |
| CN111527224B (en) * | 2017-12-27 | 2021-11-05 | 杰富意钢铁株式会社 | High-strength steel sheet and method for producing same |
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