JP2003096543A - High strength steel sheet having high baking hardenability on application of high prestrain, and production method therefor - Google Patents
High strength steel sheet having high baking hardenability on application of high prestrain, and production method thereforInfo
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- JP2003096543A JP2003096543A JP2001292147A JP2001292147A JP2003096543A JP 2003096543 A JP2003096543 A JP 2003096543A JP 2001292147 A JP2001292147 A JP 2001292147A JP 2001292147 A JP2001292147 A JP 2001292147A JP 2003096543 A JP2003096543 A JP 2003096543A
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- steel sheet
- strength
- sol
- strength steel
- strain
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、建材、家電製品、
自動車などに適する高予歪み時において高い焼付け硬化
能を持つ高強度鋼板及びその製造方法に関する。TECHNICAL FIELD The present invention relates to building materials, home electric appliances,
The present invention relates to a high-strength steel sheet having a high bake hardenability suitable for automobiles and the like at high pre-strain and a method for manufacturing the same.
【０００２】[0002]
【従来の技術】地球温暖化に対する問題意識の高まりか
ら、自動車の燃費向上のため、車体軽量化のニーズが高
まっている。この自動車の軽量化ニーズに伴い、構成材
料である鋼板を高強度化することが望まれる。これは高
強度化による板厚減少で、車体軽量化および衝突時の安
全性向上が可能となるためである。このような背景か
ら、最近では、複雑な形状の部位についても、高強度鋼
板の適用が検討されるようになった。一方、鋼板の高強
度化は加工性の劣化を伴う。これを補足するために、例
えばハイドロフォームなどの新しい加工法の適用や高強
度鋼板自体の加工性向上が検討されている。2. Description of the Related Art Due to the growing awareness of global warming issues, there is an increasing need for weight reduction of automobile bodies in order to improve fuel efficiency of automobiles. With the needs for weight reduction of automobiles, it is desired to increase the strength of the steel sheet that is a constituent material. This is because the plate thickness is reduced by increasing the strength, which makes it possible to reduce the weight of the vehicle body and improve the safety in the event of a collision. Against such a background, recently, application of high-strength steel sheets has come to be considered even for parts having complicated shapes. On the other hand, increasing the strength of a steel sheet is accompanied by deterioration of workability. In order to supplement this, application of new processing methods such as hydroforming and improvement of the workability of the high-strength steel sheet itself are being studied.
【０００３】ところで、自動車の外板には焼付硬化型の
軟鋼が多く適用されてきた。成形時は柔らかく高加工可
能で、成形後には焼付け塗装を行う際に成形時に導入さ
れた転位を固溶炭素および窒素で固着することで硬化さ
せる手法である。この手法は、外板に多く適用されてい
ることから３９０ＭＰａ級以下の鋼板に関して、非時効
性との両立を目指した研究開発がほとんどであった。ま
た焼付硬化現象に関しては数％の予歪みを付加して、１
７０℃で数十分の焼き付け塗装を行うのが一般的で、そ
の硬化量も降伏強度で３０ＭＰａ程度であることが多
い。By the way, bake hardening type mild steel has been often applied to outer panels of automobiles. It is a method that is soft and highly workable during molding, and after the molding, the dislocations introduced during molding during baking coating are fixed by solid solution carbon and nitrogen to harden. Since most of this method is applied to the outer plate, most of the research and development aimed at achieving compatibility with non-aging property regarding the steel plate of 390 MPa class or less. Regarding the bake hardening phenomenon, add a few percent of pre-strain and
It is common to perform baking coating for several tens of minutes at 70 ° C., and the curing amount is often about 30 MPa in yield strength.
【０００４】構造用や高強度化による板厚減少を狙うに
は、充分な硬化量とは言えない。また、降伏強度の上昇
に加えて引張強度の上昇も必要になってくる。さらに、
加工度の高い複雑形状部位に関しては、数％の予歪みで
は不足で１０％前後を越える予歪みを付加したときの降
伏強度および引張強度の上昇を達成する必要がある。The curing amount cannot be said to be sufficient for structural purposes and for the purpose of reducing the plate thickness by increasing the strength. In addition to the increase in yield strength, it is also necessary to increase the tensile strength. further,
With respect to a complex-shaped portion having a high degree of workability, it is necessary to achieve an increase in yield strength and tensile strength when a prestrain of about 10% is added because a prestrain of several% is insufficient.
【０００５】高強度材の歪時効についての研究例もいく
つかある。例えば、Formable HSLAand Dual-Phase Stee
ls, ed.A.T.Davenport, The Metallurgical Soc. AIME
(1977), p.315-330には、複相鋼板：０．１Ｃ−１．４
Ｍｎ−０．４９Ｓｉ−０．０７５Ｖ−０．０６Ａｌの歪
時効の研究例が示されている。これによれば、予歪が大
きくなるほど降伏強度の上昇量が小さいことや、時効温
度として１００，１７７および２６０℃を選び、２６０
℃の場合が最も硬化代が大きいこと、５％の予歪付加で
１７７℃の１０００秒までの時効では、降伏強度で４０
ＭＰａ、引張強度で３５ＭＰａであることなどが示され
ている。さらに、時効温度や時効時間が高温長時間にな
ると炭化物析出で硬化量が増すことも示唆されている。There are some examples of studies on strain aging of high strength materials. For example, Formable HSLAand Dual-Phase Stee
ls, ed.AT Davenport, The Metallurgical Soc. AIME
(1977), p.315-330, dual phase steel sheet: 0.1C-1.4.
A study example of strain aging of Mn-0.49Si-0.075V-0.06Al is shown. According to this, the larger the prestrain, the smaller the increase in yield strength, and that the aging temperature is 100, 177 and 260 ° C.
The hardening margin is the highest at ℃, and the yield strength is 40 when aging at 177 ℃ for 1000 seconds with 5% prestrain.
It is shown that MPa and the tensile strength are 35 MPa. Further, it has been suggested that when the aging temperature and the aging time increase at high temperature for a long time, the amount of hardening increases due to the precipitation of carbides.
【０００６】硬化量を大きくするには、時効温度を２６
０℃と高くしたり、１７７℃で時効処理すると１０００
０秒と長い時間が必要となる。一方では、焼付け処理温
度の低温・短時間化が指向されており、前述の文献のよ
うな高温や長時間焼付け処理による高焼付け硬化能は現
実的とはいえない。To increase the amount of hardening, the aging temperature should be 26
1000 when raised to 0 ℃ or aged at 177 ℃
A long time of 0 seconds is required. On the other hand, it is aimed to reduce the baking temperature to a low temperature and to a short time, and it cannot be said that the high bake hardening ability by the high temperature or long time baking treatment as in the above-mentioned literature is practical.
【０００７】さらに、ハイテン系の材料では、予歪量が
ある程度以上になると焼き付け硬化量が低化すると言う
報告も有る（Structure and Properties of Dual-phase
Steels, ed. By Kot and J.W.Morris, AIME, 1979, p.
211 ）。また近年、衝突安全性に関する問題意識が高ま
り、高い歪量付加における焼き付け硬化現象は、衝突時
のような高速変形に対する吸収エネルギが大きいことが
報告されており、高い予歪量における焼き付け硬化量の
増加は衝突安全性の向上に関しても有利である。Further, it has been reported that in the case of high-tensile materials, the amount of bake hardening decreases when the amount of prestrain exceeds a certain level (Structure and Properties of Dual-phase).
Steels, ed.By Kot and JW Morris, AIME, 1979, p.
211). Also, in recent years, awareness of the problem regarding collision safety has increased, and it has been reported that the bake hardening phenomenon with a high strain amount added has a large absorbed energy for high-speed deformation such as at the time of a collision. The increase is also advantageous for improving collision safety.
【０００８】以上のように、従来技術には、複雑形状の
成形や衝突安全向上に対応した高い予歪を意識した高強
度材の高い焼付け硬化能を出現させる技術はない。[0008] As described above, there is no technique in the prior art that brings out a high bake hardenability of a high-strength material in consideration of high pre-strain corresponding to molding of a complicated shape and improvement of collision safety.
【０００９】[0009]
【発明が解決しようとする課題】本発明は、上記課題を
解決し、高予歪み時において高い焼付け硬化能を持つ高
強度鋼板及びその製造方法を提供することを目的とす
る。SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a high strength steel sheet having a high bake hardenability at a high prestrain and a method for producing the same.
【００１０】[0010]
【課題を解決するための手段】本発明者らは、種々検討
を行った結果、基本的には予加工前の固溶炭素および固
溶窒素の確保が重要であるが、その両者のバランスを制
御することで、高い予加工を加えたときにも降伏強度の
みならず引張強度の上昇をも出現させ得る技術を見出す
に至った。As a result of various investigations, the inventors of the present invention have found that it is basically important to secure solid solution carbon and solid solution nitrogen before pre-processing, but the balance between them is to be secured. By controlling it, we have found a technique that can increase not only the yield strength but also the tensile strength even when high pre-processing is applied.
【００１１】降伏強度の上昇については、従来から言わ
れているように固溶炭素や固溶窒素のいずれか単独でも
それらの量を確保することで達成できる。すなわち、予
加工により導入された転位が、焼付け処理により固溶炭
素および／または固溶窒素に固着されるコットレル雰囲
気を形成することに起因している。しかしこの場合に
は、予加工により導入される転位が過多だと硬化量が低
下したり、引張強度の上昇については降伏強度の上昇に
比べ強化量が小さかったりする。The increase in yield strength can be achieved by securing the amount of either solid solution carbon or solid solution nitrogen alone, as has been conventionally said. That is, the dislocations introduced by the pre-processing form the Cottrell atmosphere which is fixed to the solid solution carbon and / or the solid solution nitrogen by the baking treatment. However, in this case, if the amount of dislocations introduced by pre-working is excessive, the amount of hardening will decrease, or the increase in tensile strength will be smaller than the increase in yield strength.
【００１２】そこで、固溶炭素および固溶窒素をある比
率で残存させると、特に高い予歪を与えた場合に降伏強
度および引張強度の双方を上昇させることができること
を見出した。この機構については明確ではないが、前述
した転位と侵入型固溶元素のコットレル雰囲気の形成に
加えて、予加工時に導入された転位上に析出する微細炭
化物および／または窒化物による析出強化または、予加
工により導入された転位近傍に形成される炭素および／
または窒素のクラスター形成による硬化を加えること
で、高い予歪付加において降伏強度および引張強度の上
昇が出現させられるものと考えられる。Therefore, it has been found that when the solid solution carbon and the solid solution nitrogen are left in a certain ratio, both the yield strength and the tensile strength can be increased particularly when a high prestrain is applied. Although this mechanism is not clear, in addition to the formation of the Cottrell atmosphere of dislocations and interstitial solid solution elements described above, precipitation strengthening by fine carbides and / or nitrides precipitated on dislocations introduced during pre-processing, or Carbon and // formed near the dislocations introduced by pre-processing
Alternatively, it is considered that the yield strength and the tensile strength are increased in the high pre-strain addition by adding the hardening by the nitrogen cluster formation.
【００１３】ここで言う、炭化物および窒化物とは一般
的に安定相ではなく準安定な析出相で、たとえばＦｅ16
（Ｃ，Ｎ）2 の微細析出物であることを見出した。これ
は、転位密度が比較的高いことに加えて固溶炭素と固溶
窒素がある比率で存在した場合にのみ析出相生成成長の
駆動力が高まることで、１７０℃付近という低温度かつ
比較的短時間でも強化に効果的な分布や状態で析出また
はクラスター形成が生じると考えられる。The carbides and nitrides referred to here are generally not stable phases but metastable precipitation phases such as Fe 16
It was found to be a fine precipitate of (C, N) 2 . This is because, in addition to the relatively high dislocation density, the driving force for precipitation phase formation growth increases only when solid solution carbon and solid solution nitrogen are present in a ratio, so that the temperature is relatively low at around 170 ° C. and relatively high. It is considered that precipitation or cluster formation occurs in a distribution and state effective for strengthening even in a short time.
【００１４】本発明は、上記知見に基づいて完成された
もので、その要旨とするところは以下の通りである。
（１） 鋼板が、質量％で、
Ｃ ：０．０００５〜０．３％、 Ｓｉ：０．００１〜３.0％、
Ｍｎ：０．０１〜３．０％、 Ａｌ：０．０００１〜０．０５％
Ｐ ：０．００１ 〜０．３％ Ｓ ：０．０００１〜０．１ ％
Ｎ ：０．００１０〜０．０５％
を含有し、残部Ｆｅ及び不可避不純物からなり、フェラ
イトを面積率最大の相とし、固溶炭素：Sol.Ｃ及び固溶
窒素：Sol.ＮがSol.Ｃ／Sol.Ｎ：０．１〜１００を満た
し、予歪みを５〜２０％付加したとき、１１０〜２００
℃で１〜６０分の焼付け処理後の降伏強度および引張強
度の上昇量の平均またはそれぞれの値が、予歪みを付加
しない焼付け処理前の鋼板に比べ５０ＭＰａ以上である
ことを特徴とする高予歪み時において高い焼付け硬化能
を持つ高強度鋼板。
（２） 鋼板が、質量％でさらに、Ｖ，Ｔｉ，Ｎｂ，Ｚ
ｒ，Ｈｆ，Ｔａのいずれか１種又は２種以上を０．００
１〜１％含有することを特徴とする前項（１）に記載の
高予歪み時において高い焼付け硬化能を持つ高強度鋼
板。
（３） 鋼板が、質量％でさらに、Ｃｒ，Ｍｏ，Ｗのい
ずれか１種又は２種を０．００１〜５％含有することを
特徴とする前記（１）又は（２）記載の高予歪み時にお
いて高い焼付け硬化能を持つ高強度鋼板。
（４） 鋼板が、質量％でさらに、
Ｎｉ：０．００１〜１０％、 Ｃｕ：０．００１〜５％、
Ｃｏ：０．００１〜５％
の１種又は２種以上を含有することを特徴とする前記
（１）〜（３）の何れか１項に記載の高予歪み時におい
て高い焼付け硬化能を持つ高強度鋼板。
（５） 鋼板が、質量％でさらに、Ｂ：０．０００１〜
０．１％を含有することを特徴とする前記（１）〜
（４）の何れか１項に記載の高予歪み時において高い焼
付け硬化能を持つ高強度鋼板。
（６） 予歪みを５％付加したとき、フェライト中に存
在する円相当径１〜１００ｎｍの転位上の析出物密度が
２個／μｍ2 以下で、その後の１１０〜２００℃で１〜
６０分の焼付け処理後には円相当径１〜１００ｎｍの析
出物密度が５〜１０００個／μｍ2 であることを特徴と
する前記（１）〜（５）の何れか１項に記載の高予歪み
時において高い焼付け硬化能を持つ高強度鋼板。The present invention has been completed based on the above findings, and the gist thereof is as follows. (1) Steel plate, in mass%, C: 0.0005 to 0.3%, Si: 0.001 to 3.0%, Mn: 0.01 to 3.0%, Al: 0.0001 to 0 0.05% P: 0.001 to 0.3% S: 0.0001 to 0.1% N: 0.0010 to 0.05%, with the balance being Fe and unavoidable impurities, and having a maximum area ratio of ferrite. When solid solution carbon: Sol. C and solid solution nitrogen: Sol. N satisfy Sol. C / Sol. N: 0.1 to 100 and a prestrain of 5 to 20% is added, 110 to 200
The high or low average value of the amount of increase in yield strength and tensile strength after baking treatment at 1 ° C for 1 to 60 minutes is 50 MPa or more as compared with the steel sheet before baking treatment without adding prestrain. A high-strength steel plate that has a high bake hardenability during distortion. (2) The steel plate further contains V, Ti, Nb, Z in mass%.
Any one or more of r, Hf, and Ta is 0.00
The high-strength steel sheet having a high bake hardenability at the time of high pre-strain as described in (1) above, which is contained in an amount of 1 to 1%. (3) The steel plate contains 0.001 to 5% by mass of any one or two of Cr, Mo, and W, and further has a high probability of (1) or (2). A high-strength steel plate that has a high bake hardenability during distortion. (4) The steel sheet is characterized by further containing, by mass%, one or more of Ni: 0.001 to 10%, Cu: 0.001 to 5%, Co: 0.001 to 5%. A high-strength steel sheet having a high bake hardenability at the time of high pre-strain according to any one of (1) to (3) above. (5) The steel sheet further contains B: 0.0001% by mass.
0.1% is contained, and the above (1) to
A high-strength steel sheet having a high bake hardenability at the time of high pre-strain according to any one of (4). (6) When a prestrain of 5% is added, the density of precipitates on dislocations having a circle-equivalent diameter of 1 to 100 nm present in ferrite is 2 / μm 2 or less, and thereafter at 110 to 200 ° C., 1 to
After the baking treatment for 60 minutes, the density of precipitates having an equivalent circle diameter of 1 to 100 nm is 5 to 1000 pieces / μm 2, which is high in the above (1) to (5). A high-strength steel plate that has a high bake hardenability during distortion.
【００１５】（７） 前記（１）〜（６）の何れか１項
に記載の高強度鋼板を製造する方法であって、（１）〜
（６）の何れか１項に記載の成分からなる鋳造スラブを
鋳造まま又は一旦冷却した後に再度１１５０〜１２５０
℃に加熱し、熱延の最終スタンドでの圧下量を５〜２０
％とし、熱延の仕上げ温度を８５０〜１１００℃とし
て、その後３０〜１００℃/sで冷却し４００℃以下で巻
取ることを特徴とする高予歪み時において高い焼付け硬
化能を持つ高強度熱延鋼板の製造方法。
（８） 前記（１）〜（６）の何れか１項に記載の高強
度鋼板を製造する方法であって、（１）〜（６）の何れ
か１項に記載の成分からなる鋳造スラブを鋳造まま又は
一旦冷却した後に再度１１５０〜１２５０℃に加熱し、
熱延の仕上げ温度を８３０〜１１００℃として巻き取
り、その熱延鋼板を酸洗、冷延し、その後（Ａｃ1 −１
００）〜（Ａｃ3 ＋５０）℃で３０秒〜１０００分間焼
鈍した後に、３〜１００℃／秒で４５０℃以下に冷却す
ることを特徴とする高予歪み時において高い焼付け硬化
能を持つ高強度鋼板の製造方法。(7) A method for producing the high-strength steel sheet according to any one of (1) to (6), which comprises:
The cast slab composed of the component according to any one of the items (6) is again cooled to 1150 to 1250 in the as-cast state or once cooled.
Heat to ℃ and reduce the rolling amount at the final stand of hot rolling by 5 to 20
%, The finishing temperature for hot rolling is 850 to 1100 ° C., and then the film is cooled at 30 to 100 ° C./s and wound up at 400 ° C. or less. Manufacturing method of rolled steel sheet. (8) A method for producing the high-strength steel sheet according to any one of (1) to (6), the casting slab including the component according to any one of (1) to (6). As-cast or once cooled and then heated again to 1150 to 1250 ° C.,
The hot rolling finish temperature was set to 830 to 1100 ° C., the hot rolled steel sheet was pickled, cold rolled, and then (Ac 1 −1
00) to (Ac 3 +50) ° C. for 30 seconds to 1000 minutes, and then cooled to 450 ° C. or less at 3 to 100 ° C./second. High strength with high bake hardenability at high pre-strain. Steel plate manufacturing method.
【００１６】[0016]
【発明の実施の形態】以下、本発明を詳細に説明する。
本発明者らは、質量％で、Ｃ：０．０００５〜０．３
％、Ｓｉ：０．０１〜３．０％、Ｍｎ：０．０１〜３．
０％、Ａｌ：０．０００１〜０．０５％、Ｐ：０．００
１〜０．３％、Ｓ：０．０００１〜０．１％、Ｎ：０．
００１０〜０．０５％を含有し、必要に応じＶ，Ｔｉ，
Ｎｂ，Ｚｒ，Ｈｆ，Ｔａのいずれか１種又は２種以上を
０．００１〜１％、Ｃｒ，Ｍｏ，Ｗのいずれか１種又は
２種以上を０．００１〜５％、Ｎｉ：０．００１〜１０
％、Ｃｕ：０．００１〜５％、Ｃｏ：０．００１〜５％
の１種又は２種以上、Ｂ：０．０００１〜０．１％を含
有し、残部Ｆｅ及び不可避不純物からなる鋼を溶製し
て、熱延〜冷延〜焼鈍（一部は熱延のみ）を施して、フ
ェライトを面積率最大の相とする薄鋼板を作製した。そ
の後、圧延方向に平行または垂直方向に予歪を１〜２０
％加えたのち焼付け処理を行い、降伏強度および引張強
度の上昇を引張試験にて行った。BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The present inventors, in mass%, have C: 0.0005 to 0.3.
%, Si: 0.01 to 3.0%, Mn: 0.01 to 3.
0%, Al: 0.0001 to 0.05%, P: 0.00
1 to 0.3%, S: 0.0001 to 0.1%, N: 0.
0010 to 0.05%, and if necessary V, Ti,
Any one or two or more of Nb, Zr, Hf and Ta is 0.001 to 1%, any one or two or more of Cr, Mo and W is 0.001 to 5%, Ni: 0. 001-10
%, Cu: 0.001-5%, Co: 0.001-5%
1 or 2 or more, B: 0.0001 to 0.1% is contained, and the steel consisting of the balance Fe and unavoidable impurities is melted and hot-rolled-cold-annealed (some are hot-rolled only). ) Was carried out to produce a thin steel sheet containing ferrite as a phase having a maximum area ratio. Then, the pre-strain is 1 to 20 in the direction parallel or perpendicular to the rolling direction.
%, And then subjected to a baking treatment to increase yield strength and tensile strength in a tensile test.
【００１７】その結果、固溶炭素：Sol.Ｃおよび固溶窒
素：Sol.ＮがSol.Ｃ／Sol.Ｎ：０．１〜１００を満たす
共存状態にあることで予歪みを５〜２０％付加後、１１
０〜２００℃で１〜６０分の焼付け処理後の、降伏強度
および引張強度の上昇量の平均またはそれぞれの値が、
予歪み付与と焼付け処理前の鋼板に比べ５０ＭＰａ以上
となることを見出した。As a result, solid solution carbon: Sol. C and solid solution nitrogen: Sol. N are in a coexisting state satisfying Sol. C / Sol. N: 0.1 to 100, so that the pre-strain is 5 to 20%. After adding, 11
After baking treatment at 0 to 200 ° C. for 1 to 60 minutes, the average or the respective values of the increase in yield strength and tensile strength are
It was found that the pre-strain was 50 MPa or more as compared with the steel sheet before the baking treatment.
【００１８】ここで、Sol.ＣおよびSol.Ｎは内部摩擦法
で求められるＱ-1から算出される。その値として、Sol.
Ｃ：０．０００１〜０．０１００、Sol.Ｎ：０．０００
１〜０．０２００の範囲で共存する事が望ましい。ま
た、Sol.Ｃ／Sol.ＮはおのおののSol.ＣおよびSol.Ｎの
値を算出せず、得られるピーク高さの比として求められ
る。ここで言うピーク高さとは、例えば２℃／min.で昇
温により振動数１〜２Ｈｚにて、幅：５ｍｍ、長さ：１
１５ｍ、板厚：２ｍｍの試験片を用いた標準的な内部摩
擦測定試験を行ったとき、窒素については０〜４０℃で
の極大値と炭素については４０〜５５℃での極大値をと
り、その比を持って、本発明で言うSol.Ｃ／Sol.Ｎの値
とする。Here, Sol.C and Sol.N are calculated from Q -1 obtained by the internal friction method. As its value, Sol.
C: 0.0001 to 0.0100, Sol.N: 0.000
Coexistence in the range of 1 to 0.0200 is desirable. Moreover, Sol.C / Sol.N is calculated as the ratio of the obtained peak heights without calculating the respective Sol.C and Sol.N values. The peak height referred to here is, for example, at a frequency of 1 to 2 Hz due to a temperature rise of 2 ° C./min., Width: 5 mm, length: 1
When a standard internal friction measurement test using a test piece of 15 m and a plate thickness of 2 mm was performed, a maximum value at 0 to 40 ° C. for nitrogen and a maximum value at 40 to 55 ° C. for carbon were obtained, The ratio is used as the value of Sol.C / Sol.N in the present invention.
【００１９】また、固溶量が小さく極大値が不明確な場
合、すなわちブロードな曲線として測定結果を得ること
もある。この場合には、固溶窒素および固溶炭素に関し
ておのおのについて正規分布があるとしてブロードな曲
線を２つの正規分布曲線としてとらえて、それぞれの正
規分布曲線の最大値の比を、ここで言うSol.Ｃ／Sol.Ｎ
の値とする。また、これに加えて、Sol.ＣおよびSol.Ｎ
はＡＰ−ＦＩＭ（Atom-Prob Fieldemmision Ion Micros
cope）を用いても統計的に信頼しうる測定回数もしくは
測定面積を確保すれば求められるものとする。In addition, when the amount of solid solution is small and the maximum value is unclear, that is, the measurement result may be obtained as a broad curve. In this case, it is assumed that there are two normal distribution curves for solid solution nitrogen and solid solution carbon, respectively, and the broad curves are regarded as two normal distribution curves, and the ratio of the maximum values of the respective normal distribution curves is referred to as Sol. C / Sol.N
Value of. In addition to this, Sol.C and Sol.N
Is AP-FIM (Atom-Prob Fieldemmision Ion Micros
Even if the measure) is used, it is required if the number of measurements or the measurement area that is statistically reliable is secured.
【００２０】また、焼き付け硬化量については、予歪み
を付加した段階でのＦｌｏｗ Ｓｒｅｓｓを基準にし
て、焼き付け処理後の下降伏点または耐力がどの程度で
上昇したかを測定する事とする。また、引張強度上昇に
ついては焼き付け処理の有無での引張強度の比較から得
る値とする。With respect to the amount of bake hardening, the flow yield at the stage when prestrain is added is used as a reference to measure the degree to which the yield point or the proof stress after the bake process has risen. The increase in tensile strength is a value obtained by comparing the tensile strengths with and without baking.
【００２１】次に、本発明における鋼板成分の限定理由
について述べる。
Ｃ：Ｃは、焼付け硬化能を制御する上でＮ同様最も重要
な元素である。一方過剰添加は時効性や延性の低下を招
くため、鋼中成分として、０．０００５〜０．３％とし
た。Next, the reasons for limiting the components of the steel sheet in the present invention will be described. C: C is the most important element like N in controlling the bake hardenability. On the other hand, excessive addition causes deterioration of aging and ductility, so the content in the steel was made 0.0005 to 0.3%.
【００２２】Ｓｉ：Ｓｉは、主相であるフェライト生成
を促進させ、強度延性バランスを改善させる。さらに
は、焼付け処理における準安定相の析出制御にも必要な
元素であり、その下限を０．００１％とした。また、過
剰添加は溶接性およびめっき濡れ性に悪影響を及ぼすた
め、上限を３．０％ととした。Si: Si promotes the formation of ferrite, which is the main phase, and improves the strength-ductility balance. Further, it is an element necessary for controlling the precipitation of the metastable phase in the baking treatment, and its lower limit was made 0.001%. Further, excessive addition adversely affects weldability and plating wettability, so the upper limit was made 3.0%.
【００２３】Ｍｎ：高強度化とＮの固溶量増加の目的で
添加する。また、マルテンサイトやオーステナイトなど
の第２相を含む場合には、強度低下と延性劣化の１つの
原因である炭化物析出やパーライト生成を抑制する目的
で添加する。これらのことから、０．０１％以上とし
た。一方、加過剰添加は延性低下、めっき性や溶接性を
劣化させることから３％を上限とした。Mn: It is added for the purpose of enhancing the strength and increasing the solid solution amount of N. When a second phase such as martensite or austenite is included, it is added for the purpose of suppressing the precipitation of carbide and the formation of pearlite, which are one of the causes of strength reduction and ductility deterioration. From these things, it was 0.01% or more. On the other hand, excessive addition causes deterioration of ductility and deterioration of plating properties and weldability, so the upper limit was made 3%.
【００２４】Ａｌ：脱酸の目的で添加する。また、固溶
窒素量の制御するためにも必要であり、０．０００１％
以上とした。一方、過剰添加はめっき性や固溶窒素量確
保の点から望ましくないため、０．０５％以下とした。
さらに、固溶窒素確保の観点からすると、Ａｌ／２８＜
Ｎ／１４を満たすことが望ましい。Al: added for the purpose of deoxidation. It is also necessary to control the amount of dissolved nitrogen, and 0.0001%
That's it. On the other hand, excessive addition is not desirable from the viewpoint of plating properties and securing the amount of solute nitrogen, so the content was made 0.05% or less.
Further, from the viewpoint of securing solid solution nitrogen, Al / 28 <
It is desirable to satisfy N / 14.
【００２５】Ｐ：Ｐの少量添加は強度延性バランスの向
上に有効であり、粒内の炭化物および窒化物の形態制御
にも有効なため０．００１％以上とした。一方、過剰添
加は粒界偏析に起因した製造性や溶接性の劣化を招くた
め０．３％以下とした。The addition of P: P in a small amount is effective in improving the strength-ductility balance, and is also effective in controlling the morphology of carbides and nitrides in the grains, so the content was made 0.001% or more. On the other hand, excessive addition causes deterioration of manufacturability and weldability due to grain boundary segregation, so the content was made 0.3% or less.
【００２６】Ｓ：Ｓは極力低下させたほうが材質が良好
であるが、極低Ｓ化は製造コストを上昇させるため０．
０００１％以上が経済性の面で望ましいと言える。一
方、Ｓ添加は製造性や溶接性の劣化を招くため０．１０
％以下とした。S: It is preferable to reduce S as much as possible in terms of material, but extremely low S causes increase in manufacturing cost, so that
It can be said that 0001% or more is desirable in terms of economy. On the other hand, addition of S causes deterioration of manufacturability and weldability, so 0.10 is added.
% Or less.
【００２７】Ｎ：Ｎは、焼付け硬化能を制御する上でＣ
同様最も重要な元素である。一方過剰添加は時効性や延
性の低下を招くため、鋼中成分として、０．００１０〜
０．０５％とした。さらに、固溶窒素確保の観点からす
ると、Ａｌ／２８＜Ｎ／１４を満たすことが望ましい。N: N is C for controlling the bake hardenability.
It is also the most important element. On the other hand, excessive addition causes deterioration of aging property and ductility, so 0.0010
It was set to 0.05%. Further, from the viewpoint of securing solid solution nitrogen, it is desirable to satisfy Al / 28 <N / 14.
【００２８】Ｖ，Ｔｉ，Ｎｂ，Ｚｒ，Ｈｆ，Ｔａ：炭化
物および窒化物形成による強化元素である。いずれか１
種又は２種以上を合計で０．００１％以上必要に応じて
添加するものとした。また、過剰添加は焼付け硬化能を
高める固溶炭素および固溶窒素を低減させるため１％を
上限とした。V, Ti, Nb, Zr, Hf, Ta: Reinforcing elements by forming carbides and nitrides. Either one
One kind or two or more kinds are added in total of 0.001% or more as needed. Further, excessive addition reduces the amount of solid solution carbon and solid solution nitrogen that enhance the bake hardenability, so the upper limit was 1%.
【００２９】Ｃｒ，Ｍｏ，Ｗ：主に固溶強化元素とし
て、いずれか１種又は２種を合計で０．００１％以上含
有しても良いこととした。また、多量添加では炭窒化物
形成による強化も期待できる半面、延性劣化が著しいた
め上限を５％とした。Cr, Mo, W: Mainly, as a solid solution strengthening element, any one or two kinds may be contained in a total amount of 0.001% or more. In addition, when a large amount is added, strengthening due to carbonitride formation can be expected, but ductility is significantly deteriorated, so the upper limit was made 5%.
【００３０】Ｎｉ、Ｃｕ、Ｃｏ：強化元素であるが、過
剰添加は延性劣化を招くため、Ｎｉ：０．００１〜１０
％、Ｃｕ：０．００１〜５％、Ｃｏ：０．００１〜５％
の１種または２種以上を必要に応じて含有して良いこと
とする。Ni, Cu, Co: Reinforcing elements, but excessive addition causes deterioration of ductility, so Ni: 0.001-10
%, Cu: 0.001-5%, Co: 0.001-5%
1 type or 2 types or more of these may be contained as needed.
【００３１】Ｂ：焼入れ性向上や２次加工脆化防止に効
果的である。一方で固溶窒素確保の点からは過剰添加は
望ましくない。このため、０．０００１〜０．１％を必
要に応じて含有することとした。また、固溶窒素確保の
点からＢ／１０＜Ｎ／１４を満たすことが望ましい。B: Effective in improving hardenability and preventing secondary work embrittlement. On the other hand, excessive addition is not desirable from the viewpoint of securing solid solution nitrogen. Therefore, it was decided to contain 0.0001 to 0.1% as necessary. Further, it is desirable that B / 10 <N / 14 is satisfied from the viewpoint of securing solid solution nitrogen.
【００３２】また、不可避的不純物としてＳｎなどがあ
るが、これら元素をＳｎ≦０．０１％以下の範囲で含有
しても本発明の効果を損なうものではない。Although unavoidable impurities include Sn, inclusion of these elements in the range of Sn ≦ 0.01% or less does not impair the effects of the present invention.
【００３３】組織：本発明は良好な強度延性バランスを
確保するために面積率最大の相をフェライトとする。そ
の他の組織として、マルテンサイト、残留オーステナイ
トおよびベイナイトの１種又は２種以上を含んでも良
い。尚、本発明において面積率は、板厚の１／８から７
／８の位置を光学顕微鏡にて５００〜１０００倍にて２
０〜１００視野観察し、切断法や画像解析により求めた
値と定義する。Structure: In the present invention, the phase has the maximum area ratio of ferrite in order to secure a good balance of strength and ductility. As the other structure, one or more of martensite, retained austenite and bainite may be contained. In the present invention, the area ratio is 1/8 to 7 of the plate thickness.
/ 8 position with optical microscope at 500 to 1000 times 2
It is defined as a value obtained by observing from 0 to 100 visual fields and by a cutting method or image analysis.
【００３４】Sol.Ｃ／Sol.Ｎ：固溶炭素および固溶窒素
の共存により、高加工時に高い焼き付け硬化性を降伏応
力および引張強度の双方について得られるもので、最も
重要な値であることから０．１以上とした。高い焼き付
け硬化能を得るためには固溶炭素および固溶窒素との共
存に加えて、ある程度以上の転位密度の共存が不可欠で
ある。予歪として５％付加後焼付け処理として１７０℃
で２０分として、予歪と焼付け処理前の鋼板に比べ降伏
強度および引張強度の上昇代の平均またはそれぞれの値
を５０ＭＰａ以上好ましくは６０ＭＰａ以上向上させる
ことができる。これは、前述したように、コットレル雰
囲気の形成に加えて、準安定な析出物および／またはク
ラスタ−形成による硬化を出現させることが重要で、そ
のためには転位密度の増加および固溶炭素および固溶窒
素のある関係（Sol.Ｃ／Sol.Ｎ：０．１〜１００）を満
たしながらの共存が特に必要である。一方、この値が１
００を超えると共存効果が失われてしまい、降伏強度は
上昇するも引張強度が上昇しないといった現象が生じ始
めるため、これを上限とした。Sol.C / Sol.N: A coexistence of solid solution carbon and solid solution nitrogen gives high bake hardenability for both yield stress and tensile strength at the time of high working, and is the most important value. To 0.1 or more. In order to obtain a high bake hardenability, in addition to coexistence with solid solution carbon and solid solution nitrogen, coexistence of dislocation density above a certain level is indispensable. Add 5% as pre-strain and 170 ° C as baking process
20 minutes, it is possible to improve the average of the increase margin of the yield strength and the tensile strength or their respective values by 50 MPa or more, preferably 60 MPa or more, as compared with the pre-strained and steel sheet before baking treatment. As described above, it is important that, in addition to the formation of the Cottrell atmosphere, the appearance of metastable precipitates and / or hardening due to cluster-formation is necessary for this purpose. Coexistence while satisfying a certain relationship of molten nitrogen (Sol. C / Sol. N: 0.1 to 100) is particularly necessary. On the other hand, this value is 1
When it exceeds 00, the coexistence effect is lost, and a phenomenon in which the yield strength increases but the tensile strength does not increase begins to occur, so this was made the upper limit.
【００３５】尚、Sol.Ｃは焼付け硬化能を向上させるの
に０．０００１％以上含有することが好ましい。また、
過剰添加は時効性や延性を劣化させることから０．０１
００％以下とすることが好ましい。Sol.Ｎについても焼
付け硬化能を飛躍的に向上させるので０．０００１％以
上含有することが好ましい。また、過剰添加は時効性や
延性を劣化させることから０．０２００％以下とするこ
とが好ましい。また、特に、準安定な窒化物の形成は、
高予歪における引張強度に関する焼付け硬化能向上には
大きな寄与がある。Sol. C is preferably contained in an amount of 0.0001% or more in order to improve the bake hardenability. Also,
Excessive addition deteriorates aging and ductility, so 0.01
It is preferable to set it to 00% or less. Since Sol.N also dramatically improves the bake hardenability, it is preferable to contain 0.0001% or more. Moreover, since excessive addition deteriorates aging property and ductility, it is preferably made 0.0200% or less. Also, in particular, the formation of metastable nitrides
There is a great contribution to improving the bake hardenability with respect to tensile strength at high prestrain.
【００３６】ここで、Sol.Ｃ／Sol.Ｎの値は内部摩擦振
動法で０．５〜４Ｈｚの振動数により得られるＱ-1とし
て得られるピーク高さの比によって得られるものとす
る。また、Sol.Ｃ、Sol.Ｎの各々の値も同様の方法で求
めることができる。また、前述のようにＡＰ−ＦＩＭに
よっても統計的に正しいと思われる範囲での測定によっ
て得ることもできる。Here, the value of Sol.C / Sol.N is obtained by the ratio of the peak height obtained as Q -1 obtained by the internal friction vibration method at the frequency of 0.5 to 4 Hz. Further, the respective values of Sol.C and Sol.N can be obtained by the same method. Further, as described above, it can also be obtained by measurement in a range that is considered statistically correct by AP-FIM.
【００３７】予歪み：焼付け処理時のクラスターおよび
微細準安定析出相の生成サイトとして５％以上の付加の
焼き付き硬化量として評価した。一方、各材質によって
異なるが均一変形以上の予加工は構造物として意味をな
さないので、予加工量は均一延性よりも低くすべきであ
る。この観点から、予歪みは２０％以下とした。ただ
し、均一のびが２０％を超える材料については均一のび
までの予加工を行っても本発明を何ら阻害するものでは
ない。Pre-strain: As a site for forming clusters and fine metastable precipitation phases during the baking treatment, the amount of additional baking hardening of 5% or more was evaluated. On the other hand, the amount of pre-working should be lower than the uniform ductility because pre-working beyond uniform deformation does not make sense as a structure, although it depends on each material. From this viewpoint, the pre-strain was set to 20% or less. However, for a material having a uniform spread of more than 20%, pre-processing to the uniform spread does not hinder the present invention at all.
【００３８】焼付処理：低温すぎると有限の時間内に高
い焼付け硬化量を得ることができないため１１０℃以上
とし、一方では高温すぎるとクラスターや準安定相の析
出が生じなくなり安定相の析出に変わってしまうので２
００℃以下とした。処理時間は、フェライト中の炭素お
よび窒素の拡散が十分起こりクラスターや準安定相の析
出が生じなくなり安定相の析出に変わらない範囲とし
て、１〜６０分とした。Baking treatment: If the temperature is too low, a high bake hardening amount cannot be obtained within a finite time, so the temperature is set to 110 ° C. or higher. On the other hand, if the temperature is too high, precipitation of clusters and metastable phases does not occur and stable phase precipitation occurs. 2
The temperature was set to 00 ° C or lower. The treatment time was set to 1 to 60 minutes as a range in which diffusion of carbon and nitrogen in the ferrite was sufficiently caused and precipitation of clusters and metastable phases did not occur and precipitation of stable phases was not changed.
【００３９】析出分布：焼付け硬化の直接的原因の１つ
である。硬化に効く粒子サイズとしては円相当径で１０
０ｎｍ以下である。焼付け処理により転位上に準安定相
を微細に分散析出させることで焼付け硬化能を高めるこ
とができる。一方、測定限界は１ｎｍである。従って、
焼付け処理前にはその析出物密度は小さいほうが良いた
め円相当径で１〜１００ｎｍの転位上の析出物の密度を
２個／μｍ2 以下とし、その後の１１０〜２００℃で１
〜６０分の焼付け処理により転位上に微細析出させる。Precipitation distribution: One of the direct causes of bake hardening. The particle size effective for curing is 10 in terms of equivalent circle diameter.
It is 0 nm or less. The bake hardening ability can be enhanced by finely dispersing and precipitating the metastable phase on the dislocations by the baking treatment. On the other hand, the measurement limit is 1 nm. Therefore,
Before the baking treatment, the density of the precipitates should be small, so the density of the precipitates on dislocations having a circle-equivalent diameter of 1 to 100 nm should be 2 / μm 2 or less, and at 110 to 200 ° C. thereafter,
Finely deposit on dislocations by baking treatment for 60 minutes.
【００４０】このときの析出密度として強化能確保の点
から円相当径で１〜１００ｎｍの析出物の密度を５個／
μｍ2 以上とし、１０００個／μｍ2 を超えると均一変
形の範囲では硬化量が飽和する傾向になる。よって、５
〜１０００固／μｍ2 とした。ここで析出密度は、フェ
ライト母相中の任意の箇所について透過電子顕微鏡やＥ
ＢＳＰ（Electron Back Scattering Pattern）、ＡＰ−
ＦＩＭなどにより粒子の分布を観察測定可能であり、こ
れらを元に円相当径により粒子径を求めて密度を測定で
きる。At this time, as the precipitation density, from the viewpoint of ensuring the strengthening ability, the density of the precipitate having a circle equivalent diameter of 1 to 100 nm is 5 /
and [mu] m 2 or more, tends to cure amount is saturated in the range of uniform deformation exceeding 1,000 / [mu] m 2. Therefore, 5
˜1000 solids / μm 2 . Here, the precipitation density is a transmission electron microscope or E
BSP (Electron Back Scattering Pattern), AP-
The distribution of particles can be observed and measured by FIM or the like, and the density can be measured by obtaining the particle diameter from the equivalent circle diameter based on these.
【００４１】次に製造方法について説明する。熱延して
本発明の鋼板を製造する場合には、所定の成分に調整さ
れたスラブを鋳造まま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、偏析軽減などの理由から再加
熱温度を１１５０℃以上かつ１２５０℃以下とする。加
熱温度が高温になると偏析は軽減されるが全面に酸化ス
ケール厚が厚くなってしまう。また、低温加熱では十分
に偏析軽減・均質化ができないことがあるからである。Next, the manufacturing method will be described. When the steel sheet of the present invention is manufactured by hot rolling, a slab adjusted to have a predetermined composition is hot-rolled by casting or after cooling once and then reheating. At this time, the reheating temperature is set to 1150 ° C. or more and 1250 ° C. or less for reasons such as segregation reduction. When the heating temperature becomes high, segregation is reduced, but the oxide scale thickness becomes thicker on the entire surface. Also, it is because the segregation reduction and homogenization may not be sufficiently performed by low temperature heating.
【００４２】熱延は、仕上げ温度が８５０℃未満となっ
たり、最終スタンドでの圧下量が２０％を超えると未再
結晶圧延率が高くなってしまい製品の転位密度が高くな
り、低延性となったり、焼付け硬化能が低下する懸念が
ある。一方、最終スタンドの圧下量が５％より小さいと
板厚制度や形状不良の原因となるので、最終スタンドの
圧下量は５〜２０％と規定する。また、仕上げ温度が１
１００℃を超えると粒径が大きくなるので、仕上げ温度
は８５０〜１１００℃と規定する。In the hot rolling, if the finishing temperature is lower than 850 ° C. or the rolling reduction in the final stand exceeds 20%, the unrecrystallized rolling rate becomes high, the dislocation density of the product becomes high, and the low ductility is obtained. There is a concern that the bake hardenability may decrease. On the other hand, if the reduction amount of the final stand is less than 5%, it causes the plate thickness accuracy and the defective shape. Therefore, the reduction amount of the final stand is specified as 5 to 20%. Also, the finishing temperature is 1
If the temperature exceeds 100 ° C, the particle size becomes large, so the finishing temperature is defined as 850 to 1100 ° C.
【００４３】その後の冷速は３０℃/s未満だとパーライ
トが生成して固溶炭素確保を阻害する。また、１００℃
/s超では低温変態による変態転位の導入により焼付け硬
化能が低下する懸念があるうえ、十分なフェライトが生
成せず強度遠征バランスが悪化する。巻き取りは、冷却
過程で極力炭化物および窒化物を生成させない目的で４
００℃以下に巻取ることとした。巻き取り温度の下限は
特に規定しないが、固溶炭素および固溶窒素を残存させ
る目的からすると低い方が望ましい。また、設備制約の
ため、室温以上で巻き取ることが好ましい。If the subsequent cooling rate is less than 30 ° C./s, pearlite is produced and hinders securing solid solution carbon. Also, 100 ℃
If it exceeds / s, there is a risk that the bake hardenability will decrease due to the introduction of transformation dislocations due to low-temperature transformation, and sufficient ferrite will not be formed, deteriorating the strength expedition balance. Winding is performed to prevent carbides and nitrides from forming as much as possible during the cooling process.
It was decided to wind it below 00 ° C. The lower limit of the winding temperature is not particularly specified, but is preferably lower for the purpose of leaving the solid solution carbon and the solid solution nitrogen. In addition, it is preferable to wind at room temperature or higher due to equipment restrictions.
【００４４】一方、冷延製品の場合には、焼付き防止の
ため熱延仕上げ温度を８３０℃以上とし巻き取ることと
した。その後は、熱延鋼板を酸洗後冷延し、焼鈍を鋼の
化学成分によって決まる温度Ａｃ1 及びＡｃ3 温度（例
えば「鉄鋼材料学」：Ｗ．Ｃ．Ｌｅｓｌｉｅ著、幸田成
康監訳、丸善発行、Ｐ２７３）で、表現されるＡｃ1−
１００（℃）未満の場合には、焼鈍温度で得られる固溶
炭素および固溶窒素量が少ないことや再結晶不測の懸念
があることからこれを焼鈍温度の下限とした。On the other hand, in the case of a cold rolled product, the hot rolling finishing temperature is set to 830 ° C. or higher to prevent seizure. After that, the hot-rolled steel sheet is pickled, cold-rolled, and then annealed at temperatures Ac 1 and Ac 3 determined by the chemical composition of the steel (for example, “Steel Material Science” by W. C. Leslie, translated by Shigeyasu Koda, published by Maruzen). , P273) and expressed as Ac 1 −.
When it is less than 100 (° C.), the amount of solid solution carbon and solid solution nitrogen obtained at the annealing temperature is small and there is a fear of unexpected recrystallization, so this was made the lower limit of the annealing temperature.
【００４５】また、焼鈍温度が高温となるほど、製造コ
ストの上昇を招くうえ結晶粒の粗大化が生じ材質に悪影
響を及ぼすために、焼鈍温度の上限をＡｃ3 ＋５０
（℃）とした。この温度域での焼鈍時間は鋼板の温度均
一化と固溶炭素および固溶窒素の確保のために３０秒以
上が必要である。しかし、１０００分超では、スケール
過多になったり、コスト上昇や結晶粗大化の懸念がある
を招くのでこれを上限とした。Further, the higher the annealing temperature is, the higher the manufacturing cost is, and the coarser the crystal grains are, which adversely affects the material. Therefore, the upper limit of the annealing temperature is Ac 3 +50.
(° C). The annealing time in this temperature range needs to be 30 seconds or more to make the temperature of the steel sheet uniform and to secure solid solution carbon and solid solution nitrogen. However, if it exceeds 1000 minutes, there is a risk of excessive scale, cost increase, and crystal coarsening, so this was made the upper limit.
【００４６】その後の冷却は極力、固溶炭素および固溶
窒素を確保する観点から炭化物および窒化物の析出を避
けるために、３〜１００℃／秒の冷却速度で４５０℃以
下に冷却する。冷却停止温度は特に定めないが、固溶炭
素および固溶窒素量を確保する目的からすると低い方が
望ましい。また、設備制約のため、室温以上とすること
が好ましい。From the viewpoint of securing solid solution carbon and solid solution nitrogen as much as possible, the subsequent cooling is carried out at a cooling rate of 3 to 100 ° C./sec to 450 ° C. or less in order to avoid precipitation of carbides and nitrides. The cooling stop temperature is not particularly specified, but is preferably lower for the purpose of securing the amounts of solid solution carbon and solid solution nitrogen. Further, it is preferable to set the temperature to room temperature or higher because of facility restrictions.
【００４７】また、その後２００〜４００℃で１０秒〜
５分保持する熱処理を付加することで所定の焼付け硬化
量を制御することも可能で、このような熱処理を付加し
ても本発明の範囲内である。また、電気鍍金、溶融亜鉛
めっき、合金化溶融亜鉛めっきを施しても本発明の固溶
炭素や固溶窒素等の規定を満たす限り範囲内である。冷
延鋼板において、面積率最大の相をフェライトとするた
めには、規定の焼鈍温度およびその後の冷却速度とする
ことで最大面積を得ることができる。After that, at 200 to 400 ° C. for 10 seconds to
It is also possible to control a predetermined bake hardening amount by adding a heat treatment for holding for 5 minutes, and it is within the scope of the present invention even if such a heat treatment is added. Even if electroplating, hot dip galvanizing, or galvannealing is applied, it is within the range as long as the requirements for the solid solution carbon, the solid solution nitrogen, etc. of the present invention are satisfied. In the cold-rolled steel sheet, in order to make the phase having the largest area ratio ferrite, the maximum area can be obtained by setting the specified annealing temperature and the subsequent cooling rate.
【００４８】[0048]
【実施例】以下、実施例によって本発明をさらに詳細に
説明する。表１に示すような組成の鋼板を、１２００℃
に加熱し、最終スタンドでの圧下量を５〜２０％とし、
仕上げ温度を９２０〜８３０℃で、その後冷却を３０〜
１００℃/sで３５０℃まで冷却し、巻き取り後、酸洗
し、１．６ｍｍ厚さおよび４ｍｍ厚さの熱延板を作成し
た。４ｍｍのものについては冷延して１．０ｍｍ厚とし
た。The present invention will be described in more detail with reference to the following examples. A steel plate having a composition as shown in Table 1 is 1200 ° C.
To 5% to 20% in the final stand,
Finishing temperature is 920-830 ° C, and then cooling is 30-
It was cooled to 350 ° C. at 100 ° C./s, wound, and pickled to prepare hot-rolled sheets of 1.6 mm thickness and 4 mm thickness. A 4 mm piece was cold rolled to a thickness of 1.0 mm.
【００４９】その後、各鋼の成分（質量％）から下記式
にしたがってＡｃ1 とＡｃ3 変態温度を計算により求め
た。
Ａｃ1 ＝７２３−１０．７×Ｍｎ％−１６．９×Ｎｉ％
＋２９．１×Ｓｉ％＋１６．９×Ｃｒ％。
Ａｃ3 ＝９１０−２０３×（Ｃ％）1/2 −１５．２×Ｎ
ｉ％＋４４．７×Ｓｉ％＋１０４×Ｖ％＋３１．５×Ｍ
ｏ％−３０×Ｍｎ％−１１×Ｃｒ％＋４００×Ａｌ％。Then, the Ac 1 and Ac 3 transformation temperatures were calculated from the components (mass%) of each steel according to the following formulas. Ac 1 = 723-10.7 × Mn% -16.9 × Ni%
+29.1 x Si% + 16.9 x Cr%. Ac 3 = 910-203 × (C% ) 1/2 -15.2 × N
i% + 44.7 × Si% + 104 × V% + 31.5 × M
o% -30xMn% -11xCr% + 400xAl%.
【００５０】これらのＡｃ1 およびＡｃ3 変態温度から
計算される焼鈍温度：Ａｃ1 −１００℃〜Ａｃ3 ＋５０
℃で１０％Ｈ2 −Ｎ2 雰囲気中で再結晶焼鈍させたのち
３〜１００℃／秒の冷却速度で、室温までまたは過時効
温度（ＯＡ：Over Aging）まで冷却して数分間保持後室
温まで冷却して、冷延焼鈍板を作成した。これら鋼板か
らＪＩＳ５号引張り試験片を採取して、予歪を加えて、
焼き付け処理を行い、おのおのの焼き付け硬化特性や機
械的性質を測定した。表１中に１７０℃×２０分焼き付
け処理後の各鋼の硬化量を併せて示す。Annealing temperature calculated from these Ac 1 and Ac 3 transformation temperatures: Ac 1 -100 ° C to Ac 3 +50.
After recrystallization annealing in a 10% H 2 -N 2 atmosphere at ℃, cool to room temperature or over aging (OA) at a cooling rate of 3 to 100 ℃ / sec, and hold for several minutes, then room temperature To a cold rolled annealed plate. JIS No. 5 tensile test pieces were taken from these steel plates, and prestrained,
A baking process was performed, and the bake hardening characteristics and mechanical properties of each were measured. Table 1 also shows the amount of hardening of each steel after baking treatment at 170 ° C. for 20 minutes.
【００５１】本発明例のＡ〜Ｋは、特に予歪が５％を超
えると降伏応力の上昇量（ΔＹＳ）および引張強度の上
昇量（ΔＴＳ）が同時に５０ＭＰａを超える。一方、比
較例のＣＡ〜ＣＥは低歪側の降伏応力の上昇量は大きい
ものも有るが、高歪側ではとくに引張強度の上昇量が低
い。In Examples A to K of the present invention, especially when the prestrain exceeds 5%, the yield stress increase amount (ΔYS) and the tensile strength increase amount (ΔTS) simultaneously exceed 50 MPa. On the other hand, in some of CA to CE of Comparative Examples, the increase amount of the yield stress on the low strain side is large, but the increase amount of the tensile strength is particularly low on the high strain side.
【００５２】表２にＪおよびＫ鋼の、各条件における予
歪１０％における焼き付け硬化量を示す。過時効処理を
行うと焼き付け処理時に生じる１〜１００ｎｍの析出物
密度が小さくなるものの、その密度が５個／μｍ2 以上
になると所定の硬化量を得ることができる。一方、焼き
付け処理が１１０℃未満２５０℃超で６０分超の保持に
なると微細析出物が生じず、効果量も小さい。Table 2 shows the amount of bake hardening of J and K steels under each condition at a prestrain of 10%. When the overaging treatment is performed, the density of precipitates of 1 to 100 nm generated during the baking treatment becomes small, but when the density becomes 5 pieces / μm 2 or more, a predetermined hardening amount can be obtained. On the other hand, if the baking treatment is maintained at less than 110 ° C. and more than 250 ° C. for more than 60 minutes, fine precipitates do not occur and the effect amount is small.
【００５３】[0053]
【表１】 [Table 1]
【００５４】[0054]
【表２】 [Table 2]
【００５５】[0055]
【表３】 [Table 3]
【００５６】[0056]
【発明の効果】本発明は、複雑形状や衝突安全性を意識
した高予歪み時において高い焼付け硬化能を持つ高強度
鋼板及びその製造方法を提供することができる。INDUSTRIAL APPLICABILITY The present invention can provide a high-strength steel sheet having a high bake hardenability at the time of high pre-strain in consideration of a complicated shape and collision safety, and a manufacturing method thereof.
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｃ２２Ｃ 38/58 Ｃ２２Ｃ 38/58 (72)発明者 吉永 直樹 富津市新富20−１ 新日本製鐵株式会社技 術開発本部内 (72)発明者 高橋 学 富津市新富20−１ 新日本製鐵株式会社技 術開発本部内 Ｆターム(参考） 4K037 EA01 EA02 EA04 EA05 EA06 EA10 EA11 EA13 EA15 EA16 EA17 EA18 EA19 EA20 EA21 EA23 EA25 EA27 EA28 EA29 EA31 EA32 EA33 EA35 EB06 EB07 EB08 EB13 FA02 FA03 FB01 FC04 FC05 FD04 FE01 FK02 FK03 GA03 HA01 ─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. 7 Identification code FI theme code (reference) C22C 38/58 C22C 38/58 (72) Inventor Naoki Yoshinaga 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Headquarters (72) Inventor Manabu Takahashi 20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd. Technology Development Headquarters F-term (reference) 4K037 EA01 EA02 EA04 EA05 EA06 EA10 EA11 EA13 EA15 EA16 EA17 EA18 EA19 EA20 EA21 EA23 EA25 EA27 EA28 EA29 EA31 EA32 EA33 EA35 EB06 EB07 EB08 EB13 FA02 FA03 FB01 FC04 FC05 FD04 FE01 FK02 FK03 GA03 HA01
Claims (8)
イトを面積率最大の相とし、固溶炭素：Sol.Ｃ及び固溶
窒素：Sol.ＮがSol.Ｃ／Sol.Ｎ：０．１〜１００を満た
し、予歪みを５〜２０％付加したとき、１１０〜２００
℃で１〜６０分の焼付け処理後の降伏強度および引張強
度の上昇量の平均またはそれぞれの値が、予歪みを付加
しない焼付け処理前の鋼板に比べ５０ＭＰａ以上である
ことを特徴とする高予歪み時において高い焼付け硬化能
を持つ高強度鋼板。1. A steel sheet, in mass%, C: 0.0005-0.3%, Si: 0.001-3.0%, Mn: 0.01-3.0%, Al: 0.0001. .About.0.05%, P: 0.001 to 0.3%, S: 0.0001 to 0.1%, N: 0.0010 to 0.05%, and the balance Fe and unavoidable impurities, Ferrite was used as the phase with the maximum area ratio, and solid solution carbon: Sol.C and solid solution nitrogen: Sol.N satisfied Sol.C / Sol.N: 0.1 to 100, and a prestrain was added to 5 to 20%. Sometimes 110-200
The high or low average value of the amount of increase in yield strength and tensile strength after baking treatment at 1 ° C for 1 to 60 minutes is 50 MPa or more as compared with the steel sheet before baking treatment without adding prestrain. A high-strength steel plate that has a high bake hardenability during distortion.
２種以上を合計で０．００１〜１％含有することを特徴
とする請求項１に記載の高予歪み時において高い焼付け
硬化能を持つ高強度鋼板。2. The steel sheet further contains, in mass%, 0.001 to 1% of V, Ti, Nb, Zr, Hf, Ta, or one or more of them in total. Item 1. A high-strength steel sheet having a high bake hardenability at the time of high pre-strain.
０１〜５％含有することを特徴とする請求項１又は２記
載の高予歪み時において高い焼付け硬化能を持つ高強度
鋼板。3. The steel sheet further comprises, in mass%, one or two of Cr, Mo and W in total of 0.0.
The high-strength steel sheet having a high bake hardenability at the time of high pre-strain according to claim 1 or 2, characterized in that the content is 01 to 5%.
１〜３の何れか１項に記載の高予歪み時において高い焼
付け硬化能を持つ高強度鋼板。4. The steel sheet further contains, in mass%, one or more of Ni: 0.001 to 10%, Cu: 0.001 to 5%, Co: 0.001 to 5%. A high-strength steel sheet having a high bake hardenability during high pre-strain according to any one of claims 1 to 3.
０１〜０．１％を含有することを特徴とする請求項１〜
４の何れか１項に記載の高予歪み時において高い焼付け
硬化能を持つ高強度鋼板。5. The steel sheet further contains B: 0.00 by mass%.
It contains 01-0.1%.
A high-strength steel sheet having a high bake hardenability at the time of high pre-strain according to any one of 4 above.
中に存在する円相当径１〜１００ｎｍ転位上の析出物密
度が２個／μｍ2 以下で、その後の１１０〜２００℃で
１〜６０分の焼付け処理後には円相当径１〜１００ｎｍ
の析出物密度が５〜１０００個／μｍ2 であることを特
徴とする請求項１〜５の何れか１項に記載の高予歪み時
において高い焼付け硬化能を持つ高強度鋼板。6. When a pre-strain of 5% is added, the density of precipitates on the circle-equivalent diameter 1 to 100 nm dislocation existing in ferrite is 2 / μm 2 or less, and thereafter 1 to 60 at 110 to 200 ° C. After baking for 1 minute, the equivalent circle diameter is 1 to 100 nm
The high-strength steel sheet having a high bake hardenability at the time of high pre-strain according to any one of claims 1 to 5, wherein the precipitate density is 5 to 1000 pieces / µm 2 .
度鋼板を製造する方法であって、請求項１〜６の何れか
１項に記載の成分からなる鋳造スラブを鋳造まま又は一
旦冷却した後に再度１１５０〜１２５０℃に加熱し、熱
延の最終スタンドでの圧下量を５〜２０％とし、熱延の
仕上げ温度を８５０〜１１００℃とし、その後３０〜１
００℃/sで冷却し４００℃以下で巻取ることを特徴とす
る高予歪み時において高い焼付け硬化能を持つ高強度鋼
板の製造方法。7. A method for producing the high-strength steel sheet according to any one of claims 1 to 6, wherein a cast slab comprising the components according to any one of claims 1 to 6 is as-cast. Alternatively, after cooling once, it is heated again to 1150 to 1250 ° C., the reduction amount in the final stand of hot rolling is 5 to 20%, the finishing temperature of hot rolling is 850 to 1100 ° C., and then 30 to 1
A method for producing a high-strength steel sheet having a high bake hardenability at high pre-strain, which comprises cooling at 00 ° C / s and winding at 400 ° C or less.
度鋼板を製造する方法であって、請求項１〜６の何れか
１項に記載の成分からなる鋳造スラブを鋳造まま又は一
旦冷却した後に再度１１５０〜１２５０℃に加熱し、熱
延の仕上げ温度を８３０〜１１００℃として巻き取り、
その熱延鋼板を酸洗、冷延し、その後（Ａｃ1 −１０
０）〜（Ａｃ3 ＋５０）℃で３０秒〜１０００分間焼鈍
した後に、３〜１００℃／秒で４５０℃以下に冷却する
ことを特徴とする高予歪み時において高い焼付け硬化能
を持つ高強度鋼板の製造方法。8. A method for producing the high-strength steel sheet according to any one of claims 1 to 6, wherein a cast slab comprising the components according to any one of claims 1 to 6 is as-cast. Or, once cooled, it is heated again to 1150 to 1250 ° C., and the finish temperature of hot rolling is set to 830 to 1100 ° C.
The hot rolled steel sheet is pickled, cold rolled, and then (Ac 1-10
0) to (Ac 3 +50) ° C., annealed for 30 seconds to 1000 minutes, and then cooled to 450 ° C. or less at 3 to 100 ° C./second. High strength with high bake hardenability at high pre-strain. Steel plate manufacturing method.
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| JP2001292147A JP4071948B2 (en) | 2001-09-25 | 2001-09-25 | High strength steel sheet having high bake hardenability at high pre-strain and its manufacturing method |
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|---|---|---|---|
| JP2001292147A JP4071948B2 (en) | 2001-09-25 | 2001-09-25 | High strength steel sheet having high bake hardenability at high pre-strain and its manufacturing method |
Publications (2)
| Publication Number | Publication Date |
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| JP2003096543A true JP2003096543A (en) | 2003-04-03 |
| JP4071948B2 JP4071948B2 (en) | 2008-04-02 |
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| JP2001292147A Expired - Fee Related JP4071948B2 (en) | 2001-09-25 | 2001-09-25 | High strength steel sheet having high bake hardenability at high pre-strain and its manufacturing method |
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