JP3530354B2 - High-workability high-strength hot-rolled steel sheet with high dynamic deformation resistance for impact absorption at impact and manufacturing method thereof - Google Patents
High-workability high-strength hot-rolled steel sheet with high dynamic deformation resistance for impact absorption at impact and manufacturing method thereofInfo
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- JP3530354B2 JP3530354B2 JP25886597A JP25886597A JP3530354B2 JP 3530354 B2 JP3530354 B2 JP 3530354B2 JP 25886597 A JP25886597 A JP 25886597A JP 25886597 A JP25886597 A JP 25886597A JP 3530354 B2 JP3530354 B2 JP 3530354B2
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- rolled steel
- impact
- deformation resistance
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Description
【０００１】[0001]
【発明の属する技術分野】本発明は、自動車部材等に使
用され、衝突時の衝撃エネルギーを効率よく吸収するこ
とによって乗員の安全性確保に寄与することの出来る高
い動的変形抵抗を示す衝突時衝撃吸収用高強度熱延鋼板
とその製造方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for automobile members and the like, and at the time of collision showing high dynamic deformation resistance which can contribute to ensuring safety of passengers by efficiently absorbing impact energy at the time of collision. The present invention relates to a high-strength hot-rolled steel sheet for impact absorption and a method for manufacturing the same.
【０００２】[0002]
【従来の技術】近年、自動車衝突時の乗員保護が自動車
の最重要性能として認識され、それに対応するための高
い高速変形抵抗を示す材料への期待が高まっている。例
えば乗用車の前面衝突においては、フロントサイドメン
バと呼ばれる部材にこの様な材料を適用すれば、該部材
が圧潰することで衝撃のエネルギーが吸収され、乗員に
かかる衝撃を和らげることが出来る。2. Description of the Related Art In recent years, occupant protection in the event of an automobile collision has been recognized as the most important performance of an automobile, and there is an increasing expectation for a material having a high high-speed deformation resistance in order to cope with it. For example, in the case of a frontal collision of a passenger car, if such a material is applied to a member called a front side member, the energy of the shock is absorbed when the member is crushed, and the shock applied to the occupant can be softened.
【０００３】自動車の衝突時に各部位が受ける変形の歪
み速度は１０3 （１／ｓ）程度まで達するため、材料の
衝撃吸収性能を考える場合には、この様な高歪み速度領
域での動的変形特性の解明が必要である。また同時に、
省エネルギー、ＣＯ2 排出削減を目指して自動車車体の
軽量化を同時に達成することが必須と考えられ、このた
めに有効な高強度鋼板へのニーズが高まっている。Since the strain rate of deformation which each part receives at the time of a collision of an automobile reaches up to about 10 3 (1 / s), when considering the shock absorbing performance of a material, dynamic strain in such a high strain rate range is considered. It is necessary to clarify the deformation characteristics. At the same time,
At the same time, it is indispensable to achieve the weight reduction of the automobile body aiming at energy saving and reduction of CO 2 emission, and for this reason, there is a growing need for effective high strength steel sheets.
【０００４】例えば本発明者らは、ＣＡＭＰ−ＩＳＩＪ
Ｖｏｌ．９（１９９６）Ｐ．１１１２〜１１１５に、
高強度薄鋼板の高速変形特性と衝撃エネルギー吸収能に
ついて報告し、その中で、１０3 （１／ｓ）程度の高歪
み速度領域での動的強度は、１０-3 （１／ｓ）の低歪
み速度での静的強度と比較して大きく上昇すること、材
料の強化機構によって変形抵抗の歪み速度依存性が変化
すること、この中で、ＴＲＩＰ（変態誘起塑性）型の鋼
やＤＰ（フェライト、マルテンサイト２相）型の鋼が他
の高強度鋼板に比べて優れた成形性と衝撃吸収能を兼ね
備えていることを報告している。[0004] For example, the present inventors have found that CAMP-ISIJ
Vol. 9 (1996) P.I. 1112 to 1115,
Reported on high speed deformation properties and impact energy absorption capacity of high-strength thin steel sheet, in which the dynamic strength at high strain rate region of the order of 10 3 (1 / s) is 10 -3 (1 / s) A large increase in static strength at low strain rate, a change in strain rate dependence of deformation resistance due to the strengthening mechanism of the material, among which TRIP (transformation induced plasticity) type steel and DP ( It has been reported that ferritic and martensitic two-phase type steels have both excellent formability and impact absorption capacity compared to other high strength steel sheets.
【０００５】また、残留オーステナイトを含む耐衝撃特
性に優れた高強度鋼板とその製造方法を提供するものと
して特開平７−１８３７２号公報に開示されているよう
に、衝撃吸収能を変形速度の上昇に伴う降伏応力の上昇
のみで解決するという記載はあるが、衝撃吸収能を向上
させるために、残留オーステナイトの量以外に残留オー
ステナイトの性質をどの様に制御すべきかは明確に開示
されていない。Further, as disclosed in Japanese Patent Application Laid-Open No. 7-18372, which provides a high-strength steel sheet containing retained austenite and having excellent impact resistance and a method for producing the same, as described in Japanese Patent Application Laid-Open No. 7-18372, the impact absorption capacity and the deformation rate are increased. Although it is described that the problem can be solved only by increasing the yield stress accompanying the above, it is not clearly disclosed how to control the properties of the retained austenite other than the amount of the retained austenite in order to improve the impact absorption capacity.
【０００６】[0006]
【発明が解決しようとする課題】このように、自動車衝
突時の衝撃エネルギーの吸収に及ぼす部材構成材料の動
的変形特性は少しづつ解明されつつあるものの、衝撃エ
ネルギー吸収能に優れた自動車部品用鋼材としてどのよ
うな特性に注目し、どのような基準に従って材料選定を
行うべきかは未だ明らかにされていない。また、自動車
用部品は、鋼材をプレス成形によって要求された部品形
状に成形され、その後、一般的には塗装焼き付けされた
後に自動車に組み込まれ、実際の衝突現象に直面する。
しかしながら、このような予変形＋焼き付け処理を行っ
た後の鋼材の衝突時の衝撃エネルギー吸収能の向上にど
のような鋼材強化機構が適しているかも未だ明らかには
されていない。As described above, although the dynamic deformation characteristics of the material constituting the members that affect the absorption of impact energy in the event of an automobile collision are being elucidated little by little, it is for automobile parts having excellent impact energy absorption ability. It has not yet been clarified what characteristics should be paid attention to as a steel material and what criteria should be used for material selection. Further, automobile parts are formed into a required part shape by press forming a steel material, and then are generally baked in a paint and then incorporated into an automobile to face an actual collision phenomenon.
However, it has not been clarified yet what kind of steel material strengthening mechanism is suitable for improving the impact energy absorption capacity at the time of collision of the steel material after such pre-deformation + baking treatment.
【０００７】[0007]
【課題を解決するための手段】本発明は、フロントサイ
ドメンバー等の衝突時の衝撃エネルギー吸収を担う部品
に成形加工されて使用される鋼材で、高い衝撃エネルギ
ー吸収能を示す高強度鋼板とその製造方法を提供するこ
とを目的としている。その要旨は次のとおりである。DISCLOSURE OF THE INVENTION The present invention is a steel material that is used by being formed into a part that absorbs impact energy at the time of collision, such as a front side member, and a high-strength steel sheet that exhibits a high impact energy absorption capacity. It is intended to provide a manufacturing method. The summary is as follows.
【０００８】（１）重量％で、Ｃ：０．０４％以上０．
３％以下、ＳｉとＡｌの一方または双方を合計で０．５
％以上３．０％以下、Ｍｎ，Ｎｉ，Ｃｒ，Ｃｕ，Ｍｏの
１種または２種以上を合計で０．５％以上３．５％以下
含み、残部がＦｅ及び不可避的不純物からなり、最終的
に得られる冷延鋼板のミクロ組織がフェライトおよびベ
イナイトを含み、このいずれかを主相とし、体積分率で
３％以上の残留オーステナイトを含む第３相との複合組
織であり、残留オーステナイト中の固溶〔Ｃ〕量と鋼材
の平均Ｍｎ等量｛Ｍｎｅｑ＝Ｍｎ＋（Ｎｉ＋Ｃｒ＋Ｃｕ
＋Ｍｏ）／２｝によって決まる値（Ｍ＝６７８−４２８
×〔Ｃ〕−３３×Ｍｎｅｑ）が−１４０以上７０未満
で、５８８ MPa 以上の引張り強度を有し、その鋼材に相
当歪みで０％超１０％以下の予変形を与えた後、５×１
０2 〜５×１０3 （１／ｓ）の歪み速度範囲で変形した
時の３〜１０％の相当歪み範囲における変形応力の平均
値σｄｙｎ（ＭＰａ）と５×１０-4〜５×１０-3（１／
ｓ）の歪み速度範囲で変形した時の３〜１０％の相当歪
み範囲における変形応力の平均値σｓｔ（ＭＰａ）の差
が５×１０-4〜５×１０-3（１／ｓ）の歪み速度範囲で
測定された静的な引張り試験における最大応力ＴＳ（Ｍ
Ｐａ）によって表現される式（σｄｙｎ−σｓｔ）≧−
０．２７２×ＴＳ＋３００を満足することを特徴とする
高い動的変形抵抗を有する衝突時衝撃吸収用良加工性高
強度熱延鋼板。(1) C: 0.04% or more by weight%, 0.
3% or less, 0.5 of Si or Al or both in total
% Or more and 3.0% or less, and one or more of Mn, Ni, Cr, Cu, Mo in a total amount of 0.5% or more and 3.5% or less, and the balance consisting of Fe and inevitable impurities. The cold-rolled steel sheet thus obtained has a microstructure containing ferrite and bainite, which is a composite structure with a third phase containing either of them as a main phase and containing 3% or more of retained austenite by volume fraction. Amount of solid solution [C] and average Mn equivalent of steel material {Mneq = Mn + (Ni + Cr + Cu
+ Mo) / 2} (M = 678-428)
X [C] -33xMneq) is -140 or more and less than 70 , has a tensile strength of 588 MPa or more , and after pre-deformation of more than 0% and 10% or less by equivalent strain to the steel material, it is 5x1.
Mean value σdyn (MPa) of deformation stress and 5 × 10 −4 to 5 × 10 − in the equivalent strain range of 3 to 10% when deformed in the strain rate range of 0 2 to 5 × 10 3 (1 / s). 3 (1 /
s) the strain is 5 × 10 −4 to 5 × 10 −3 (1 / s) when the strain is deformed in the strain rate range and the difference in the average value σst (MPa) of the deformation stress in the equivalent strain range of 3 to 10% is 5 × 10 −4 to 5 × 10 −3 (1 / s). Maximum stress TS (M in a static tensile test measured in the velocity range
Pa) expressed by (σdyn−σst) ≧ −
0.272 × TS + 300 good workability high strength hot rolled steel sheet for collision impact absorption with <br/> high dynamic deformation resistance which satisfies the.
【０００９】（２）Ｎｂ，Ｔｉ，Ｖの１種又は２種以上
を合計で０．３重量％以下更に含むことを特徴とする
（１）記載の高い動的変形抵抗を有する衝突時衝撃吸収
用良加工性高強度熱延鋼板。
（３）Ｐを０．２重量％以下更に含むことを特徴とする
（１）または（２）記載の高い動的変形抵抗を有する衝
突時衝撃吸収用良加工性高強度熱延鋼板。(2) Absorption at impact with high dynamic deformation resistance as described in (1), further containing one or more of Nb, Ti and V in a total amount of 0.3% by weight or less.
Use good workability high-strength hot-rolled steel sheet. (3) An impeller having a high dynamic deformation resistance as described in (1) or (2), which further contains 0.2% by weight or less of P.
Good workability and high strength hot rolled steel sheet for shock absorption at the time of impact .
【００１０】（４）Ｂを０．０１重量％以下更に含むこ
とを特徴とする（１）〜（３）のいずれか１に記載の高
い動的変形抵抗を有する衝突時衝撃吸収用良加工性高強
度熱延鋼板。
（５）０％超１０％以下の予変形を与えた後の鋼材の残
留オーステナイト体積分率が２．５％超であり、かつ、
予変形前の残留オーステナイト体積分率と予変形後の残
留オーステナイト体積分率の比が０．４以上であること
を特徴とする（１）〜（４）のいずれか１に記載の高い
動的変形抵抗を有する衝突時衝撃吸収用良加工性高強度
熱延鋼板。(4) B: 0.01% by weight or less is further contained, and good workability for impact shock absorption with high dynamic deformation resistance according to any one of (1) to (3) is provided. High strength hot rolled steel sheet. (5) The residual austenite volume fraction of the steel material after pre-deformation of more than 0% and 10% or more is more than 2.5%, and
The high dynamics according to any one of (1) to (4), characterized in that the ratio of the retained austenite volume fraction before pre-deformation to the retained austenite volume fraction after pre-deformation is 0.4 or more. Good workability and high strength hot rolled steel sheet with impact resistance at the time of collision with deformation resistance.
【００１１】（６）最終的に得られる熱延鋼板のミクロ
組織中の残留オーステナイトの平均粒径と、主相である
フェライトもしくはベイナイトの平均粒径の比が０．６
以下であることを特徴とする（１）〜（５）のいずれか
１に記載の高い動的変形抵抗を有する衝突時衝撃吸収用
良加工性高強度熱延鋼板。
（７）重量％で、Ｃ：０．０４％以上０．３％以下、Ｓ
ｉとＡｌの一方または双方を合計で０．５％以上３．０
％以下、Ｍｎ，Ｎｉ，Ｃｒ，Ｃｕ，Ｍｏの１種または２
種以上を合計で０．５％以上３．５％以下含み、残部が
Ｆｅ及び不可避的不純物からなる鋳造スラブを、鋳造ま
まで熱延工程へ直送し、もしくは一旦冷却した後に１０
００℃〜１３００℃の範囲に再度加熱した後、熱延をＡ
ｒ3 変態温度−１０℃以上Ａｒ3 変態温度＋１００℃以
下の熱延仕上げ温度（ＦＴ）で完了し、その後５℃／秒
以上１００℃／秒以下の冷却速度で冷却し、巻き取る際
に、熱延仕上げ温度がＡｒ3 変態温度＋５０℃以上の場
合には４００℃以上５００℃未満の温度で巻き取り、熱
延仕上げ温度がＡｒ3 変態温度＋５０℃未満の場合には
４２０℃超５００℃未満の温度で巻き取り、最終的に得
られる熱延鋼板のミクロ組織がフェライトおよびベイナ
イトを含み、このいずれかを主相とし、体積分率で３％
以上の残留オーステナイトを含む第３相との複合組織で
あり、５８８ MPa 以上の引張り強度を有し、残留オース
テナイト中の固溶〔Ｃ〕量と鋼材の平均Ｍｎ等量｛Ｍｎ
ｅｑ＝Ｍｎ＋（Ｎｉ＋Ｃｒ＋Ｃｕ＋Ｍｏ）／２｝によっ
て決まる値（Ｍ＝６７８−４２８×〔Ｃ〕−３３×Ｍｎ
ｅｑ）が７０以上１８０以下で、その鋼材に相当歪みで
０％超１０％以下の予変形を与えた後、５×１０2 〜５
×１０3 （１／ｓ）の歪み速度範囲で変形した時の３〜
１０％の相当歪み範囲における変形応力の平均値σｄｙ
ｎ（ＭＰａ）と５×１０-4〜５×１０-3（１／ｓ）の歪
み速度範囲で変形した時の３〜１０％の相当歪み範囲に
おける変形応力の平均値σｓｔ（ＭＰａ）の差が５×１
０-4〜５×１０-3（１／ｓ）の歪み速度範囲で測定され
た静的な引張り試験における最大応力ＴＳ（ＭＰａ）に
よって表現される式（σｄｙｎ−σｓｔ）≧−０．２７
２×ＴＳ＋３００を満足することを特徴とする高い動的
変形抵抗を有する衝突時衝撃吸収用良加工性高強度熱延
鋼板の製造方法。[0011] (6) and the average particle size of the residual austenite in the microstructure of the finally obtained hot-rolled steel sheet, the ratio of the average particle size of the ferrite or bainite is the main phase 0.6
Good workability high strength hot rolled steel sheet for impact absorption during collision having high dynamic deformation resistance according to any one of (1) to (5), characterized in that : (7) Weight%, C: 0.04% or more and 0.3% or less, S
One or both of i and Al total 0.5% or more 3.0
% Or less, one or two of Mn, Ni, Cr, Cu, Mo
A casting slab containing 0.5% or more and 3.5% or less in total of the seeds and the balance of Fe and unavoidable impurities is sent directly to the hot rolling step as it is, or after being cooled once, 10
After heating again in the range of 00 ° C to 1300 ° C, hot rolling is performed with A
r 3 transformation temperature −10 ° C. or higher Ar 3 transformation temperature + 100 ° C. or higher
When completed at the lower hot rolling finish temperature (FT), then cooled at a cooling rate of 5 ° C./sec or more and 100 ° C./sec or less, and wound, when the hot rolling finish temperature is Ar 3 transformation temperature + 50 ° C. or more wound at a temperature below 400 ° C. or higher 500 ° C. the hot-rolled is that Ri taken up at a temperature below 420 ° C. ultra 500 ° C., finally obtained when the hot rolling finishing temperature is lower than Ar 3 transformation temperature + 50 ℃ The microstructure of the steel sheet contains ferrite and bainite, and either of them is the main phase, and the volume fraction is 3%.
It is a composite structure with the above-described third phase containing retained austenite, has a tensile strength of 588 MPa or more, and has a solid solution [C] amount in the retained austenite and an average Mn equivalent amount {Mn
eq = Mn + (Ni + Cr + Cu + Mo) / 2} (M = 678-428 × [C] -33 × Mn)
eq) is 70 or more and 180 or less, and after subjecting the steel material to pre-deformation of more than 0% and 10% or less by equivalent strain, 5 × 10 2 to 5
3 to 3 when deformed in a strain rate range of × 10 3 (1 / s)
Average value of deformation stress σdy in the equivalent strain range of 10%
n (MPa) and the difference between the mean value σst (MPa) of the deformation stress in the equivalent strain range of 3 to 10% when deformed in the strain rate range of 5 × 10 −4 to 5 × 10 −3 (1 / s). Is 5 × 1
The expression (σdyn−σst) ≧ −0.27 expressed by the maximum stress TS (MPa) in the static tensile test measured in the strain rate range of 0 −4 to 5 × 10 −3 (1 / s).
2 × TS + 300 high dynamic deformation method for producing a collision impact absorption for good workability high-strength hot-rolled steel sheet having a resistance that satisfies the.
【００１２】（８）Ｎｂ，Ｔｉ，Ｖの１種又は２種以上
を合計で０．３重量％以下更に含むことを特徴とする
（７）記載の高い動的変形抵抗を有する衝突時衝撃吸収
用良加工性高強度熱延鋼板の製造方法。
（９）Ｐを０．２重量％以下更に含むことを特徴とする
（７）または（８）記載の高い動的変形抵抗を有する衝
突時衝撃吸収用良加工性高強度熱延鋼板の製造方法。(8) The impact absorption at the time of collision with high dynamic deformation resistance as described in (7), which further contains one or more of Nb, Ti and V in a total amount of 0.3% by weight or less.
Manufacturing method of use good workability high-strength hot-rolled steel sheet. (9) The impact having a high dynamic deformation resistance according to (7) or (8), further containing 0.2% by weight or less of P.
A method of manufacturing a high-strength hot-rolled steel sheet with good workability for shock absorption during a collision .
【００１３】（１０）Ｂを０．０１重量％以下更に含む
ことを特徴とする（７）〜（９）のいずれか１に記載の
高い動的変形抵抗を有する衝突時衝撃吸収用良加工性高
強度熱延鋼板の製造方法。(10) Good workability for impact shock absorption at high impact having high dynamic deformation resistance as set forth in any one of (7) to (9), further containing 0.01% by weight or less of B. Manufacturing method of high strength hot rolled steel sheet.
【００１４】[0014]
【発明の実施の形態】自動車のフロントサイドメンバー
等の衝突時の衝撃吸収用部材は、鋼板に曲げ加工やプレ
ス成形加工によって製造される。自動車の衝突時の衝撃
は、このようにして加工されて後に一般的には塗装焼き
付けされた後に加えられる。従って、この様に部材への
加工、処理が行われた後に高い衝撃エネルギーの吸収能
を示す鋼板が必要となる。BEST MODE FOR CARRYING OUT THE INVENTION A shock absorbing member such as a front side member of an automobile at the time of collision is manufactured by bending or press forming a steel plate. The impact of a car crash is applied after it has been processed in this way and is generally subsequently baked on. Therefore, a steel sheet that exhibits a high impact energy absorption capacity after being processed and processed into a member in this manner is required.
【００１５】本発明者らの研究の結果、このような成形
加工された実部材において鋼板に適量の残留オーステナ
イトを含むことが優れた衝撃吸収特性を示す高強度鋼板
が適していることが判明した。すなわち、熱延された鋼
板中に存在する最適なミクロ組織は、種々の置換型元素
によって容易に固溶強化されるフェライトおよびベイナ
イトを含み、このいずれかを主相として、変形中に硬質
のマルテンサイトに変態する残留オーステナイトを体積
分率で３％以上含む場合に、高い動的変形抵抗を示すこ
とが判明した。また、初期ミクロ組織の第３相にマルテ
ンサイト粒子を含む場合にも、他の条件が満足されれば
本発明の目的とする高い動的変形抵抗を有する良加工性
熱延鋼板を得ることが可能である。As a result of the research conducted by the present inventors, it has been found that a high-strength steel sheet which exhibits excellent impact absorption characteristics is suitable for containing a proper amount of retained austenite in the steel sheet formed as described above. . That is, the optimum microstructure present in the hot-rolled steel sheet contains ferrite and bainite that are easily solid solution strengthened by various substitutional elements. It has been found that when the retained austenite transformed into a site contains 3% or more by volume fraction, high dynamic deformation resistance is exhibited. Further, even when martensite particles are contained in the third phase of the initial microstructure, a good workable hot rolled steel sheet having high dynamic deformation resistance, which is the object of the present invention, can be obtained if other conditions are satisfied. It is possible.
【００１６】本発明の熱延鋼板に含まれる各成分の限定
理由は下記のとおりである。
Ｃ：Ｃはオーステナイトを室温で安定化させて残留させ
るために必要なオーステナイトの安定化に貢献する最も
安価な元素であるために、本発明において最も重要な元
素といえる。鋼材の平均Ｃ量は、室温で確保できる残留
オーステナイト体積分率に影響を及ぼすのみならず、製
造の加工熱処理中に未変態オーステナイト中に濃化する
ことで、残留オーステナイトの加工に対する安定性を向
上させることが出来る。しかしながら、この添加量が
０．０４重量％未満の場合には、最終的に得られる残留
オーステナイト体積分率が３％以上を確保することが出
来ないので０．０４重量％を下限とした。一方、鋼材の
平均Ｃ量が増加するに従って確保可能な残留オーステナ
イト体積分率は増加し、残留オーステナイト体積率を確
保しつつ残留オーステナイトの安定性を確保することが
可能となる。しかしながら、鋼材のＣ添加量が過大にな
ると、必要以上に鋼材の強度を上昇させ、プレス加工等
の成形性を阻害するのみならず、静的な強度上昇に比し
て動的な応力上昇が阻害されると共に、溶接性を低下さ
せることによって部品としての鋼材の利用が制限される
ようになるためにＣ量の上限を０．３重量％とした。The reasons for limiting the components contained in the hot-rolled steel sheet of the present invention are as follows. C: C is the most important element in the present invention because it is the cheapest element that contributes to the stabilization of austenite necessary for stabilizing and remaining austenite at room temperature. The average C content of steel not only affects the retained austenite volume fraction that can be secured at room temperature, but also improves the stability of retained austenite during processing by concentrating it in untransformed austenite during the manufacturing heat treatment. It can be done. However, if the added amount is less than 0.04% by weight, the finally obtained retained austenite volume fraction cannot be 3% or more, so 0.04% by weight was set as the lower limit. On the other hand, the retained austenite volume fraction that can be ensured increases as the average C content of the steel material increases, and it becomes possible to secure the stability of the retained austenite while securing the retained austenite volume ratio. However, if the amount of C added to the steel material becomes excessively large, the strength of the steel material is increased more than necessary, and not only the formability such as press working is hindered but also the dynamic stress increase is caused as compared with the static strength increase. The upper limit of the amount of C is set to 0.3% by weight because the use of the steel material as a part is restricted due to the impediment and deterioration of the weldability.
【００１７】Ａｌ，Ｓｉ：ＡｌとＳｉは共にフェライト
の安定化元素であり、フェライト体積率を増加させるこ
とによって鋼材の加工性を向上させる働きがある。ま
た、Ａｌ，Ｓｉ共にセメンタイトの生成を抑制し、効果
的にオーステナイト中へのＣを濃化させることを可能と
することから、室温で適当な体積分率のオーステナイト
を残留させるためには不可避的な添加元素である。この
ようなセメンタイト生成抑制機能を持つ添加元素として
は、Ａｌ，Ｓｉ以外に、ＰやＣｕ，Ｃｒ，Ｍｏ等が挙げ
られ、このような元素を適切に添加することも同様な効
果が期待される。しかしながら、ＡｌとＳｉの一種もし
くは双方の合計が０．５重量％未満の場合には、セメン
タイト生成抑制の効果が十分でなく、オーステナイトの
安定化に最も効果的な添加されたＣの多くが炭化物の形
で浪費され、本発明に必要な残留オーステナイト体積率
を確保することが出来ないか、もしくは残留オーステナ
イトの確保に必要な製造条件が大量生産工程の条件に適
しないため下限を０．５重量％とした。また、ＡｌとＳ
ｉの一種もしくは双方の合計が３．０重量％を越える場
合には、母相であるフェライトもしくはベイナイトの硬
質化や脆化を招き、歪み速度上昇による変形抵抗の増加
を阻害するばかりでなく、鋼材の加工性の低下、靱性の
低下、さらには鋼材コストの上昇を招き、また化成処理
性等の表面処理特性が著しく劣化するために、３．０重
量％を上限値とした。Al, Si: Al and Si are both stabilizing elements of ferrite, and have the function of improving the workability of the steel material by increasing the ferrite volume ratio. Further, both Al and Si suppress the generation of cementite and enable effective concentration of C in austenite. Therefore, it is unavoidable to retain a suitable volume fraction of austenite at room temperature. Is an additional element. Examples of additional elements having such a cementite formation suppressing function include P, Cu, Cr, and Mo in addition to Al and Si. Proper addition of such elements is expected to have the same effect. . However, when the total amount of one or both of Al and Si is less than 0.5% by weight, the effect of suppressing the formation of cementite is not sufficient, and most of the added C that is most effective for stabilizing austenite is a carbide. The amount of residual austenite volume ratio required for the present invention cannot be secured, or the manufacturing conditions necessary for securing retained austenite are not suitable for the conditions of mass production process. %. Also, Al and S
When the amount of one or both of i exceeds 3.0% by weight, not only the ferrite or bainite as the matrix phase is hardened or embrittled, but also the increase of the deformation resistance due to the increase of the strain rate is hindered. Since the workability of the steel material is lowered, the toughness is lowered, the cost of the steel material is increased, and the surface treatment characteristics such as chemical conversion treatment property are remarkably deteriorated, 3.0% by weight is set as the upper limit value.
【００１８】Ｍｎ，Ｎｉ，Ｃｒ，Ｃｕ，Ｍｏ：Ｍｎ，Ｎ
ｉ，Ｃｒ，Ｃｕ，Ｍｏは全てオーステナイト安定化元素
であり、室温でオーステナイトを安定化させるためには
有効な元素である。特に、溶接性の観点からＣの添加量
が制限される場合には、このようなオーステナイト安定
化元素を適量添加することによって効果的にオーステナ
イトを残留させることが可能となる。また、これらの元
素はＡｌやＳｉ程ではないがセメンタイトの生成を抑制
する効果があり、オーステナイトへのＣの濃化を助ける
働きもする。更に、これらの元素はＡｌ，Ｓｉと共にマ
トリックスであるフェライトやベイナイトを固溶強化さ
せることによって、高速での動的変形抵抗を高める働き
も持つ。しかしながら、これらの元素の１種もしくは２
種以上の添加の合計が０．５重量％未満の場合には、必
要な残留オーステナイトの確保が出来なくなるととも
に、鋼材の強度が低くなり、有効な車体軽量化が達成で
きなくなることから、下限を０．５重量％とした。一
方、これらの合計が３．５重量％を越える場合には、母
相であるフェライトもしくはベイナイトの硬質化を招
き、歪み速度上昇による変形抵抗の増加を阻害するばか
りでなく、鋼材の加工性の低下、靱性の低下、さらには
鋼材コストの上昇を招くために、上限を３．５重量％と
した。Mn, Ni, Cr, Cu, Mo: Mn, N
i, Cr, Cu and Mo are all austenite stabilizing elements and are effective elements for stabilizing austenite at room temperature. In particular, when the amount of C added is limited from the viewpoint of weldability, it is possible to effectively retain austenite by adding an appropriate amount of such an austenite stabilizing element. Further, these elements have an effect of suppressing the formation of cementite, though not so much as Al or Si, and also have a function of helping the concentration of C in austenite. Further, these elements also have a function of enhancing the dynamic deformation resistance at high speed by solid-solution strengthening the matrix ferrite or bainite together with Al and Si. However, one or two of these elements
If the total addition of at least one species is less than 0.5% by weight, it becomes impossible to secure the necessary retained austenite and the strength of the steel material decreases, making it impossible to achieve effective weight reduction of the vehicle body. It was 0.5% by weight. On the other hand, when the total amount of these exceeds 3.5% by weight, the matrix ferrite or bainite is hardened, which not only hinders the increase of the deformation resistance due to the increase of the strain rate, but also the workability of the steel material. The upper limit was set to 3.5% by weight in order to lower the toughness and the steel cost.
【００１９】Ｎｂ，Ｔｉ，Ｖ：また、必要に応じて添加
するＮｂ，Ｔｉ，Ｖは、炭化物、窒化物もしくは炭窒化
物を形成することによって鋼材を高強度化することが出
来るが、その合計が０．３重量％を越えた場合には母相
であるフェライトやベイナイト粒内もしくは粒界に多量
の炭化物、窒化物もしくは炭窒化物として析出し、高速
変形時の可動転位発生源となって、高い動的変形抵抗を
得ることが出来なくなる。また、炭化物の生成は、本発
明にとって最も重要な残留オーステナイト中へのＣの濃
化を阻害し、Ｃを浪費することから上限を０．３重量％
とした。Nb, Ti, V: In addition, Nb, Ti, V added as necessary can strengthen the steel material by forming carbides, nitrides or carbonitrides, but the total of them. When it exceeds 0.3% by weight, a large amount of carbides, nitrides or carbonitrides are precipitated in the matrix of ferrite or bainite grains or in grain boundaries, and become a source of mobile dislocations during high speed deformation. , It becomes impossible to obtain high dynamic deformation resistance. Further, the formation of carbides inhibits the concentration of C in the retained austenite, which is the most important for the present invention, and wastes C, so the upper limit is 0.3% by weight.
And
【００２０】Ｐ：更に、必要に応じて添加するＰは、鋼
材の高強度化や前述のように残留オーステナイトの確保
に有効ではあるが、０．２重量％を越えて添加された場
合には鋼材のコストの上昇を招くばかりでなく、主相で
あるフェライトやベイナイトの変形抵抗を必要以上に高
め、かつ高速変形時の変形抵抗の上昇を阻害する。更
に、耐置き割れ性の劣化や疲労特性、靱性の劣化を招く
ことから、０．２重量％をその上限とした。P: Further, P added as necessary is effective for increasing the strength of the steel material and securing retained austenite as described above. However, when P is added in excess of 0.2% by weight, Not only does this lead to an increase in the cost of the steel material, but it also increases the deformation resistance of the main phase ferrite and bainite more than necessary, and hinders the increase of the deformation resistance during high-speed deformation. Further, 0.2 wt% is set as the upper limit because deterioration of resistance to cracking due to placement, deterioration of fatigue characteristics and deterioration of toughness are caused.
【００２１】Ｂ：また、必要に応じて添加するＢは、粒
界の強化や鋼材の高強度化に有効ではあるが、その添加
量が０．０１重量％を越えるとその効果が飽和するばか
りでなく、必要以上に鋼板強度を上昇させ、高速変形時
の変形抵抗の上昇を阻害すると共に、部品への加工性も
低下させることから、上限を０．０１重量％とした。次
に、本発明者らの実験・検討の結果、フロントサイドメ
ンバー等の衝撃吸収用部材の成形加工に相当する予変形
の量は、部材中の部位によっては最大２０％以上に達す
る場合もあるが、相当歪みとして０％超１０％以下の部
位が大半であり、またこの範囲の予変形の効果を把握す
ることで、部材全体としての予加工後の挙動を推定する
ことが可能であることを見いだした。従って、本発明に
おいては、部材への加工時に与えられる予変形量として
相当歪みにして０％超１０％以下の変形を選択した。B: B, which is added as necessary, is effective for strengthening grain boundaries and strengthening the steel material, but when the addition amount exceeds 0.01% by weight, the effect is saturated. In addition, the steel plate strength is increased more than necessary, the increase of the deformation resistance at the time of high-speed deformation is hindered, and the workability of parts is also decreased. Therefore, the upper limit was made 0.01% by weight. Next, as a result of experiments and studies by the present inventors, the amount of pre-deformation corresponding to the forming process of the impact absorbing member such as the front side member may reach up to 20% or more depending on the part in the member. However, most of the equivalent strains are more than 0% and less than 10%, and by grasping the effect of pre-deformation in this range, it is possible to estimate the behavior of the entire member after pre-processing. I found it. Therefore, in the present invention, as the amount of pre-deformation given to the member during processing, a strain of not less than 0% and not more than 10% in equivalent strain is selected.
【００２２】また、フロントサイドメンバー等の衝撃吸
収用部材は、特徴的にハット型の断面形状をしており、
このような部材の高速での衝突圧潰時の変形を本発明者
らが解析した結果、最大では４０％以上の高い歪みまで
変形が進んでいるものの、吸収エネルギー全体の約７０
％以上が、高速の応力−歪み線図の１０％以下の歪み範
囲で吸収されていることを見いだした。従って、高速で
の衝突エネルギーの吸収能の指標として、１０％以下で
の高速変形時の動的変形抵抗を採用した。特に、歪み量
として３％〜１０％の範囲が最も重要であることから、
高速引張り変形時の相当歪みで３％〜１０％の範囲の平
均応力σｄｙｎをもって衝撃エネルギー吸収能の指標と
した。Further, the shock absorbing member such as the front side member characteristically has a hat-shaped cross section,
As a result of the analysis by the present inventors of the deformation at the time of high-speed collision crushing of such a member, the deformation has advanced to a high strain of 40% or more at the maximum, but about 70% of the total absorbed energy.
It has been found that% or more is absorbed in the strain range of 10% or less of the high-speed stress-strain diagram. Therefore, the dynamic deformation resistance during high-speed deformation at 10% or less was adopted as an index of the impact energy absorption capacity at high speed. Especially, since the range of 3% to 10% is the most important as the strain amount,
The equivalent strain during high-speed tensile deformation was used as an index of impact energy absorption capacity with an average stress σdyn in the range of 3% to 10%.
【００２３】この高速変形時の３％〜１０％の平均応力
σｄｙｎは、鋼材の静的な引張り強度（５×１０-4〜５
×１０-3（１／ｓ）の歪み速度範囲で測定された静的な
引張り試験における最大応力：ＴＳ）の上昇に伴って大
きくなることが一般的である。従って、鋼材の静的な引
張り強度を増加させることは部材の衝撃エネルギー吸収
能の向上に直接寄与する。しかしながら、鋼材の強度が
上昇すると部材への成形性が劣化し、必要な部材形状を
得ることが困難となる。従って、同一の引張り強度（Ｔ
Ｓ）で高いσｄｙｎを持つ鋼材が望ましい。特に部材へ
の加工時の歪みレベルが主に１０％以下であることか
ら、部材への成型時の形状凍結性等の成形性の指標とな
る低歪み領域での応力が低いことが成形性向上のために
は重要である。従って、σｄｙｎ（ＭＰａ）と５×１０
-4〜５×１０-3（１／ｓ）の歪み速度範囲で変形した時
の３〜１０％の相当歪み範囲における変形応力の平均値
σｓｔ（ＭＰａ）の差が大きいほど静的には成形性に優
れ、動的には高い衝撃エネルギーの吸収能を持つと言え
る。この関係で、特に（σｄｙｎ−σｓｔ）≧−０．２
７２×ＴＳ＋３００の関係を満足する鋼材は、実部材へ
の成形性に優れると同時に衝撃エネルギー吸収能が他の
鋼材に比べて高く、部材の総重量を増加させることなく
衝撃エネルギー吸収能を向上させることができる。The average stress σdyn of 3% to 10% at the time of high-speed deformation is the static tensile strength (5 × 10 -4 to 5) of the steel material.
It generally increases as the maximum stress (TS) in a static tensile test measured in a strain rate range of × 10 -3 (1 / s) increases. Therefore, increasing the static tensile strength of the steel material directly contributes to the improvement of the impact energy absorption capacity of the member. However, if the strength of the steel material increases, the formability of the member deteriorates, and it becomes difficult to obtain the required member shape. Therefore, the same tensile strength (T
A steel material having a high σdyn in S) is desirable. In particular, since the strain level during processing into a member is mainly 10% or less, the low stress in the low strain region, which is an index of formability such as shape fixability during the forming into a member, improves the formability. Is important for. Therefore, σdyn (MPa) and 5 × 10
-The more the difference in the average value σst (MPa) of deformation stress in the equivalent strain range of 3 to 10% when deformed in the strain rate range of -4 to 5 × 10 -3 (1 / s), the more statically forming It is said that it has excellent properties and dynamically has a high ability to absorb impact energy. In this relationship, in particular (σdyn−σst) ≧ −0.2
A steel material satisfying the relation of 72 × TS + 300 is excellent in formability into an actual member and has a higher impact energy absorption capacity than other steel materials, and improves impact energy absorption capacity without increasing the total weight of the member. be able to.
【００２４】本発明者らの実験・検討の結果、同一レベ
ルの引張り強度（ＴＳ）に対して、（σｄｙｎ−σｓ
ｔ）は部材への加工が行われる以前の鋼板中に含まれる
残留オーステナイト中の固溶炭素量〔Ｃ〕と鋼材の平均
Ｍｎ等量（Ｍｎｅｑ＝Ｍｎ＋（Ｎｉ＋Ｃｒ＋Ｃｕ＋Ｍ
ｏ）／２）（重量％）によって変化することが見いださ
れた。残留オーステナイト中の炭素濃度は、Ｘ線解析や
メスバウアー分光により実験的に求めることが出来、例
えばＭｏのＫα線を用いたＸ線解析によりフェライトの
（２００）面、（２１１）面及びオーステナイトの（２
００）面、（２２０）面、（３１１）面の積分反射強度
を用いて、Journal of The Iron and SteelInstitute,
206 (1968) p60 に示された方法にて算出できる。本発
明者らが行った実験結果から、このようにして得られた
残留オーステナイト中の固溶〔Ｃ〕と鋼材に添加されて
いる置換型合金元素から求められるＭｎｅｑを用いて計
算される値（Ｍ＝６７８−４２８×〔Ｃ〕−３３×Ｍｎ
ｅｑ）が−１４０以上７０未満の場合に、同一の静的な
引張り強度（ＴＳ）に対して大きな（σｄｙｎ−σｓ
ｔ）を示すことが見いだされた。このときＭが７０以上
では、残留オーステナイトが低歪み領域で硬質のマルテ
ンサイトに変態することから、成形性を支配する低歪み
領域での静的な応力を上昇させてしまい、形状凍結性等
の成形性を劣化させるのみならず、（σｄｙｎ−σｓ
ｔ）の値を小さくすることから、良好な成形性と高い衝
撃エネルギー吸収能の両立が得られないためにＭを７０
未満とした。また、Ｍが−１４０未満の場合には、残留
オーステナイトの変態が高い歪み領域に限定されるため
に、良好な成形性は得られるものの（σｄｙｎ−σｓ
ｔ）を増大させる効果がなくなることからＭの下限を−
１４０とした。As a result of experiments and examinations conducted by the present inventors, for the same level of tensile strength (TS), (σdyn−σs
t) is the amount of solid solution carbon [C] in the retained austenite contained in the steel sheet before processing into a member and the average Mn equivalent amount of the steel material (Mneq = Mn + (Ni + Cr + Cu + M).
It was found to vary depending on o) / 2) (wt%). The carbon concentration in the retained austenite can be experimentally obtained by X-ray analysis or Moessbauer spectroscopy. For example, the (200) plane, (211) plane of ferrite and austenite (2
Using the integrated reflection intensities of the (00) plane, the (220) plane, and the (311) plane, the Journal of The Iron and Steel Institute,
206 (1968) It can be calculated by the method shown in p60. From the results of experiments conducted by the present inventors, a value calculated using Mneq obtained from the solid solution [C] in the retained austenite thus obtained and the substitutional alloying elements added to the steel material ( M = 678-428 × [C] -33 × Mn
eq) is −140 or more and less than 70, a large (σdyn−σs) is obtained for the same static tensile strength (TS).
It was found to exhibit t). At this time, when M is 70 or more, the retained austenite transforms into hard martensite in the low strain region, so that the static stress in the low strain region that governs the formability is increased, and the shape freezeability and the like are increased. Not only does the moldability deteriorate, but (σdyn−σs
Since the value of t) is made small, it is not possible to obtain both good moldability and high impact energy absorption capacity, so M is set to 70
Less than Further, when M is less than −140, the transformation of retained austenite is limited to a high strain region, so that good formability is obtained (σdyn−σs).
Since the effect of increasing t) is lost, the lower limit of M is −
It was set to 140.
【００２５】熱延条件：熱延ままで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
まで熱延工程へ直送し、もしくは一旦冷却した後に１０
００℃〜１３００℃の範囲に再度加熱した後、熱間圧延
を行う。再加熱温度を１０００℃未満とする場合には、
スラブの均一加熱が困難となり、表面キズ発生等の問題
を生じるので、再加熱温度の下限を１０００℃とした。
また、再加熱温度が１３００℃超では、スラブの変形が
激しくなると同時にコスト高となることから、１３００
℃を上限とした。また、熱延仕上げ温度（ＦＴ）がＡｒ
3 変態温度−１０℃未満である場合には（σｄｙｎ−σ
ｓｔ）が低くなる。従って、Ａｒ3 変態温度−１０℃を
熱延仕上げ温度の下限値とする。また熱延仕上げ温度が
Ａｒ3 ＋１００℃超の場合には必要以上に鋼板の強度が
上昇するのみならず、組織の粗大化が起こり、鋼板動的
変形抵抗の上昇を阻害する。また、このような高温で熱
延が完了された場合には鋼板の表面粗度が大きくなり、
表面品位を落とすためＡｒ3 ＋１００℃以下を熱延仕上
げ温度の上限値とする。Hot rolling condition: When the steel sheet of the present invention is produced by hot rolling, the slab adjusted to have a predetermined composition is directly sent to the hot rolling step as it is, or after being cooled once, 10
After heating again in the range of 00 ° C to 1300 ° C, hot rolling is performed. When the reheating temperature is less than 1000 ° C,
Since it becomes difficult to uniformly heat the slab and problems such as surface scratches occur, the lower limit of the reheating temperature is set to 1000 ° C.
If the reheating temperature is higher than 1300 ° C, the slab becomes severely deformed and the cost becomes high.
The upper limit was ℃. Also, the hot rolling finish temperature (FT) is Ar
3 If the transformation temperature is lower than -10 ° C, (σdyn-σ
st) becomes low. Therefore, the Ar 3 transformation temperature of −10 ° C. is set as the lower limit of the hot rolling finish temperature. Further, when the hot rolling finishing temperature is higher than Ar 3 + 100 ° C., not only the strength of the steel sheet is increased more than necessary, but also the structure is coarsened and the increase of the dynamic deformation resistance of the steel sheet is hindered. Further, when hot rolling is completed at such a high temperature, the surface roughness of the steel sheet increases,
In order to reduce the surface quality, the upper limit of the hot rolling finish temperature is Ar 3 + 100 ° C. or less .
【００２６】熱延完了後に鋼板は冷却されるが、このと
きの冷却速度を５℃／秒未満もしくは１００℃／秒超と
することは、大量生産の工程条件上困難であることか
ら、上記値を下限、上限とした。また冷却の方法は一定
の冷却速度で行っても、途中で低冷却速度の領域を含む
ような複数種類の冷却速度の組み合わせであってもよ
い。After the hot rolling is completed, the steel sheet is cooled. However, it is difficult to set the cooling rate at this time to less than 5 ° C./sec or more than 100 ° C./sec because of the process conditions of mass production. Was set as the lower limit and the upper limit. The cooling method may be a constant cooling rate or a combination of a plurality of types of cooling rates including a low cooling rate region in the middle.
【００２７】冷却後鋼板は巻き取り処理が行われるが、
５００℃以上では所定の量の残留オーステナイトを確保
することができないために５００℃未満を上限とした。
また、熱延仕上げ温度（ＦＴ）がＡｒ3 ＋５０℃以上の
場合には４００℃未満で巻取ると、必要以上の強度上昇
を招くと共に、（σｄｙｎ−σｓｔ）の値が小さくなる
ことから熱延仕上げ温度がＡｒ3 ＋５０℃以上の場合の
巻取温度の下限を４００℃とした。また、熱延仕上げ温
度がＡｒ3 ＋５０℃未満の場合には、４２０℃以下で巻
き取った場合に（σｄｙｎ−σｓｔ）の値が小さくなる
ことから、熱延仕上げ温度がＡｒ3 ＋５０℃未満の場合
の巻取温度の下限を４２０℃超とした。最終的に得られ
た鋼板の（σｄｙｎ−σｓｔ）を高めるためには巻き取
り温度を４８０℃以下とすることが望ましい。After cooling, the steel sheet is wound up,
Since it is not possible to secure a predetermined amount of retained austenite at 500 ° C or higher, the upper limit is set to less than 500 ° C.
Further, when the hot rolling finishing temperature (FT) is Ar 3 + 50 ° C. or higher, if the coiling temperature is lower than 400 ° C., the strength is increased more than necessary, and the value of (σdyn−σst) becomes small. The lower limit of the winding temperature when the finishing temperature is Ar 3 + 50 ° C. or higher is 400 ° C. Further, the hot rolling finishing temperature is of less than Ar 3 + 50 ° C., since the when wound at 420 ° C. or less the value of (σdyn-σst) decreases, the hot rolling finishing temperature is lower than Ar 3 + 50 ° C. In this case, the lower limit of the coiling temperature was set to more than 420 ° C. In order to increase (σdyn−σst) of the finally obtained steel plate, it is desirable that the winding temperature be 480 ° C. or lower.
【００２８】[0028]
【実施例】〈実施例１〉
表１に示す２４種類の鋼材を１２００℃に加熱し、各鋼
の成分からＡｒ3 ＝９０１−３２５×％Ｃ＋３３×％Ｓ
ｉ−９２×％Ｍｎｅｑの式（％Ｍｎｅｑ＝％Ｍｎ＋％Ｎ
ｉ／２＋％Ｃｒ／２＋％Ｃｕ／２＋％Ｍｏ／２）で計算
されるＡｒ3 変態温度＋５０℃〜Ａｒ3 変態温度＋１０
０℃の範囲内で熱延を完了し、４５℃／秒の冷却速度で
冷却し、４００℃〜４５０℃の範囲で巻き取った。なお
熱延された鋼板の板厚は３．０mmとした。このようにし
て得られた熱延鋼板の熱延方向（Ｌ方向）とこれに直行
する方向（Ｃ方向）に単軸引張りにより５％の予変形を
付加し、焼き付け処理を模擬するために１７０℃×２０
分の熱処理を行った後に鋼材の動的な特性を調査し、予
変形する前の静的な特性と比較した結果を表２に示し
た。５８８ MPa 以上の引張り強度を有し、鋼の成分が本
発明の範囲内のものについては表中の＊１の欄に示した
値が正すなわち、目的通り（σｄｙｎ−σｓｔ）が（−
０．２７２×ＴＳ＋３００）以上であることがわかる。
〈実施例２〉
表１に示した本発明の成分範囲内である鋼Ｐ２を用い
て、熱延条件、予変形条件及び熱処理条件、を変化させ
た場合の特性を調査した結果を表３および表４に示す。
Ｐ２鋼のＡｒ3 変態温度は上記の式から７６４℃と計算
された。加熱温度は１２００℃一定とした。熱延仕上げ
温度（ＦＴ）がＡｒ3 ＋５０℃以上の８３０℃の場合に
は、No. １，４では巻取り温度が本発明の範囲外である
ために所定の動的変形抵抗の上昇（σｄｙｎ−σｓｔ）
が得られていない。また、No. ５では、熱延仕上げ温度
が本発明の範囲外であるために結果的に残留オーステナ
イト粒径とフェライト粒径の比が０．６よりも大きくな
り、所定の動的変形抵抗σｄｙｎが得られていない。他
の例はすべて本発明の例であり、熱延仕上げ温度、巻取
り温度、予変形量が本発明の範囲内であれば、予変形付
与の形態や予変形後の加工硬化処理（ＢＨ処理：１７０
℃×２０分の熱処理）の有無に関わらず表３中の＊１の
欄の値が正、すなわち所定の動的変形抵抗の上昇（σｄ
ｙｎ−σｓｔ）が得られることがわかる。ここで、Ｌ方
向とは熱延と同一の方向を指し、Ｃ方向はこれと直行す
る方向を指す。EXAMPLES <Example 1> 24 kinds of steel materials shown in Table 1 were heated to 1200 ° C., and from the composition of each steel, Ar 3 = 901-325 ×% C + 33 ×% S.
Formula of i-92 ×% Mneq (% Mneq =% Mn +% N
i / 2 +% Cr / 2 +% Cu / 2 +% Mo / 2) Ar 3 transformation temperature + 50 ° C. to Ar 3 transformation temperature +10
Hot rolling was completed within the range of 0 ° C, cooled at a cooling rate of 45 ° C / sec, and wound in the range of 400 ° C to 450 ° C. The plate thickness of the hot rolled steel plate was 3.0 mm. The hot-rolled steel sheet thus obtained was subjected to uniaxial tension to pre-deform 5% in the hot-rolling direction (L direction) and the direction orthogonal to this (C direction) to simulate the baking process. ℃ × 20
Table 2 shows the results of examining the dynamic properties of the steel material after the heat treatment for a minute and comparing it with the static properties before pre-deforming. For those having a tensile strength of 588 MPa or more and a steel composition within the range of the present invention, the value shown in the column of * 1 in the table is positive, that is, (σdyn-σst) is (-d) as intended.
It is understood that it is 0.272 × TS + 300) or more. <Example 2> The results of investigating the characteristics when the hot rolling conditions, the pre-deformation conditions and the heat treatment conditions were changed using the steel P2 within the composition range of the present invention shown in Table 1 are shown in Table 3 and It shows in Table 4.
The Ar 3 transformation temperature of P2 steel was calculated to be 764 ° C. from the above equation. The heating temperature was constant at 1200 ° C. When the hot rolling finishing temperature (FT) is 830 ° C., which is higher than Ar 3 + 50 ° C., in Nos. 1 and 4, the coiling temperature is out of the range of the present invention, so that the predetermined dynamic deformation resistance increase (σdyn). −σst)
Has not been obtained. Further, in No. 5, since the hot rolling finishing temperature is out of the range of the present invention, the ratio of the retained austenite grain size to the ferrite grain size is consequently larger than 0.6, and the predetermined dynamic deformation resistance σdyn Has not been obtained. All other examples are examples of the present invention, and if the hot rolling finishing temperature, the winding temperature, and the amount of pre-deformation are within the scope of the present invention, the form of pre-deformation and work hardening treatment (BH treatment after pre-deformation) : 170
The value in the column of * 1 in Table 3 is positive regardless of the presence or absence of heat treatment (° C x 20 minutes), that is, a predetermined increase in dynamic deformation resistance (σd
It can be seen that yn-σst) is obtained. Here, the L direction refers to the same direction as the hot rolling, and the C direction refers to the direction orthogonal to this.
【００２９】[0029]
【表１】 [Table 1]
【００３０】[0030]
【表２】 [Table 2]
【００３１】[0031]
【表３】 [Table 3]
【００３２】[0032]
【表４】 [Table 4]
【００３３】[0033]
【発明の効果】本発明により、自動車の軽量化と衝突安
全性の確保の要求に応えることのできる高い動的変形抵
抗を有する衝突時衝撃吸収用良加工性高強度熱延鋼板を
確実に提供することができる。EFFECTS OF THE INVENTION According to the present invention, a good workable high strength hot rolled steel sheet for impact absorption at the time of collision having high dynamic deformation resistance capable of satisfying the requirements for weight reduction of automobiles and ensuring of collision safety can be reliably provided. can do.
【図１】本発明における、衝突時の衝撃エネルギー吸収
能の指標である、５×１０2 〜５×１０3 （１／ｓ）の
歪み速度範囲で変形した時の３〜１０％の相当歪み範囲
における変形応力の平均値σｄｙｎと５×１０-4〜５×
１０-3（１／ｓ）の歪み速度範囲で変形した時の３〜１
０％の相当歪み範囲における変形応力の平均値σｓｔの
差（σｄｙｎ−σｓｔ）と静的な素材強度との関係を示
す図である。FIG. 1 is an equivalent strain of 3 to 10% when deformed in a strain velocity range of 5 × 10 2 to 5 × 10 3 (1 / s), which is an index of impact energy absorption capacity during collision in the present invention. Mean value of deformation stress σdyn in the range and 5 × 10 −4 to 5 ×
3-1 when deformed in the strain rate range of 10 -3 (1 / s)
It is a figure which shows the relationship between the difference ((sigma) dyn- (sigma) st) of the average value (sigma) st of the deformation stress in the equivalent strain range of 0%, and static material strength.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 平９−241788（ＪＰ，Ａ) 特開 平７−62485（ＪＰ，Ａ) 特開 平７−252592（ＪＰ，Ａ) 特開 平７−207413（ＪＰ，Ａ) 特開 平１−184226（ＪＰ，Ａ) 特開 昭64−79345（ＪＰ，Ａ) 国際公開95／029268（ＷＯ，Ａ１) 三浦ら，自動車用衝撃吸収高張力鋼板 の開発，まてりあ ，1996年 ５月20 日，Ｖｏｌ．35 Ｎｏ．３， Ｐ，570 −572 板橋ら，予ひずみを与えられた建築構 造用圧延鋼材ＳＮ490Ｂの高速引張特性, 日本材料学会学術講演会講演論文集, 1997年 ５月22日，Ｖｏｌ．46ｔｈ , Ｐ．291−292 (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 - 38/60 C21D 8/00 - 8/04 C21D 9/46 - 9/48 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-9-241788 (JP, A) JP-A-7-62485 (JP, A) JP-A-7-252592 (JP, A) JP-A-7- 207413 (JP, A) JP-A-1-184226 (JP, A) JP-A 64-79345 (JP, A) International Publication 95/029268 (WO, A1) Miura et al., Development of shock absorbing high-strength steel sheet for automobiles Materia, May 20, 1996, Vol. 35 No. 3, P, 570-572 Itabashi et al., High-speed tensile properties of prestrained rolled steel SN490B for building structures, Proc. Of the Japan Society of Materials Science, May 22, 1997, Vol. 46th, P. 291-292 (58) Fields investigated (Int.Cl. 7 , DB name) C22C 38/00-38/60 C21D 8/00-8/04 C21D 9/46-9/48
Claims (10)
以下、ＳｉとＡｌの一方または双方を合計で０．５％以
上３．０％以下、Ｍｎ，Ｎｉ，Ｃｒ，Ｃｕ，Ｍｏの１種
または２種以上を合計で０．５％以上３．５％以下含
み、残部がＦｅ及び不可避的不純物からなり、最終的に
得られる冷延鋼板のミクロ組織がフェライトおよびベイ
ナイトを含み、このいずれかを主相とし、体積分率で３
％以上の残留オーステナイトを含む第３相との複合組織
であり、残留オーステナイト中の固溶〔Ｃ〕量と鋼材の
平均Ｍｎ等量｛Ｍｎｅｑ＝Ｍｎ＋（Ｎｉ＋Ｃｒ＋Ｃｕ＋
Ｍｏ）／２｝によって決まる値（Ｍ＝６７８−４２８×
〔Ｃ〕−３３×Ｍｎｅｑ）が−１４０以上７０未満で、
５８８ MPa 以上の引張り強度を有し、その鋼材に相当歪
みで０％超１０％以下の予変形を与えた後、５×１０2
〜５×１０3 （１／ｓ）の歪み速度範囲で変形した時の
３〜１０％の相当歪み範囲における変形応力の平均値σ
ｄｙｎ（ＭＰａ）と５×１０-4〜５×１０-3（１／ｓ）
の歪み速度範囲で変形した時の３〜１０％の相当歪み範
囲における変形応力の平均値σｓｔ（ＭＰａ）の差が５
×１０-4〜５×１０-3（１／ｓ）の歪み速度範囲で測定
された静的な引張り試験における最大応力ＴＳ（ＭＰ
ａ）によって表現される式（σｄｙｎ−σｓｔ）≧−
０．２７２×ＴＳ＋３００を満足することを特徴とする
高い動的変形抵抗を有する衝突時衝撃吸収用良加工性高
強度熱延鋼板。1. C: 0.04% or more and 0.3% by weight
Hereinafter, one or both of Si and Al are 0.5% or more and 3.0% or less in total, and one or more of Mn, Ni, Cr, Cu, and Mo are 0.5% or more and 3.5% or more in total. % Or less, the balance consisting of Fe and unavoidable impurities, and the microstructure of the finally obtained cold-rolled steel sheet contains ferrite and bainite. Either of them is the main phase and the volume fraction is 3
% Is a composite structure with a third phase containing at least% retained austenite, and the amount of solid solution [C] in the retained austenite and the average Mn equivalent of steel {Mneq = Mn + (Ni + Cr + Cu +
Mo) / 2} determined value (M = 678-428 ×
[C] −33 × Mneq) is −140 or more and less than 70,
It has a tensile strength of 588 MPa or more, and after subjecting the steel material to pre- deformation of more than 0% and 10% or less with equivalent strain, 5 × 10 2
Average value σ of deformation stress in an equivalent strain range of 3 to 10% when deformed in a strain rate range of ˜5 × 10 3 (1 / s)
dyn (MPa) and 5 × 10 −4 to 5 × 10 −3 (1 / s)
The difference of the average value σst (MPa) of the deformation stress in the equivalent strain range of 3 to 10% when deformed in the strain rate range of 5 is
Maximum stress TS (MP in a static tensile test measured in a strain rate range of × 10 -4 to 5 × 10 -3 (1 / s))
a) expressed by (adyn−σst) ≧ −
0.272 × TS + 300 good workability high strength hot rolled steel sheet for collision impact absorption with <br/> high dynamic deformation resistance which satisfies the.
計で０．３重量％以下更に含むことを特徴とする請求項
１記載の高い動的変形抵抗を有する衝突時衝撃吸収用良
加工性高強度熱延鋼板。2. The impact-absorbing shock having high dynamic deformation resistance according to claim 1, further comprising one or more of Nb, Ti and V in a total amount of 0.3% by weight or less . Good workability and high strength hot rolled steel sheet.
徴とする請求項１または２記載の高い動的変形抵抗を有
する衝突時衝撃吸収用良加工性高強度熱延鋼板。3. The good workability high strength hot rolled steel sheet for impact shock absorption having a high dynamic deformation resistance according to claim 1, further comprising P in an amount of 0.2% by weight or less.
特徴とする請求項１〜３のいずれか１項に記載の高い動
的変形抵抗を有する衝突時衝撃吸収用良加工性高強度熱
延鋼板。4. Better content of 0.01% by weight or less , good workability and high strength for impact shock absorption with high dynamic deformation resistance according to any one of claims 1 to 3. Hot rolled steel sheet.
鋼材の残留オーステナイト体積分率が２．５％超であ
り、かつ、予変形前の残留オーステナイト体積分率と予
変形後の残留オーステナイト体積分率の比が０．４以上
であることを特徴とする請求項１〜４のいずれか１項に
記載の高い動的変形抵抗を有する衝突時衝撃吸収用良加
工性高強度熱延鋼板。5. The residual austenite volume fraction of the steel material after pre-deformation of more than 0% and 10% or more is more than 2.5%, and the residual austenite volume fraction before pre-deformation and after pre-deformation. The ratio of residual austenite volume fraction of is 0.4 or more, good workability and high strength for impact absorption at impact having high dynamic deformation resistance according to any one of claims 1 to 4. Hot rolled steel sheet.
中の残留オーステナイトの平均粒径と、主相であるフェ
ライトもしくはベイナイトの平均粒径の比が０．６以下
であることを特徴とする請求項１〜５のいずれか１項に
記載の高い動的変形抵抗を有する衝突時衝撃吸収用良加
工性高強度熱延鋼板。6. The ratio of the average grain size of retained austenite in the microstructure of the finally obtained hot rolled steel sheet to the average grain size of ferrite or bainite as the main phase is 0.6 or less. A high-workability, high-strength hot-rolled steel sheet having a high dynamic deformation resistance as described in any one of claims 1 to 5 for impact absorption during collision .
以下、ＳｉとＡｌの一方または双方を合計で０．５％以
上３．０％以下、Ｍｎ，Ｎｉ，Ｃｒ，Ｃｕ，Ｍｏの１種
または２種以上を合計で０．５％以上３．５％以下含
み、残部がＦｅ及び不可避的不純物からなる鋳造スラブ
を、鋳造ままで熱延工程へ直送し、もしくは一旦冷却し
た後に１０００℃〜１３００℃の範囲に再度加熱した
後、熱延をＡｒ3 変態温度−１０℃以上Ａｒ3 変態温度
＋１００℃以下の熱延仕上げ温度（ＦＴ）で完了し、そ
の後５℃／秒以上１００℃／秒以下の冷却速度で冷却
し、巻き取る際に、熱延仕上げ温度がＡｒ3 変態温度＋
５０℃以上の場合には４００℃以上５００℃未満の温度
で巻き取り、熱延仕上げ温度がＡｒ3 変態温度＋５０℃
未満の場合には４２０℃超５００℃未満の温度で巻き取
り、最終的に得られる熱延鋼板のミクロ組織がフェライ
トおよびベイナイトを含み、このいずれかを主相とし、
体積分率で３％以上の残留オーステナイトを含む第３相
との複合組織であり、５８８ MPa 以上の引張り強度を有
し、残留オーステナイト中の固溶〔Ｃ〕量と鋼材の平均
Ｍｎ等量｛Ｍｎｅｑ＝Ｍｎ＋（Ｎｉ＋Ｃｒ＋Ｃｕ＋Ｍ
ｏ）／２｝によって決まる値（Ｍ＝６７８−４２８×
〔Ｃ〕−３３×Ｍｎｅｑ）が７０以上１８０以下で、そ
の鋼材に相当歪みで０％超１０％以下の予変形を与えた
後、５×１０2 〜５×１０3 （１／ｓ）の歪み速度範囲
で変形した時の３〜１０％の相当歪み範囲における変形
応力の平均値σｄｙｎ（ＭＰａ）と５×１０-4〜５×１
０-3（１／ｓ）の歪み速度範囲で変形した時の３〜１０
％の相当歪み範囲における変形応力の平均値σｓｔ（Ｍ
Ｐａ）の差が５×１０-4〜５×１０-3（１／ｓ）の歪み
速度範囲で測定された静的な引張り試験における最大応
力ＴＳ（ＭＰａ）によって表現される式（σｄｙｎ−σ
ｓｔ）≧−０．２７２×ＴＳ＋３００を満足することを
特徴とする高い動的変形抵抗を有する衝突時衝撃吸収用
良加工性高強度熱延鋼板の製造方法。7. C: 0.04% or more and 0.3% by weight%
Hereinafter, one or both of Si and Al are 0.5% or more and 3.0% or less in total, and one or more of Mn, Ni, Cr, Cu, and Mo are 0.5% or more and 3.5% or more in total. % Or less, with the balance being Fe and unavoidable impurities, the cast slab is sent directly to the hot rolling process as it is, or once cooled and then heated again in the range of 1000 ° C. to 1300 ° C., the hot rolling is performed with Ar 3 Transformation temperature −10 ° C. or higher and Ar 3 transformation temperature + 100 ° C. or lower is completed at the hot rolling finish temperature (FT), and thereafter, cooling is performed at a cooling rate of 5 ° C./sec or more and 100 ° C./sec or less, and heat is applied when winding. Rolling finish temperature is Ar 3 transformation temperature +
When the temperature is 50 ° C or higher, it is wound at a temperature of 400 ° C or higher and lower than 500 ° C, and the hot rolling finish temperature is Ar 3 transformation temperature + 50 ° C.
Preparative coiled at a temperature below 420 ° C. Ultra 500 ° C. in the case of less than
Ri, microstructure of the finally obtained hot-rolled steel sheet comprises a ferrite and bainite, and this one with the main phase,
It has a composite structure with a third phase containing retained austenite in a volume fraction of 3% or more, and has a tensile strength of 588 MPa or more.
However, the amount of solid solution [C] in the retained austenite and the average Mn equivalent of steel materials {Mneq = Mn + (Ni + Cr + Cu + M
o) / 2} (M = 678-428 ×
[C] -33 × Mneq) is 70 or more and 180 or less, and after subjecting the steel material to pre-deformation of more than 0% and 10% or less with equivalent strain, 5 × 10 2 to 5 × 10 3 (1 / s) of Mean value σdyn (MPa) of deformation stress in the equivalent strain range of 3 to 10% when deformed in the strain rate range and 5 × 10 −4 to 5 × 1
3 to 10 when deformed in the strain rate range of 0 -3 (1 / s)
Mean value of deformation stress σst (M
Pa) difference expressed by the maximum stress TS (MPa) in the static tensile test measured in the strain rate range of 5 × 10 −4 to 5 × 10 −3 (1 / s) (σdyn−σ)
that satisfies the st) ≧ -0.272 × TS + 300
A method for manufacturing a high-strength hot-rolled steel sheet with good workability for impact absorption during collision having high dynamic deformation resistance.
計で０．３重量％以下更に含むことを特徴とする請求項
７記載の高い動的変形抵抗を有する衝突時衝撃吸収用良
加工性高強度熱延鋼板の製造方法。8. The impact-absorbing shock having high dynamic deformation resistance according to claim 7, further comprising one or more of Nb, Ti and V in a total amount of 0.3% by weight or less . Good workability High strength hot rolled steel sheet manufacturing method.
徴とする請求項７または８記載の高い動的変形抵抗を有
する衝突時衝撃吸収用良加工性高強度熱延鋼板の製造方
法。9. The method for producing a good workable high-strength hot-rolled steel sheet for impact shock absorption having high dynamic deformation resistance according to claim 7, further comprising P in an amount of 0.2% by weight or less. .
を特徴とする請求項７〜９のいずれか１項に記載の高い
動的変形抵抗を有する衝突時衝撃吸収用良加工性高強度
熱延鋼板の製造方法。10. A good workability and high strength for impact absorption at impact having a high dynamic deformation resistance according to claim 7, further comprising 0.01% by weight or less of B. Method of manufacturing hot rolled steel sheet.
Priority Applications (9)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25886597A JP3530354B2 (en) | 1997-09-24 | 1997-09-24 | High-workability high-strength hot-rolled steel sheet with high dynamic deformation resistance for impact absorption at impact and manufacturing method thereof |
| EP98900718.2A EP0974677B2 (en) | 1997-01-29 | 1998-01-23 | A method for producing high strength steels having excellent formability and high impact energy absorption properties |
| CN98802157A CN1072272C (en) | 1997-01-29 | 1998-01-23 | High-strength steel sheet highly resistant to dynamic deformation and excellent in workability and process for production thereof |
| US09/355,435 US6544354B1 (en) | 1997-01-29 | 1998-01-23 | High-strength steel sheet highly resistant to dynamic deformation and excellent in workability and process for the production thereof |
| AU55767/98A AU716203B2 (en) | 1997-01-29 | 1998-01-23 | High strength steels having excellent formability and high impact energy absorption properties, and a method for production the same |
| CA002278841A CA2278841C (en) | 1997-01-29 | 1998-01-23 | High strength steels having excellent formability and high impact energy absorption properties, and a method for producing the same |
| PCT/JP1998/000272 WO1998032889A1 (en) | 1997-01-29 | 1998-01-23 | High-strength steel sheet highly resistant to dynamic deformation and excellent in workability and process for the production thereof |
| EP10181439A EP2312008B1 (en) | 1997-01-29 | 1998-01-23 | High-strength steels having high impact energy absorption properties. |
| KR1019997006826A KR100334948B1 (en) | 1997-01-29 | 1998-01-23 | High-strength steel sheet highly resistant to dynamic deformation and excellent in workability and process for the production thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25886597A JP3530354B2 (en) | 1997-09-24 | 1997-09-24 | High-workability high-strength hot-rolled steel sheet with high dynamic deformation resistance for impact absorption at impact and manufacturing method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11100639A JPH11100639A (en) | 1999-04-13 |
| JP3530354B2 true JP3530354B2 (en) | 2004-05-24 |
Family
ID=17326117
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP25886597A Expired - Fee Related JP3530354B2 (en) | 1997-01-29 | 1997-09-24 | High-workability high-strength hot-rolled steel sheet with high dynamic deformation resistance for impact absorption at impact and manufacturing method thereof |
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| Country | Link |
|---|---|
| JP (1) | JP3530354B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH11189839A (en) * | 1997-12-26 | 1999-07-13 | Nippon Steel Corp | High strength steel plate with high dynamic deformation resistance, and its production |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4646871B2 (en) * | 2006-08-12 | 2011-03-09 | 株式会社神戸製鋼所 | Hot-rolled steel sheet with excellent stretch flangeability |
| JP5339765B2 (en) * | 2007-04-17 | 2013-11-13 | 株式会社中山製鋼所 | High strength hot rolled steel sheet and method for producing the same |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6479345A (en) * | 1987-06-03 | 1989-03-24 | Nippon Steel Corp | High-strength hot rolled steel plate excellent in workability and its production |
| JPH0735536B2 (en) * | 1988-01-14 | 1995-04-19 | 株式会社神戸製鋼所 | Manufacturing method of high ductility and high strength composite structure steel sheet |
| JP3066689B2 (en) * | 1993-08-25 | 2000-07-17 | 新日本製鐵株式会社 | High-strength composite structure hot-rolled steel sheet excellent in workability and fatigue properties, and method for producing the same |
| JP3569307B2 (en) * | 1994-01-12 | 2004-09-22 | 新日本製鐵株式会社 | High strength composite structure cold rolled steel sheet having excellent workability and a tensile strength of 45 to 65 kgf / mm2, and a method for producing the same |
| JPH07252592A (en) * | 1994-03-15 | 1995-10-03 | Nippon Steel Corp | Hot rolled high strength steel sheet excellent in formability, low temperature toughness and fatigue property |
| TW363082B (en) * | 1994-04-26 | 1999-07-01 | Nippon Steel Corp | Steel sheet having high strength and being suited to deep drawing and process for producing the same |
| JPH09241788A (en) * | 1996-03-04 | 1997-09-16 | Kawasaki Steel Corp | High tensile strength steel plate excellent in impact resistance and its production |
-
1997
- 1997-09-24 JP JP25886597A patent/JP3530354B2/en not_active Expired - Fee Related
Non-Patent Citations (2)
| Title |
|---|
| 三浦ら，自動車用衝撃吸収高張力鋼板の開発，まてりあ ，１９９６年 ５月２０日，Ｖｏｌ．３５ Ｎｏ．３， Ｐ，５７０−５７２ |
| 板橋ら，予ひずみを与えられた建築構造用圧延鋼材ＳＮ４９０Ｂの高速引張特性，日本材料学会学術講演会講演論文集，１９９７年 ５月２２日，Ｖｏｌ．４６ｔｈ ， Ｐ．２９１−２９２ |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH11189839A (en) * | 1997-12-26 | 1999-07-13 | Nippon Steel Corp | High strength steel plate with high dynamic deformation resistance, and its production |
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|---|---|
| JPH11100639A (en) | 1999-04-13 |
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