JPH11100635A - High strength cold rolled steel sheet having high dynamic deformation resistance and its production - Google Patents
High strength cold rolled steel sheet having high dynamic deformation resistance and its productionInfo
- Publication number
- JPH11100635A JPH11100635A JP25883497A JP25883497A JPH11100635A JP H11100635 A JPH11100635 A JP H11100635A JP 25883497 A JP25883497 A JP 25883497A JP 25883497 A JP25883497 A JP 25883497A JP H11100635 A JPH11100635 A JP H11100635A
- Authority
- JP
- Japan
- Prior art keywords
- steel sheet
- less
- rolled steel
- deformation resistance
- strain
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Landscapes
- Heat Treatment Of Sheet Steel (AREA)
Abstract
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高強度冷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 relates to a high-strength steel having a high dynamic deformation resistance which can be used for automobile parts and the like and which can contribute to ensuring the safety of occupants by efficiently absorbing impact energy at the time of collision. The present invention relates to a cold-rolled steel sheet and a method for producing 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 has been an increasing expectation for a material exhibiting 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 member is crushed to absorb the energy of the impact, so that the impact on the occupant can be reduced.
【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。[0003] Since the strain rate of deformation applied to each part at the time of an automobile collision reaches up to about 10 3 (1 / s), when considering the shock absorbing performance of a material, dynamic deformation in such a high strain rate region is considered. It is necessary to clarify the deformation characteristics. At the same time,
It is considered essential to simultaneously reduce the weight of automobile bodies with the aim of conserving energy and reducing CO 2 emissions, and for this purpose 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 proposed CAMP-ISIJ.
Vol. 9 (1996) p. 1112 to 1115,
We report the high-speed deformation characteristics and the impact energy absorption capacity of a high-strength thin steel sheet. Among them, the dynamic strength in the high strain rate region of about 10 3 (1 / s) is 10 −3 (1 / s). It greatly increases compared to the static strength at a low strain rate, and the strain rate dependence of the deformation resistance changes by the strengthening mechanism of the material. Among them, TRIP (transformation induced plasticity) type steel and DP ( It is reported that a ferrite / martensite (two phase) type steel has both excellent formability and shock absorbing ability as compared with 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号公報には、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こと
を開示しているが、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
をどのように制御すべきかは明確にされていない。Japanese Patent Application Laid-Open No. 7-18372 discloses a high-strength steel sheet having excellent impact resistance including retained austenite and a method of manufacturing the same. Although it is disclosed that the problem is solved only by raising, it is not clarified how to control the properties of the retained austenite other than the amount of the retained austenite in order to improve the shock absorbing ability.
【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、どの様な基準に従って材料選定を行
うべきかは未だ明らかにはされていない。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 constituent materials affecting the absorption of the impact energy at the time of the collision of the automobile are gradually being elucidated, the automotive parts having excellent impact energy absorption capability are being elucidated. It has not yet been clarified what characteristics should be focused on and what criteria should be used for material selection as steel materials. In addition, automotive parts are formed by pressing steel into the required part shape and then, after being generally painted and baked, are assembled into the automobile and face an actual collision phenomenon.
However, it has not yet been clarified what steel material strengthening mechanism is suitable for improving the impact energy absorbing ability at the time of collision of the steel material after performing such pre-deformation and 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。本発明の要旨は次のとおりであ
る。SUMMARY OF THE INVENTION The present invention relates to a high-strength steel sheet having high impact energy absorbing ability, which is a steel material formed into a part for absorbing impact energy at the time of collision such as a front side member and used. It is intended to provide a manufacturing method. The gist of the present invention 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〕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７０以上２５０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）が予変形を与える前の
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≧０．７６６×ＴＳ
＋２５０を満足することを特徴とする高い動的変形抵抗
を有する高強度冷延鋼板。(1) By weight%, C: 0.04% or more.
3% or less, one or both of Si and Al in total of 0.5
% Or more and 3.0% or less, one or more of Mn, Ni, Cr, Cu and Mo are contained in a total of 0.5% or more and 3.5% or less, with the balance being Fe and inevitable impurities. The microstructure of the cold-rolled steel sheet obtained as described above contains a ferrite and bainite, and is a composite structure with a third phase containing either one of the main phases and having a retained volume of 3% or more of retained austenite. [C] and average Mn equivalent of steel material 材 Mneq = Mn + (Ni + Cr + Cu +
Mo) / 2} (M = 678-428 ×
[C] −33 × Mneq) is 70 or more and 250 or less, and after giving a predeformation of more than 0% and 10% or less with considerable strain to the steel material, 5 × 10 2 to 5 × 10 3 (1 / s). The average value σdyn (MPa) of the deformation stress in the equivalent strain range of 3 to 10% when deformed in the strain rate range is 5 × 10 −4 to 5 × 10 −3 (1 / s) before giving the pre-deformation. Maximum stress TS (MP) in a static tensile test measured in the strain rate range
The expression σdyn ≧ 0.766 × TS expressed by a)
A high-strength cold-rolled steel sheet having high dynamic deformation resistance, which satisfies +250.
【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高強度冷延鋼
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高
強度冷延鋼板。 （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
抗を有する高強度冷延鋼板。(2) A high-strength cold-rolled steel having high dynamic deformation resistance according to (1), further comprising one or more of Nb, Ti and V in a total amount of 0.3% by weight or less. steel sheet. (3) The high-strength cold-rolled steel sheet having high dynamic deformation resistance according to (1) or (2), further containing P in an amount of 0.2% by weight or less. (4) The high-strength cold-rolled steel sheet having high dynamic deformation resistance according to any one of (1) to (3), further comprising 0.01% by weight or less of B.
【００１０】（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０．３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高強度冷延鋼板。 （６）最終的に得られた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高強度冷延鋼板。(5) The residual austenite volume fraction of the steel after the pre-deformation of more than 0% and 10% or less is more than 2.5%, and the residual austenite volume fraction and pre-deformation before the pre-deformation Any one of (1) to (4), wherein the ratio of the remaining retained austenite volume fraction is 0.3 or more
A high-strength cold-rolled steel sheet having a high dynamic deformation resistance according to 1. (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 a main phase is 0.6 or less. The high-strength cold-rolled steel sheet having high dynamic deformation resistance according to any one of (1) to (5).
【００１１】（７）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
した後に再度加熱し、熱延後巻き取った熱延鋼板を酸洗
後冷延し、連続焼鈍工程で焼鈍して最終的な製品とする
際に、０．１×（Ａｃ3 −Ａｃ1 ）＋Ａｃ1 ℃以上Ａｃ
3 ＋５０℃以下の温度で１０秒〜３分焼鈍した後に、１
〜１０℃／秒の一次冷却速度で５５０〜７００℃の範囲
の一次冷却停止温度まで冷却し、引き続いて１０〜２０
０℃／秒の二次冷却速度で２００〜３２０℃の二次冷却
停止温度まで冷却した後、２５０〜５００℃の温度範囲
で１５秒〜２０分保持し、室温まで冷却することを特徴
とする、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〕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＝６
７８−４２８×〔Ｃ〕−３３×Ｍｎｅｑ）が７０以上２
５０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）が予変
形を与える前の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≧
０．７６６×ＴＳ＋２５０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高強度冷延鋼板の製造方法。(7) By weight%, C: 0.04% or more.
3% or less, one or both of Si and Al in total of 0.5
% Or more and 3.0% or less, and one or more of Mn, Ni, Cr, Cu and Mo in total of 0.5% or more and 3.5% or less, with the balance being Fe and unavoidable impurities. Is directly sent to the hot rolling process as cast, or once cooled and then heated again, hot rolled and rolled hot rolled steel sheet is pickled, cold rolled, and annealed in a continuous annealing process to obtain the final product. In this case, 0.1 × (Ac 3 −Ac 1 ) + Ac 1 ° C. or more
3 After annealing for 10 seconds to 3 minutes at a temperature of
Cool at a primary cooling rate of 〜１０10 ° C./sec to a primary cooling stop temperature in the range of 550 to 700 ° C., followed by 10 to 20 ° C.
After cooling to a secondary cooling stop temperature of 200 to 320 ° C. at a secondary cooling rate of 0 ° C./sec, hold for 15 seconds to 20 minutes in a temperature range of 250 to 500 ° C. and cool to room temperature. The microstructure of the finally obtained cold-rolled steel sheet contains ferrite and bainite, and has a composite structure with a third phase containing any one of these as a main phase and containing retained austenite of 3% or more by volume. Average Mn equivalent of solid solution [C] in austenite and steel material ｛Mneq = Mn + (Ni
+ Cr + Cu + Mo) / 2} (M = 6
78-428 × [C] -33 × Mneq) 70 or more 2
After giving a pre-deformation of more than 0% and not more than 10% with a considerable strain to the steel material at 50 or less, 5 × 10 2 to 5 × 10 3 (1 / s)
The average value σdyn (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) before applying the pre-deformation Σdyn ≧ expressed by the maximum stress TS (MPa) in a static tensile test measured in the strain rate range of
A method for producing a high-strength cold-rolled steel sheet having high dynamic deformation resistance, which satisfies 0.766 × TS + 250.
【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高強度冷延鋼板
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高
強度冷延鋼板の製造方法。(8) A high-strength cold-rolled steel having high dynamic deformation resistance according to (7), further comprising one or more of Nb, Ti, and V in a total amount of 0.3% by weight or less. Steel plate manufacturing method. (9) The method for producing a high-strength cold-rolled steel sheet having high dynamic deformation resistance according to (7) or (8), further comprising 0.2% by weight or less of P.
【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高強度冷延鋼板の製造方法。(10) The method for producing a high-strength cold-rolled steel sheet having high dynamic deformation resistance according to any one of (7) to (9), further comprising B in an amount of 0.01% by weight or less. .
【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、この様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、このように部材への
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。DESCRIPTION OF THE PREFERRED EMBODIMENTS A member for absorbing a shock such as a front side member of an automobile at the time of a collision is manufactured by bending or pressing a steel plate. The impact of an automobile collision is applied after it has been worked in this way, and generally after it has been baked. Therefore, it is necessary to provide a steel sheet having a high impact energy absorbing ability after the members are processed and processed.
【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
板に適していることが判明した。すなわち、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高強度冷延鋼板の提供が可能と
なる。As a result of the research conducted by the present inventors, it has been found that in such a molded real member, it is suitable for a high-strength steel plate exhibiting excellent shock absorption characteristics if the steel plate contains an appropriate amount of retained austenite. did. In other words, the optimal microstructure includes ferrite and bainite, which are easily solid-solution strengthened by various substitutional elements, and the volume of residual austenite, which is transformed into hard martensite during deformation, is defined as the main phase. It was found that when containing 3% or more in percentage, high dynamic deformation resistance was exhibited. In addition, even when martensite particles are contained in the third phase of the initial microstructure, if other conditions are satisfied, it is possible to provide a high-strength cold-rolled steel sheet having high dynamic deformation resistance, which is the object of the present invention. Becomes
【００１６】本発明に規定する冷延鋼板の各成分の限定
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Ｃ含有量の上限を０．３重量％とした。The reasons for limiting each component of the cold-rolled steel sheet specified in 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, which is necessary for stabilizing austenite at room temperature to remain. The average C content of the steel material not only affects the retained austenite volume fraction that can be secured at room temperature, but also increases the stability of the retained austenite to processing by enriching in untransformed austenite during the thermomechanical heat treatment during production. Can be done. However, if the addition amount is less than 0.04% by weight, the finally obtained residual austenite volume fraction cannot be 3% or more, so the lower limit was made 0.04% by weight. On the other hand, the retained austenite volume fraction that can be secured increases as the average C content of the steel material increases, and it becomes possible to secure the stability of retained austenite while securing the retained austenite volume fraction. However, when the amount of C added to the steel material is excessive, the strength of the steel material is increased more than necessary, not only impairing the formability such as press working, but also increasing the dynamic stress as compared with the static strength increase. Since the use of steel as a part is restricted by lowering the weldability while inhibiting the weldability, the upper limit of the C content is set to 0.3% by weight.
【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すること
から、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，Ｍ
ｏ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に添加された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Ｓｉの一種もしくは双方の合計が３．０％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 ferrite stabilizing elements, and have a function of improving the workability of steel by increasing the volume ratio of ferrite. In addition, since both Al and Si suppress the generation of cementite, it is possible to effectively enrich C in austenite. Therefore, it is necessary to leave austenite having an appropriate volume fraction at room temperature. It is an inevitable additional element. Examples of the additive element having such a cementite generation suppressing function include P, Cu, Cr, and M in addition to Al and Si.
and the like, and the same effect can be expected by appropriately adding such an element. However, Al and Si
If one or both of them are less than 0.5% by weight, the effect of suppressing the formation of cementite is not sufficient, and most of the most effectively added C for stabilizing austenite is wasted in the form of carbide. Since the volume ratio of retained austenite required for the present invention cannot be secured, or the manufacturing conditions required for securing the retained austenite are not suitable for the conditions of the mass production process, the lower limit was set to 0.5% by weight. On the other hand, if the sum of one or both of Al and Si exceeds 3.0%, hardening or embrittlement of the ferrite or bainite as the mother phase is caused, and the increase in deformation resistance due to an increase in strain rate is hindered. On the other hand, the upper limit was set to 3.0% by weight because the workability and toughness of the steel material were lowered, the cost of the steel material was increased, and the surface treatment properties such as chemical conversion property were significantly deteriorated.
【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 addition amount of C 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. In addition, these elements are not as effective as Al and Si, but have the effect of suppressing the generation of cementite, and also work to assist the enrichment of C in austenite. Further, these elements have a function of increasing the dynamic deformation resistance at high speed by solid-solution strengthening the matrix ferrite and bainite together with Al and Si. However, one or two of these elements
If the total of the addition of more than one kind is less than 0.5% by weight, the required residual austenite cannot be secured, and the strength of the steel material becomes low, so that effective vehicle weight reduction cannot be achieved. 0.5 wt%. On the other hand, if the sum of them exceeds 3.5% by weight, hardening of the ferrite or bainite which is the parent phase is caused, and not only the increase in deformation resistance due to the increase in strain rate is inhibited, but also the workability of the steel material is reduced. The upper limit is set at 3.5% by weight in order to cause a decrease in the toughness, a decrease in the toughness, and an increase in the cost of the steel material.
【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: Nb, Ti, V added as necessary can increase the strength of steel by forming carbide, nitride or carbonitride. Exceeds 0.3% by weight, a large amount of carbides, nitrides or carbonitrides precipitates in ferrite or bainite grains which are a parent phase or in grain boundaries, and becomes a mobile dislocation generating source during high-speed deformation. High dynamic deformation resistance cannot be obtained. Also, the formation of carbides inhibits the enrichment of C in the retained austenite, which is the most important for the present invention, and wastes C, so that 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: P added as necessary is effective in increasing the strength of the steel material and securing the retained austenite as described above. However, when added in excess of 0.2% by weight, Not only does the cost of the steel material rise, but also the deformation resistance of the main phase, ferrite and bainite, is unnecessarily increased, and the deformation resistance during high-speed deformation is hindered. In addition, 0.2% by weight was set as the upper limit because deterioration of storage crack resistance and deterioration of fatigue characteristics and 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変形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 required, is effective for strengthening grain boundaries and increasing the strength of steel materials. However, if the added amount exceeds 0.01% by weight, the effect is only saturated. Rather, the upper limit was set to 0.01% by weight because the steel sheet strength was unnecessarily increased to prevent an increase in deformation resistance at the time of high-speed deformation and the workability to parts was also reduced. Next, as a result of experiments and studies conducted by the present inventors, the amount of pre-deformation corresponding to the forming process of the shock 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 parts have an equivalent strain of more than 0% and 10% or less, and by grasping the effect of the pre-deformation in this range, it is possible to estimate the behavior of the member as a whole after the pre-deformation. Was found. Therefore, in the present invention, a deformation of more than 0% and 10% or less is selected as a substantial strain as a pre-deformation amount given at the time of processing the member.
【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、
この様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。The shock absorbing member such as the front side member has a characteristic hat-shaped cross section.
As a result of analyzing the deformation of such a member at the time of collision crushing at high speed, the deformation has progressed to a high strain of 40% or more at the maximum, but about 70% of the total absorbed energy.
The above was found to be absorbed in the strain range of 10% or less of the high-speed stress-strain diagram. Therefore, the dynamic deformation resistance at the time of high-speed deformation of 10% or less was adopted as an index of the absorption capacity of the collision energy at high speed. In particular, since the range of 3% to 10% is the most important as the amount of strain, an average stress σdyn in the range of 3% to 10% of the equivalent strain during high-speed tensile deformation was used as an index of the impact energy absorbing ability.
【００２３】この高速変形時の３％〜１０％の平均応力
σｄｙｎ（ＭＰａ）は、予変形や焼き付け処理が行われ
る前の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（ＭＰａ））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
（ＴＳ）で高いσｄｙｎを持つ鋼材が望ましい。この関
係で、特にσｄｙｎ≧０．７６６×ＴＳ＋２５０の関係
を満足する鋼材は、実部材としての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
ることを見いだした。The average stress σdyn (MPa) of 3% to 10% during the high-speed deformation is determined by the static tensile strength (5 × 10 −4 to 5 × 10 −4 ) of the steel material before the pre-deformation or the baking treatment is performed.
Generally, it increases as the maximum stress (TS (MPa) in a static tensile test measured in a strain rate range of −3 (1 / s)) increases. Therefore, increasing the static tensile strength of the steel material directly contributes to improving the impact energy absorbing ability of the member. However, when the strength of the steel material increases, the formability of the member deteriorates, and it becomes difficult to obtain a required member shape. Therefore, a steel material having the same tensile strength (TS) and high σdyn is desirable. In this connection, a steel material that satisfies the relationship of σdyn ≧ 0.766 × TS + 250 in particular has a higher impact energy absorption capacity as a real member than other steel materials, and does not increase the total weight of the member. Can be improved.
【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〕（重量％）と鋼材の平均Ｍｎ
等量｛Ｍｎｅｑ＝Ｍｎ＋（Ｎｉ＋Ｃｒ＋Ｃｕ＋Ｍｏ）／
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（２
００）面、（２１１）面及びオーステナイトの（２０
０）面、（２２０）面、（３１１）面の積分反射強度を
用いて、Journal of The Iron and SteelInstitute,206
(1968),p.60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、この様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×Ｍｎｅｑ）
が７０以上２５０以下の場合に、同一の静的な引張り強
度（ＴＳ）に対して大きなσｄｙｎを示すことが見いだ
された。この場合において、Ｍ＞２５０では、実質的に
変形中の残留オーステナイトの変態による強度上昇の効
果が極めて低い歪み領域にのみ限られるために、部材へ
の予変形時にほぼすべての残留オーステナイトが浪費さ
れ、高速変形時のσｄｙｎの上昇に寄与しなくなること
から、Ｍの上限を２５０とした。また、Ｍが７０未満の
場合には、変形途中での残留オーステナイトの変態は進
行するものの、変態の進行が低歪み領域では十分に起こ
らないことから、相当歪みで３％〜１０％の範囲での平
均応力σｄｙｎが低いままに保たれ、静的な引張り強度
ＴＳに対してσｄｙｎ≧０．７６６×ＴＳ＋２５０の関
係を満足しなくなるので、Ｍの下限を７０とした。As a result of experiments and studies conducted by the present inventors, for the same level of tensile strength (TS), σdyn is the amount of dissolved carbon in the retained austenite contained in the steel sheet before the member is processed. [C] (% by weight) and average Mn of steel material
Equivalent ΔMneq = Mn + (Ni + Cr + Cu + Mo) /
It was found to vary by 2% (% by weight).
The carbon concentration in the retained austenite can be determined experimentally by X-ray analysis or Mossbauer spectroscopy.
By X-ray analysis using Mo's Kα ray, (2
(00) plane, (211) plane and austenitic (20) plane.
Journal of The Iron and Steel Institute, 206, using the integrated reflection intensity of the (0), (220), and (311) planes.
(1968), p.60. From the experimental results performed by the present inventors, a value calculated using the solid solution [C] in the residual austenite thus obtained and Mneq obtained from the substitutional alloy element added to the steel material ( M = 678-428 × [C] −33 × Mneq)
Is greater than or equal to 70 and less than or equal to 250, it is found that a large σdyn is exhibited for the same static tensile strength (TS). In this case, when M> 250, substantially all of the retained austenite is wasted at the time of pre-deformation of the member, since the effect of the increase in strength due to the transformation of the retained austenite during deformation is substantially limited to only a very low strain region. The upper limit of M is set to 250 because it does not contribute to the increase in σdyn during high-speed deformation. When M is less than 70, the transformation of the retained austenite during the deformation progresses, but the progress of the transformation does not sufficiently occur in the low strain region, so that the equivalent strain is in the range of 3% to 10%. Is kept low and the relationship of σdyn ≧ 0.766 × TS + 250 is not satisfied with respect to the static tensile strength TS, so the lower limit of M was set to 70.
【００２５】製造条件：熱延後冷延・焼鈍して本発明の
鋼板を製造する場合には、所定の成分に調整されたスラ
ブを、鋳造ままで熱延工程へ直送し、もしくは一旦冷却
した後再加熱して熱延を行い、その後酸洗し、冷延し、
次いで連続焼鈍することで最終製品とする。この時、熱
延仕上げ温度は鋼の化学成分によって決まるＡｒ3 変態
温度以上で行うのが一般的であるが、Ａｒ3 から１０℃
程度低温までであれば最終的な鋼板の特性を劣化させな
い。また、冷却後の巻取温度は鋼の化学成分によって決
まるベイナイト変態開始温度以上とすることで、冷延時
の荷重を必要以上に高めることがさけられるが、冷延の
全圧下率が小さい場合にはこの限りでなく、鋼のベイナ
イト変態温度以下で巻き取られても最終的な鋼板の特性
を劣化させない。また、冷延の全圧下率は、最終板厚と
冷延荷重の関係から設定されるが、４０％以上であれば
最終的な鋼板の特性を劣化させない。Manufacturing conditions: When manufacturing the steel sheet of the present invention by cold rolling and annealing after hot rolling, a slab adjusted to a predetermined component is directly sent to a hot rolling process as cast, or once cooled. After reheating and hot rolling, then pickling, cold rolling,
Then, it is made into a final product by continuous annealing. At this time, the hot rolling finishing temperature is generally carried out by determined by Ar 3 transformation temperature or more chemical components of the steel, Ar 3 from 10 ° C.
Up to a low temperature, the properties of the final steel sheet are not deteriorated. In addition, by setting the coiling temperature after cooling to be higher than the bainite transformation start temperature determined by the chemical composition of the steel, the load during cold rolling can be increased more than necessary, but when the total rolling reduction of the cold rolling is small. Is not limited to this, and the properties of the final steel sheet are not deteriorated even if the steel sheet is wound below the bainite transformation temperature of the steel. Further, the total rolling reduction of the cold rolling is set from the relationship between the final sheet thickness and the cold rolling load, but if it is 40% or more, the properties of the final steel sheet are not deteriorated.
【００２６】冷延後焼鈍する際に、焼鈍温度が鋼の化学
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Ｐ２７３、で表現される０．１×（Ａｃ3 −Ａ
ｃ1 ）＋Ａｃ1 ℃未満の場合には、焼鈍温度で得られる
オーステナイト量が少ないので、最終的な鋼板中に安定
して残留オーステナイトを残すことができないために、
０．１×（Ａｃ3 −Ａｃ1 ）＋Ａｃ1 ℃を焼鈍温度の下
限とした。また焼鈍温度がＡｃ3 ＋５０℃を越えても何
ら鋼板の特性を改善することができない一方で製造コス
トの上昇を招くために、焼鈍温度の上限をＡｃ3 ＋５０
℃とした。この温度での焼鈍時間は鋼板の温度均一化と
オーステナイト量の確保のために最低１０秒以上必要で
ある。しかし、３分超では効果が飽和するのみならずコ
ストアップにつながることから、３分を上限とした。When performing annealing after cold rolling, the temperatures Ac 1 and Ac 3 are determined by the chemical composition of the steel (for example, “Steel and Materials Science”: W. C. Leslie, translated by Shigeyasu Koda, Maruzen P273). 0.1 × (Ac 3 -A
When the temperature is less than c 1 ) + Ac 1 ° C., the amount of austenite obtained at the annealing temperature is small, so that the residual austenite cannot be stably left in the final steel sheet.
0.1 × (Ac 3 −Ac 1 ) + Ac 1 ° C. was set as the lower limit of the annealing temperature. In order to cause an increase in manufacturing cost while the annealing temperature is not possible to improve the properties of any steel sheet exceeds the Ac 3 + 50 ℃, Ac 3 +50 the upper limit of the annealing temperature
° C. The annealing time at this temperature is required to be at least 10 seconds or more in order to equalize the temperature of the steel sheet and secure the austenite amount. However, if the time exceeds 3 minutes, not only the effect is saturated but also the cost increases, so the upper limit is 3 minutes.
【００２７】その後の一次冷却はオーステナイトからフ
ェライトへの変態を促して、未変態のオーステナイト中
にＣを濃化させてオーステナイトの安定化をはかるのに
重要である。この冷却速度が１℃／秒未満にすること
は、必要な生産ライン長を長くしたり、生産速度を極め
て遅くするといった製造上のデメリットを生じるため
に、この冷却速度の下限を１℃／秒とした。一方、冷却
速度が１０℃／秒超の場合にはフェライト変態が十分に
起こらず、最終的な鋼板中の残留オーステナイト確保が
困難となるためにこれを上限とした。この冷却が５５０
℃未満まで行われると、冷却中にパーライトが生成し、
オーステナイト安定化元素であるＣを浪費し、最終的に
十分な量の残留オーステナイトが得られないために、５
５０℃を下限とした。しかしながら、冷却が７００℃超
までしか行われなかった場合にはフェライト変態の進行
が十分ではないので７００℃を上限とした。Subsequent primary cooling is important for promoting the transformation from austenite to ferrite, and for enriching C in untransformed austenite to stabilize austenite. If the cooling rate is less than 1 ° C./sec, there is a disadvantage in manufacturing that the required production line length is lengthened or the production rate is extremely slowed. Therefore, the lower limit of the cooling rate is set to 1 ° C./sec. And On the other hand, when the cooling rate is more than 10 ° C./sec, the ferrite transformation does not sufficiently occur, and it becomes difficult to secure the retained austenite in the final steel sheet. This cooling is 550
When performed below ℃, pearlite is formed during cooling,
Since C, which is an austenite stabilizing element, is wasted and a sufficient amount of retained austenite is not finally obtained, 5
The lower limit was 50 ° C. However, when the cooling was performed only up to over 700 ° C., the progress of ferrite transformation was not sufficient, so 700 ° C. was set as the upper limit.
【００２８】引き続き行われる二次冷却の急速冷却は、
冷却中にパーライト変態や鉄炭化物の析出などが起こら
ないような冷却速度として最低１０℃／秒以上が必要と
なる。但し、この冷却速度を２００℃／秒超にすること
は設備能力上困難であることから、１０〜２００℃を冷
却速度の範囲とした。この二次冷却の冷却停止温度が２
００℃未満の場合には、冷却前に残っていたオーステナ
イトのほぼすべてがマルテンサイトに変態して、最終的
に残留オーステナイトを確保できないので２００℃を下
限とした。また、二次冷却停止温度が３２０℃超の場合
には、最終的に得られる冷延鋼板の動的変形抵抗σｄｙ
ｎが低下するために３２０℃を上限とした。The rapid cooling of the subsequent secondary cooling is as follows.
A cooling rate of at least 10 ° C./sec is required so that pearlite transformation and precipitation of iron carbide do not occur during cooling. However, since it is difficult to increase the cooling rate to more than 200 ° C./sec in terms of facility capacity, the cooling rate is set to 10 to 200 ° C. The cooling stop temperature of this secondary cooling is 2
When the temperature is lower than 00 ° C., almost all of the austenite remaining before cooling is transformed into martensite, and finally retained austenite cannot be secured. Further, when the secondary cooling stop temperature is higher than 320 ° C., the dynamic deformation resistance σdy of the finally obtained cold rolled steel sheet
320 ° C. was set as the upper limit because n decreased.
【００２９】鋼板中に残留しているオーステナイトを室
温で安定にするためには、その一部をベイナイトへ変態
させることでオーステナイト中の炭素濃度を更に高める
ことが必須である。二次冷却停止温度がベイナイト変態
処理のために保持される温度より低温である場合には、
保持温度まで加熱される。このときの加熱速度は５℃／
秒〜５０℃／秒の範囲であれば最終的な特性を劣化させ
ることはない。また逆に二次冷却停止温度がベイナイト
処理温度よりも高温の場合は、ベイナイト処理温度まで
５℃／秒〜２００℃／秒の冷却速度で強制的に冷却して
も、予め目標温度が設定された加熱ゾーンに直接搬送さ
れても、鋼板の最終的な特性を劣化させない。一方、鋼
板が２５０℃未満で保持された場合にも、また５００℃
超に保持された場合にも、十分な量の残留オーステナイ
トを確保できないことから、保持温度の範囲を２５０℃
〜５００℃とした。このとき、２５０℃〜５００℃での
保持が１５秒未満ではベイナイト変態の進行が十分でな
いことから最終的に必要な量の残留オーステナイトを得
ることができず、また、２０分超ではベイナイト変態の
後に鉄炭化物の析出やパーライト変態が起こり、残留オ
ーステナイト生成に不可欠なＣを浪費してしまい、残留
オーステナイトを得ることができなくなるために保持時
間を１５秒から２０分の範囲とした。ベイナイト変態を
促進させるために行う２５０℃〜５００℃の保持は、等
温での保持であっても、または、この温度範囲であれば
意識的に温度変化を与えても最終的な鋼板の特性を劣化
させることはない。In order to stabilize the austenite remaining in the steel sheet at room temperature, it is essential to further increase the carbon concentration in the austenite by transforming a part of it to bainite. If the secondary cooling stop temperature is lower than the temperature maintained for the bainite transformation process,
Heat to holding temperature. The heating rate at this time is 5 ° C /
In the range of seconds to 50 ° C./second, the final characteristics are not deteriorated. Conversely, when the secondary cooling stop temperature is higher than the bainite processing temperature, the target temperature is set in advance even if the secondary cooling stop temperature is forcibly cooled to the bainite processing temperature at a cooling rate of 5 ° C./sec to 200 ° C./sec. Even if the steel sheet is directly conveyed to a heated zone, the final properties of the steel sheet are not deteriorated. On the other hand, if the steel sheet is kept below 250 ° C,
Since a sufficient amount of retained austenite cannot be ensured even when the temperature is kept extremely high, the range of the holding temperature is set to 250 ° C.
~ 500 ° C. At this time, if the holding at 250 ° C. to 500 ° C. is less than 15 seconds, the progress of bainite transformation is not sufficient, so that a finally required amount of retained austenite cannot be obtained. Later, precipitation of iron carbide and pearlite transformation occur, wasting C which is indispensable for generation of retained austenite, and it becomes impossible to obtain retained austenite, so that the retention time was set in the range of 15 seconds to 20 minutes. The holding at 250 ° C. to 500 ° C. to promote the bainite transformation may be carried out at an isothermal temperature, or the properties of the final steel sheet may be changed even if the temperature is intentionally changed within this temperature range. It does not deteriorate.
【００３０】[0030]
【実施例】 〔実施例１〕表１に示す２５種類の鋼材を１２００℃に
加熱し、Ａｒ3 変態温度以上で熱延を完了し、冷却後各
鋼の化学成分で決まるベイナイト変態開始温度以上で巻
き取った鋼帯を酸洗後、冷延して１．０mm厚とした。そ
の後、各鋼の成分からＡｃ1＝７２３−１０．７×Ｍｎ
％−１６．９×Ｎｉ％＋２９．１×Ｓｉ％＋１６．９×
Ｃｒ，Ａｃ3 ＝９１０−２０３×（Ｃ％）1/2 −１５．
２×Ｎｉ％＋４４．７×Ｓｉ％＋１０４×Ｖ％＋３１．
５×Ｍｏ％−３０×Ｍｎ％−１１×Ｃｒ％−２０×Ｃｕ
％＋７００×Ｐ％＋４００×Ａｌ％＋４００×Ｔｉ％、
で計算されるＡｃ1 変態温度とＡｃ3 変態温度から計算
される温度（Ａｃ1 ＋Ａｃ3 ）／２に９０秒加熱し、５
℃／秒で６７０℃まで冷却した後１００℃／秒で３００
℃まで冷却し、再加熱後４００℃で５分のベイナイト変
態処理を行った後に室温まで冷却した冷延鋼板の冷延方
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。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が（０．７６６×ＴＳ＋２５
０）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、焼鈍条件、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Ａｃ1 ，Ａｃ3 変態温度は７４２，
８４８℃と計算された。熱延鋼板を酸洗後１．０mm厚ま
で冷延し、各種の焼鈍条件で焼鈍した。EXAMPLES Example 1 25 kinds of steel materials shown in Table 1 were heated to 1200 ° C., hot rolling was completed at an Ar 3 transformation temperature or higher, and after cooling, a bainite transformation starting temperature determined by a chemical composition of each steel was obtained. After pickling, the steel strip was rolled and cold rolled to a thickness of 1.0 mm. Then, Ac 1 = 723-10.7 × Mn from the components of each steel.
%-16.9 x Ni% + 29.1 x Si% + 16.9 x
Cr, Ac 3 = 910-203 × (C%) 1/2 −15.
2 × Ni% + 44.7 × Si% + 104 × V% + 31.
5 x Mo%-30 x Mn%-11 x Cr%-20 x Cu
% + 700 × P% + 400 × Al% + 400 × Ti%
Is heated for 90 seconds to a temperature (Ac 1 + Ac 3 ) / 2 calculated from the Ac 1 transformation temperature and the Ac 3 transformation temperature calculated in
After cooling to 670 ° C. at 100 ° C./sec.
C., reheated, subjected to bainite transformation treatment at 400 ° C. for 5 minutes, then cooled to room temperature, and then uniaxially tensioned in the cold rolling direction (L direction) and the direction perpendicular thereto (C direction). After adding a 5% pre-deformation and performing a heat treatment at 170 ° C. for 20 minutes to simulate the baking treatment, the dynamic properties of the steel were investigated and compared with the static properties before pre-deformation. The results are shown in Table 2. When the steel composition is within the range of the present invention, the value shown in the column of * 1 in the table is positive, that is, σdyn is (0.766 × TS + 25) as intended.
0) or more. [Example 2] Annealing conditions, pre-deformation conditions and heat treatment conditions, using steel P2 within the component range of the present invention shown in Table 1,
Tables 3 and 4 show the results of investigating the characteristics in the case where is changed. The Ac 1 and Ac 3 transformation temperature of P2 steel is 742,
848 ° C. The hot rolled steel sheet was cold rolled to a thickness of 1.0 mm after pickling, and annealed under various annealing conditions.
【００３１】Ｎｏ．１は焼鈍温度が本発明範囲外であ
り、必要量の残留オーステナイトが得られていない。ま
た、Ｎｏ．２は一次冷却の冷却停止温度が５００℃と本
発明の範囲外であるために、冷却中に出たパーライトに
より、残留オーステナイトの確保が阻害されている。ま
た、Ｎｏ．３は二次冷却の冷却速度が本発明外であるた
めに、冷却中に生成したパーライトにより、残留オース
テナイトの確保が達成されていない。またＮｏ．４は二
次冷却の冷却停止温度が低すぎたためにマルテンサイト
の生成量が多くなり、残留オーステナイトの確保が達成
できていない。また、Ｎｏ．７はベイナイト変態処理温
度が高すぎて、鉄炭化物の生成により残留オーステナイ
トの確保が出来ていない。Ｎｏ．８は二次冷却の停止温
度が本発明の範囲外であるために目標とした高いσｄｙ
ｎが得られていない。更に、Ｎｏ．９では、焼鈍温度を
必要以上に高温としたために、組織の粗大化がすすみ、
残留オーステナイトの粒径が大きくなり、結果として十
分な動的変形抵抗を得ることが出来ない。その他の例に
ついてはすべて本発明の例であり、焼鈍条件が本発明の
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
に関わらず表中の＊１の欄の値が正、すなわち所定の動
的変形抵抗σｄｙｎ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。No. In No. 1, the annealing temperature was out of the range of the present invention, and a required amount of retained austenite was not obtained. In addition, No. In No. 2, since the cooling stop temperature of the primary cooling was 500 ° C., which is outside the range of the present invention, securing of the retained austenite was hindered by pearlite generated during cooling. In addition, No. In No. 3, since the cooling rate of the secondary cooling was outside the present invention, the retention of retained austenite was not achieved by pearlite generated during cooling. No. In No. 4, since the cooling stop temperature of the secondary cooling was too low, the amount of generated martensite increased, and the securing of retained austenite could not be achieved. In addition, No. In No. 7, the bainite transformation treatment temperature was too high, and the retained austenite could not be secured due to the formation of iron carbide. No. 8 is a target high σdy because the secondary cooling stop temperature is outside the range of the present invention.
n has not been obtained. In addition, No. In No. 9, since the annealing temperature was higher than necessary, the structure became coarser,
The particle size of the retained austenite increases, and as a result, sufficient dynamic deformation resistance cannot be obtained. The other examples are all examples of the present invention. If the annealing conditions are within the scope of the present invention, the form of pre-deformation imparting and the work hardening treatment after pre-deformation (BH treatment: heat treatment at 170 ° C. × 20 minutes) It can be seen that the value in the column of * 1 in the table is positive, that is, a predetermined dynamic deformation resistance σdyn is obtained irrespective of the presence or absence of. here,
The L direction refers to the same direction as hot rolling, and the C direction refers to a direction perpendicular to this direction.
【００３２】[0032]
【表１】 [Table 1]
【００３３】[0033]
【表２】 [Table 2]
【００３４】[0034]
【表３】 [Table 3]
【００３５】[0035]
【表４】 [Table 4]
【００３６】[0036]
【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
抗を有する高強度冷延鋼板を確実に提供することができ
る。According to the present invention, it is possible to reliably provide a high-strength cold-rolled steel sheet having a high dynamic deformation resistance and capable of meeting the demand for reducing the weight of an automobile and ensuring the safety of collision.
【図面の簡単な説明】[Brief description of the drawings]
【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 rate range of 5 × 10 2 to 5 × 10 3 (1 / s), which is an index of impact energy absorption capacity at the time of collision in the present invention. It is a figure showing relation between average value σdyn of deformation stress in a range, and static material strength.
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〕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２５０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）が予変形を与える前の
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≧０．７６６×ＴＳ
＋２５０を満足することを特徴とする高い動的変形抵抗
を有する高強度冷延鋼板。C: 0.04% to 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 two or more of Mn, Ni, Cr, Cu, and Mo are 0.5% or more and 3.5 in total. % Or less, the balance being Fe and unavoidable impurities, and the microstructure of the finally obtained cold-rolled steel sheet contains ferrite and bainite.
% And a third phase containing at least 3% of retained austenite. The solid solution [C] in the retained austenite and the average Mn equivalent of the steel material 材 Mneq = Mn + (Ni + Cr + Cu + M)
o) / 2} (M = 678-428 ×
[C] −33 × Mneq) is 70 or more and 250 or less, and after giving a predeformation of more than 0% and 10% or less with considerable strain to the steel material, 5 × 10 2 to 5 × 10 3 (1 / s). The average value σdyn (MPa) of the deformation stress in the equivalent strain range of 3 to 10% when deformed in the strain rate range is 5 × 10 −4 to 5 × 10 −3 (1 / s) before giving the pre-deformation. Maximum stress TS (MP) in a static tensile test measured in the strain rate range
The expression σdyn ≧ 0.766 × TS expressed by a)
A high-strength cold-rolled steel sheet having high dynamic deformation resistance, which satisfies +250.
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高強度冷延鋼板。2. The high-strength cold-rolled steel sheet 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. .
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
する高強度冷延鋼板。3. The high-strength cold-rolled steel sheet having high dynamic deformation resistance according to claim 1, further comprising 0.2% by weight or less of P.
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高強度冷延鋼板。4. The high-strength cold-rolled steel sheet having high dynamic deformation resistance according to claim 1, further comprising B in an amount of 0.01% by weight or less.
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０．３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高強度冷延鋼板。5. A steel material after a predeformation of more than 0% and 10% or less has a retained austenite volume fraction of more than 2.5%, and a residual austenite volume fraction before predeformation and after predeformation. The high-strength cold-rolled steel sheet having high dynamic deformation resistance according to any one of claims 1 to 4, wherein the ratio of the retained austenite volume fraction is 0.3 or more.
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高強度冷延鋼板。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 a main phase is 0.6 or less. The high-strength cold-rolled steel sheet having high dynamic deformation resistance according to any one of claims 1 to 5.
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
た後に再度加熱した後、熱延後巻き取った熱延鋼板を酸
洗後冷延し、連続焼鈍工程で焼鈍して最終的な製品とす
る際に、０．１×（Ａｃ3 −Ａｃ 1 ）＋Ａｃ1 ℃以上Ａ
ｃ3 ＋５０℃以下の温度で１０秒〜３分焼鈍した後に、
１〜１０℃／秒の一次冷却速度で５５０〜７００℃の範
囲の一次冷却停止温度まで冷却し、引き続いて１０〜２
００℃／秒の二次冷却速度で２００〜３２０℃の二次冷
却停止温度まで冷却した後、２５０〜５００℃の温度範
囲で１５秒〜２０分保持し、室温まで冷却することを特
徴とする、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〕と鋼材の平均Ｍｎ等量｛Ｍｎｅｑ＝Ｍｎ＋（Ｎ
ｉ＋Ｃｒ＋Ｃｕ＋Ｍｏ）／２｝によって決まる値（Ｍ＝
６７８−４２８×〔Ｃ〕−３３×Ｍｎｅｑ）が７０以上
２５０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）が
予変形を与える前の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
≧０．７６６×ＴＳ＋２５０を満足する高い動的変形抵
抗を有する高強度冷延鋼板の製造方法。7. C: 0.04% to 0.3% by weight
Hereinafter, one or both of Si and Al should be 0.5% or less in total.
3.0% or less, one of Mn, Ni, Cr, Cu, Mo
Or a total of 0.5% or more and 3.5% or less of two or more
Cast slab with the balance being Fe and unavoidable impurities
Directly to the hot rolling process as cast, or once cooled
After heating again, the rolled hot-rolled steel sheet
After washing, cold rolled and annealed in a continuous annealing process to obtain the final product
0.1 × (AcThree-Ac 1) + Ac1Over A
cThreeAfter annealing for 10 seconds to 3 minutes at a temperature of + 50 ° C. or less,
The primary cooling rate of 1 to 10 ° C / sec is in the range of 550 to 700 ° C.
To the primary cooling stop temperature, and then 10-2
Secondary cooling at 200-320 ° C at a secondary cooling rate of 00 ° C / sec
After cooling to the cooling stop temperature,
Hold for 15 seconds to 20 minutes under ambient temperature and cool to room temperature.
The microstructure of the finally obtained cold rolled steel sheet
Ferrite and bainite, either of which
Contains 3% or more of retained austenite in volume fraction
This is a composite structure with the third phase,
Melt [C] and average Mn equivalent of steel material 材 Mneq = Mn + (N
i + Cr + Cu + Mo) / 2} (M =
678-428 × [C] -33 × Mneq) is 70 or more
250 or less, the equivalent strain of the steel is more than 0% and 10% or less
5 × 10Two~ 5 × 10Three(1 /
s) Equivalent strain of 3 to 10% when deformed in the strain speed range of
The average value of deformation stress σdyn (MPa)
5 × 10 before pre-deformation-Four~ 5 × 10-3(1 / s)
In a static tensile test measured over a range of strain rates
Expression σdyn expressed by the maximum stress TS (MPa)
High dynamic deformation resistance satisfying ≧ 0.766 × TS + 250
A method for producing a high-strength cold-rolled steel sheet having 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高強度冷延鋼板の製
造方法。8. The high-strength cold-rolled steel sheet 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. 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
する高強度冷延鋼板の製造方法。9. The method for producing a high-strength cold-rolled steel sheet having high dynamic deformation resistance according to claim 7, further comprising 0.2% by weight or less of P.
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高強度冷延鋼板の製造方法。10. The method for producing a high-strength cold-rolled steel sheet having high dynamic deformation resistance according to claim 7, further comprising B in an amount of 0.01% by weight or less.
Priority Applications (18)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25883497A JP3530353B2 (en) | 1997-09-24 | 1997-09-24 | High-strength cold-rolled steel sheet with high dynamic deformation resistance for impact absorption at the time of collision and manufacturing method thereof |
| CA002273334A CA2273334C (en) | 1996-11-28 | 1997-11-28 | High strength steels having high impact energy absorption properties and a method for producing the same |
| KR1019997004657A KR100318213B1 (en) | 1996-11-28 | 1997-11-28 | High-strength steel plate having high dynamic deformation resistance and method of manufacturing the same |
| CN97180921A CN1078623C (en) | 1996-11-28 | 1997-11-28 | High-strength steel having high impact energy absorption power and method for mfg. same |
| PCT/JP1997/004359 WO1998023785A1 (en) | 1996-11-28 | 1997-11-28 | High-strength steel plate having high dynamic deformation resistance and method of manufacturing the same |
| EP97913471.5A EP0952235B2 (en) | 1996-11-28 | 1997-11-28 | Method for producing high-strength steels having high impact energy absorption properties |
| AU50679/98A AU711873B2 (en) | 1996-11-28 | 1997-11-28 | High-strength steels having high impact energy absorption properties and a method for producing the same |
| TW086117962A TW384313B (en) | 1996-11-28 | 1997-11-28 | High strength steels having high impact energy absorption properties and a method for producing the same |
| EP10181458A EP2314730B1 (en) | 1996-11-28 | 1997-11-28 | High-strength steels having high impact energy absorption properties. |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| EP10181439A EP2312008B1 (en) | 1997-01-29 | 1998-01-23 | High-strength steels having 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 |
| TW087101096A TW349126B (en) | 1997-01-29 | 1998-01-26 | High strength steels having excellent formability and high impact energy absorption properties, and a method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25883497A JP3530353B2 (en) | 1997-09-24 | 1997-09-24 | High-strength cold-rolled steel sheet with high dynamic deformation resistance for impact absorption at the time of collision and manufacturing method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11100635A true JPH11100635A (en) | 1999-04-13 |
| JP3530353B2 JP3530353B2 (en) | 2004-05-24 |
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| Application Number | Title | Priority Date | Filing Date |
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| JP25883497A Expired - Fee Related JP3530353B2 (en) | 1996-11-28 | 1997-09-24 | High-strength cold-rolled steel sheet with high dynamic deformation resistance for impact absorption at the time of collision and manufacturing method thereof |
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| Country | Link |
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| JP (1) | JP3530353B2 (en) |
Cited By (4)
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| JP2006510802A (en) * | 2002-12-20 | 2006-03-30 | ユジノール（ソシエテ アノニム） | Steel composition for the production of cold rolled multiphase steel products |
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| WO2021125878A1 (en) * | 2019-12-20 | 2021-06-24 | 주식회사 포스코 | Steel for hot forming, hot-formed member, and manufacturing methods therefor |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3619357B2 (en) * | 1997-12-26 | 2005-02-09 | 新日本製鐵株式会社 | High strength steel sheet having high dynamic deformation resistance and manufacturing method thereof |
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