JPH10317096A - High strength steel sheet for automobile use, excellent in collision-proof stability, and its production - Google Patents
High strength steel sheet for automobile use, excellent in collision-proof stability, and its productionInfo
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- JPH10317096A JPH10317096A JP8054698A JP8054698A JPH10317096A JP H10317096 A JPH10317096 A JP H10317096A JP 8054698 A JP8054698 A JP 8054698A JP 8054698 A JP8054698 A JP 8054698A JP H10317096 A JPH10317096 A JP H10317096A
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- steel sheet
- weight
- automobiles
- strength steel
- collision
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- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は主に自動車の構造部
材や補強材に使用することを企図した優れた耐衝突安全
性を有する自動車用高強度鋼及び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 for automobiles having excellent crash resistance and intended for use as a structural member or reinforcing material of an automobile, and a method for producing the same.
【０００２】[0002]
【従来の技術】自動車の燃費規制を背景とした車体軽量
化を目的に、高強度鋼の適用が拡大してきたが、直近で
は自動車事故を想定した耐衝突安全性に関する法規制が
国内外で急速に拡大・強化されつつあり、高強度鋼への
期待がますます高まっている。2. Description of the Related Art The application of high-strength steel has been expanding for the purpose of weight reduction of a vehicle body in the background of fuel efficiency regulations of automobiles. The expectation for high-strength steel is increasing more and more.
【０００３】しかし、従来の高強度鋼は成形性の向上を
主眼として開発されたものであり、耐衝突安全性の観点
では適用が疑問視されている。耐衝突安全性に優れた自
動車用鋼板及びその製造方法にかかわる従来技術として
特開平７−１８３７２が開示され、耐衝突安全性の指標
として鋼板の高歪速度下における降伏強さを高めること
が提案されているが、部材は成形加工時及び衝突変形時
に歪を受けるため、耐衝撃性の指標としては降伏強さに
加工硬化分を加味することが必要であり、従来技術では
不十分である。However, conventional high-strength steels have been developed with an emphasis on improving formability, and their application has been questioned from the viewpoint of collision safety. Japanese Patent Application Laid-Open No. 7-18372 discloses a prior art relating to a steel sheet for automobiles excellent in collision safety and a method for manufacturing the same, and it is proposed to increase the yield strength of the steel sheet under a high strain rate as an index of collision safety. However, since the member is distorted at the time of forming processing and collision deformation, it is necessary to add work hardening to yield strength as an index of impact resistance, and the conventional technology is insufficient.
【０００４】[0004]
【発明が解決しようとする課題】本発明は上記問題を解
決すべく考案されたもので、優れた耐衝突安全性を有す
る自動車用高強度鋼及びその製造方法を提供することを
目的とするものである。SUMMARY OF THE INVENTION The present invention has been devised to solve the above-mentioned problems, and has as its object to provide a high-strength steel for automobiles having excellent collision safety and a method for producing the same. It is.
【０００５】[0005]
【課題を解決するための手段】本発明は上記課題を達成
するためになされたものであり、耐衝突安全性の向上に
は鋼の加工硬化指数を高めることが基本的に重要であ
り、降伏強さと加工硬化指数を特定範囲に制御すること
により、優れた耐衝突安全性を達成できることを見いだ
し、本発明に到ったのである。その手段は以下に示す通
りである。DISCLOSURE OF THE INVENTION The present invention has been made to achieve the above object, and it is basically important to increase the work hardening index of steel in order to improve collision safety. By controlling the strength and the work hardening index in a specific range, it has been found that excellent collision safety can be achieved, and the present invention has been accomplished. The means are as follows.
【０００６】（１） 鋼板の５％成形加工後のミクロ組
織において、マルテンサイト占積率が３％以上であり、
鋼板の特性として加工硬化指数が０．１３０以上である
ことを特徴とする耐衝突安全性に優れた自動車用高強度
鋼板。(1) In the microstructure of a steel sheet after forming by 5%, the martensite space factor is 3% or more;
A high-strength steel sheet for automobiles having excellent crash safety, characterized by a work hardening index of 0.130 or more as a property of the steel sheet.
【０００７】（２） 化学成分としてＣ：０．０４超〜
０．２５重量％、ＭｎとＣｒの内の１種又は２種：０．
１５〜３．５重量％、ＳｉとＡｌの内の１種又は２種：
０．０１％〜４．０重量％を含み、残部がＦｅを主成分
とし、鋼板の５％成形加工後のミクロ組織において、マ
ルテンサイト占積率が３％以上であり、鋼板特性として
加工硬化指数が０．１３０以上であることを特徴とする
耐衝突安全性に優れた自動車用高強度鋼板。(2) C as a chemical component: more than 0.04
0.25% by weight, one or two of Mn and Cr:
15 to 3.5% by weight, one or two of Si and Al:
0.01% to 4.0% by weight, with the balance being Fe as the main component, the microstructure of the steel sheet after 5% forming, the martensite space factor is 3% or more, and work hardening as a property of the steel sheet. An automotive high-strength steel sheet having an index of 0.130 or more and having excellent collision safety.
【０００８】（３） 化学成分としてＣ：０．０４超〜
０．２５重量％、ＭｎとＣｒの内の１種又は２種：０．
１５〜３．５重量％、ＳｉとＡｌの内の１種又は２種：
０．０１％〜４．０重量％を含み、残部がＦｅを主成分
とし、鋼板の５％成形加工後のミクロ組織において、マ
ルテンサイト占積率が３％以上、フェライト占積率が５
０％以上、平均結晶粒径が１０μｍ以下であり、鋼板特
性として加工硬化指数が０．１３０以上、降伏強さ×加
工硬化指数７０以上であることを特徴とする耐衝突安全
性に優れた自動車用高強度鋼板。(3) C: more than 0.04 as a chemical component
0.25% by weight, one or two of Mn and Cr:
15 to 3.5% by weight, one or two of Si and Al:
The steel sheet contains 0.01% to 4.0% by weight, with the balance being Fe as the main component, and having a martensite space factor of 3% or more and a ferrite space factor of 5% in the microstructure of the steel sheet after 5% forming.
0% or more, an average crystal grain size of 10 μm or less, a work hardening index of 0.130 or more, and a yield strength × work hardening index of 70 or more as characteristics of a steel sheet. For high strength steel sheet.
【０００９】（４） さらに、Ｐ≦０．２重量％を含む
ことを特徴とする前記（２）又は前記（３）に記載の耐
衝突安全性に優れた自動車用高強度鋼板。(4) The high-strength steel sheet for automobiles according to (2) or (3), further comprising P ≦ 0.2% by weight, which is excellent in collision resistance.
【００１０】（５） さらに、Ｓ≦０．０２重量％を含
むことを特徴とする前記（２）又は前記（３）に記載の
耐衝突安全性に優れた自動車用高強度鋼板。(5) The high-strength steel sheet for automobiles according to the above (2) or (3), further comprising S ≦ 0.02% by weight.
【００１１】（６） さらに、Ｃａ：０．０００５〜
０．０１重量％及び／又はＲＥＭ：０．００５〜０．０
５重量％を含むことを特徴とする前記（２）〜前記
（５）の内のいずれか１つに記載の耐衝突安全性に優れ
た自動車用高強度鋼板。(6) Ca: 0.0005-0.05
0.01% by weight and / or REM: 0.005 to 0.0
The high-strength steel sheet for automobiles having excellent collision resistance according to any one of (2) to (5), which contains 5% by weight.
【００１２】（７） さらに、Ｎｉ、Ｃｕ及びＭｏの内
の１種又は２種以上を３．５重量％以下含むことを特徴
とする前記（２）〜前記（６）のいずれか１つに記載の
耐衝突安全性に優れた自動車用高強度鋼板。(7) Further, any one of (2) to (6), wherein one or more of Ni, Cu and Mo is contained in an amount of 3.5% by weight or less. A high-strength steel sheet for automobiles with excellent crash resistance as described.
【００１３】（８） さらに、Ｎｂ、Ｔｉ及びＶの内の
１種又は２種以上を０．３重量％以下含むことを特徴と
する前記（２）〜前記（７）いずれか１つに記載の耐衝
突安全性に優れた自動車用高強度鋼板。(8) The method according to any one of the above (2) to (7), further comprising 0.3% by weight or less of one or more of Nb, Ti and V. High-strength steel sheets for automobiles with excellent collision safety.
【００１４】（９） さらに、Ｂ≦０．０１重量％を含
むことを特徴とする前記（２）〜前記（８）のいずれか
１つに記載の耐衝突安全性に優れた自動車用高強度鋼
板。(9) High strength for automobiles excellent in collision resistance according to any one of (2) to (8), further comprising B ≦ 0.01% by weight. steel sheet.
【００１５】（１０） 鋼片を初期鋼片厚が２５ｍｍ以
上、仕上温度が７６０℃〜９２０℃、最終パス圧延速度
が５００ｍｐｍ以上で熱間圧延を行い、その後、ランア
ウトテーブルにおける７００℃〜３５０℃の平均冷却速
度を２０℃／秒超とする冷却を行い、さらに、３５０℃
以下で巻取を行うことを特徴とする前記（１）〜前記
（９）の内のいずれか１つに記載の耐衝突安全性に優れ
た自動車用熱延高強度鋼板の製造方法。(10) The slab is subjected to hot rolling at an initial slab thickness of 25 mm or more, a finishing temperature of 760 ° C. to 920 ° C., and a final pass rolling speed of 500 mpm or more, and then 700 ° C. to 350 ° C. in a run-out table. Cooling at an average cooling rate of more than 20 ° C./sec.
The method for producing a hot-rolled high-strength steel sheet for automobiles according to any one of the above (1) to (9), wherein the high-strength steel sheet is excellent in collision resistance.
【００１６】（１１） 鋼片を熱間圧延、酸洗、冷延
し、その後、連続焼鈍する際において、Ａｃ1〜Ａｃ3の
温度で１０秒以上保持し、７００℃〜３５０℃の平均冷
却速度を１０℃／秒以上とすることを特徴とする前記
（１）〜前記（９）の内のいずれか１つに記載の耐衝突
安全性に優れた自動車用冷延高強度鋼板の製造方法。(11) When hot rolling, pickling and cold rolling a steel slab, and then performing continuous annealing, the steel slab is kept at a temperature of Ac 1 to Ac 3 for 10 seconds or more, and average cooled at 700 ° C. to 350 ° C. The method for producing a cold-rolled high-strength steel sheet for automobiles having excellent collision resistance according to any one of the above (1) to (9), wherein the speed is 10 ° C./sec or more. .
【００１７】[0017]
【発明の実施の形態】本発明者らは種々の実験検討を重
ねた結果、耐衝突安全性の向上には鋼の加工硬化指数を
高めること（０．１３０以上、好ましくは０．１６０以
上）が基本的に重要であり、降伏強さと加工硬化指数を
特定範囲に制御することにより、優れた耐衝突安全性を
達成できることを見いだし、本発明に到ったのである。BEST MODE FOR CARRYING OUT THE INVENTION As a result of repeated experiments and studies, the present inventors have found that a work hardening index of steel is increased (0.130 or more, preferably 0.160 or more) to improve collision safety. Are fundamentally important, and it has been found that by controlling the yield strength and the work hardening index in a specific range, it is possible to achieve excellent collision safety, and thus have arrived at the present invention.
【００１８】以下にその要旨を述べる。The summary is described below.
【００１９】図１は、部材の耐衝突安全性の指標となる
動的エネルギー吸収量と、鋼板の加工硬化指数の関係を
同一降伏強さクラスのものについて示すものである。鋼
板の加工硬化指数の増大により部材の耐衝突安全性（動
的エネルギー吸収量）が向上しており、部材の耐衝突安
全性の指標として、同一降伏強さクラスであれば鋼板の
加工硬化指数が妥当であることを示している。FIG. 1 shows the relationship between the amount of dynamic energy absorbed as an index of the collision safety of a member and the work hardening index of a steel sheet for the same yield strength class. The collision safety (dynamic energy absorption) of the member is improved by increasing the work hardening index of the steel sheet. As an index of the collision safety of the member, the work hardening index of the steel sheet with the same yield strength class Is valid.
【００２０】さらに降伏強さが異なる場合には図２に示
すように、降伏強さ×加工硬化指数を部材の耐衝突安全
性の指標とすることができることを見いだした。Further, it has been found that when the yield strengths are different, as shown in FIG. 2, the yield strength × work hardening index can be used as an index of the collision safety of the member.
【００２１】ただし、部材が成形加工時に歪を受けるこ
とを考慮して、加工硬化指数は歪５％〜１０％のｎ値で
表現したが、本質的には成形加工後の加工硬化指数が高
いことに最大の特徴を有するものであり、動的エネルギ
ー吸収量向上の観点からは、歪５％以下の加工硬化指
数、歪１０％以上の加工硬化指数も高いことが好まし
い。However, in consideration of the fact that the member is distorted during molding, the work hardening index is represented by an n value of 5% to 10% of strain, but the work hardening index after the forming is essentially high. In particular, it has the largest feature, and from the viewpoint of improving the amount of dynamic energy absorption, it is preferable that the work hardening index of strain 5% or less and the work hardening index of strain 10% or more are also high.
【００２２】部材の動的エネルギー吸収量は次のように
して求めた。すなわち、鋼板を図３、図４に示す部品形
状（コ−ナ−Ｒ＝５ｍｍ）に成形し、先端径５．５ｍｍ
の電極によりチリ発生電流の０．９倍の電流で３５ｍｍ
ピッチでスポット溶接し、１７０℃×２０分の焼付塗装
処理を行った後、約１５０ｋｇの落錘を約１０ｍの高さ
から落下させ、部材を長手方向に圧壊し、その際の荷重
変位線図の面積から変位＝０〜１５０ｍｍの変形仕事を
算出して、動的エネルギー吸収量とした。試験方法の模
式図を図５に示す。The dynamic energy absorption of the member was determined as follows. That is, a steel plate is formed into the part shape (corner R = 5 mm) shown in FIGS. 3 and 4, and the tip diameter is 5.5 mm.
35mm with 0.9 times the current generated by dust
After spot welding at a pitch and performing baking coating treatment at 170 ° C for 20 minutes, a falling weight of about 150 kg is dropped from a height of about 10 m to crush the member in the longitudinal direction, and the load displacement diagram at that time The deformation work with a displacement of 0 to 150 mm was calculated from the area of, and was determined as the dynamic energy absorption. FIG. 5 shows a schematic diagram of the test method.
【００２３】鋼板の加工硬化指数、降伏強さは次のよう
にして求めた。すなわち、鋼板をＪＩＳ−５号試験片
（標点距離５０ｍｍ、平行部幅２５ｍｍ）に加工し、引
張速度１０ｍｍ／分で引張試験し、降伏強さと加工硬化
指数（歪５％〜１０％のｎ値）を求めた。The work hardening index and the yield strength of the steel sheet were determined as follows. That is, a steel plate is processed into a JIS-5 test piece (gauge length 50 mm, parallel part width 25 mm), and subjected to a tensile test at a tensile speed of 10 mm / min, yield strength and work hardening index (strain 5% to 10% n Value).
【００２４】なお、用いた鋼板は板厚１．２ｍｍであ
り、Ｃ＝０．０４超〜０．２５重量％、ＭｎとＣｒの１
種又は２種の合計＝０．１５〜３．５重量％、ＳｉとＡ
ｌの１種又は２種の合計＝０．０１重量％〜４．０重量
％を含み、残部はＦｅを主成分とするものである。The steel plate used had a thickness of 1.2 mm, C was more than 0.04 to 0.25% by weight, and Mn and Cr were 1%.
Species or sum of two = 0.15-3.5% by weight, Si and A
1 or 2 kinds = 0.01% to 4.0% by weight, and the balance is mainly composed of Fe.
【００２５】次に、本発明の鋼板ミクロ組織について詳
述する。Next, the microstructure of the steel sheet of the present invention will be described in detail.
【００２６】マルテンサイトは５％成形加工後における
その占積率を３％以上とすることが必須要件である。マ
ルテンサイトは硬質であり、主に周囲のフェライトに可
動転位を発生させること等により、加工硬化指数を高め
る作用を有している。その占積率が３％未満では成形後
の部材が衝突変形を受けた際に優れた加工硬化能（加工
硬化指数≧０．１３０）を発揮することができず、変形
抵抗（荷重）が低いレベルに留まり変形仕事量が小さく
なるため、動的エネルギー吸収量が低く、耐衝突安全性
の向上が達成できない。It is essential that martensite has a space factor of 3% or more after 5% forming. Martensite is hard and has an effect of increasing the work hardening index mainly by generating movable dislocations in the surrounding ferrite. If the space factor is less than 3%, the member after molding cannot exhibit excellent work hardening ability (work hardening index ≧ 0.130) when subjected to collision deformation, and the deformation resistance (load) is low. Since the amount of deformation work is small at the level, the amount of dynamic energy absorption is low, and improvement in collision safety cannot be achieved.
【００２７】さらにフェライトを占積率で５０％以上
（好ましくは７０％以上）含有させ、平均結晶粒径を円
相当径にして１０μｍ以下（好ましくは５μｍ以下）と
し、マルテンサイトをフェライトに隣接させることが好
ましい。これにより、マルテンサイトがフェライト地中
に微細分散し、加工硬化指数向上作用が局所的な影響に
留まらず鋼板全体に及ぶ様、有効に作用する。Further, ferrite is contained in a space factor of 50% or more (preferably 70% or more), the average crystal grain size is made 10 μm or less (preferably 5 μm or less) in circle equivalent diameter, and martensite is made adjacent to the ferrite. Is preferred. As a result, the martensite is finely dispersed in the ground of the ferrite, and the work hardening index improving effect works effectively so as to extend not only to the local effect but to the entire steel sheet.
【００２８】また、マルテンサイトやフェライト以外の
残部組織はパーライト、ベイナイト、残留γ等の１種あ
るいは２種以上の組合せでよいが、穴拡げ特性が要求さ
れる場合はベイナイト主体とすることが望ましい。The remaining structure other than martensite and ferrite may be one or a combination of two or more of pearlite, bainite, residual γ, and the like. When hole expanding characteristics are required, bainite is preferably used. .
【００２９】なお、残留γは成形加工によりマルテンサ
イトへ加工誘起変態するため、成形加工前に残留オ−ス
テナイトを含むことは好ましく、少量（５％以下）でも
効果を有する。Since the residual γ undergoes work-induced transformation into martensite by molding, it is preferable to contain residual austenite before molding, and even a small amount (5% or less) is effective.
【００３０】次に、化学成分の規制値とその制限理由を
説明する。Next, the regulated values of the chemical components and the reasons for the restrictions will be described.
【００３１】Ｃは、マルテンサイトの確保のために、
０．０４重量％超添加するが、スポット溶接性不良によ
る耐衝突安全性劣化を防止する観点から、その添加上限
を０．２５重量％以下（好ましくは０．２０％以下）と
する。すなわち、耐衝突安全用の部材においてはスポッ
ト溶接が使用されることが多いが、０．２５重量％を越
えるＣを含有している場合、衝突時に接合部が容易に剥
離を起こし、耐衝突安全用部材として用をなさなくなる
のである。C is for securing martensite.
Although it is added in an amount exceeding 0.04% by weight, the upper limit of the addition is set to 0.25% by weight or less (preferably 0.20% or less) from the viewpoint of preventing deterioration of collision safety due to poor spot weldability. That is, although spot welding is often used for members for collision safety, when the content of C exceeds 0.25% by weight, the joint easily peels off at the time of collision, and It is no longer useful as a service member.
【００３２】Ｍｎ、Ｃｒは、オーステナイトを安定化し
てマルテンサイトを確保する作用があるとともに強化元
素である。上記観点から、ＭｎとＣｒの内の１種又は２
種の添加下限量は０．１５重量％以上とする必要があ
る。ただし、過度に添加しても上記効果は飽和し、かえ
ってフェライト変態抑制等の悪影響を生ずるため、添加
上限量は３．５重量％以下とする。Mn and Cr act to stabilize austenite and secure martensite, and are strengthening elements. From the above viewpoint, one or two of Mn and Cr
The lower limit of seed addition must be 0.15% by weight or more. However, even if added excessively, the above effect is saturated and adverse effects such as suppression of ferrite transformation are caused. Therefore, the upper limit of the addition is set to 3.5% by weight or less.
【００３３】Ｓｉ、Ａｌは、マルテンサイトを生成させ
るために有用な元素であり、フェライトの生成を促進
し、炭化物の生成を抑制することにより、マルテンサイ
トを確保する作用があると同時に固溶強化作用と脱酸作
用を有する。上記観点から、ＳｉとＡｌの１種又は２種
の添加下限量は０．０１重量％以上とする必要がある。
ただし、過度に添加しても上記効果は飽和し、かえって
鋼を脆化させるため、ＳｉとＡｌの１種又は２種の添加
上限量は４．０重量％以下とする。Si and Al are elements useful for forming martensite, and have an action of securing martensite by promoting the formation of ferrite and suppressing the formation of carbides. Has action and deoxidation action. From the above viewpoint, the lower limit of the addition of one or two of Si and Al needs to be 0.01% by weight or more.
However, even if added excessively, the above effect is saturated and the steel is rather embrittled. Therefore, the upper limit of the addition of one or two of Si and Al is set to 4.0% by weight or less.
【００３４】特に優れた表面性状が要求される場合は、
Ｓｉ＜０．１重量％とすることにより、Ｓｉスケ−ルを
回避するか、逆にＳｉ≧１．０重量％とすることによ
り、Ｓｉスケ−ルを全面に発生させ目立たなくすること
が望ましい。When particularly excellent surface properties are required,
It is desirable to avoid Si scale by setting Si <0.1% by weight, or conversely, to generate Si scale over the entire surface and make it inconspicuous by setting Si ≧ 1.0% by weight. .
【００３５】Ｐは、マルテンサイトを生成させるために
有用な元素であり、フェライトの生成を促進し同時に固
溶強化作用を有する。ただし、過度に添加しても上記効
果は飽和し、かえって鋼を脆化させる等の悪影響がある
ため、その添加上限量は０．２重量％以下とする。特に
優れた２次加工性、靭性、スポット溶接性、リサイクル
性が要求される場合はその含有量はＰ≦０．０５％（好
ましくは≦０．０２％）とする。P is a useful element for forming martensite, and promotes the formation of ferrite and also has a solid solution strengthening action. However, even if added excessively, the above-mentioned effects are saturated and rather have an adverse effect such as embrittlement of the steel. Therefore, the upper limit of the addition is set to 0.2% by weight or less. When particularly excellent secondary workability, toughness, spot weldability and recyclability are required, the content is set to P ≦ 0.05% (preferably ≦ 0.02%).
【００３６】Ｃａは、硫化物系介在物の形状制御（球状
化）により、成形性（特に穴拡げ比）をより向上させる
ために０．０００５重量％以上添加するが、効果の飽和
さらには介在物の増加による逆効果（穴拡げ比の劣化）
の点からその上限を０．０１重量％とする。また、ＲＥ
Ｍも同様の理由からその添加量を０．００５〜０．０５
重量％とする。Ca is added in an amount of 0.0005% by weight or more to further improve the formability (particularly the hole expansion ratio) by controlling the shape (spheroidization) of the sulfide-based inclusions. The adverse effect of increasing the number of objects (deterioration of hole expansion ratio)
In view of the above, the upper limit is set to 0.01% by weight. Also, RE
M is also added in an amount of 0.005 to 0.05 for the same reason.
% By weight.
【００３７】以上が本発明における主たる成分の添加理
由であるが、強度確保、細粒化等を目的にＮｂ、Ｔｉ、
Ｖを１種または２種以上添加してもよい。ただし、その
上限はコストと効果の兼ね合いからＮｂ、Ｔｉ及びＶの
内の１種又は２種以上を０．３％以下とすることが好ま
しい。The above is the main reason why the main components are added in the present invention.
V may be added alone or in combination of two or more. However, the upper limit is preferably set to 0.3% or less of one or more of Nb, Ti and V in consideration of cost and effect.
【００３８】また、強度確保、耐食性向上等を目的にＣ
ｕ、Ｎｉ、Ｍｏを１種または２種以上添加してもよい。
その上限はコストと効果の兼ね合いからＣｕ、Ｎｉ及び
Ｍｏの内の１種又は２種以上を３．５％以下とすること
が好ましい。In order to ensure strength and improve corrosion resistance, C
One, two or more of u, Ni and Mo may be added.
The upper limit is preferably set to 3.5% or less for one or more of Cu, Ni and Mo from the viewpoint of cost and effect.
【００３９】さらに、強度向上等の目的でＢを添加して
もよい。その上限はコストと効果の兼ね合いからＢ≦
０．０１％とする。Further, B may be added for the purpose of improving the strength and the like. The upper limit is B ≤ due to the balance between cost and effectiveness.
0.01%.
【００４０】Ｓは、硫化物系介在物による成形性（特に
穴拡げ比）、スポット溶接性の劣化防止の観点から、Ｓ
≦０．０２％（好ましくは≦０．００３％）とすること
が好ましい。S is selected from the viewpoints of moldability (particularly hole expansion ratio) due to sulfide-based inclusions and prevention of deterioration of spot weldability.
It is preferable that ≦ 0.02% (preferably ≦ 0.003%).
【００４１】次に、熱延鋼板の製造条件規制値とその制
限理由を説明する。Next, the production condition regulation values of the hot-rolled steel sheet and the reasons for the restriction will be described.
【００４２】第１に、熱間圧延における仕上温度は７６
０℃〜９２０℃とする。７６０℃未満では加工フェライ
トが生成し、加工硬化能や成形性を劣化させる。９２０
℃超ではフェライト占積率の低下や鋼板ミクロ組織の平
均円相当径の粗大化が起こるとともに、所望のマルテン
サイトを得ることが困難となる。First, the finishing temperature in hot rolling is 76
0 ° C to 920 ° C. If the temperature is lower than 760 ° C., processed ferrite is generated, and work hardening ability and moldability are deteriorated. 920
If the temperature exceeds ℃, the ferrite space factor will decrease and the average equivalent circle diameter of the steel sheet microstructure will increase, and it will be difficult to obtain the desired martensite.
【００４３】第２に、熱間圧延における初期鋼片厚は２
５ｍｍ以上とする。なお、鋼片の製造に際しては一般的
な連続鋳造のみならず、いわゆる薄肉連続鋳造の適用も
可能である。また、熱延連続化技術（いわゆるエンドレ
ス圧延）の適用も可能である。２５ｍｍ未満ではフェラ
イト占積率の低下や鋼板ミクロ組織の平均円相当径の粗
大化が起こるとともに、所望のマルテンサイトを得るこ
とが困難となる。Second, the initial billet thickness in hot rolling is 2
5 mm or more. In the production of billets, not only general continuous casting but also so-called thin continuous casting can be applied. In addition, application of a hot rolling continuous technology (so-called endless rolling) is also possible. If it is less than 25 mm, a decrease in the space factor of ferrite and an increase in the average equivalent circle diameter of the microstructure of the steel sheet occur, and it is difficult to obtain desired martensite.
【００４４】第３に、熱間圧延における最終パス圧延速
度は５００ｍｐｍ以上（好ましくは６００ｍｐｍ以上）
とする。５００ｍｐｍ未満ではフェライト占積率の低下
や鋼板ミクロ組織の平均円相当径の粗大化が起こるとと
もに、所望のマルテンサイトを得ることが困難となる。Third, the final pass rolling speed in hot rolling is 500 mpm or more (preferably 600 mpm or more).
And If it is less than 500 mpm, a decrease in the space factor of ferrite and an increase in the average equivalent circle diameter of the steel sheet microstructure occur, and it is difficult to obtain desired martensite.
【００４５】第４に、ランアウトテーブルにおける冷却
は７００〜３５０℃の平均冷却速度を２０℃／秒超とす
る。２０℃／秒以下では所望のマルテンサイトを得るこ
とが困難となる。Fourth, the cooling in the run-out table is performed at an average cooling rate of 700 to 350 ° C. exceeding 20 ° C./sec. At 20 ° C./second or less, it is difficult to obtain desired martensite.
【００４６】７００℃超の冷却については特に規定しな
いが、鋼板ミクロ組織の微細化やフェライト占積率の増
大を狙って、「仕上温度〜７５０℃の平均冷却速度を
２０℃／秒超とする」、「７５０℃〜７００℃の平均
冷却速度を２０℃／秒以下とする」を単独ないしは複合
して行うことが好ましい。Although the cooling at over 700 ° C. is not particularly specified, the average cooling rate from the finishing temperature to 750 ° C. is set to over 20 ° C./sec with the aim of refining the microstructure of the steel sheet and increasing the space factor of ferrite. And "making the average cooling rate at 750 ° C. to 700 ° C. not more than 20 ° C./sec” alone or in combination.
【００４７】第５に、巻取温度は３５０℃以下とする。
３５０℃超では所望のマルテンサイトを得ることが困難
となる。Fifth, the winding temperature is set at 350 ° C. or lower.
If it exceeds 350 ° C., it becomes difficult to obtain desired martensite.
【００４８】次に、冷延鋼板の製造条件規制値とその制
限理由を説明する。Next, the production condition regulation value of the cold rolled steel sheet and the reason for the limitation will be described.
【００４９】冷延鋼板を製造するに際しては、連続焼鈍
条件が最も重要であり、熱延、酸洗、冷延の各製造条件
には特に規制値を設けない。ただし、ミクロ組織の微細
分散化の観点から、熱間圧延における最終パス圧延速度
は５００ｍｐｍ以上（好ましくは６００ｍｐｍ以上）と
することが好ましい。また、焼鈍後に必要に応じ、調質
圧延、電気めっき等を施しても良い。In producing a cold-rolled steel sheet, continuous annealing conditions are the most important, and there are no particular regulated values for the hot rolling, pickling and cold rolling production conditions. However, from the viewpoint of fine dispersion of the microstructure, the final pass rolling speed in hot rolling is preferably 500 mpm or more (preferably 600 mpm or more). After annealing, if necessary, temper rolling, electroplating, or the like may be performed.
【００５０】以下に連続焼鈍条件規制値とその制限理由
を説明する。The continuous annealing condition regulation value and the reason for the limitation will be described below.
【００５１】第１に、Ａｃ1〜Ａｃ3の温度範囲におい
て、１０秒以上保持することが必要である。Ａｃ1未満
ではオ−ステナイトが生成しないため、その後、マルテ
ンサイトを得る事ができず、Ａｃ3超では粗大なオ−ス
テナイトの単相組織となるため、その後、所望のマルテ
ンサイトを得る事ができない。また、１０秒未満ではオ
−ステナイトの生成量が不足するため、その後、所望の
マルテンサイトを得る事ができない。なお、滞在時間の
上限は設備の長大化、ミクロ組織の粗大化を避ける観点
から、２００秒以下が好ましい。[0051] First, in the temperature range of Ac 1 to Ac 3, it is necessary to hold at least 10 seconds. Since austenite is not generated, then it is impossible to obtain martensite, coarse Oh the Ac 3 exceeds - - In Ac less than 1 o to become the austenite single phase structure of, then, to obtain the desired martensite Can not. If the time is less than 10 seconds, the amount of austenite generated is insufficient, so that desired martensite cannot be obtained thereafter. Note that the upper limit of the stay time is preferably 200 seconds or less from the viewpoint of avoiding lengthening of the equipment and coarsening of the microstructure.
【００５２】第２に、７００℃〜３５０℃の平均冷却速
度を１０℃／秒以上とすることが必要である。１０℃／
秒未満では所望のマルテンサイトが得られない。その上
限は特に設けるものではないが、冷却時の温度制御性か
ら、３００℃／秒が好ましい。Second, it is necessary to set the average cooling rate between 700 ° C. and 350 ° C. to 10 ° C./sec or more. 10 ° C /
If the time is less than seconds, desired martensite cannot be obtained. The upper limit is not particularly set, but is preferably 300 ° C./sec from the viewpoint of temperature controllability during cooling.
【００５３】[0053]
【実施例】表１に示す化学成分を有する鋼を鋳造して得
た鋼片を用いて、第２の表１及び第２の表２に示す製造
条件により、鋼板を得た。本発明例が鋼番１〜１２、鋼
番１６〜１７、鋼番２２〜３１であり、比較例が鋼番１
３〜１５、鋼番１８〜２１である。得られた鋼板の最終
製品板厚は鋼番１が１．２ｍｍ、鋼番２〜３が２．９ｍ
ｍ、鋼番４及び鋼番２２〜３１が１．４ｍｍ、鋼番５〜
７が２．３ｍｍ、鋼番８が１．６ｍｍ、鋼番９〜１５が
１．８ｍｍ、鋼番１６〜２１が０．８ｍｍである。な
お、鋼番１〜１５及び鋼番２２〜３１は最終製品が熱延
鋼板、鋼番１６〜２１は最終製品が冷延鋼板である。鋼
板ミクロ組織と機械的性質を表３に示す。EXAMPLE A steel sheet was obtained from a steel slab obtained by casting steel having the chemical components shown in Table 1 under the manufacturing conditions shown in Tables 2 and 3. The invention examples are steel numbers 1 to 12, steel numbers 16 to 17, steel numbers 22 to 31, and the comparative example is steel number 1
3 to 15, steel numbers 18 to 21. As for the final product thickness of the obtained steel sheet, steel number 1 is 1.2 mm, steel numbers 2-3 are 2.9 m.
m, steel number 4 and steel numbers 22 to 31 are 1.4 mm, steel number 5
7 is 2.3 mm, steel number 8 is 1.6 mm, steel numbers 9 to 15 are 1.8 mm, and steel numbers 16 to 21 are 0.8 mm. Steel numbers 1 to 15 and steel numbers 22 to 31 are hot rolled steel sheets as final products, and steel numbers 16 to 21 are cold rolled steel sheets as final products. Table 3 shows the steel sheet microstructure and mechanical properties.
【００５４】本発明例では比較例を格段に越える優れた
耐衝突安全性（加工硬化指数≧０．１３０、降伏強さ×
加工硬化指数≧７０）を有する自動車用高強度鋼板が得
られている。なお、本発明例はスポット溶接性もたがね
試験において剥離破断がなく、良好であった。In the examples of the present invention, excellent collision resistance (work hardening index ≧ 0.130, yield strength ×
A high-strength steel sheet for automobiles having a work hardening index ≧ 70) has been obtained. In addition, the example of this invention did not have peeling fracture | rupture in the spot test also in spot welding property, and was favorable.
【００５５】ミクロ組織は以下の方法で評価した。The microstructure was evaluated by the following method.
【００５６】フェライト、マルテンサイト及び残部組織
の同定、存在位置の観察、及び平均円相当径と占積率の
測定はナイタ−ル試薬及び特開昭５９−２１９４７３に
開示された試薬により鋼板圧延方向断面を腐食した倍率
１０００倍の光学顕微鏡写真により行った。The identification of ferrite, martensite and the remaining structure, the observation of the existing position, and the measurement of the average equivalent circle diameter and the space factor were carried out using a nitral reagent and a reagent disclosed in JP-A-59-219473. The cross section was corroded by an optical microscope photograph at a magnification of 1000 times.
【００５７】特性評価は以下の方法で実施した。The characteristics were evaluated by the following methods.
【００５８】引張試験はＪＩＳ−５号（標点距離５０ｍ
ｍ、平行部幅２５ｍｍ）を用い引張速度１０ｍｍ／分で
実施し、引張強さ（ＴＳ）、降伏強さ（ＹＳ）、全伸び
（Ｔ．Ｅｌ）、加工硬化指数（歪５％〜１０％のｎ値）
を求め、ＹＳ×加工硬化指数を計算した。The tensile test was conducted according to JIS-5 (gauge length 50 m).
m, parallel part width 25 mm) at a tensile speed of 10 mm / min, tensile strength (TS), yield strength (YS), total elongation (T.El), work hardening index (strain 5% to 10%) N value of
And YS × work hardening index was calculated.
【００５９】スポット溶接性は鋼板板厚の平方根の５倍
の先端径を有する電極によりチリ発生電流の０．９倍の
電流で接合したスポット溶接試験片をたがねで破断させ
た時にいわゆる剥離破断を生じたら不適とした。The spot weldability is so-called peeling when a spot weld test piece joined by an electrode having a tip diameter 5 times the square root of the thickness of the steel sheet with a current 0.9 times the dust generation current is broken with a chisel. If it broke, it was unsuitable.
【００６０】[0060]
【表１】 [Table 1]
【００６１】[0061]
【表２】 [Table 2]
【００６２】[0062]
【表３】 [Table 3]
【００６３】[0063]
【表４】 [Table 4]
【００６４】[0064]
【発明の効果】本発明により従来にない優れた耐衝突安
全性を有する自動車用高強度鋼板を低コストかつ安定的
に提供することが可能となったため、高強度鋼板の使用
用途・使用条件が格段に広がり、工業上、経済上の効果
は非常に大きい。According to the present invention, it has become possible to stably provide low-cost and high-strength steel sheets for automobiles having unprecedented excellent collision safety. It spreads dramatically, and the industrial and economic effects are extremely large.
【図１】 鋼板の加工硬化指数と動的エネルギー吸収量
との関係を示す図である。FIG. 1 is a diagram showing a relationship between a work hardening index of a steel sheet and a dynamic energy absorption amount.
【図２】 鋼板の降伏強さ×加工硬化指数と動的エネル
ギー吸収量（Ｊ）との関係を示す図である。FIG. 2 is a view showing a relationship between a yield strength of a steel sheet × a work hardening index and a dynamic energy absorption (J).
【図３】 衝撃圧壊試験方法に用いられる部品（ハット
モデル）の概観図である。FIG. 3 is a schematic view of a part (hat model) used in an impact crush test method.
【図４】 試験片形状の断面図であるFIG. 4 is a sectional view of a test piece shape.
【図５】 衝撃圧壊試験方法の模式図である。FIG. 5 is a schematic view of an impact crush test method.
１ 天板 ２ 試験片 ３ スポット溶接 ４ 落錘 ５ 架台 ６ ショック・アブソーバー DESCRIPTION OF SYMBOLS 1 Top plate 2 Test piece 3 Spot welding 4 Drop weight 5 Mounting base 6 Shock absorber
Claims (11)
いて、マルテンサイト占積率が３％以上であり、鋼板の
特性として加工硬化指数が０．１３０以上であることを
特徴とする耐衝突安全性に優れた自動車用高強度鋼板。1. A steel sheet having a microstructure after 5% forming of a steel sheet having a martensite space factor of 3% or more and a work hardening index of 0.130 or more as a characteristic of the steel sheet. High-strength steel sheets for automobiles with excellent safety.
５重量％、ＭｎとＣｒの内の１種又は２種：０．１５〜
３．５重量％、ＳｉとＡｌの内の１種又は２種：０．０
１％〜４．０重量％を含み、残部がＦｅを主成分とし、
鋼板の５％成形加工後のミクロ組織において、マルテン
サイト占積率が３％以上であり、鋼板特性として加工硬
化指数が０．１３０以上であることを特徴とする耐衝突
安全性に優れた自動車用高強度鋼板。2. As a chemical component, C: more than 0.04 to 0.2.
5% by weight, one or two of Mn and Cr: 0.15
3.5% by weight, one or two of Si and Al: 0.0
1% to 4.0% by weight, the balance being Fe as a main component,
An automobile having excellent crash safety characterized in that the steel sheet has a microstructure after forming processing of 5%, a martensite space factor of 3% or more, and a work hardening index of 0.130 or more as a characteristic of the steel sheet. For high strength steel sheet.
５重量％、ＭｎとＣｒの内の１種又は２種：０．１５〜
３．５重量％、ＳｉとＡｌの内の１種又は２種：０．０
１％〜４．０重量％を含み、残部がＦｅを主成分とし、
鋼板の５％成形加工後のミクロ組織において、マルテン
サイト占積率が３％以上、フェライト占積率が５０％以
上、平均結晶粒径が１０μｍ以下であり、鋼板特性とし
て加工硬化指数が０．１３０以上、降伏強さ×加工硬化
指数７０以上であることを特徴とする耐衝突安全性に優
れた自動車用高強度鋼板。3. The chemical component as C: more than 0.04 to 0.2
5% by weight, one or two of Mn and Cr: 0.15
3.5% by weight, one or two of Si and Al: 0.0
1% to 4.0% by weight, the balance being Fe as a main component,
In the microstructure of the steel sheet after 5% forming, the martensite space factor is 3% or more, the ferrite space factor is 50% or more, the average crystal grain size is 10 μm or less, and the work hardening index is 0. A high-strength steel sheet for automobiles excellent in collision safety, characterized by being 130 or more and yield strength x work hardening index of 70 or more.
特徴とする請求項２又は請求項３に記載の耐衝突安全性
に優れた自動車用高強度鋼板。4. The high-strength steel sheet for automobiles excellent in collision resistance according to claim 2, further comprising P ≦ 0.2% by weight.
を特徴とする請求項２又は請求項３に記載の耐衝突安全
性に優れた自動車用高強度鋼板。5. The high-strength steel sheet for automobiles excellent in collision resistance according to claim 2, further comprising S ≦ 0.02% by weight.
重量％及び／又はＲＥＭ：０．００５〜０．０５重量％
を含むことを特徴とする請求項２〜請求項５の内のいず
れか１つに記載の耐衝突安全性に優れた自動車用高強度
鋼板。6. Ca: 0.0005 to 0.01
% By weight and / or REM: 0.005 to 0.05% by weight
The high-strength steel sheet for automobiles having excellent crash safety according to any one of claims 2 to 5, characterized by comprising:
又は２種以上を３．５重量％以下含むことを特徴とする
請求項２〜請求項６のいずれか１つに記載の耐衝突安全
性に優れた自動車用高強度鋼板。7. The resistance to any one of claims 2 to 6, further comprising 3.5% by weight or less of one or more of Ni, Cu and Mo. High-strength steel sheets for automobiles with excellent collision safety.
は２種以上を０．３重量％以下含むことを特徴とする請
求項２〜請求項７いずれか１つに記載の耐衝突安全性に
優れた自動車用高強度鋼板。8. The collision resistance according to claim 2, further comprising 0.3% by weight or less of one or more of Nb, Ti and V. High-strength steel sheets for automobiles with excellent safety.
を特徴とする請求項２〜請求項８のいずれか１つに記載
の耐衝突安全性に優れた自動車用高強度鋼板。9. The high-strength steel sheet for automobiles excellent in collision resistance according to claim 2, further comprising B ≦ 0.01% by weight.
上温度が７６０℃〜９２０℃、最終パス圧延速度が５０
０ｍｐｍ以上で熱間圧延を行い、その後、ランアウトテ
ーブルにおける７００℃〜３５０℃の平均冷却速度を２
０℃／秒超とする冷却を行い、さらに、３５０℃以下で
巻取を行うことを特徴とする請求項１〜請求項９の内の
いずれか１つに記載の耐衝突安全性に優れた自動車用熱
延高強度鋼板の製造方法。10. A slab having an initial slab thickness of 25 mm or more, a finishing temperature of 760 ° C. to 920 ° C., and a final pass rolling speed of 50 mm.
Hot rolling is performed at 0 mpm or more, and then the average cooling rate of 700 ° C. to 350 ° C. in the run-out table is set to 2
Cooling is performed at a temperature exceeding 0 ° C./sec, and winding is performed at 350 ° C. or less, and the collision safety is excellent according to any one of claims 1 to 9. A method for manufacturing hot-rolled high-strength steel sheets for automobiles.
後、連続焼鈍する際において、Ａｃ1〜Ａｃ3の温度で１
０秒以上保持し、７００℃〜３５０℃の平均冷却速度を
１０℃／秒以上とすることを特徴とする請求項１〜請求
項９の内のいずれか１つに記載の耐衝突安全性に優れた
自動車用冷延高強度鋼板の製造方法。11. When hot rolling, pickling and cold rolling a steel slab, and thereafter performing continuous annealing, the steel slab is heated to a temperature of Ac 1 to Ac 3 at a temperature of 1 to 3.
The collision safety according to any one of claims 1 to 9, wherein the temperature is maintained for 0 second or more, and the average cooling rate of 700 ° C to 350 ° C is 10 ° C / second or more. Manufacturing method of excellent cold rolled high strength steel sheet for automobiles.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8054698A JPH10317096A (en) | 1997-03-17 | 1998-03-13 | High strength steel sheet for automobile use, excellent in collision-proof stability, and its production |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8243497 | 1997-03-17 | ||
| JP9-82434 | 1997-03-17 | ||
| JP8054698A JPH10317096A (en) | 1997-03-17 | 1998-03-13 | High strength steel sheet for automobile use, excellent in collision-proof stability, and its production |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH10317096A true JPH10317096A (en) | 1998-12-02 |
Family
ID=26421541
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP8054698A Pending JPH10317096A (en) | 1997-03-17 | 1998-03-13 | High strength steel sheet for automobile use, excellent in collision-proof stability, and its production |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH10317096A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1028167A2 (en) * | 1999-02-09 | 2000-08-16 | Kawasaki Steel Corporation | High tensile strength hot-rolled steel sheet and method of producing the same |
| JP2006520431A (en) * | 2003-02-05 | 2006-09-07 | ユジノール | Method for producing cold rolled ferritic / martensitic duplex steel strip and steel strip obtained thereby |
| WO2008078902A1 (en) * | 2006-12-22 | 2008-07-03 | Posco | Weather-resistant hot rolled steel sheet superior high-strength, and manufacturing method |
-
1998
- 1998-03-13 JP JP8054698A patent/JPH10317096A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1028167A2 (en) * | 1999-02-09 | 2000-08-16 | Kawasaki Steel Corporation | High tensile strength hot-rolled steel sheet and method of producing the same |
| EP1028167A3 (en) * | 1999-02-09 | 2002-04-17 | Kawasaki Steel Corporation | High tensile strength hot-rolled steel sheet and method of producing the same |
| JP2006520431A (en) * | 2003-02-05 | 2006-09-07 | ユジノール | Method for producing cold rolled ferritic / martensitic duplex steel strip and steel strip obtained thereby |
| WO2008078902A1 (en) * | 2006-12-22 | 2008-07-03 | Posco | Weather-resistant hot rolled steel sheet superior high-strength, and manufacturing method |
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