JP3458416B2 - Cold rolled thin steel sheet excellent in impact resistance and method for producing the same - Google Patents
Cold rolled thin steel sheet excellent in impact resistance and method for producing the sameInfo
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- JP3458416B2 JP3458416B2 JP23476293A JP23476293A JP3458416B2 JP 3458416 B2 JP3458416 B2 JP 3458416B2 JP 23476293 A JP23476293 A JP 23476293A JP 23476293 A JP23476293 A JP 23476293A JP 3458416 B2 JP3458416 B2 JP 3458416B2
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Description
【０００１】[0001]
【産業上の利用分野】本発明は、主として自動車用部品
として、プレス成形等の加工が施されて用いられる薄鋼
板に関し、とくに自動車が走行中に万一衝突した場合の
特性, 即ち耐衝撃性が求められる部位の素材として好適
に用いられる冷延薄鋼板に関しての提案である。なお、
本発明における上記「冷延薄鋼板」とは、冷延鋼板およ
びその表面処理鋼板を含むものとする。以下、単に「薄
鋼板」と略記する。最近、地球環境保全の機運が高まっ
てきたことから、自動車からのＣＯ2排出量の低減が求
められている。そのために、自動車車体の軽量化が図ら
れており、それはまた、鋼板の高強度化によって板厚を
低減させることを意味することから、素材としてはプレ
ス成形性と強度の両方に優れたものが求められている。
さらに、自動車車体の設計思想に着目すると、鋼板の単
なる高強度化のみでなく、より大切なことは走行中に万
一衝突した場合の耐衝撃性に優れた鋼板、すなわち高歪
速度で変形した場合の変形抵抗の大きくしかも薄い鋼板
の開発が必要であり、これを実現してこそ自動車の安全
性の向上を伴った車体の軽量化が図られ、より望ましい
自動車用鋼板を提供することができる。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin steel sheet mainly used as an automobile part after being subjected to processing such as press forming, and particularly to a characteristic in the case of collision of the automobile during traveling, that is, impact resistance. This is a proposal regarding a cold-rolled thin steel sheet that is preferably used as a material of a portion where is required. In addition,
The "cold rolled steel sheet" in the present invention means a cold rolled steel sheet and
And its surface-treated steel sheet. Below, simply
"Steel plate". Since the momentum for global environment conservation has recently increased, it has been required to reduce CO 2 emission from automobiles. For this reason, the weight of automobile bodies has been reduced, which means that the strength of the steel sheet is increased to reduce the thickness of the steel sheet.Therefore, materials with both excellent press formability and strength must be used. It has been demanded.
Furthermore, focusing on the design concept of automobile bodies, it is not only the strength of the steel plate that is simply strengthened, but more importantly, the steel plate has excellent impact resistance in the event of a collision during traveling, that is, it is deformed at a high strain rate. In this case, it is necessary to develop a steel sheet that has large deformation resistance and is thin, and it is only when this is realized that the weight of the vehicle body can be reduced while improving the safety of the automobile, and a more desirable automobile steel sheet can be provided. .
【０００２】[0002]
【従来の技術】従来、自動車用鋼板の材質強化の方法
は、フェライト単相組織鋼では主としてSi, Mn, Ｐとい
った置換型元素添加による固溶強化、あるいはフェライ
ト相中にマルテンサイト相, ベイナイト相あるいはオー
ステナイト相を析出させて組織強化した方法が一般的で
ある。例えば、特開昭56−139654号公報等に記載されて
いるように、加工性、時効性を改善するために極低炭素
鋼にTi, Nbを含有させ、さらに加工性を害しない範囲で
Ｐ等の強化成分を含有させて高強度化を図った鋼板が数
多く提案されている。この他にも、例えば特開昭59−19
3221号公報には、Si添加によってさらに高強度化を図る
方法、さらに特開昭60−52528 号公報には低炭素鋼を高
温で焼鈍し、冷却後にマルテンサイト相を析出させて延
性に優れた高強度鋼を製造するという提案もなされてい
る。2. Description of the Related Art Conventionally, a method for strengthening the material of a steel sheet for automobiles has been a solid solution strengthening of ferrite single-phase structure steel mainly by addition of substitutional elements such as Si, Mn and P, or a martensite phase and a bainite phase in a ferrite phase. Alternatively, a method of precipitating an austenite phase to strengthen the structure is common. For example, as described in JP-A-56-139654, etc., ultra-low carbon steel contains Ti and Nb in order to improve workability and aging property, and P is added within a range not impairing workability. Many steel sheets have been proposed that contain strengthening components such as to improve the strength. In addition to this, for example, JP-A-59-19
3221 discloses a method for further strengthening by adding Si, and JP-A-60-52528 discloses that low carbon steel is annealed at a high temperature and, after cooling, precipitates a martensite phase, which is excellent in ductility. Proposals have also been made to produce high strength steel.
【０００３】たしかに、このような方法での鋼板の高強
度化によって、自動車ボディーの板厚減少はある程度可
能となった。しかしながら、これらの提案は、鋼板強度
の指標である降伏強度あるいは引張強度を、歪速度が10
-3〜10-2(s-1) と極めて遅い静的な評価方法に基づいて
判断している。しかしながら、実際の自動車ボディの設
計では、このような“静的”な強度よりも、衝突時の安
全性を考慮した、歪速度10〜104 (s-1) での衝撃的な変
形を伴う“動的”な強度の方がより重要になるため、従
来のかような提案では、自動車車体の軽量化に対しては
真に有効な手段を提供するものとは言えない。Certainly, by increasing the strength of the steel sheet by such a method, the thickness of the automobile body can be reduced to some extent. However, in these proposals, the yield rate or tensile strength, which is an index of steel plate strength, is determined by
-3 to 10 -2 (s -1 ) based on a very slow static evaluation method. However, in actual car body design, rather than such "static" strength, shock deformation at a strain rate of 10 4 to 10 4 (s -1 ) is taken into consideration in consideration of safety at the time of collision. Since "dynamic" strength becomes more important, such conventional proposals do not provide a truly effective means for reducing the weight of automobile bodies.
【０００４】[0004]
【発明が解決しようとする課題】というのは、従来、上
述した静的な強度と動的な強度とは、同じ傾向をもつも
のとして一義的に取り扱っており、主として静的な強度
のみを基準にして判断していた。ところが、発明者らの
研究によると、動的な強度は、必ずしも静的な強度に対
応しておらず、従って、各種改良素材の静的強度の改良
がそのまま動的強度の向上にはつながらないということ
が判った。そして、この傾向は、とくに高張力鋼板につ
いて著しいものがあった。Conventionally, the above-mentioned static strength and dynamic strength are uniquely treated as having the same tendency, and the static strength is mainly used as a standard. I was making a decision. However, according to the research conducted by the inventors, the dynamic strength does not always correspond to the static strength, so that the improvement of the static strength of various improved materials does not directly lead to the improvement of the dynamic strength. I knew that. And this tendency was remarkable especially in high-strength steel sheets.
【０００５】図１は、変形速度と強度との関係に及ぼす
軟鋼と高張力鋼との影響を示すものである。この図に明
らかなように、軟鋼板における変形速度10-3〜10
-2(s-1) の静的強度と、10〜104 (s-1) の動的強度は軟
鋼板の静的強度ほどには高い値を示さないことが判る。
このことは、自動車用高張力鋼板の板厚を静的強度値に
基づいて薄肉化した場合には、動的強度, 即ち、耐衝撃
強度の方は不足するという結果になることを意味してい
る。そして、このことはまた、静的強度値だけを基準に
して高張力鋼板の薄肉化を図ってきた従来の考え方は見
直さなければならないことを示唆している。本発明の目
的は、上述した従来技術が抱えている問題点を克服する
ことにあり、とくに高張力鋼板における静的強度値に対
する動的強度の値が、軟鋼板のそれと同等以上に高い耐
衝撃性に優れた薄鋼板を提供することにある。FIG. 1 shows the effect of mild steel and high-strength steel on the relationship between deformation rate and strength. As is clear from this figure, the deformation rate of mild steel plate is 10 -3 to 10
It can be seen that the static strength of -2 (s -1 ) and the dynamic strength of 10 to 10 4 (s -1 ) are not as high as those of mild steel.
This means that if the thickness of the high-strength steel sheet for automobiles is reduced based on the static strength value, the dynamic strength, that is, the impact strength will be insufficient. There is. And, this also suggests that the conventional concept that has attempted to reduce the thickness of high-strength steel sheet based on only the static strength value must be reviewed. An object of the present invention is to overcome the problems of the above-mentioned conventional techniques, and in particular, the value of the dynamic strength with respect to the static strength value in the high-strength steel sheet is as high as or higher than that of the mild steel sheet. It is to provide a thin steel sheet having excellent properties.
【０００６】[0006]
【課題を解決するための手段】上述した課題に対してそ
の解決を目指して鋭意研究した結果、軟鋼のように低歪
速度下における強度のみならず、高歪速度下における強
度、即ち、耐衝撃強度にも優れた高張力鋼板とするに
は、単に静的強度だけが高い値を示すものでは不十分で
あることが判った。このことはまた、単に高歪速度下に
おける強度、即ち動的強度だけが高い値を示すものを開
発すること（不経済である）で足りることを意味してお
らず、いわゆる、静的強度と動的強度とがうまく釣り合
っていることが必要であるということが判った。すなわ
ち、プレス成形性に優れかつ高歪速度下での耐衝撃強度
にも優れた鋼板は、静動比＝（歪速度 102(s-1) での降
伏応力) ／ (歪速度10-3(s-1) での降伏応力）で定義さ
れる、静動比が 1.6以上の高張力鋼板であれば、自動車
用部品として用いられた場合に、高歪速度下でも軟鋼板
と同等以上の高い強度の歪速度依存性が得られるので、
自動車車体の安全性向上を軽量化の実現にあわせて達成
することができることが判った。[Means for Solving the Problems] As a result of intensive research aimed at solving the above-mentioned problems, as a result, not only the strength under a low strain rate such as mild steel but also the strength under a high strain rate, that is, the impact resistance It has been found that, in order to obtain a high-strength steel sheet that is also excellent in strength, it is not enough that only the static strength shows a high value. This also does not mean that it is sufficient to develop a material having a high strain rate, that is, only a high dynamic strength (which is uneconomical). It has been found that it is necessary to have a good balance with the dynamic strength. In other words, a steel sheet with excellent press formability and impact strength at high strain rate has a static-dynamic ratio = (yield stress at strain rate 10 2 (s -1 )) / (strain rate 10 -3 High yield strength steel sheet with a static-dynamic ratio of 1.6 or more, which is defined by (yield stress at (s -1 )), is equivalent to or better than mild steel sheet even under high strain rate when used as automobile parts. Since high strain rate dependence is obtained,
It has been found that the improvement in safety of the automobile body can be achieved along with the realization of weight reduction.
【０００７】このような知見に基づき発明者らはさら
に、上記静動比におよぼす化学組成と製造条件の影響を
詳細に検討し、以下に述べるような要旨構成からなる自
動車用鋼板を開発した。すなわち、本発明は、Ｃ：0.01
0〜0.10wt％、Si：0.2wt％以下、Mn：0.50〜3.00wt％、
Ｐ：0.01〜0.15wt％、Ｓ：0.01wt％以下を含み、そして
Ti：0.03wt％以下およびNb：0.03wt％以下を、このTiと
Nbおよび前記Ｃとの関係が、次式；0.1≦（２Nb＋Ti）
／Ｃ≦0.5の関係を満たすように含有し、残部はFeおよ
び不可避的不純物からなり、かつフェライトと体積比で
10〜50％のマルテンサイトとの２相組織を有する耐衝撃
性に優れた冷延薄鋼板である。Based on such knowledge, the inventors further studied in detail the influence of the chemical composition and the manufacturing conditions on the above-mentioned static-dynamic ratio, and developed a steel sheet for automobile having the following constitution. That is, the present invention uses C: 0.01
0 to 0.10 wt%, Si: 0.2 wt% or less, Mn: 0.50 to 3.00 wt%,
P: 0.01 to 0.15 wt%, S: 0.01 wt% or less, and
Ti: 0.03 wt% or less and Nb: 0.03 wt% or less with this Ti
The relationship between Nb and C is as follows; 0.1 ≦ (2Nb + Ti)
/C≦0.5, the balance is Fe and unavoidable impurities, and the volume ratio to ferrite is
It is a cold-rolled thin steel sheet having a two-phase structure with 10 to 50% martensite and having excellent impact resistance.
【０００８】そして、上記冷延薄鋼板は、Ｃ：0.010〜
0.10wt％、Si：0.2 wt％以下、Mn：0.50〜3.00wt％、
Ｐ：0.01〜0.15wt％、Ｓ：0.01wt％以下を含み、そして
Ti：0.03wt％以下およびNb：0.03wt％以下を、このTiと
Nbおよび前記Ｃとの関係が、次式；
0.1≦（２Nb＋Ti）／Ｃ≦0.5
の関係を満たすように含有し、残部はFeおよび不可避的
不純物からなる成分組成を有する鋼材を熱間，冷間で圧
延し、その冷間圧延後の仕上焼鈍を、780〜900℃の温度
で行い、その冷却過程において 500℃までの冷却を15℃
/sec以上50℃/sec以下で行い、さらに500℃〜300℃まで
の冷却を５℃/sec〜35℃/secの冷却速度で行うことによ
って得ることができる。The cold-rolled thin steel sheet has a C: 0.010-
0.10 wt%, Si: 0.2 wt% or less, Mn: 0.50 to 3.00 wt%,
P: 0.01 to 0.15 wt%, S: 0.01 wt% or less, and
Ti: 0.03 wt% or less and Nb: 0.03 wt% or less with this Ti
Relationship between the Nb and the C has the following formula: contain so as to satisfy the relation of 0.1 ≦ (2Nb + Ti) /C≦0.5 , balance steel hot having composed of Fe and unavoidable impurities, cold After that, the final annealing after cold rolling is performed at a temperature of 780 to 900 ° C, and in the cooling process, cooling to 500 ° C is performed at 15 ° C.
/ sec over 50 ° C. / sec complete the following can be obtained I further <br/> by the and this for cooling up to 500 ° C. to 300 ° C. at a cooling rate of 5 ℃ / sec~35 ℃ / sec.
【０００９】[0009]
【作用】発明者らは、薄鋼板の静動比を向上させるべ
く、まず、静的な強度を向上させる目的で、TiおよびNb
を微量に含有させたMn含有低炭素鋼をベースに、静動比
に及ぼす冶金学的要因の影響、とくに化学組成と熱処理
条件とについて検討を重ねた。その結果、鋼中のＣとTi
およびNbの各成分のバランスを適正化すること、および
焼鈍時の冷却条件を制御することが該静動比の向上に極
めて有効であることを知見した。これらの操作によって
静動比が向上する理由については、必ずしも明らかにな
った訳ではないが、少なくとも高強度鋼板における上記
の静動比を、軟鋼板の静動比： 1.6以上を示すようにす
るには、上記成分組成の適正化, とりわけＣとTiおよび
Nbの添加、即ち、マルテンサイト組織強化鋼において、
Ｃに対してTiとNbを微量添加することによって、熱延中
あるいは焼鈍中の組織（炭化物）の粗大化を阻止するこ
とが有効に作用するものと考えられる。また、TiとNbを
制御することは、静動比に有害な変形中の非熱活性的な
応力場の減衰を導く上で有効である。In order to improve the static-dynamic ratio of the thin steel sheet, the inventors of the present invention firstly improve the static strength of Ti and Nb.
The effect of metallurgical factors on the static-dynamic ratio, especially the chemical composition and heat treatment conditions, was repeatedly studied based on the low carbon steel containing Mn in a trace amount. As a result, C and Ti in steel
It was found that optimizing the balance of each component of Nb and Nb and controlling the cooling conditions during annealing are extremely effective in improving the static-dynamic ratio. The reason why the static-dynamic ratio is improved by these operations is not always clear, but at least the above-mentioned static-dynamic ratio of the high-strength steel plate should be set so that the static-dynamic ratio of the mild steel plate is 1.6 or more. Includes the optimization of the above composition, especially C and Ti and
Addition of Nb, that is, in the martensitic strengthened steel,
It is considered that the addition of a small amount of Ti and Nb to C effectively prevents the coarsening of the structure (carbide) during hot rolling or annealing. In addition, controlling Ti and Nb is effective in guiding the damping of the non-thermally active stress field during deformation, which is detrimental to the static-dynamic ratio.
【００１０】このために、本発明は、TiとNbとＣの関係
式として、
0.1 ≦（２Nb＋Ti）／Ｃ≦ 0.5 …(1)
を提案し、そしてまた、マルテンサイト相が10〜50％占
める鋼組織にすることを提案する。To this end, the present invention proposes a relational expression of Ti, Nb and C of 0.1 ≦ (2Nb + Ti) /C≦0.5 (1), and also the martensite phase accounts for 10 to 50%. Propose to have a steel structure.
【００１１】本発明を構成する各成分元素とそれの含有
量は、静動比や機械的諸性質向上のために、次のような
理由によって限定される。
Ｃ：0.010 〜0.10wt％
Ｃは、プレス成形性の指標である伸び、ｒ値の向上の観
点からできるだけ少ない方が望ましいが、0.010 ％より
も少ないと、マルテンサイト相の析出が少なくなって十
分な強度を確保できない。即ち、いかに静動比が高くて
も絶対的な強度が強度が不足する場合は軽量化の効果を
期待することができない。また、耐二次加工脆性の劣化
や溶接部の強度低下をもたらし好ましくない。一方、こ
のＣの含有量が0.10wt％を超えると、かえって静動比の
低減を招く傾向が強くなり、また、Ｃを安定化させるた
めに過剰なTi, Nbの添加が必要となり経済的にも好まし
くないし、スポット溶接性も劣化する。したがって、Ｃ
含有量は、0.010 〜0.10wt％の範囲に限定した。The constituent elements constituting the present invention and their contents are limited for the following reasons in order to improve the static-dynamic ratio and various mechanical properties. C: 0.010 to 0.10 wt% C is preferably as small as possible from the viewpoint of improving the elongation and r value, which are indicators of press formability, but if it is less than 0.010%, precipitation of martensite phase is reduced, which is sufficient. Cannot secure sufficient strength. That is, no matter how high the static-dynamic ratio is, if the absolute strength is insufficient, the effect of weight reduction cannot be expected. In addition, it is not preferable because it deteriorates the secondary processing brittleness and reduces the strength of the welded portion. On the other hand, if the content of C exceeds 0.10 wt%, the static-dynamic ratio tends to be rather reduced, and excessive addition of Ti and Nb to stabilize C is economically necessary. Is also not preferable, and spot weldability also deteriorates. Therefore, C
The content was limited to the range of 0.010 to 0.10 wt%.
【００１２】Si：0.2 wt％以下
Siは、基本的には必要に応じて目標とする強度レベルを
得るために添加すればよいが、0.2 wt％を超えて含有さ
せた場合には、静動比が劣化する。したがって、Si含有
量を0.2 wt％以下とした。Si: 0.2 wt% or less Basically, Si may be added as necessary to obtain a target strength level. The ratio deteriorates. Therefore, the Si content is set to 0.2 wt% or less.
【００１３】Mn：0.50〜3.00wt％
Mnは、0.50wt％よりも少ないと、マルテンサイト相の析
出が少なくなって十分な強度が得られない。一方、3.00
wt％を超えて多量に含有すると、静動比とスポット溶接
性が劣化する。従って、Mn含有量は0.50〜3.00wt％の範
囲内に限定した。Mn: 0.50 to 3.00 wt% When Mn is less than 0.50 wt%, precipitation of martensite phase is reduced and sufficient strength cannot be obtained. On the other hand, 3.00
If it is contained in a large amount in excess of wt%, the static-dynamic ratio and spot weldability deteriorate. Therefore, the Mn content is limited to the range of 0.50 to 3.00 wt%.
【００１４】Ｐ：0.01〜0.15wt％
Ｐは、0.01wt％よりも少ないとマルテンサイト相の析出
が少なくなって十分な強度が得られず、一方0.15wt％を
超えて含有させた場合には、静動比とスポット溶接性が
劣化することに加えて表面処理特性も顕著に劣化する。
したがって、Ｐ含有量は0.01〜0.15wt％の範囲内に限定
した。P: 0.01 to 0.15 wt% If P is less than 0.01 wt%, the precipitation of martensite phase is reduced and sufficient strength cannot be obtained. On the other hand, if P is contained in excess of 0.15 wt%, In addition to the deterioration of static-dynamic ratio and spot weldability, the surface treatment characteristics are also significantly deteriorated.
Therefore, the P content is limited to the range of 0.01 to 0.15 wt%.
【００１５】Ｓ：0.01wt％以下
Ｓは、少ないほど、鋼中の析出物が減少して加工性の向
上の寄与する他、Ｃを固定するためのTi量の増加をもた
らすので好ましい。このような効果は、Ｓ量を0.01wt％
以下とすることで得られる。S: 0.01 wt% or less S is preferably as small as possible because precipitates in the steel are reduced to contribute to the improvement of workability and the amount of Ti for fixing C is increased. Such an effect is that the amount of S is 0.01 wt%
It can be obtained by the following.
【００１６】Ti：0.03wt％以下
Tiは、ｒ値向上に不可欠な元素であり、しかも静動比の
向上に必要な成分である。この量は 0.015％以上含有さ
せるとｒ値および静動比の効果が顕れるが、0.03wt％を
超えて含有させてもその効果が飽和することに加えて、
表面性状の劣化を招く。従って、Ti含有量は0.03wt％以
下の範囲に限定した。Ti: 0.03 wt% or less Ti is an element indispensable for improving the r value, and is a component necessary for improving the static-dynamic ratio. When this amount is contained in 0.015% or more, the effect of r value and static-dynamic ratio becomes apparent, but even if it is contained in excess of 0.03 wt%, the effect saturates.
This leads to deterioration of surface properties. Therefore, the Ti content is limited to the range of 0.03 wt% or less.
【００１７】Nb：0.03wt％以下
Nbは、ｒ値向上に不可欠な元素であり、しかも静動比の
向上に必要な成分である。その上、鋼板組織の均一化と
微細化にも有効である。ただし、このNbは、0.03wt％を
超えて含有させてもその効果が飽和するので、Nb含有量
は0.03wt％以下に限定した。なお、このNbは、単独で添
加するよりもTiと共に複合添加し、さらにＣとの関連の
下で添加した場合の方が、その特性向上の効果は大き
い。Nb: 0.03 wt% or less Nb is an element indispensable for improving the r value and is a component necessary for improving the static-dynamic ratio. In addition, it is effective for making the steel sheet structure uniform and fine. However, even if the Nb content exceeds 0.03 wt%, the effect is saturated, so the Nb content is limited to 0.03 wt% or less. The effect of improving the characteristics is greater when Nb is added in combination with Ti and added in association with C, rather than added alone.
【００１８】本発明にかかる薄鋼板は、基本的に上述の
ような化学成分と組成よりなるものであるが、本発明は
さらに、Ti, NbおよびＣを、これらの関係が下記式を満
足するような割合いで含有させることが必要である。す
なわち、この式は、上述した成分組成よりなる高強度鋼
板について、この鋼板の静動比を 1.6以上のものにする
のに必要な条件の１つを規定したものである。
0.1 ≦（２Nb＋Ti）／Ｃ≦ 0.5
なお、この式は、TiおよびNbを、Ｃ量に対して微量添加
することによって、静動比を 1.6以上とすることができ
る条件を規定しており、この値が 0.1未満および 0.5を
超えると、いずれも静動比の低下とともにマルテンサイ
ト相の析出が少なくなって強度が不足する。The thin steel sheet according to the present invention is basically composed of the chemical components and compositions as described above. The present invention further includes Ti, Nb and C, the relationship of which satisfies the following formula. It is necessary to contain such a ratio. That is, this formula defines one of the conditions necessary for the steel plate having the above-described composition to have a static-dynamic ratio of 1.6 or more. 0.1 ≤ (2Nb + Ti) / C ≤ 0.5 This formula defines the condition that the static-dynamic ratio can be 1.6 or more by adding a small amount of Ti and Nb to the C amount. When the value is less than 0.1 and exceeds 0.5, the static-dynamic ratio decreases and precipitation of martensite phase decreases, resulting in insufficient strength.
【００１９】また、本発明にかかる薄鋼板は、フェライ
ト相に対して10〜50％のマルテンサイト相が共存するよ
うに制御された組織を有する。体積比で10％以上のマル
テンサイト相の析出を限定する理由は、それ未満では十
分な強度と静動比が得られないからである。一方、体積
比で50％以下のマルテンサイト相の析出を限定する理由
は、それを超えると鋼板が硬質化して良好なプレス成形
性が得られないからである。Further, the thin steel sheet according to the present invention has a structure controlled such that 10 to 50% of the martensite phase coexists with the ferrite phase. The reason why the precipitation of the martensite phase of 10% or more by volume is limited is that if it is less than that, sufficient strength and static-dynamic ratio cannot be obtained. On the other hand, the reason for limiting the precipitation of the martensite phase at a volume ratio of 50% or less is that if it exceeds that, the steel sheet becomes hard and good press formability cannot be obtained.
【００２０】次に、本発明鋼板の特徴について説明す
る。本発明の薄鋼板は、上述した成分組成の鋼素材を溶
製, 鋳造して得た鋼片について、常法に従って熱間圧延
あるいは冷間圧延を行う。即ち、鋼材はまず1200℃に加
熱し、フェライト相が析出する温度以上、好ましくは約
850℃以上で終了する熱間圧延を施した後、650 ℃以上
の温度で巻取りを行い、引続き冷間圧延を施してから、
本発明において特徴的な仕上焼鈍を経て製品薄鋼板とす
る。Next, the features of the steel sheet of the present invention will be described. In the thin steel sheet of the present invention, a steel slab obtained by melting and casting a steel material having the above-described composition is hot-rolled or cold-rolled according to a conventional method. That is, the steel material is first heated to 1200 ° C., and at a temperature above the temperature at which the ferrite phase precipitates, preferably about
After performing hot rolling ending at 850 ° C or higher, winding at a temperature of 650 ° C or higher, followed by cold rolling, and then
In the present invention, a product thin steel sheet is obtained through the finish annealing characteristic of the present invention.
【００２１】上記の冷間圧延後の処理は、冷間圧延後に
780℃以上 900℃の温度で仕上焼鈍をした後、冷却過程
において 500℃までの冷却を15℃/sec以上50℃/sec以下
の冷却速度で行い、さらに 500℃から 300℃までの冷却
を５℃/sec以上35℃/sec以下の冷却速度で行う処理であ
る。上記の処理において、冷間圧延後仕上焼鈍を 780℃
以上で行う理由は、それ未満では十分な強度と静動比が
得られないからである。一方、この焼鈍を 900℃以下の
温度で行う理由は、それを超えると結晶粒が粗大化して
強度が低下するからである。また、 500℃までの冷却を
15℃/sec以上50℃/sec以下の範囲で行う理由は、15℃/s
ec未満ではマルテンサイト相が析出して静動比が低下
し、50℃/secを超えるとフェライト相中の炭化物が微細
化して、静動比が低下するからである。そして、 500℃
からの冷却を５℃/sec以上35℃/sec以下の速度で行うの
は、５℃/sec未満ではマルテンサイト相の析出が減少し
て強度と静動比が低下し、35℃/secを超えるとフェライ
ト相中の炭化物が微細化して、静動比が低下するので、
500℃からの冷却は５℃/sec以上35℃/sec以下の速度に
限定した。The above-mentioned treatment after cold rolling is performed after cold rolling.
After finishing annealing at a temperature of 780 ℃ or more and 900 ℃, cooling is performed to 500 ℃ in the cooling process at a cooling rate of 15 ℃ / sec or more and 50 ℃ / sec or less, and further from 500 ℃ to 300 ℃. This is a process performed at a cooling rate of ℃ / sec or more and 35 ℃ / sec or less. In the above treatment, finish annealing after cold rolling was performed at 780 ° C.
The reason for performing the above is that if it is less than that, sufficient strength and static-dynamic ratio cannot be obtained. On the other hand, the reason why this annealing is performed at a temperature of 900 ° C. or lower is that if the temperature is exceeded, the crystal grains become coarse and the strength decreases. Also, cooling up to 500 ° C
The reason for performing in the range of 15 ° C / sec or more and 50 ° C / sec or less is 15 ° C / s.
When it is less than ec, the martensite phase is precipitated and the static-dynamic ratio is lowered, and when it exceeds 50 ° C./sec, the carbide in the ferrite phase is refined and the static-dynamic ratio is lowered. And 500 ℃
The cooling rate from 5 ° C / sec to 35 ° C / sec is less than 5 ° C / sec, the precipitation of martensite phase decreases and the strength and static-dynamic ratio decrease. If it exceeds, the carbides in the ferrite phase become finer and the static-dynamic ratio decreases, so
Cooling from 500 ° C was limited to a rate of 5 ° C / sec or more and 35 ° C / sec or less.
【００２２】なお、本発明が対象としているものは、冷
延鋼板であるが、これのみならず表面処理鋼板に対して
も同じように、静動比向上の効果を付与できる。また、
本発明鋼は、自動車用鋼板を対象としているが、同様に
高歪速度下での強度を要求される用途にも有効であるこ
とはいうまでもない。The object of the present invention is a cold- rolled steel sheet, but not only this but also a surface-treated steel sheet can be similarly provided with the effect of improving the static-dynamic ratio. Also,
The steel of the present invention is intended for steel sheets for automobiles, but it goes without saying that it is also effective for applications in which strength under a high strain rate is required.
【００２３】[0023]
【実施例】表１に示すような種々の成分組成の鋼を転炉
にて溶製し、連続鋳造して鋳片を得た。その鋳片を1200
℃に加熱したのち熱間圧延して３mmｔの熱延鋼板を得
た。さらにこれらの熱延鋼板を冷間圧延して0.7mmtの冷
延鋼板を製造した。その後、この冷延鋼板を表１に示す
焼鈍温度にて焼鈍すると共に、同表に示す冷却速度にて
冷却した。そして、このようにして得られた鋼板につい
て、引張試験により歪速度10-3と102 (S-1) での降伏強
度(YS) MPaを測定して静動比を求めるとともに、マルテ
ンサイト量を求めた。それらの測定値を表１にまとめて
示す。表１に示す結果から明らかなように、本発明に適
合する鋼（No.1〜4)は、102(S-1) および10-3(S-1) と
もに高い値を示すと共に、優れた静動比を示す薄鋼板で
あることがわかった。EXAMPLES Steels having various compositional compositions as shown in Table 1 were melted in a converter and continuously cast to obtain cast pieces. 1200 for that slab
After heating to ℃, it was hot-rolled to obtain a 3 mmt hot-rolled steel sheet. Furthermore, these hot-rolled steel sheets were cold-rolled to produce 0.7 mmt cold-rolled steel sheets. Then, the cold rolled steel sheet was annealed at the annealing temperature shown in Table 1 and cooled at the cooling rate shown in the same table. Then, for the steel sheet thus obtained, the yield strength (YS) MPa at strain rates of 10 -3 and 10 2 (S -1 ) was measured by a tensile test to determine the static-dynamic ratio and the martensite content. I asked. The measured values are summarized in Table 1. As is clear from the results shown in Table 1, the steels conforming to the present invention (Nos. 1 to 4) show high values for both 10 2 (S -1 ) and 10 -3 (S -1 ), and are excellent. It was found that it was a thin steel plate showing a static-dynamic ratio.
【００２４】しかし、たとえばＣに対するNb, Tiの量が
不適当( No.5, 6)であれば、静動比が悪く、また仕上焼
鈍後の冷却速度が不適当( No.7〜10) 、焼鈍温度が不適
当(No. 12) では、いずれも静動比が低い。また、Ｃ, S
i, Mn, Ｐ, Ｓの各含有量が本発明範囲を外れる比較例
も同じ傾向を示し、また、Ｃ, MnおよびＰが低い組成の
ものではいずれも降伏強度が低い結果となった。このこ
とから、本発明例の方が明らかに優れた静動比と強度を
有する様子が窺える。However, for example, if the amounts of Nb and Ti relative to C are inappropriate (Nos. 5 and 6), the static-dynamic ratio is poor and the cooling rate after finish annealing is inappropriate (Nos. 7 to 10). When the annealing temperature is inappropriate (No. 12), the static-dynamic ratio is low. Also, C, S
Comparative examples in which the contents of i, Mn, P, and S were out of the range of the present invention also showed the same tendency, and the compositions having low C, Mn, and P all had low yield strength. From this, it can be seen that the example of the present invention has a clearly superior static-dynamic ratio and strength.
【００２５】[0025]
【表１】 [Table 1]
【００２６】[0026]
【発明の効果】以上説明したようにこの発明によれば、
Mn含有低炭素鋼のTi, NbおよびＣの組成を適正化するこ
と、および冷延後の熱処理を制御することによって、従
来よりも格段に静動比に優れる高張力薄鋼板を製造する
ことができ、これらを自動車用鋼板に利用することによ
って、自動車車体の軽量化と安全性の向上を図ることが
できる。As described above, according to the present invention,
By optimizing the composition of Ti, Nb and C of Mn-containing low carbon steel and controlling the heat treatment after cold rolling, it is possible to produce a high-strength steel sheet with a significantly higher static-dynamic ratio than before. It is possible to reduce the weight of the automobile body and improve the safety by using these for the steel sheet for automobiles.
【図１】変形速度と強度との関係に及ぼす軟鋼と高張力
鋼との影響を示す説明図。FIG. 1 is an explanatory diagram showing the effect of mild steel and high-strength steel on the relationship between deformation rate and strength.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭64−47815（ＪＰ，Ａ) 特開 平２−38525（ＪＰ，Ａ) 特公 平２−33768（ＪＰ，Ｂ２) 特公 平５−25941（ＪＰ，Ｂ２) (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 - 38/60 C21D 9/46 - 9/48 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 64-47815 (JP, A) JP-A-2-38525 (JP, A) JP-B 2-333768 (JP, B2) JP-B 5- 25941 (JP, B2) (58) Fields surveyed (Int.Cl. 7 , DB name) C22C 38/00-38/60 C21D 9/46-9/48
Claims (2)
Mn：0.50〜3.00wt％、Ｐ：0.01〜0.15wt％、Ｓ：0.01wt
％以下を含み、そしてTi：0.03wt％以下およびNb：0.03
wt％以下を、このTiとNbおよび前記Ｃとの関係が、次
式； 0.1≦（２Nb＋Ti）／Ｃ≦0.5 の関係を満たすように含有し、残部はFeおよび不可避的
不純物からなり、かつフェライトと体積比で10〜50％の
マルテンサイトとの２相組織を有する耐衝撃性に優れた
冷延薄鋼板。1. C: 0.010 to 0.10 wt%, Si: 0.2 wt% or less,
Mn: 0.50 to 3.00 wt%, P: 0.01 to 0.15 wt%, S: 0.01 wt
% Or less, and Ti: 0.03 wt% or less and Nb: 0.03
wt% or less is contained so that the relationship between Ti and Nb and the above C satisfies the following formula: 0.1 ≦ (2Nb + Ti) /C≦0.5, the balance being Fe and inevitable impurities, and ferrite. And has a two-phase structure of 10 to 50% by volume of martensite and has excellent impact resistance.
Cold rolled thin steel sheet.
Mn：0.50〜3.00wt％、Ｐ：0.01〜0.15wt％、Ｓ：0.01wt
％以下を含み、そしてTi：0.03wt％以下およびNb：0.03
wt％以下を、このTiとNbおよび前記Ｃとの関係が、次
式； 0.1≦（２Nb＋Ti）／Ｃ≦0.5 の関係を満たすように含有し、残部はFeおよび不可避的
不純物からなる成分組成を有する鋼材を熱間，冷間で圧
延し、その冷間圧延後の仕上焼鈍を、780〜900℃の温度
で行い、その冷却過程において500℃までの冷却を15℃
／sec以上50℃／sec以下で行い、さらに500℃〜300℃ま
での冷却を５℃／sec〜35℃／secの冷却速度で行うこと
により、フェライトと体積比で10〜50％のマルテンサイ
トとの２相組織とすることを特徴とする耐衝撃性に優れ
た冷延薄鋼板の製造方法。2. C: 0.010 to 0.10 wt%, Si: 0.2 wt% or less,
Mn: 0.50 to 3.00 wt%, P: 0.01 to 0.15 wt%, S: 0.01 wt
% Or less, and Ti: 0.03 wt% or less and Nb: 0.03
less wt%, the relationship between the Ti and Nb, and the C, the following formula: contain so as to satisfy the relation of 0.1 ≦ (2Nb + Ti) /C≦0.5 , the component composition balance consisting of Fe and unavoidable impurities The steel material it has is hot- or cold-rolled, and the finish annealing after the cold-rolling is performed at a temperature of 780 to 900 ° C. In the cooling process, cooling to 500 ° C is performed at 15 ° C.
/ Sec over 50 ° C. / sec complete the following further be cooled to 500 ° C. to 300 ° C. at a cooling rate of 5 ℃ / sec~35 ℃ / sec
The volume ratio of ferrite to martensite is 10 to 50%.
And a cold-rolled thin steel sheet having excellent impact resistance, which is characterized by having a two-phase structure with a steel sheet.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23476293A JP3458416B2 (en) | 1993-09-21 | 1993-09-21 | Cold rolled thin steel sheet excellent in impact resistance and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23476293A JP3458416B2 (en) | 1993-09-21 | 1993-09-21 | Cold rolled thin steel sheet excellent in impact resistance and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0790482A JPH0790482A (en) | 1995-04-04 |
| JP3458416B2 true JP3458416B2 (en) | 2003-10-20 |
Family
ID=16975964
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP23476293A Expired - Fee Related JP3458416B2 (en) | 1993-09-21 | 1993-09-21 | Cold rolled thin steel sheet excellent in impact resistance and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3458416B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011148490A1 (en) | 2010-05-27 | 2011-12-01 | 住友金属工業株式会社 | Steel sheet, and process for production thereof |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TW426742B (en) * | 1997-03-17 | 2001-03-21 | Nippon Steel Corp | Dual-phase type high strength steel sheets having high impact energy absorption properties and a method of producing the same |
| DE60121266T2 (en) * | 2000-02-29 | 2006-11-09 | Jfe Steel Corp. | HIGH-WET HOT-ROLLED STEEL PLATE WITH EXCELLENT RECALTERING CHARACTERISTICS |
| DE60121162T2 (en) * | 2000-05-26 | 2006-11-09 | Jfe Steel Corp. | COLD-ROLLED STEEL PLATE AND GALVANIZED STEEL PLATE WITH GOOD RECOILING CHARACTERISTICS AND METHOD OF MANUFACTURING THEREOF |
| US20030015263A1 (en) | 2000-05-26 | 2003-01-23 | Chikara Kami | Cold rolled steel sheet and galvanized steel sheet having strain aging hardening property and method for producing the same |
| JP3901039B2 (en) * | 2002-06-28 | 2007-04-04 | Ｊｆｅスチール株式会社 | Ultra-high strength cold-rolled steel sheet having excellent formability and method for producing the same |
| CN103290307B (en) * | 2012-02-27 | 2016-09-21 | 株式会社神户制钢所 | High-strength steel sheet that resistance to impact is superior and manufacture method thereof |
-
1993
- 1993-09-21 JP JP23476293A patent/JP3458416B2/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011148490A1 (en) | 2010-05-27 | 2011-12-01 | 住友金属工業株式会社 | Steel sheet, and process for production thereof |
| US10538823B2 (en) | 2010-05-27 | 2020-01-21 | Nippon Steel Corporation | Steel sheet and a method for its manufacture |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0790482A (en) | 1995-04-04 |
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