JPH093550A - Production of cold rolled low carbon steel sheet having deep drawability and aging resistance - Google Patents
Production of cold rolled low carbon steel sheet having deep drawability and aging resistanceInfo
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- JPH093550A JPH093550A JP15142595A JP15142595A JPH093550A JP H093550 A JPH093550 A JP H093550A JP 15142595 A JP15142595 A JP 15142595A JP 15142595 A JP15142595 A JP 15142595A JP H093550 A JPH093550 A JP H093550A
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- steel sheet
- deep drawability
- slab
- aging resistance
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- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、連続焼鈍による低炭素
冷延鋼板の製造方法に関し、より詳述すれば、それぞれ
特定の鋼成分、熱間圧延条件および連続焼鈍条件を組合
せることにより、深絞り性および耐時効性に優れた低炭
素冷延鋼板を製造する方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a low carbon cold-rolled steel sheet by continuous annealing, and more specifically, by combining specific steel components, hot rolling conditions and continuous annealing conditions, The present invention relates to a method for producing a low carbon cold rolled steel sheet having excellent deep drawability and aging resistance.
【０００２】[0002]
【従来の技術】従来より、連続焼鈍による深絞り性に優
れた非時効性鋼板の製造方法として、鋼中Ｃ量を0.005
％未満とし、さらにTi、Nb等の元素を添加する方法があ
る。しかし、そのような従来法はＣの低減および高価な
添加元素を用いるため製鋼コストが高いという問題点が
ある。一方、このようなコスト上昇を防ぐために低炭素
Alキルド鋼に深絞り性と耐時効性を付与しようとした製
造方法が種々試みられている。2. Description of the Related Art Conventionally, as a method for producing a non-aging steel sheet excellent in deep drawability by continuous annealing, the C content in steel is 0.005.
%, And elements such as Ti and Nb may be added. However, such a conventional method has a problem that the steelmaking cost is high because of the reduction of C and the use of expensive additive elements. On the other hand, low carbon to prevent such cost increase
Various manufacturing methods have been attempted to impart deep drawability and aging resistance to Al-killed steel.
【０００３】低炭素Alキルド鋼の深絞り性を向上させる
製造方法としては、熱間圧延後700℃以上の高温で巻取
ることにより、固溶Ｃの低減、セメンタイトの凝集析
出、AlN の析出・粗大化を促進させ、高いｒ値を得る手
法が一般に知られている。しかし、高温巻取りは厚いス
ケールの生成による酸洗性の低下およびコイル内材質の
不均一性に起因する歩留まり低下を招くなどの問題点が
ある。As a manufacturing method for improving the deep drawability of low carbon Al killed steel, hot rolling is followed by winding at a high temperature of 700 ° C. or higher to reduce the solid solution C, the cohesive precipitation of cementite, the precipitation of AlN. A method of promoting coarsening and obtaining a high r value is generally known. However, the high-temperature winding has problems that the pickling property is deteriorated due to the formation of thick scale and the yield is decreased due to the nonuniformity of the material inside the coil.
【０００４】また、高温巻取りによらずに深絞り性を付
与しようとした例として特開昭62−37323 号公報に開示
されているように微量のＢを添加するとともに、sol.Al
を0.010 ％未満に制御する方法がある。しかし、このよ
うにAl添加量を著しく低減させることは工業的には困難
である。Further, as an example in which deep drawability is imparted without depending on high temperature winding, a slight amount of B is added as disclosed in JP-A-62-37323 and sol.Al.
Can be controlled to less than 0.010%. However, it is industrially difficult to significantly reduce the amount of Al added in this way.
【０００５】また、スラブ加熱温度を通常より低くして
MnS 、AlN の析出を促進させることにより、ｒ値向上を
図った例は特開昭63−72828 号公報に開示されている。
ここでは加熱炉装入前のスラブの熱履歴は特に限定され
ていないが、「鉄と鋼」74(1988)、p.313 に示されるよ
うに、連続鋳造により得られたスラブを一旦Ar3 変態点
以下に冷却した後、低温でスラブを再加熱することによ
りAlN の析出が促進されることから、真にスラブ低温加
熱の効果を得るためには加熱炉装入温度をAr3変態点以
下に低下させる必要があり、この場合には再加熱するた
めにエネルギーコストの増加を招くことになる。Also, the slab heating temperature should be set lower than usual.
An example in which the r value is improved by promoting the precipitation of MnS and AlN is disclosed in JP-A-63-72828.
Here, the thermal history of the slab before charging into the heating furnace is not particularly limited, but as shown in “Iron and Steel” 74 (1988), p.313, the slab obtained by continuous casting was once treated with Ar 3 After cooling below the transformation point, reheating the slab at low temperature promotes precipitation of AlN.Therefore, in order to truly obtain the effect of low temperature heating of the slab, the furnace charging temperature should be below the Ar 3 transformation point. However, in this case, reheating is required, resulting in an increase in energy cost.
【０００６】一方、低炭素Alキルド鋼の耐時効性を連続
焼鈍のような短時間の過時効処理により向上させるに
は、固溶炭素の析出サイトとなる炭化物を粒内に微細分
散させ、析出に必要な拡散距離を短くすることが有効で
あることが知られている。しかし、粒内炭化物密度の増
加は材料の硬質化を招くことから、耐時効性に優れた軟
質冷延鋼板の製造には粒内炭化物密度の適正化に努力が
注がれている。On the other hand, in order to improve the aging resistance of the low carbon Al killed steel by a short-time overaging treatment such as continuous annealing, a carbide serving as a precipitation site of solute carbon is finely dispersed in the grains and precipitation is performed. It is known that it is effective to shorten the diffusion distance required for the. However, since an increase in the intragranular carbide density leads to hardening of the material, efforts are being made to optimize the intragranular carbide density in the production of a soft cold-rolled steel sheet having excellent aging resistance.
【０００７】時効性の改善方法については近年、連続焼
鈍過程における冷却および過時効処理の適正化により固
溶炭素を低減させ時効性を抑制する発明が数多く提案さ
れている。Regarding the method of improving the aging property, in recent years, many inventions have been proposed in which the solid solution carbon is reduced and the aging property is suppressed by optimizing the cooling and the overaging treatment in the continuous annealing process.
【０００８】この点に関して結晶粒内炭化物の析出は核
生成と成長段階に分けられることから、それぞれの段階
について適正化を行った例として、特開平５−45654 号
公報などに示されるように焼鈍急冷後の粒内炭化物の核
生成を促進するために過時効温度より低い温度まで一旦
冷却し、核生成を促進させ、その後再加熱して過時効処
理を行い炭化物の成長を促進させる製造方法が開示され
ている。しかし、このような方法では時効性改善には有
効であるものの急冷後の再加熱には特別な設備が必要と
なり、またエネルギーコストの増加につながるという欠
点を有する。In this respect, since the precipitation of carbide in the crystal grains is divided into nucleation and growth stages, as an example of optimizing each stage, as shown in JP-A-5-45654, etc. In order to promote the nucleation of intragranular carbide after quenching, it is once cooled to a temperature lower than the overaging temperature, promotes nucleation, and then reheats to perform overaging treatment to promote carbide growth. It is disclosed. However, although such a method is effective in improving the aging property, it has the drawbacks that special equipment is required for reheating after quenching and it leads to an increase in energy cost.
【０００９】[0009]
【発明が解決しようとする課題】本発明の目的は、上記
した従来法の問題点を鑑み、深絞り性および耐時効性に
優れた軟質の低炭素冷延鋼板の製造方法を提供すること
である。本発明の具体的な目的は、自動車用外装鋼板に
特に適するように100 ℃×60分の人工時効促進処理後、
降伏強度180 N/mm2 以下、破断伸び45％以上、降伏点伸
び0.3 ％以下、そして平均ｒ値1.5 以上の深絞り性およ
び耐時効性に優れた軟質の低炭素冷延鋼板の製造方法を
提供することである。SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a soft low carbon cold-rolled steel sheet excellent in deep drawability and aging resistance in view of the above-mentioned problems of the conventional method. is there. A specific object of the present invention is to perform artificial aging acceleration treatment at 100 ° C. for 60 minutes so as to be particularly suitable for automobile exterior steel sheets,
Yield strength of 180 N / mm 2 or less, elongation at break of 45% or more, elongation at yield of 0.3% or less, and average r value of 1.5 or more for deep drawability and aging resistance. Is to provide.
【００１０】[0010]
【課題を解決するための手段】本発明者等は、連続焼鈍
による深絞り性および耐時効性に優れた軟質冷延鋼板の
製造方法に関して種々の検討を行ったところ、鋼成分の
適正化を行うとともにスラブの熱履歴、すなわち熱間圧
延条件、そして連続焼鈍条件を制御することにより、高
い深絞り性を付与し、良好な耐時効性の実現できること
を見い出した。[Means for Solving the Problems] The inventors of the present invention conducted various studies on a method for producing a soft cold-rolled steel sheet having excellent deep drawability and aging resistance by continuous annealing, and found that the steel components were optimized. It was found that by controlling the thermal history of the slab, that is, the hot rolling condition and the continuous annealing condition, high deep drawability can be imparted and good aging resistance can be realized.
【００１１】すなわち、粒成長性を向上させるＢ添加の
効果を最大限に得ることに着目し、そのためにはスラブ
の熱履歴を制御することが効果的であることを知り、本
発明を完成した。That is, focusing on maximizing the effect of B addition for improving grain growth, it was found that controlling the thermal history of the slab is effective for that purpose, and the present invention was completed. .
【００１２】本発明は上記知見に基づいて構成されたも
のであり、その要旨とするところは、重量％でＣ：0.01
0 〜0.025 ％、Mn：0.05〜0.25％、Ｓ：0.003 〜0.020
％、sol.Al：0.01〜0.05％、Ｎ：0.0030％以下、Ｂ：0.
0003〜0.0030％、残部: 鉄および不可避的不純物から成
る組成を有する鋼を連続鋳造し、スラブがAr3 変態点以
下とならないように温度を保持し、1000〜1180℃の温度
で圧延を開始し、Ar3 変態点以上で仕上げ圧延を行い63
0 〜720 ℃で巻取り、圧下率70％以上で冷間圧延を行
い、続いて連続焼鈍において800 〜880 ℃で10〜60秒の
再結晶焼鈍をした後、650 〜740 ℃まで７℃/s以下の冷
却速度で徐冷し、40〜250 ℃/sで350 〜400 ℃まで冷却
した後、そのときの冷却終点温度から０〜0.5 ℃/s以下
の冷却速度 (冷却速度＝０である保定を含む) で２〜５
分の過時効処理を行うことを特徴とする深絞り性および
耐時効性に優れた低炭素冷延鋼板の製造方法である。The present invention is constructed on the basis of the above findings, and the gist of the present invention is C: 0.01 in% by weight.
0 to 0.025%, Mn: 0.05 to 0.25%, S: 0.003 to 0.020
%, Sol.Al: 0.01 to 0.05%, N: 0.0030% or less, B: 0.
0003 ~ 0.0030%, balance: Steel having a composition consisting of iron and unavoidable impurities is continuously cast, the temperature is maintained so that the slab does not fall below the Ar 3 transformation point, and rolling is started at a temperature of 1000 ~ 1180 ° C. , Ar 3 Finish rolling at transformation point or higher 63
Winding at 0 to 720 ℃, cold rolling at a rolling reduction of 70% or more, followed by recrystallization annealing at 800 to 880 ℃ for 10 to 60 seconds in continuous annealing, and then to 650 to 740 ℃ at 7 ℃ / After gradually cooling at a cooling rate of s or less and cooling to 350 to 400 ° C at 40 to 250 ° C / s, a cooling rate of 0 to 0.5 ° C / s or less from the end temperature of cooling at that time (cooling rate = 0 2-5 in including retention
The method for producing a low carbon cold-rolled steel sheet excellent in deep drawability and aging resistance is characterized by performing overaging treatment for minutes.
【００１３】[0013]
【作用】次に、本発明において上述のようにＣ、Mn、
Ｓ、sol.Al、Ｎ、Ｂの各成分について数値限定した理由
について、その作用とともに説明する。Next, in the present invention, as described above, C, Mn,
The reason why the numerical values of the respective components of S, sol.Al, N and B are limited will be explained together with the action thereof.
【００１４】Ｃ:Ｃは、鋼板に所定の強度を付与するた
めに必須の成分である。Ｃの下限は時効性の観点から制
限される。すなわち少な過ぎる場合には過時効析出にあ
たって焼鈍後の冷却速度を大きくしてもＣの過飽和度が
増加しないため粒内炭化物の密度が低下し、時効性の劣
化を招くので0.010 ％を下限とする。また、上限は粒成
長性の観点から制限され、0.025 ％超とすると焼鈍過程
において粒成長性が阻害されるため、上限を0.025 ％と
する。好ましくは0.013 〜0.020 ％である。C: C is an essential component for imparting a predetermined strength to the steel sheet. The lower limit of C is limited from the viewpoint of aging. That is, when the amount is too small, the supersaturation degree of C does not increase even if the cooling rate after annealing during overaging precipitation is increased, so that the density of intragranular carbides is lowered and the aging is deteriorated. Therefore, 0.010% is the lower limit. . Also, the upper limit is limited from the viewpoint of grain growth, and if it exceeds 0.025%, grain growth is impaired in the annealing process, so the upper limit is made 0.025%. It is preferably 0.013 to 0.020%.
【００１５】Mn、Ｓ:MnおよびＳはMnS を形成し、窒化
物および粒内炭化物の析出核として重要であることか
ら、Mnを0.05％以上、Ｓを0.003 ％以上とする。また、
Mnが多い場合には材料の硬質化を招くことから0.25％以
下とし、Ｓは熱間脆性の観点から０．０２０％以下とす
る。好ましくはＭｎが0.07〜0.015 ％、Ｓが0.003 〜0.
010 ％である。Since Mn, S: Mn and S form MnS and are important as precipitation nuclei for nitrides and intragranular carbides, Mn is 0.05% or more and S is 0.003% or more. Also,
If the Mn content is large, the material is hardened, so it is 0.25% or less, and S is 0.020% or less from the viewpoint of hot embrittlement. Preferably Mn is 0.07 to 0.015% and S is 0.003 to 0.
It is 010%.
【００１６】Al:AlはAlN 形成を促進させるために必要
であることから下限を0.01％とする。また多すぎると材
料の硬質化を招くので上限を0.05％とする。Al: Al is necessary to promote the formation of AlN, so the lower limit is made 0.01%. If the amount is too large, the material becomes hard, so the upper limit is made 0.05%.
【００１７】Ｎ:Ｎは加工性の面から少ない方が好まし
いが、製鋼コスト上昇を防ぐために上限を0.0030％とす
る。It is preferable that N: N is small in terms of workability, but the upper limit is made 0.0030% in order to prevent an increase in steelmaking cost.
【００１８】Ｂ:Ｂは本発明の主要構成因子であり、Al
より窒化物形成能が高くBNを形成し焼鈍前の残留固溶Ｎ
を低減させることにより焼鈍後の粒成長性を向上させ
る。したがってこの効果を得るために下限を0.0003％と
する。しかし過剰なＢは固溶Ｂとなり逆に焼鈍時の粒成
長を阻害するので上限を0.0030％とする。好ましくは0.
0005〜0.0025％である。B: B is the main constituent of the present invention, and
It has a higher ability to form nitrides, forms BN, and remains solid solution N before annealing.
The grain growth property after annealing is improved by reducing Therefore, in order to obtain this effect, the lower limit is made 0.0003%. However, excess B becomes solid solution B and conversely hinders grain growth during annealing, so the upper limit is made 0.0030%. Preferably 0.
It is 0005 to 0.0025%.
【００１９】次に、本発明の熱延条件の限定理由を述べ
る。本発明ではスラブの熱履歴およびスラブ加熱温度を
特定することが重要な構成要件である。図１に、後述の
実施例の表１の例No.3の場合について機械特性に及ぼす
加熱炉装入温度の影響を示す。Next, the reasons for limiting the hot rolling conditions of the present invention will be described. In the present invention, it is important to specify the heat history of the slab and the slab heating temperature. FIG. 1 shows the influence of the heating furnace charging temperature on the mechanical characteristics in the case of Example No. 3 in Table 1 of the Examples described later.
【００２０】本発明例ではAr3 点は860 〜880 ℃程度で
あり、加熱炉装入温度がAr3 変態点未満になると粒成長
性が著しく劣化し、硬質な特性となる。したがって、ス
ラブをAr3 変態点より低い温度にならないように温度を
保持する必要がある。In the example of the present invention, the Ar 3 point is about 860 to 880 ° C., and when the charging temperature in the heating furnace is lower than the Ar 3 transformation point, the grain growth property is remarkably deteriorated and hard characteristics are obtained. Therefore, it is necessary to maintain the temperature so that the temperature of the slab does not fall below the Ar 3 transformation point.
【００２１】このような挙動の原因は明らかではない
が、Ar3 変態点より低温になると一旦フェライト変態し
たスラブが再加熱される際にMnS の形態が変化し、析出
核として機能を消失することにより、粒成長を阻害する
微細な析出物の割合が増加するためであり、さらに、フ
ェライト変態することによりBNとして析出していたＮの
一部がAlN として析出し、粒成長を阻害しない粗大なBN
の析出率が低下し、粒成長を阻害する微細AlN の析出率
が増加するためと考えられる。Although the cause of such behavior is not clear, when the temperature is lower than the Ar 3 transformation point, the morphology of MnS changes when the slab once ferrite transformed is reheated, and the function disappears as a precipitation nucleus. This increases the proportion of fine precipitates that hinder grain growth. Furthermore, a part of N that had been precipitated as BN due to ferrite transformation precipitates as AlN, which is a coarse grain that does not hinder grain growth. BN
It is thought that this is because the precipitation rate of Al decreases and the precipitation rate of fine AlN 3 which hinders grain growth increases.
【００２２】図２に図１と同様の場合について機械特性
に及ぼすスラブ加熱温度の影響を示す。スラブ加熱温度
が高い場合には既存析出物の再溶解が生じ、その結果、
微細析出物が増加し、粒成長性が劣化し硬質となる。し
たがって、本発明においてスラブ加熱温度は上限を1180
℃とする。また低すぎる場合にはコイル全長にわたり仕
上げ温度をAr3 変態点以上に確保することが困難となる
ので、下限を1000℃とする。好ましくは1050〜1150℃で
ある。FIG. 2 shows the influence of the slab heating temperature on the mechanical characteristics in the same case as in FIG. When the slab heating temperature is high, re-dissolution of existing precipitates occurs, and as a result,
The fine precipitates increase, the grain growth property deteriorates, and it becomes hard. Therefore, in the present invention, the slab heating temperature has an upper limit of 1180.
℃. If it is too low, it will be difficult to secure the finishing temperature over the Ar 3 transformation point over the entire length of the coil, so the lower limit is set to 1000 ° C. It is preferably 1050-1150 ° C.
【００２３】また、本発明は熱間圧延の前段階でスラブ
の温度がAr3 変態点以下にならないようにすれば良いの
であるから、連続鋳造により製造したスラブの温度が十
分に高く、再加熱せずとも仕上げ温度が確保でき、上記
加熱温度と同等の条件であるならば、直接熱間圧延を実
施しても構わない。つまり、1000〜1180℃という上記ス
ラブ加熱温度で圧延を開始できればよい。したがって、
本発明においては直接熱間圧延を行う場合も含めて、上
述のスラブ加熱温度を圧延開始温度とも称する。Further, in the present invention, since it is sufficient that the temperature of the slab does not fall below the Ar 3 transformation point before the hot rolling, the temperature of the slab manufactured by continuous casting is sufficiently high and the reheating is not performed. If the finishing temperature can be secured without doing so and the conditions are equivalent to the above heating temperature, the hot rolling may be carried out directly. That is, it is only necessary to start rolling at the slab heating temperature of 1000 to 1180 ° C. Therefore,
In the present invention, the above slab heating temperature is also referred to as the rolling start temperature, including the case where direct hot rolling is performed.
【００２４】仕上げ圧延はAr3 変態点以上で行われる
が、これは熱延板粗粒化による冷延焼鈍板のｒ値の低下
を防止するためである。図３に図１と同じ場合について
平均ｒ値に及ぼす巻取温度の影響を示す。The finish rolling is carried out at the Ar 3 transformation point or higher, in order to prevent the reduction of the r value of the cold rolled annealed sheet due to the coarsening of the hot rolled sheet. FIG. 3 shows the influence of the winding temperature on the average r value in the same case as in FIG.
【００２５】ここに、平均ｒ値は、圧延方向 ( 0°) の
ｒ値をｒ0°、対角方向 (45°) のｒ値をｒ45°、直角
方向 (90°) のｒ値をｒ90°としたときに下記式で定義
される３方向平均ｒ値をいう。[0025] Here, the average r value, the r value r 0 ° in the rolling direction (0 °), the r value r 45 ° diagonal (45 °), the r value of the perpendicular direction (90 °) When r is 90 °, it means a three-direction average r value defined by the following formula.
【００２６】[0026]
【数１】 [Equation 1]
【００２７】これらの結果からも分かるように、深絞り
性は巻取温度に大きく依存し、巻取温度が高いほど高ｒ
値となるので下限を630 ℃とする。また、巻取温度が高
すぎる場合には厚いスケールが生成するため、酸洗性の
劣化を招く。したがって、巻取温度は上限を720 ℃とす
る。好ましくは650 〜700 ℃である。図４に図１と同様
の場合について平均ｒ値に及ぼす冷間圧延率の影響を示
す。As can be seen from these results, the deep drawability greatly depends on the winding temperature, and the higher the winding temperature, the higher the r.
The lower limit is set to 630 ° C. Further, when the winding temperature is too high, a thick scale is generated, which causes deterioration of pickling performance. Therefore, the upper limit of coiling temperature is 720 ℃. It is preferably 650 to 700 ° C. FIG. 4 shows the effect of the cold rolling rate on the average r value in the same case as in FIG.
【００２８】これによって冷間圧延条件の限定理由につ
いて述べると、まず、圧下率が小さい場合には十分なｒ
値を得ることができないので冷間圧延率の下限を70％と
する。上限はとくに制限しない。好ましい冷間圧延率は
75〜85％である。次に、本発明の連続焼鈍条件の限定理
由を述べる。The reason for limiting the cold rolling conditions will be described below. First, when the reduction ratio is small, sufficient r
Since the value cannot be obtained, the lower limit of the cold rolling rate is set to 70%. There is no particular upper limit. The preferred cold rolling rate is
75-85%. Next, the reasons for limiting the continuous annealing conditions of the present invention will be described.
【００２９】焼鈍条件は、十分な粒成長を行い高ｒ値を
得るために規定するもので、本発明では少なくとも800
℃以上で10秒以上の焼鈍を行う。焼鈍温度が高すぎる場
合には結晶方位のランダム化による特性劣化を招くため
上限を880 ℃とする。また焼鈍処理設備の長大化および
エネルギーコストの増加を防ぐために焼鈍時間の上限を
60秒とする。The annealing conditions are specified in order to achieve sufficient grain growth to obtain a high r value, and in the present invention, at least 800.
Anneal at 10 ℃ or more for 10 seconds or more. If the annealing temperature is too high, the characteristics are deteriorated due to randomization of crystal orientation, so the upper limit is set to 880 ° C. In addition, the upper limit of the annealing time is set in order to prevent the annealing treatment equipment from becoming longer and the energy cost from increasing.
60 seconds.
【００３０】焼鈍が終了した時点で後述する急冷開始温
度にまで冷却するが、このときの冷却速度は７℃/s以
下、好ましくは５℃/s以下とする。このような徐冷はフ
ェライト中の固溶Ｃ量を高め、後に続く急冷、過時効過
程において効果的に粒内炭化物を生成させるためであ
る。When the annealing is completed, the material is cooled to a quenching start temperature described later, and the cooling rate at this time is 7 ° C./s or less, preferably 5 ° C./s or less. Such slow cooling is to increase the amount of solid solution C in the ferrite and to effectively form intragranular carbides in the subsequent rapid cooling and overaging processes.
【００３１】ところで、フェライト中へのＣの固溶限の
関係から、急冷開始温度が650 ℃より低い場合あるいは
740 ℃より高い場合には十分な固溶Ｃの過飽和度が得ら
れないため、粒内の炭化物密度が減少して時効性が劣化
する。したがって、急冷開始温度を650 〜740 ℃とす
る。By the way, when the quenching start temperature is lower than 650 ° C. or because of the solid solubility limit of C in ferrite,
When the temperature is higher than 740 ° C, a sufficient degree of supersaturation of solid solution C cannot be obtained, so that the carbide density in the grains decreases and the aging property deteriorates. Therefore, the quenching start temperature is set to 650-740 ° C.
【００３２】この後に続く急冷過程は、粒内炭化物の析
出駆動力を確保するために行うのであるが、本発明にか
かる製造条件では粒内炭化物の析出サイトであるMnS が
粗大に析出し、粒内炭化物の析出が促進される。そのた
め、従来の技術にみられるように過時効温度よりも低い
温度まで過冷却を行い核生成を行った後に再加熱を行う
という処理を施さずとも、十分に良好な耐時効性を実現
できる。The subsequent quenching process is carried out in order to secure the driving force for precipitation of intragranular carbides. Under the manufacturing conditions of the present invention, MnS, which is the precipitation site of intragranular carbides, is coarsely precipitated, The precipitation of internal carbide is promoted. Therefore, sufficiently good aging resistance can be realized without performing the process of performing supercooling to a temperature lower than the overaging temperature to perform nucleation and then reheating as in the conventional technique.
【００３３】冷却速度については、40℃/sより小さい場
合には粒内炭化物密度が低下するため長い過時効処理時
間を要するようになる。また、冷却速度が250 ℃/sより
大きくなると粒内炭化物が微細に分散するため降伏強度
を増加させ、延性を低下させる。したがって、冷却速度
は40〜250 ℃/sとする。好ましくは60〜150 ℃/sであ
る。Regarding the cooling rate, if it is lower than 40 ° C./s, the intragranular carbide density is lowered and a long overaging treatment time is required. If the cooling rate is higher than 250 ° C / s, the intragranular carbide is finely dispersed, so that the yield strength is increased and the ductility is decreased. Therefore, the cooling rate is 40 to 250 ° C / s. It is preferably 60 to 150 ° C / s.
【００３４】急冷終点温度および過時効温度は粒内炭化
物の分布と成長を決定する。急冷終点温度が400 ℃より
高い場合には固溶Ｃの拡散は十分に確保できるが固溶Ｃ
の溶解度が大きいため固溶Ｃの低減が十分に行われな
い。また350 ℃未満の場合には固溶Ｃの拡散が不十分と
なり固溶Ｃが大量に残留してしまう。これより急冷終点
温度は350 〜400 ℃とする。The quench end point temperature and the overaging temperature determine the distribution and growth of intragrain carbides. When the quenching end temperature is higher than 400 ° C, the diffusion of solid solution C can be sufficiently secured, but solid solution C
Since the solubility of C is large, the solid solution C cannot be sufficiently reduced. On the other hand, if the temperature is lower than 350 ° C., the solid solution C is not sufficiently diffused and a large amount of the solid solution C remains. From this, the end temperature of quenching shall be 350-400 ° C.
【００３５】過時効過程における冷却速度が0.5 ℃/sよ
り大きい場合には固溶Ｃの析出サイトまでの拡散が不十
分となり時効性が劣化するので0.5 ℃/s以下の傾斜過時
効または等温過時効を適用する。このとき冷却速度＝０
の保定を行ってもよい。いずれの場合も過時効処理時間
は２〜５分間である。If the cooling rate in the overaging process is higher than 0.5 ° C / s, the diffusion of the solid solution C to the precipitation site becomes insufficient and the aging property deteriorates. Apply a prescription. Cooling rate = 0 at this time
May be held. In either case, the overaging treatment time is 2 to 5 minutes.
【００３６】以上のような本発明にかかる製造方法によ
れば、深絞り性および耐時効性に優れた軟質の低炭素冷
延鋼板が得られ、特に自動車用外装鋼板の用途などにそ
の特性が発揮される。According to the manufacturing method of the present invention as described above, a soft low carbon cold-rolled steel sheet excellent in deep drawability and aging resistance can be obtained, and its characteristics are particularly suitable for use as an automobile exterior steel sheet. To be demonstrated.
【００３７】[0037]
(実施例１)表１に示す化学成分を有する鋼を溶製、出鋼
し、連続鋳造法によってスラブを製造した後、スラブ温
度をAr3 変態点より低い温度にすることなく、930 〜98
0℃で加熱炉へ装入し、1100〜1150℃までスラブを加熱
し、次いで熱間圧延において880 〜920 ℃で仕上げ圧延
を行い板厚を4.0 mmとし、640 〜660 ℃でコイルに巻取
った。その後、酸洗し、0.8 mmまで冷間圧延を行い (冷
間圧延率80％) 、連続焼鈍を行った。連続焼鈍条件は焼
鈍温度850 ℃で、均熱時間を30秒とし、700℃まで４℃/
sで徐冷してから、380 ℃まで80℃/sで急冷し、次いで3
80 ℃から330 ℃まで2.5 分間の時間をかけて過時効処
理を行った。最後に、1.2 ％の伸び率でスキンパス圧延
を行った。Steels having the chemical components shown in (Example 1) Table 1, and tapping, after producing a slab by continuous casting, without the slab temperature to a temperature lower than the Ar 3 transformation point, 930-98
It is charged into a heating furnace at 0 ° C, the slab is heated to 1100 to 1150 ° C, and then finish rolling is performed at 880 to 920 ° C in hot rolling to a plate thickness of 4.0 mm and coiled at 640 to 660 ° C. It was Then, it pickled, cold-rolled to 0.8 mm (cold rolling rate 80%), and performed continuous annealing. The continuous annealing conditions are an annealing temperature of 850 ° C, a soaking time of 30 seconds, and 700 ° C at 4 ° C /
Slowly cool down to 380 ° C, then rapidly cool down to 380 ° C at 80 ° C / s, then
Overaging treatment was performed from 80 ° C to 330 ° C for 2.5 minutes. Finally, skin pass rolling was performed at an elongation of 1.2%.
【００３８】このようにして製造した冷延鋼板について
100 ℃×60分の人工促進時効処理を行った後の機械特性
を求めた。この結果を表１に併せて示す。一般に遅時効
と見なすには耐ストレッチャーストレインの観点から、
100 ℃×60分の人工促進時効後で降伏点伸び (YP−El)
を0.3 ％以下にする必要がある。また、深絞り用鋼板と
して用いるには、同様に100 ℃×60分の人工促進時効後
で降伏強度 (YS) を180 N/mm2 以下、破断伸び (El) を
45％以上、平均ｒ値を1.5以上とする必要がある。Cold-rolled steel sheet produced in this way
The mechanical properties after the artificial accelerated aging treatment at 100 ° C. for 60 minutes were obtained. The results are shown in Table 1. Generally, from the perspective of stretcher strain resistance, it can be regarded as delayed aging.
Yield point elongation (YP-El) after artificial accelerated aging at 100 ° C for 60 minutes
Must be less than 0.3%. Similarly, for use as a deep-drawing steel sheet, the yield strength (YS) is 180 N / mm 2 or less and the elongation at break (El) is also after artificial accelerated aging at 100 ° C for 60 minutes.
It is necessary to set the average r value to 45% or more and the average r value to 1.5 or more.
【００３９】表１に示す結果から分かるように、例No.9
はＣが低すぎるため連続焼鈍過程における粒内炭化物の
析出が不十分となり、固溶Ｃが残留してしまうため時効
性が劣る。例No.10 はＣが高過ぎるため十分な粒成長が
実現できず、硬質となり深絞り性も劣る。例No.11 はAl
添加量が少な過ぎるため固溶Ｎが残留してしまい時効性
が劣る。例No.12 はAl添加量が過剰であるため硬質とな
る。例No.13 ではＮが高過ぎるため硬質となる。例No.1
4 はＢが添加されていないため粒成長が悪く深絞り性が
劣る。例No.15 の場合にはＢ添加量が多すぎるため粒成
長が阻害され深絞り性が劣る。例No.1〜８の成分組成は
本発明の範囲内にあり、十分な粒成長により優れた深絞
り性と耐時効性が実現されている。As can be seen from the results shown in Table 1, Example No. 9
Since C is too low, the precipitation of intragranular carbide in the continuous annealing process becomes insufficient, and solid solution C remains, so that the aging property is deteriorated. In Example No. 10, since C is too high, sufficient grain growth cannot be realized, and it becomes hard and the deep drawability is poor. Example No. 11 is Al
Since the amount of addition is too small, solute N remains, resulting in poor aging. Example No. 12 becomes hard because the added amount of Al is excessive. In Example No. 13, N is too high, so it becomes hard. Example No.1
In No. 4, since B was not added, the grain growth was poor and the deep drawability was poor. In the case of Example No. 15, since the amount of B added was too large, grain growth was hindered and the deep drawability was poor. The component compositions of Examples Nos. 1 to 8 are within the scope of the present invention, and excellent deep drawing property and aging resistance are realized by sufficient grain growth.
【００４０】(実施例２)表２に示すように、Ｃ：0.015
〜0.020 ％、Mn：0.08〜0.15％、Ｓ：0.005 〜0.007
％、sol.Al：0.021 〜0.036 ％、Ｎ：0.0016〜0.0028
％、Ｂ：0.0005〜0.0010％を含有する本発明範囲内の鋼
Ａ〜Ｘについて、表３に示す条件で冷延鋼板を製造し、
100 ℃×60分の人工促進時効後の特性を調査した。結果
を同じく表３に併せて示す。(Example 2) As shown in Table 2, C: 0.015
~ 0.020%, Mn: 0.08 ~ 0.15%, S: 0.005 ~ 0.007
%, Sol.Al: 0.021 to 0.036%, N: 0.0016 to 0.0028
%, B: 0.0005 to 0.0010% containing steel within the scope of the present invention, a cold rolled steel sheet is manufactured under the conditions shown in Table 3,
The properties after artificial accelerated aging at 100 ° C for 60 minutes were investigated. The results are also shown in Table 3.
【００４１】表３の結果からも分かるように、例No.28
、29では加熱炉装入温度が低いため、例No.30 、31で
はスラブ加熱温度が高すぎるため、粒成長が不足し、深
絞り性が劣化する。例No.32 では巻取温度が低いため、
例No.33 では冷間圧延率が低いため、深絞り性が劣る。
例No.34 では焼鈍温度が低いため粒成長が不足し、深絞
り性に劣る。例No.35 では焼鈍温度が高過ぎるため結晶
方位のランダム化が生じ、深絞り性が劣化している。例
No.36 、37は過時効処理温度が適正温度から外れている
ため時効性が悪い。例No.38 は過時効処理温度の傾斜が
大きく時効性が悪い。例No.39 では過時効処理時間が短
すぎるため時効性が悪い。例No.16 〜27の製造条件は本
発明条件内にあり、良好な深絞り性と過時効化が実現さ
れている。As can be seen from the results in Table 3, Example No. 28
, 29, the heating furnace charging temperature was low, and the slab heating temperature was too high in Examples Nos. 30 and 31, resulting in insufficient grain growth and poor deep drawability. Example No. 32 has a low winding temperature, so
In Example No. 33, since the cold rolling rate is low, the deep drawability is poor.
In Example No. 34, since the annealing temperature is low, grain growth is insufficient and the deep drawability is poor. In Example No. 35, the annealing temperature was too high, so the crystal orientation was randomized and the deep drawability deteriorated. An example
Nos. 36 and 37 have poor aging properties because the overaging temperature is outside the proper temperature range. Example No. 38 has a large gradient of overaging temperature and poor aging property. In Example No. 39, the overaging treatment time is too short and the aging property is poor. The manufacturing conditions of Examples No. 16 to 27 are within the conditions of the present invention, and good deep drawability and overaging are realized.
【００４２】[0042]
【表１】 [Table 1]
【００４３】[0043]
【表２】 [Table 2]
【００４４】[0044]
【表３】 [Table 3]
【００４５】[0045]
【発明の効果】本発明は、鋼組成の調整とスラブの熱履
歴、つまり熱間圧延条件と連続焼鈍熱サイクルの適正化
により、深絞り性および耐時効性に優れた軟質冷延鋼板
の製造することを可能とし、さらにスラブの再加熱に要
するエネルギーコストの増加を防ぎ生産性を向上させる
等の効果を有する優れた発明である。INDUSTRIAL APPLICABILITY The present invention produces a soft cold-rolled steel sheet excellent in deep drawability and aging resistance by adjusting the steel composition and heat history of the slab, that is, by optimizing hot rolling conditions and continuous annealing heat cycle. It is an excellent invention that has the effect of enabling to do so, and further, increasing the energy cost required for reheating the slab and improving productivity.
【図１】機械特性に及ぼす加熱炉装入温度の影響を示す
グラフである。FIG. 1 is a graph showing the effect of heating furnace charging temperature on mechanical properties.
【図２】機械特性に及ぼすスラブ加熱温度の影響を示す
グラフである。FIG. 2 is a graph showing the effect of slab heating temperature on mechanical properties.
【図３】深絞り性に及ぼす巻取温度の影響を示すグラフ
である。FIG. 3 is a graph showing the effect of winding temperature on deep drawability.
【図４】深絞り性に及ぼす冷間圧延率の影響を示すグラ
フである。FIG. 4 is a graph showing the effect of cold rolling rate on deep drawability.
Claims (1)
〜0.020 ％、 sol.Al：0.01〜0.05％、Ｎ：0.0030％以下、Ｂ：0.0003
〜0.0030％、 残部: 鉄および不可避的不純物 から成る組成を有する鋼を連続鋳造し、スラブがAr3 変
態点以下とならないように温度を保持し、1000〜1180℃
の温度で圧延を開始し、Ar3 変態点以上で仕上げ圧延を
行い630 〜720 ℃で巻取り、圧下率70％以上で冷間圧延
を行い、続いて連続焼鈍において800 〜880 ℃で10〜60
秒の再結晶焼鈍をした後、650 〜740 ℃まで７℃/s以下
の冷却速度で徐冷し、40〜250 ℃/sで350 〜400 ℃まで
冷却した後、そのときの冷却終点温度から０〜0.5 ℃/s
以下の冷却速度で２〜５分の過時効処理を行うことを特
徴とする深絞り性および耐時効性に優れた低炭素冷延鋼
板の製造方法。1. By weight%, C: 0.010 to 0.025%, Mn: 0.05 to 0.25%, S: 0.003
~ 0.020%, sol.Al: 0.01-0.05%, N: 0.0030% or less, B: 0.0003
~ 0.0030%, balance: Continuous casting of steel with composition consisting of iron and unavoidable impurities, keeping temperature so that the slab does not fall below Ar 3 transformation point, 1000 ~ 1180 ℃
Rolling is started at this temperature, finish rolling is performed at the Ar 3 transformation point or higher, winding is performed at 630 to 720 ℃, cold rolling is performed at a reduction rate of 70% or higher, and then continuous annealing is performed at 800 to 880 ℃ for 10 to 10 ℃. 60
After recrystallization annealing for 2 seconds, it is gradually cooled to 650 to 740 ° C at a cooling rate of 7 ° C / s or less, and is cooled to 350 to 400 ° C at 40 to 250 ° C / s. 0-0.5 ℃ / s
A method for producing a low carbon cold-rolled steel sheet having excellent deep drawability and aging resistance, which comprises performing overaging treatment for 2 to 5 minutes at the following cooling rate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15142595A JPH093550A (en) | 1995-06-19 | 1995-06-19 | Production of cold rolled low carbon steel sheet having deep drawability and aging resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15142595A JPH093550A (en) | 1995-06-19 | 1995-06-19 | Production of cold rolled low carbon steel sheet having deep drawability and aging resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH093550A true JPH093550A (en) | 1997-01-07 |
Family
ID=15518346
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP15142595A Pending JPH093550A (en) | 1995-06-19 | 1995-06-19 | Production of cold rolled low carbon steel sheet having deep drawability and aging resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH093550A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6171413B1 (en) | 1997-07-28 | 2001-01-09 | Nkk Corporation | Soft cold-rolled steel sheet and method for making the same |
-
1995
- 1995-06-19 JP JP15142595A patent/JPH093550A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6171413B1 (en) | 1997-07-28 | 2001-01-09 | Nkk Corporation | Soft cold-rolled steel sheet and method for making the same |
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