JPH1161274A - Manufacture of steel sheet for extra deep drawing, excellent in baking hardenability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of a steel sheet for extra deep drawing, mainly used for automobile outer sheet panel and excellent in baking hardenability. SOLUTION: A steel slab, which has a composition containing, by weight, 0.001-0.01% C, 0.01-0.1% Al, and <=0.005% N and further containing <=0.05% of one or more elements among Ti, Nb, and V in the range satisfying (Ti/48+ Nb/93+V/51)/(C/12+N/14)<1, is subjected to ordinary hot rolling and formed into a hot rolled steel strip. After acid pickling, the steel strip is cold-rolled at >=50% draft, annealed at a temp. not lower than the recrystallization temp., and cold-rolled again at >=50% draft. Then, the resultant steel sheet is annealed at a temp. between the recrystallization temp. an followed by temper rolling.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【発明の属する技術分野】本願発明は自動車の外板パネ
ルに主として用いられる焼付硬化性に優れた超深絞り用
鋼板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 method for producing an ultra-deep drawing steel sheet having excellent bake hardenability, which is mainly used for an outer panel of an automobile.

【０００２】[0002]

【従来の技術】自動車のルーフおよびドアアウター等に
使用される外板パネルには、成形時には形状性に優れる
低降伏強度が、成形後には耐デント性（指等の押込みで
凹みができにくい特性）に優れる高降伏点となるような
相反する特性が要求される。さらに最近、高生産性の観
点から外板パネルの一体成形化を可能とする優れた深絞
り性も要求されている。これらの要求に対し、特開昭５
３−１１４７１７号公報には、プレス後の自動車の塗装
焼付工程を利用した時効硬化により加工後の強度を高め
た焼付硬化型鋼板が開示されている。この焼付硬化性
（以後ＢＨ性と称す）は鋼中の固溶Ｃあるいは固溶Ｎに
よって、成形時の低降伏点と成形後の高降伏点を両立す
ることができる有効な特性である。さらに、特開昭５７
−７０２５８号公報と特開昭５９−３１８２７号公報に
は、ＢＨ性と同時に深絞り性を付与したものとして、Ｎ
ｂ添加鋼またはＴｉ、Ｎｂ複合添加鋼を連続焼鈍により
製造する方法が開示されている。これは、連続焼鈍前に
は深絞り性に良好な集合組織の形成を阻害する鋼中の
Ｃ、Ｎを固定し、連続焼鈍後は炭窒化物を分解させ、固
溶ＣおよびＮを残してＢＨ性を付与する方法である。2. Description of the Related Art Outer panels used for roofs and door outers of automobiles have low yield strength, which is excellent in shape during molding, and dent resistance after molding. ) Are required to have contradictory characteristics such as a high yield point. Furthermore, recently, from the viewpoint of high productivity, excellent deep drawability that enables integral molding of the outer panel has been required. To meet these demands,
Japanese Patent Application Publication No. 3-114717 discloses a bake hardening type steel sheet in which the strength after working is increased by age hardening utilizing a paint baking process after pressing. This bake hardenability (hereinafter referred to as BH property) is an effective property that a low yield point at the time of forming and a high yield point after the forming can be achieved at the same time by solid solution C or solid solution N in steel. Further, Japanese Unexamined Patent Publication No.
JP-A-70258 and JP-A-59-31827 disclose NH as having a deep drawing property as well as a BH property.
A method is disclosed for producing b-added steel or Ti / Nb composite-added steel by continuous annealing. This is because, before continuous annealing, C and N in steel that inhibit the formation of a good texture for deep drawing are fixed, and after continuous annealing, carbonitrides are decomposed, leaving solid solution C and N. This is a method for imparting BH properties.

【０００３】[0003]

【発明が解決しようとする課題】上に述べたようにＢＨ
性と深絞り性を同時に付与して外板パネルの要求特性を
満たしたＮｂ添加またはＴｉ、Ｎｂ複合添加技術では、
焼鈍中の炭窒化物の分解により生成した固溶Ｃを室温ま
で残留させてＢＨ性を付与するため、炭窒化物の分解に
８５０℃以上の高い焼鈍温度が、また室温までの冷却時
に再析出を防ぐための急冷が必要になる。そのため、こ
の技術では原理上、焼鈍温度依存性ならびに冷却速度依
存性が大きく安定したＢＨ性を得ることが難しいこと、
さらに、高い焼鈍温度が要求されるため、通板性の悪化
に伴う生産性の低下やロール起因の疵による表面品質の
低下などの問題点がある。また、ＢＨ性は、固溶Ｃ、Ｎ
量に対しｐｐｍレベルの微量な制御が必要であるが、製
鋼工程におけるＣ、Ｎ量のばらつきの影響を受けやす
く、上記の方法ではこの影響も大きい。これに対し、連
続焼鈍前に固溶Ｃを残す方法は、炭窒化物の溶解を利用
することなくＢＨ性を付与できるため高温焼鈍する必要
もなく、また製鋼段階でのＣ、Ｎ量ばらつきによるＢＨ
性ばらつきの影響も小さいため安定して生産できるが、
この方法では、良好な深絞り性が得られない問題があっ
た。従って、本発明の目的は、上記の問題を解決すべ
く、安定したＢＨ性と一体成形化を可能とする超深絞り
性とを有した鋼板を製造することにある。As described above, BH
Nb addition or Ti, Nb composite addition technology that satisfies the required characteristics of the outer panel by simultaneously imparting properties and deep drawability,
A high annealing temperature of 850 ° C. or more is required for the decomposition of carbonitrides, and the solid solution C generated by the decomposition of carbonitrides during annealing is left at room temperature to impart BH property. Quenching is needed to prevent this. Therefore, in this technology, it is difficult to obtain a stable and stable BH property having a large dependence on annealing temperature and cooling rate in principle.
Further, since a high annealing temperature is required, there are problems such as a decrease in productivity due to deterioration of sheet passing property and a decrease in surface quality due to a roll-induced flaw. In addition, the BH properties are as follows: solid solution C, N
Although it is necessary to control the amount to a very small amount of ppm level, it is easily affected by variations in the amounts of C and N in the steel making process, and the above method has a large effect. On the other hand, the method of leaving solid solution C before continuous annealing does not require high-temperature annealing because BH property can be imparted without using dissolution of carbonitride, and also involves a variation in C and N contents at the steelmaking stage. BH
The effect of gender variation is small, so stable production is possible,
This method has a problem that good deep drawability cannot be obtained. Accordingly, an object of the present invention is to produce a steel sheet having stable BH properties and ultra-deep drawability enabling integrated molding to solve the above-mentioned problems.

【０００４】[0004]

【課題を解決するための手段】その具体的な手段は、重
量比にて Ｃ：０．００１〜０．０１ｍａｓｓ％ Ａｌ：０．０１〜０．１ｍａｓｓ％ Ｎ：０．００５ｍａｓｓ％以下 さらにＴｉ、Ｎｂ、Ｖのうち１種以上を０．０５％以下
でかつ （Ｔｉ／４８＋Ｎｂ／９３＋Ｖ／５１）／（Ｃ／１２＋
Ｎ／１４）＜１ の範囲で含有する鋼片を、通常の熱間圧延後、熱延鋼帯
とし酸洗した後、圧下率５０％以上の冷間圧延を行い、
再結晶温度以上の温度で焼鈍し、再び圧下率５０％以上
で冷間圧延を行った後、再結晶温度以上、８５０℃以下
の焼鈍を行い、調質圧延を施すことを特徴とする焼付硬
化性に優れる超深絞り用鋼板の製造方法。The specific means are as follows: C: 0.001 to 0.01 mass% Al: 0.01 to 0.1 mass% N: 0.005 mass% or less by weight ratio At least one of Nb and V is 0.05% or less and (Ti / 48 + Nb / 93 + V / 51) / (C / 12 +
N / 14) <1 The steel slab contained in the range of <1 is usually hot-rolled, then hot-rolled steel strip, pickled, and then cold-rolled at a reduction of 50% or more.
Annealing at a temperature higher than the recrystallization temperature, cold rolling again at a reduction rate of 50% or higher, annealing at a temperature higher than the recrystallization temperature and lower than 850 ° C., and performing temper rolling. For producing ultra-deep drawing steel sheet with excellent heat resistance.

【０００５】[0005]

【発明の実施の形態】発明者らは、深絞り性および焼付
硬化性に優れた特性を満足する鋼板を開発すべく、極低
炭素化した鋼にＴｉ、ＮｂならびにＶなどの炭窒化物形
成元素を添加し、さらに、強化元素としてＰ、Ｍｎを添
加した高張力鋼板も含めてその製造方法を詳細に検討し
た。その結果、Ｃを原子モル量で炭窒化物形成元素必要
量より多く含む鋼を通常の熱間圧延により熱延鋼帯と
し、酸洗後、圧下率５０％以上で冷延し、十分な再結晶
温度で焼鈍を施した後、再び圧下率５０％以上で冷延
し、８００℃前後の再結晶焼鈍を施すことにより、３０
ＭＰａ以上のＢＨ性と２．２以上のランクフォード値を
兼ね備えた鋼板が得られることを見出した。BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have developed carbon steel nitrides such as Ti, Nb and V on ultra-low carbon steel in order to develop a steel sheet satisfying excellent properties of deep drawability and bake hardenability. The production method was studied in detail, including a high-strength steel sheet to which elements were added and further added P and Mn as strengthening elements. As a result, a steel containing C in an atomic molar amount more than the required amount of carbonitride forming element is formed into a hot-rolled steel strip by ordinary hot rolling, and after pickling, cold-rolled at a rolling reduction of 50% or more and sufficiently re-rolled. After annealing at the crystallization temperature, the steel sheet is cold-rolled again at a reduction of 50% or more, and recrystallized at around 800 ° C.
It has been found that a steel sheet having both a BH property of not less than MPa and a Rankford value of not less than 2.2 can be obtained.

【０００６】この知見を得た実験について以下に記す。An experiment which has obtained this finding will be described below.

【０００７】Ｃ；０．００４０ｗｔ％、（以下単に％と
示す）、Ｎｂ；０．０２５％、Ｍｎ；０．５％、Ｓｉ；
０．０２％、Ｐ；０．０６％、Ｓ；０．００６％、Ａ
ｌ；０．０３％、Ｎ；０．００１８％を含有する鋼を、
６．０ｍｍ厚まで熱間圧延後、種々の冷間圧延率で圧延
し、これを７７５℃で連続焼鈍、あるいは６８０℃で１
２時間の箱焼鈍を施し、均一な再結晶粒を生成させたの
ち、再び冷間圧延を行った。これを８００℃で１分均熱
する連続焼鈍サイクルで焼鈍し、ついで圧下率０．８％
の調質圧延を施した後、ＪＩＳ５号試験片として引張試
験を行い、その材質を調査した。なお、ＢＨ性の評価は
２％予歪みを与えた後１７０℃で２０分の焼付工程相当
の時効処理による降伏点の上昇量を測定することで評価
した。C: 0.0040 wt% (hereinafter simply referred to as%), Nb: 0.025%, Mn: 0.5%, Si;
0.02%, P: 0.06%, S: 0.006%, A
l; 0.03%, N; 0.0018% steel containing
After hot rolling to a thickness of 6.0 mm, it is rolled at various cold rolling reductions, and this is continuously annealed at 775 ° C or 1 hour at 680 ° C.
After performing box annealing for 2 hours to generate uniform recrystallized grains, cold rolling was performed again. This is annealed in a continuous annealing cycle of soaking at 800 ° C. for 1 minute, and then the rolling reduction is 0.8%.
After temper rolling, a tensile test was performed as a JIS No. 5 test piece, and the material was examined. The BH property was evaluated by giving a 2% prestrain and measuring the amount of increase in the yield point by aging treatment equivalent to a baking step at 170 ° C. for 20 minutes.

【０００８】図１に、冷延焼鈍後の再冷延率（以後、２
次冷延率と称す）７０％における１回目の冷延率（以
後、１次冷延率と称す）とｒ値およびＢＨ性の関係を示
す。１次冷延率が０％の従来法と比較し、本法では１次
冷延率５０％以上の範囲でｒ値の著しい向上が見られ
る。このとき、ＢＨ性は冷延率によらず安定している。
また、図２に１次冷延率７０％における２次冷延率とｒ
値およびＢＨ性の関係を示す。２次冷延率が０％すなわ
ち従来法と比較し、本法ではやはり冷延率５０％以上の
範囲でｒ値の向上が著しい。このｒ値の向上する理由に
ついて、必ずしも明らかではないが以下のように推測さ
れる。１次冷延焼鈍は、鋼板に微細かつ均一な再結晶組
織を生じさせ、しかも深絞り性に有効な集合組織の形成
を阻害する微細な炭窒化物を成長、消失させる。そのた
め２次冷延焼鈍時の深絞り性に有効な集合組織を発達さ
せる密度が増加したためと考えられる。一方、１次冷延
率が小さい４０％以下においてｒ値が向上しないのは、
１回目の焼鈍後の組織を観察したところ均一な再結晶組
織が形成されてなく、２次冷延焼鈍しても、深絞り性に
有利な再結晶集合組織が得られなかったためと考えられ
る。また、２次冷延率が４０％以下の場合にも同様であ
ると考えられる。また、ＢＨ性は１次および２次冷延率
に依存せず安定して得られていることがわかる。この原
因について、１次冷延焼鈍によって粗大な析出物が生成
したため、冷却時の再析出サイト密度が低く、焼鈍後に
安定した固溶Ｃが残りやすくなったためと考えられる。FIG. 1 shows the re-rolling rate after cold rolling annealing (hereinafter referred to as 2%).
The relationship between the first cold rolling reduction (hereinafter referred to as the primary cold rolling reduction) at 70%, the r value, and the BH property is shown. Compared with the conventional method in which the primary cold rolling reduction is 0%, in the present method, a remarkable improvement in the r value is seen in the range of the primary cold rolling reduction of 50% or more. At this time, the BH property is stable regardless of the cold rolling rate.
FIG. 2 shows the secondary cold rolling reduction and r at a primary cold rolling reduction of 70%.
The relationship between the value and the BH property is shown. As compared with the conventional method, in which the secondary cold rolling reduction is 0%, the r-value is remarkably improved in the present method also in the range of the cold rolling reduction of 50% or more. The reason why the r value is improved is not necessarily clear, but is presumed as follows. The primary cold rolling annealing causes a fine and uniform recrystallized structure to be generated in the steel sheet, and also causes growth and disappearance of fine carbonitrides that inhibit formation of a texture effective for deep drawing. This is probably because the density for developing a texture effective for deep drawing at the time of secondary cold rolling annealing was increased. On the other hand, the reason that the r value does not improve at a primary cold rolling reduction of 40% or less is as follows.
Observation of the structure after the first annealing revealed that a uniform recrystallized structure was not formed, and even if the secondary cold rolling annealing was performed, a recrystallized texture advantageous for deep drawability could not be obtained. It is also considered that the same applies when the secondary cold rolling reduction is 40% or less. Further, it can be seen that the BH property is obtained stably without depending on the primary and secondary cold rolling reduction. It is considered that the cause is that coarse precipitates were formed by the primary cold rolling annealing, so that the density of reprecipitation sites during cooling was low, and stable solid solution C was likely to remain after annealing.

【０００９】以下にこの発明における成分組成範囲の限
定理由について説明する。The reasons for limiting the component composition range in the present invention will be described below.

【００１０】Ｃ：０．００１〜０．０１％ Ｃは低い程延性および深絞り性を向上させるが、低すぎ
るとＢＨ性を得られないため、その下限は０．００１０
％となる。多量の固溶Ｃの存在は、プレス時においてス
トレッチャーストレインの発生など外観を損ねる原因と
なるため、後に述べるような炭窒化物形成元素を添加し
て固溶Ｃ量を適正化するが、Ｃ量が多いほど析出物も多
く、多量の析出物の存在は著しく延性を損ねる。そのた
め、Ｃ量の上限は０．０１％とする。C: 0.001 to 0.01% As C is lower, the ductility and the deep drawability are improved, but if the C is too low, the BH property cannot be obtained, so the lower limit is 0.0010.
%. Since the presence of a large amount of solid solution C causes deterioration of appearance such as generation of stretcher strain during pressing, the amount of solid solution C is optimized by adding a carbonitride forming element described later. The larger the amount, the more precipitates, and the presence of a large amount of precipitates significantly impairs ductility. Therefore, the upper limit of the amount of C is set to 0.01%.

【００１１】Ａｌ：０．０１〜０．１％ Ａｌは、脱酸材として用いられ十分な脱酸を行うには
０．０１％以上が必要である。また、固溶しているＮを
ＡｌＮとして無害化する。しかし、多量の添加は鋼中の
介在物を増加させ、連続鋳造での生産性を低下させる原
因となり、また鋼の清浄度を落とし延性が劣化するなど
の問題が生じる。そのため鋼中Ａｌ量は０．１％以下と
する。Al: 0.01 to 0.1% Al is used as a deoxidizing material, and 0.01% or more is required for performing sufficient deoxidizing. In addition, the solid solution N is rendered harmless as AlN. However, a large amount of addition increases inclusions in the steel and causes a decrease in productivity in continuous casting, and also causes problems such as a decrease in cleanliness of the steel and deterioration in ductility. Therefore, the Al content in steel is set to 0.1% or less.

【００１２】Ｎ：０．００５％以下 鋼中の侵入型元素であるＮは、Ｃと同様ＢＨ性を発現す
る。しかし、室温での時効特性はＣに劣る。そのため、
本発明ではＡｌおよびＴｉなどの窒化物形成元素を添加
してＮを無害化する。なお、Ｎを過剰に含む場合、固定
するための合金添加量も多くコスト的に不利であり、ま
た多量の析出物の存在は延性を劣化する。そのため、Ｎ
量の上限を０．００５％とする。N: 0.005% or less N, which is an interstitial element in steel, exhibits BH properties like C. However, the aging characteristics at room temperature are inferior to C. for that reason,
In the present invention, N is rendered harmless by adding nitride forming elements such as Al and Ti. When N is contained excessively, the amount of alloy for fixing is large, which is disadvantageous in cost, and the presence of a large amount of precipitates deteriorates ductility. Therefore, N
The upper limit of the amount is 0.005%.

【００１３】Ｔｉ、Ｎｂ、Ｖ Ｔｉ、Ｎｂ、Ｖは炭窒化物の形成により鋼中のＣ、Ｎを
固定するために添加する。本発明では適量のＣを鋼中に
残すことで主たるＢＨ性を発現させるため、原子モル量
で（Ｃ＋Ｎ）量以上の添加はさける。すなわち、Ｔｉ、
Ｎｂ、Ｖのうち１種以上を０．０５％以下でかつ（Ｔｉ
／４８＋Ｎｂ／９３＋Ｖ／５１）／（Ｃ／１２＋Ｎ／１
４）＜１の範囲をその含有量とする。Ti, Nb, V Ti, Nb, V are added to fix C, N in steel by forming carbonitride. In the present invention, since the main BH property is developed by leaving an appropriate amount of C in the steel, addition of an amount of (C + N) or more in an atomic molar amount is avoided. That is, Ti,
At least one of Nb and V is 0.05% or less and (Ti
/ 48 + Nb / 93 + V / 51) / (C / 12 + N / 1
4) The content of <1 is defined as the content.

【００１４】上記の成分範囲を満たすことで、本製造法
により優れた深絞り性と焼付硬化性を確保できるが、さ
らに下記の元素を含有しても優れた特性が得られる。そ
れらを以下に述べる。By satisfying the above component ranges, excellent deep drawability and bake hardenability can be ensured by the present production method, but excellent characteristics can be obtained even when the following elements are further contained. They are described below.

【００１５】Ｍｎ：０．０５〜２．０％ Ｍｎは成形性を損なわずに鋼板を高強度化する有効な元
素である。しかし、２．０％以上の添加は延性を極端に
下げるため、十分な成形性が得られず、また、０．０５
％以上含まない場合には、Ｓに起因する熱間割れを抑止
する効果が薄れる。したがって、その含有範囲は０．０
５〜２．０％が適正である。Mn: 0.05 to 2.0% Mn is an effective element for increasing the strength of a steel sheet without impairing formability. However, the addition of 2.0% or more extremely lowers the ductility, so that sufficient moldability cannot be obtained.
%, The effect of suppressing hot cracking caused by S is diminished. Therefore, its content range is 0.0
5 to 2.0% is appropriate.

【００１６】Ｓｉ：≦１．５％ ＳｉはＭｎと同様、延性を損なうことなく鋼板強度を上
昇させる有効な元素である。しかし、１．５％以上の添
加は延性を極端に下げるため、十分な成形性を確保でき
ない。そのため１．５％を上限とする。Si: ≤1.5% Si is an effective element for increasing the strength of a steel sheet without impairing ductility, like Mn. However, the addition of 1.5% or more extremely lowers the ductility, so that sufficient formability cannot be secured. Therefore, the upper limit is 1.5%.

【００１７】Ｐ≦０．１５％ ＰはＳｉ、Ｍｎと同様、鋼板強度を上昇させるのに有効
な元素であり、しかも添加量あたりの強度上昇量が大き
いため、低コストで高強度化できる元素である。しか
し、０．１５％を超える添加はプレス成形性を劣化さ
せ、また、粒界偏析により二次加工性を悪化させる。そ
のため上限は０．１５％とする。P ≦ 0.15% P, like Si and Mn, is an effective element for increasing the strength of a steel sheet, and an element which can increase the strength at low cost because the strength increase per addition amount is large. It is. However, the addition exceeding 0.15% deteriorates press formability, and deteriorates secondary workability due to grain boundary segregation. Therefore, the upper limit is set to 0.15%.

【００１８】Ｓ：≦０．０１５％ Ｓは熱間工程での割れを発生しやすいため、添加量は少
ないほど良いが、Ｓ含有量の低減は精錬コストを増大さ
せ、また生産性も阻害するなどの問題点がある。しかし
本法ではＭｎあるいはＴｉなどの硫化物形成元素が添加
されているため、Ｓは無害化されている。そのためＳ量
は０．０１５％まで許容される。S: ≦ 0.015% Since S is liable to crack in the hot step, the smaller the addition amount, the better, but the reduction of the S content increases the refining cost and impairs the productivity. There are problems such as. However, in this method, S is made harmless because a sulfide-forming element such as Mn or Ti is added. Therefore, the S amount is allowed up to 0.015%.

【００１９】Ｂ：≦０．００５％ 鋼中のＢはＮと強い親和力をもつため、鋼中の固溶Ｎを
固定する効果を有する。また、Ｂは粒界に偏析して粒界
強度を高め、Ｐが多量に含まれる鋼板などの２次加工性
を向上させる効果をもつ。但し、２次加工性への効果は
１５ｐｐｍ程度で飽和し、これ以上は成形性に悪影響を
及ぼす。そこで、Ｎを固定するＢ含有量も考慮し、上限
を０．００５％とする。B: ≦ 0.005% Since B in steel has a strong affinity with N, it has an effect of fixing solid solution N in steel. In addition, B segregates at the grain boundary to increase the grain boundary strength, and has the effect of improving the secondary workability of a steel sheet or the like containing a large amount of P. However, the effect on the secondary workability is saturated at about 15 ppm, and beyond this, the moldability is adversely affected. Therefore, the upper limit is made 0.005% in consideration of the B content for fixing N.

【００２０】次に本発明鋼の製造条件について説明す
る。Next, the production conditions of the steel of the present invention will be described.

【００２１】熱延条件は、通常の熱延で構わず、後述す
る冷延焼鈍を２回するための条件と最終の製品厚から定
まる所定の厚みまで減ずればよい。The hot rolling condition may be ordinary hot rolling, and may be reduced to a predetermined thickness determined from the condition for performing twice cold rolling annealing described later and the final product thickness.

【００２２】酸洗後の１次冷延率が５０％以下では、焼
鈍後に微細均一な再結晶組織が得られず、２回冷延焼鈍
時に良好な深絞り性が期待できない。したがって、その
下限を５０％とする。If the primary cold rolling rate after pickling is 50% or less, a fine and uniform recrystallized structure cannot be obtained after annealing, and good deep drawability cannot be expected during cold rolling annealing twice. Therefore, the lower limit is set to 50%.

【００２３】１回目の焼鈍温度（以後、中間焼鈍温度と
称す）は、均一な再結晶粒が生成すれば良いので、再結
晶温度以上であればよい。なお、焼鈍方式は連続焼鈍方
式よりも箱焼鈍方式で本発明の効果が十分に得られる。
理由として、箱焼鈍方式は長時間加熱保定されるため、
熱延時の微細で密度の高い析出物は消失あるいは成長
し、粗大で低密度の析出物になる。これにより、深絞り
性に有利な集合組織形成を阻害する微細析出物が減少す
るため、深絞り性が向上することと、さらに、ＢＨ性に
関しては２回目の冷延後の焼鈍温度が高く炭化物が再溶
解しても、再析出サイトの密度が減少しているため安定
したＢＨ性が得られるためと推測している。The first annealing temperature (hereinafter referred to as "intermediate annealing temperature") may be equal to or higher than the recrystallization temperature since uniform recrystallized grains may be generated. The effect of the present invention is sufficiently obtained by the box annealing method as compared with the continuous annealing method.
The reason is that the box annealing method is heated and held for a long time,
The fine and high-density precipitates during hot rolling disappear or grow and become coarse and low-density precipitates. As a result, fine precipitates that inhibit the formation of a texture advantageous for deep drawability are reduced, so that the deep drawability is improved. Further, with respect to the BH property, the annealing temperature after the second cold rolling is increased and the carbide is increased. It is presumed that even if is redissolved, the density of the reprecipitation site is reduced, so that a stable BH property can be obtained.

【００２４】２次冷延率が高いほど深絞り性が向上する
が、低圧下率では１回目の冷延と同様均一な再結晶組織
が得らず、深絞り性は向上しない。そこで２次冷延率は
５０％以上とする。The higher the secondary cold rolling reduction, the better the deep drawability. However, at a low rolling reduction, a uniform recrystallization structure cannot be obtained as in the first cold rolling, and the deep drawability does not improve. Therefore, the secondary cold rolling reduction is set to 50% or more.

【００２５】２回目の焼鈍温度（以後、最終焼鈍温度と
称す）は、本発明では過剰な固溶Ｃを利用してＢＨ性を
得るため、高温焼鈍により炭化物を溶解させる必要がな
く、再結晶温度以上で十分である。The second annealing temperature (hereinafter referred to as the final annealing temperature) is used in the present invention to obtain the BH property by using excess solid solution C. Therefore, it is not necessary to dissolve carbides by high temperature annealing, and recrystallization is performed. Above the temperature is sufficient.

【００２６】調圧率は通常の範囲で構わず、０．５〜
３．０％でよい。The pressure regulation ratio may be in a normal range, and is 0.5 to
It may be 3.0%.

【００２７】[0027]

【実施例】表１に示す組成の鋼を転炉−脱ガス法で溶製
し、連続鋳造法にてスラブとし、ついで通常の熱間圧延
を施し６．０ｍｍの板とし酸洗した後、表２に示す条件
で、２回冷延焼鈍を行い、板厚０．７ｍｍとした鋼板に
圧下率０．７％〜１．５％で調質圧延を施した。得られ
た鋼板をＪＩＳ５号試験片に加工し、該試験片の機械的
性質について調べた結果を表２に示す。なおＢＨ性は前
述の通り２％予歪み後、１７０℃で２０分焼付相当処理
後の降伏点の上昇量で評価した。EXAMPLE A steel having the composition shown in Table 1 was melted by a converter-degassing method, formed into a slab by a continuous casting method, and then subjected to ordinary hot rolling to form a 6.0 mm plate and pickled. Under the conditions shown in Table 2, cold-rolled annealing was performed twice, and temper rolling was performed on a steel sheet having a sheet thickness of 0.7 mm at a rolling reduction of 0.7% to 1.5%. The obtained steel sheet was processed into a JIS No. 5 test piece, and the results of examining the mechanical properties of the test piece are shown in Table 2. As described above, the BH property was evaluated by the amount of increase in the yield point after a treatment equivalent to baking at 170 ° C. for 20 minutes after 2% prestrain.

【００２８】[0028]

【表１】 [Table 1]

【００２９】[0029]

【表２】 表２より、発明鋼（Ａ〜Ｆ）では強度ＴＳが３００〜４
５０ＭＰａの範囲において形状凍結性に優れるＹＳ≦２
５０ＭＰａを満足し、かつｒ値＞２．２の深絞り性を得
ているにも関わらず、３０〜５０ＭＰａのＢＨ性を熱延
および焼鈍条件に関わらず安定して得られていることが
わかる。しかし、Ｃ量が適合範囲外の比較鋼Ｇ、Ｈ、及
びＴｉ量が適合範囲外の比較鋼Ｉ、及びＣ、Ｎ量と炭化
物形成元素の原子モル比が適合範囲外の比較鋼Ｊでは、
適正範囲内のＢＨ性が得られていない。また、製造条件
の影響を見ると１次冷延率の低い比較鋼Ｋ、及び２次冷
延率の低い比較鋼Ｌにおいては、適度なＢＨ性は得られ
ているものの、深絞り性に劣る。[Table 2] Table 2 shows that the strength TS of the invention steels (A to F) is 300 to 4
YS ≦ 2 excellent in shape freezing property in the range of 50 MPa
It can be seen that, despite satisfying 50 MPa and obtaining a deep drawability with an r value of> 2.2, a BH property of 30 to 50 MPa is stably obtained regardless of hot rolling and annealing conditions. . However, the comparative steels G, H, and C, in which the C content is out of the compatible range, and the comparative steel J, in which the C and N amounts and the atomic molar ratio of the carbide forming element are out of the compatible range,
BH property within an appropriate range is not obtained. Looking at the influence of the manufacturing conditions, the comparative steel K having a low primary cold-rolling rate and the comparative steel L having a low secondary cold-rolling rate have an appropriate BH property but are inferior in deep drawability. .

【００３０】[0030]

【発明の効果】この発明によれば、製鋼、熱延、焼鈍の
制約条件の影響を受けにくく、安定した焼付硬化性を有
し、かつ一体成形化を可能とする超深絞り用鋼板が製造
できる。According to the present invention, a steel plate for ultra-deep drawing which is hardly affected by the constraints of steel making, hot rolling and annealing, has stable bake hardening properties, and can be integrally formed is manufactured. it can.

【図面の簡単な説明】[Brief description of the drawings]

【図１】ｒ値およびＢＨ性に及ぼす１次冷延率の影響を
示す図である。FIG. 1 is a diagram showing the influence of the primary cold rolling reduction on the r value and BH property.

【図２】ｒ値およびＢＨ性に及ぼす２次冷延率の影響を
示す図である。FIG. 2 is a view showing the influence of a secondary cold rolling reduction on r value and BH property.

Claims (1)

【特許請求の範囲】[Claims] 【請求項１】 重量比にて Ｃ：０．００１〜０．０１ｍａｓｓ％ Ａｌ：０．０１〜０．１ｍａｓｓ％ Ｎ：０．００５ｍａｓｓ％以下 さらにＴｉ、Ｎｂ、Ｖのうち１種以上を０．０５％以下
でかつ （Ｔｉ／４８＋Ｎｂ／９３＋Ｖ／５１）／（Ｃ／１２＋
Ｎ／１４）＜１ の範囲で含有する鋼片を、通常の熱間圧延後、熱延鋼帯
とし酸洗した後、圧下率５０％以上の冷間圧延を行い、
再結晶温度以上で焼鈍し、再び圧下率５０％以上で冷間
圧延を行った後、再結晶温度以上で焼鈍を行い、調質圧
延を施すことを特徴とする焼付硬化性に優れる超深絞り
用鋼板の製造方法。(1) C: 0.001 to 0.01 mass% Al: 0.01 to 0.1 mass% N: 0.005 mass% or less by weight ratio Not more than 05% and (Ti / 48 + Nb / 93 + V / 51) / (C / 12 +
N / 14) <1 The steel slab contained in the range of <1 is usually hot-rolled, then hot-rolled steel strip, pickled, and then cold-rolled at a reduction of 50% or more.
An ultra deep drawing with excellent bake hardenability, characterized by annealing at a recrystallization temperature or higher, cold rolling again at a rolling reduction of 50% or higher, annealing at a recrystallization temperature or higher, and performing temper rolling. Manufacturing method for steel sheet.