JP2000192188A - High strength cold rolled steel sheet excellent in resistance to secondary working brittleness and deep drawability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength cold rolled steel sheet for deep drawing, combining drawability, strength, and resistance to secondary working brittleness and used for automobile members or the like. SOLUTION: This steel sheet has a composition containing, by mass, 0.0010-0.0040% C, <=1.0% Si, 0.5-2.0% Mn, 0.03-0.12% P, <=0.02% S, 0.01-0.10% Al, <=0.004% N, 0.015-0.060% Ti, 0.005-0.040% Nb, and 0.0003-0.0020% B, also containing respective elements satisfying inequalities C<= Ti-(48/14)N+(48/93) Nb}/10, 0.05×Mn-0.02<=P<=0.1×Mn+0.02, and 0.5×Ti-0.01<=Nb<=0.5×Ti+0.02, and having the balance Fe with inevitable impurities. Each symbol of element in the inequalities represents its content (%).

Description

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

【０００１】[0001]

【発明が属する技術分野】本発明は、例えば自動車用部
材の素材鋼板として用いられる深絞り用高強度冷延鋼板
に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength cold-rolled steel sheet for deep drawing used, for example, as a material steel sheet for automobile parts.

【０００２】[0002]

【従来の技術】かつて、深絞り用高強度鋼板はＰ添加ア
ルミキルド鋼をバッチ焼鈍することにより製造されてい
たが、生産性および加工性向上の観点から、近年は極低
炭素ＩＦ鋼にＰ，Ｍｎ，Ｓｉ等の固溶強化元素を添加し
た所謂ＩＦハイテンでの製造が主流になっている。しか
しながら、そもそも極低炭素ＩＦ鋼はＴｉ，Ｎｂ等の炭
窒化物形成元素により固溶Ｃ，Ｎを固定しているため粒
界が脆弱であり、さらにＩＦハイテンで多用される強化
元素であるＰは粒界に偏析して脆化を促進する元素であ
るため、耐二次加工脆性に劣るという欠点を有してい
る。このような事情から、ＩＦハイテンの製造において
は、Ｔｉ，Ｎｂに加えてＢを添加し、さらにＰ，Ｍｎ，
Ｓｉ，Ｃｒ等の強化元素を複合添加する方法が採られる
ことが多い。2. Description of the Related Art In the past, high-strength steel sheets for deep drawing were manufactured by batch annealing P-added aluminum killed steel. Production using a so-called IF high tensile steel to which a solid solution strengthening element such as Mn or Si is added has become mainstream. However, in the first place, ultra-low carbon IF steel has a weak grain boundary because solid solution C and N are fixed by carbonitride forming elements such as Ti and Nb, and P is a strengthening element frequently used in IF high tensile steel. Is an element that segregates at the grain boundaries and promotes embrittlement, and thus has a drawback of being inferior in secondary working embrittlement resistance. Under these circumstances, in the production of IF hyten, B is added in addition to Ti and Nb, and P, Mn,
In many cases, a method in which reinforcing elements such as Si and Cr are combined and added is employed.

【０００３】例えば、特開平５−２１４４８７号公報に
はＴｉ，Ｎｂ，Ｂ添加鋼をベースに、耐二次加工脆性に
悪影響を及ぼすＰに比較してＭｎを多量に添加すること
により、耐二次加工脆性に優れた深絞り用高強度鋼板を
製造する技術が開示されている。しかしながら、Ｍｎの
添加量が多いことから、高温焼鈍による深絞り性向上が
困難であり、またＮｂ添加量も多くコストアップが避け
られない。また、特開平２−１４９６２４号公報および
特開平５−２６３１８４号公報にはＴｉ，Ｎｂ，Ｂ添加
鋼にＭｎ，Ｐを複合添加することによる深絞り用高強度
鋼板の製造方法が開示されている。しかしながら本発明
者らの検討によると、Ｔｉ，Ｎｂ，Ｂ添加高強度ＩＦ鋼
において深絞り性と耐二次加工脆性を両立させるために
は、Ｔｉ，Ｎｂ量に対するＣ量の適正化およびＭｎ，Ｐ
バランスの適正化が必要である。[0003] For example, Japanese Patent Application Laid-Open No. 5-214487 discloses that, based on a steel containing Ti, Nb, and B, a large amount of Mn is added as compared with P which adversely affects the resistance to secondary working embrittlement. A technique for manufacturing a high-strength steel sheet for deep drawing excellent in secondary working brittleness is disclosed. However, since the added amount of Mn is large, it is difficult to improve the deep drawability by high-temperature annealing, and the added amount of Nb is too large to increase the cost. JP-A-2-149624 and JP-A-5-263184 disclose a method for producing a high-strength steel sheet for deep drawing by adding Mn and P to Ti, Nb, and B-added steel in a complex manner. . However, according to the study of the present inventors, in order to achieve both the deep drawability and the resistance to secondary working embrittlement in the Ti, Nb, and B-added high-strength IF steel, the optimization of the amount of C with respect to the amounts of Ti and Nb and Mn, P
It is necessary to optimize the balance.

【０００４】一方、Ｃ，Ｎに対する当量以下のＴｉ添
加、ないしはＴｉ，Ｎｂ添加鋼を高温焼鈍することによ
るＮｂＣの溶解により焼付硬化性鋼板を得る技術が提案
されており、固溶Ｃの存在から耐二次加工脆性も良好で
あると考えられる。しかしながら、焼付硬化性を現出さ
せるほどの量の固溶Ｃは、調質圧延により導入される転
位への集積により時効劣化を惹起し、深絞り性の劣化を
招く恐れがある。On the other hand, there has been proposed a technique for obtaining a bake-hardenable steel sheet by dissolving NbC by adding Ti in an amount equal to or less than that of C and N or by annealing Ti and Nb-added steel at a high temperature. It is considered that the secondary work brittleness resistance is also good. However, solid solution C in such an amount that bake hardenability appears may cause aging deterioration due to accumulation in dislocations introduced by temper rolling, which may lead to deterioration of deep drawability.

【０００５】[0005]

【発明が解決しようとする課題】強化能に優れたＰは耐
二次加工脆性への悪影響が大きく、Ｍｎについても、Ｐ
に比較すれば軽微であるが、やはり耐二次加工脆性を阻
害する元素であり、また、強化量あたりの延性・絞り性
の劣化が大きく、深絞り用鋼板への添加量は制限され
る。一方、Ｓｉは耐二次加工脆性への弊害が比較的少な
い強化元素であるが、多量の添加は冷延鋼板での化成処
理性を劣化させ、また溶融亜鉛めっき製造時の不めっき
の原因となるので好ましくない。これらの元素の他にＣ
ｒ，Ｍｏ等の強化元素も存在するが、添加量あたりの強
化量が小さく、高価であることから、補助的な強化元素
の域を出ないのが実状である。このように、深絞り用高
強度鋼板を製造するために添加する強化元素にはそれぞ
れ長所・短所があり、理想的な添加バランスは明確でな
い。一方、数ｐｐｍの添加により耐二次加工脆性を改善
する元素であるＢに関しても、その効果は２０ｐｐｍ程
度の添加で飽和し、さらなる添加により深絞り性の劣化
がみられるので、強化元素の添加量が増した場合には、
耐二次加工脆性の改善が不十分となる。[0006] P, which is excellent in strengthening ability, has a large adverse effect on the brittleness resistance to secondary working.
Although it is a small element as compared with, it is also an element that inhibits secondary work brittleness resistance, and also has a large deterioration in ductility and drawability per amount of reinforcement, and the amount of addition to the steel sheet for deep drawing is limited. On the other hand, Si is a strengthening element that has relatively little adverse effect on the brittleness resistance to secondary working, but the addition of a large amount degrades the chemical conversion property of cold-rolled steel sheets and causes non-plating during hot-dip galvanizing production. Is not preferred. In addition to these elements,
There are strengthening elements such as r and Mo. However, since the amount of strengthening per added amount is small and expensive, the fact is that they do not fall into the range of auxiliary strengthening elements. As described above, the strengthening elements added to produce a high-strength steel sheet for deep drawing each have advantages and disadvantages, and the ideal balance of addition is not clear. On the other hand, the effect of B, which is an element that improves the resistance to secondary working embrittlement by the addition of several ppm, is saturated by the addition of about 20 ppm, and the deep drawability is deteriorated by the further addition. If the amount increases,
The improvement in secondary work brittleness resistance is insufficient.

【０００６】本発明はこれらの諸問題を解決し、自動車
用部材等に用いられる、絞り性、強度および耐二次加工
脆性を兼備した深絞り用高強度冷延鋼板を提供するもの
である。The present invention solves these problems and provides a high-strength cold-rolled steel sheet for deep drawing, which has both drawability, strength, and resistance to secondary working brittleness, and is used for automobile parts and the like.

【０００７】[0007]

【課題を解決するための手段】本発明者らはかかる課題
を解決するために鋭意研究を行った結果、以下の知見を
得てこの発明を完成させるに至った。すなわち、深絞り
性、強度および耐二次加工脆性を同時に満足させるため
に、鋼組成として適正なＴｉ，Ｎｂ量のもとでのＣ量の
調整、Ｍｎ，Ｐ量のバランスの調整およびＢ添加を行う
ことが本発明鋼板の基本原理である。Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve such problems, and as a result, have obtained the following findings and completed the present invention. That is, in order to simultaneously satisfy the deep drawability, the strength, and the resistance to secondary working embrittlement, the adjustment of the C content under the appropriate Ti and Nb amounts as the steel composition, the adjustment of the balance of the Mn and P amounts, and the addition of B Is the basic principle of the steel sheet of the present invention.

【０００８】極低炭素ＩＦ鋼において一般的なＴｉ単独
添加鋼は、軟鋼の強度レベルではコスト・特性面から有
利であるといえるが、高強度ＩＦ鋼、特にＰ添加鋼にお
いては、Ｎ，Ｃを固定するために充分なＴｉを添加する
と、リン化物の析出量の増加を通じて深絞り性を阻害す
る要因となり好ましくない。一方、リン化物を形成せず
固溶元素を固定する元素としてはＮｂが考えられ、Ｔｉ
の作用の一部を代替させることによりＴｉ添加量の低減
が可能となり、リン化物による悪影響を軽減できる。さ
らに焼鈍板粒径の微細化およびＴｉに比較して弱い炭化
物形成能による固溶Ｃ残存効果とが相まって、耐二次加
工脆性の改善に大きく寄与する。但し、Ｎｂ添加量が過
剰になると再結晶温度の上昇等の理由により加工性劣化
を招くので、総量およびＴｉに対する添加比率に適正範
囲が存在し、それはＴｉ量の概ね１／２であることが明
らかとなった。[0008] It can be said that the Ti-only steel generally used in the ultra-low carbon IF steel is advantageous in terms of cost and characteristics at the strength level of mild steel. However, in the high-strength IF steel, particularly in the P-added steel, N, C If Ti is added sufficiently to fix the content, the drawability of deep drawability is impaired through an increase in the amount of phosphide precipitated, which is not preferable. On the other hand, Nb is considered as an element that does not form a phosphide and fixes a solid solution element.
By substituting a part of the action of the above, the amount of Ti added can be reduced, and the adverse effect of the phosphide can be reduced. Furthermore, the refinement of the grain size of the annealed sheet and the effect of the solid solution C remaining due to the ability to form a carbide that is weaker than that of Ti contribute significantly to the improvement in the brittleness resistance in secondary working. However, an excessive amount of Nb causes deterioration of workability due to an increase in the recrystallization temperature or the like. Therefore, there is an appropriate range in the total amount and the ratio of addition to Ti, which is approximately 1/2 of the Ti amount. It became clear.

【０００９】極低炭素ＩＦ鋼のＣ量は、深絞り性を改善
するという観点からは減じるほど好ましいとされている
が、耐二次加工脆性に対しては鋼中の若干量の固溶Ｃが
寄与するため、少なくとも総量で１０ｐｐｍ程度のＣが
必要である。ただし、Ｃ量が多くなると炭化物析出の駆
動力が増し、却って耐二次加工脆性確保に必要な固溶Ｃ
の残存が図りにくくなるとともに、微細炭化物量の増加
にともなって延性の劣化を生じるので、総Ｃ量は炭化物
形成に寄与するＴｉ，Ｎｂ量に応じて最適化する必要が
ある。本発明鋼のようにＭｎを多量に含有する場合には
Ｓは専らＭｎＳとなりＴｉとの化合物は形成し難いた
め、窒化物を除いたＴｉとＮｂが炭化物を形成し、この
場合、鋼中のＣ含有量が原子当量比でこれらの元素の４
割を越えると耐二次加工脆性が劣化することを見出し
た。It is said that the carbon content of the ultra-low carbon IF steel is preferably as small as possible from the viewpoint of improving the deep drawability, but a small amount of solid solution C in the steel is required for the resistance to secondary working embrittlement. Contributes at least, a total amount of C of about 10 ppm is required. However, when the amount of C increases, the driving force of carbide precipitation increases, and on the contrary, the solid solution C necessary for securing the secondary work brittleness resistance is obtained.
It is difficult to achieve the remaining, and the ductility is deteriorated with the increase in the amount of fine carbides. Therefore, the total C amount needs to be optimized according to the Ti and Nb amounts that contribute to carbide formation. When Mn is contained in a large amount as in the steel of the present invention, S is exclusively MnS and a compound with Ti is difficult to form, so that Ti and Nb excluding nitride form carbides. The C content is 4% of these elements in atomic equivalent ratio.
It has been found that when it exceeds a certain value, the resistance to secondary working brittleness deteriorates.

【００１０】次に、強化元素であるＭｎ，Ｐ、さらにＢ
添加の技術思想を以下に述べる。強化を専らＭｎに頼っ
た場合、ｒ値向上に寄与する熱延板粒径微細化の効果が
期待でき、特にＢとの複合添加時にその効果は顕著とな
る。しかし、Ｂを添加した場合には再結晶温度の上昇が
生ずるため、できるだけ高温での焼鈍が望まれるが、Ｍ
ｎ添加によるＡc₃変態点降下のため、焼鈍中の変態温度
通過により延性が劣化してしまい、高加工性高強度鋼板
の製造には不向きである。一方、Ｐ主体の強化鋼におい
ては、Ｔｉ存在時にリン化物の析出を招きやすく、深絞
り性を阻害する要因となる。Ｂ添加はリン化物の粒界析
出を抑制し、さらに熱延板微細化効果も得られることか
ら好都合ではあるが、そのためにはかなり大量のＢ添加
が必要であり、再結晶温度上昇による加工性劣化の弊害
の方が顕著となってしまう。ところが、最適なＭｎ−Ｐ
バランス、すなわち本発明のＴｉ−Ｎｂ添加超極低Ｃ鋼
においては、Ｐ量に対してＭｎ量をおおよそ１０〜２０
倍含有させた場合、Ｂ添加との相乗効果により、きわめ
て優れた加工性および耐二次加工脆性を確保しつつ、高
強度化が図れるのである。これは前述のＭｎ，Ｐ単独強
化時のＢ複合添加の弊害が減少し、Ｍｎとの相乗効果に
よる少量のＢ添加での熱延板微細化効果およびリン化物
析出抑制効果が最大限に発揮されるためである。このよ
うに、加工性、耐二次加工脆性改善の観点から添加する
Ｂの存在時に、Ｍｎ−Ｐの添加バランスを最適化するこ
とにより、きわめて優れた特性を現出可能なことが判明
した。Next, strengthening elements Mn, P, and B
The technical concept of the addition is described below. When Mn is exclusively used for strengthening, an effect of reducing the grain size of the hot-rolled sheet, which contributes to the improvement of the r value, can be expected, and the effect becomes remarkable especially when B and B are added in combination. However, when B is added, the recrystallization temperature rises. Therefore, it is desirable to perform annealing at as high a temperature as possible.
Due to the lowering of the Ac ₃ transformation point due to the addition of n, the ductility deteriorates due to the passage of the transformation temperature during annealing, which is not suitable for the production of a high-workability, high-strength steel sheet. On the other hand, in a strengthened steel mainly composed of P, precipitation of phosphide easily occurs in the presence of Ti, which is a factor that hinders deep drawability. The addition of B is advantageous because it suppresses grain boundary precipitation of phosphide and also has the effect of making the hot-rolled sheet finer, but for that purpose a considerably large amount of B is required, and the workability due to the increase in the recrystallization temperature is increased. The adverse effects of the degradation become more pronounced. However, the optimal Mn-P
The balance, that is, in the Ti-Nb-added ultra-low C steel of the present invention, the Mn content is approximately 10 to 20 with respect to the P content.
When it is doubled, the synergistic effect with the addition of B makes it possible to achieve high strength while securing extremely excellent workability and secondary work brittleness resistance. This reduces the adverse effects of the addition of B compound when Mn and P alone are strengthened as described above, and maximizes the effect of adding a small amount of B by the synergistic effect with Mn to refine the hot-rolled sheet and suppress phosphide precipitation. That's because. Thus, it was found that by optimizing the Mn-P addition balance in the presence of B added from the viewpoint of improving workability and secondary work brittleness resistance, extremely excellent properties can be exhibited.

【００１１】以上の知見に基づいて完成された本発明の
深絞り用高強度冷延鋼板は、質量％で、 Ｃ ： ０．００１０≦Ｃ ≦０．００４０、 Ｓｉ： Ｓｉ ≦１．０、 Ｍｎ： ０．５ ≦Ｍｎ ≦２．０、 Ｐ ： ０．０３ ≦Ｐ ≦０．１２、 Ｓ ： Ｓ ≦０．０２、 Ａｌ： ０．０１ ≦Ａｌ ≦０．１０、 Ｎ ： Ｎ ≦０．００４、 Ｔｉ： ０．０１５ ≦Ｔｉ ≦０．０６０、 Ｎｂ： ０．００５ ≦Ｎｂ ≦０．０４０、 Ｂ ： ０．０００３≦Ｂ ≦０．００２０ かつ、下記式(1) 、(2) および(3) を満足する各元素を
含有し、残部がＦｅ及び不可避的不純物よりなるもので
ある。なお、式中の元素記号は、その元素の含有％を意
味する。 Ｃ≦｛Ｔｉ−（４８／１４）Ｎ＋（４８／９３）Ｎｂ｝／１０……式(1) ０．０５×Ｍｎ−０．０２≦Ｐ≦０．１×Ｍｎ＋０．０２ ……式(2) ０．５×Ｔｉ−０．０１≦Ｎｂ≦０．５×Ｔｉ＋０．０２ ……式(3) [0011] The high-strength cold-rolled steel sheet for deep drawing of the present invention completed on the basis of the above findings is, by mass%, C: 0.0010 ≦ C ≦ 0.0040, Si: Si ≦ 1.0, and Mn. : 0.5 ≦ Mn ≦ 2.0, P: 0.03 ≦ P ≦ 0.12, S: S ≦ 0.02, Al: 0.01 ≦ Al ≦ 0.10, N: N ≦ 0.004 , Ti: 0.015 ≦ Ti ≦ 0.060, Nb: 0.005 ≦ Nb ≦ 0.040, B: 0.0003 ≦ B ≦ 0.0020 and the following formulas (1), (2) and (3) ), And the balance consists of Fe and inevitable impurities. The symbol of the element in the formula means the content% of the element. C ≦ {Ti− (48/14) N + (48/93) Nb} / 10 Formula (1) 0.05 × Mn−0.02 ≦ P ≦ 0.1 × Mn + 0.02 Formula (2) ) 0.5 × Ti−0.01 ≦ Nb ≦ 0.5 × Ti + 0.02 (3)

【００１２】以下、本発明鋼板の成分限定理由を説明す
る。単位は質量％である。 Ｃ：０．００１０≦Ｃ≦０．００４０ 深絞り性を改善するためには、冷延・焼鈍時に固溶状態
として存在するＣをできるだけ低減することが望まし
く、そのために後述のＴｉ・Ｎｂ等の元素を添加する。
これらの添加により形成される炭化物量の増大が延性の
劣化を招くこと、および総Ｃ量の増加により炭化物析出
の駆動力が増し、耐二次加工脆性の確保に必要な最低限
の固溶Ｃの残存が困難となるので、Ｃ量の上限は０．０
０４０％かつ下記式(1) にて規定される量以下とする。
一方、耐二次加工脆性を確保するためには数ｐｐｍの固
溶Ｃが存在しなければならず、そのために総Ｃ量は少な
くとも０．００１０％必要であるので、Ｃ量の下限は
０．００１０％である。 Ｃ≦｛Ｔｉ−（４８／１４）Ｎ＋（４８／９３）Ｎｂ｝／１０……式(1) Hereinafter, the reasons for limiting the components of the steel sheet of the present invention will be described. The unit is mass%. C: 0.0010 ≦ C ≦ 0.0040 In order to improve the deep drawability, it is desirable to reduce C existing as a solid solution state during cold rolling and annealing as much as possible. Add elements.
An increase in the amount of carbides formed by these additions leads to deterioration of ductility, and an increase in the total amount of carbon increases the driving force for carbide precipitation, and minimizes the amount of solid solution C necessary to secure secondary work brittleness resistance. Is difficult to remain, the upper limit of the amount of C is 0.0
040% and the amount specified by the following formula (1).
On the other hand, in order to ensure secondary work brittleness resistance, a few ppm of solid solution C must be present, and therefore, the total C content is required to be at least 0.0010%. 0010%. C ≦ {Ti− (48/14) N + (48/93) Nb} / 10 Formula (1)

【００１３】Ｓｉ：Ｓｉ≦１．０ Ｓｉは深絞り性、耐二次加工脆性を阻害することなく高
強度化が可能な元素であるが、過剰の添加は、冷延鋼板
の化成処理性、また溶融亜鉛めっき時の濡れ性等を悪化
させるので、上限を１．０％とする。Si: Si ≦ 1.0 Si is an element capable of increasing the strength without impairing the deep drawability and the resistance to secondary working embrittlement. Further, since the wettability during hot-dip galvanizing is deteriorated, the upper limit is made 1.0%.

【００１４】Ｍｎ：０．５≦Ｍｎ≦２．０ Ｍｎは強化を目的として０．５％以上添加するが、添加
量の増加と共に強化への寄与が減少し、加工性の低下を
招くことになる。またＡc₃変態温度を低下させ、高温焼
鈍による材質改善を阻害するので、その上限を２．０％
とする。Mn: 0.5 ≦ Mn ≦ 2.0 Mn is added in an amount of 0.5% or more for the purpose of strengthening. However, as the amount of Mn increases, the contribution to strengthening decreases, leading to a decrease in workability. Become. Further, since the Ac ₃ transformation temperature is lowered and the material improvement by high-temperature annealing is hindered, the upper limit is 2.0%.
And

【００１５】Ｐ：０．０３≦Ｐ≦０．１２ Ｐは強化のために０．０３％以上の添加が必要である
が、過剰な添加は耐二次加工脆性の劣化を招くため、上
限を０．１２％以下とする必要がある。さらに、深絞り
性と耐二次加工脆性を良好とするためには、Ｍｎ量との
間で下記式(2) に示す範囲とする必要がある。 ０．０５×Ｍｎ−０．０２≦Ｐ≦０．１×Ｍｎ＋０．０２ ……式(2) P: 0.03 ≦ P ≦ 0.12 P needs to be added in an amount of 0.03% or more for strengthening. However, excessive addition causes degradation of secondary work brittleness resistance. Must be 0.12% or less. Further, in order to improve the deep drawability and the resistance to secondary working embrittlement, it is necessary to set the range between the Mn content and the value represented by the following formula (2). 0.05 × Mn−0.02 ≦ P ≦ 0.1 × Mn + 0.02 Equation (2)

【００１６】Ｓ：Ｓ≦０．０２ ＳはＭｎを多量に含有する鋼板内で硫化物系介在物とな
るが、圧延後伸張した介在物は鋼板の延性劣化の原因と
なるので、上限を０．０２％とする。S: S ≦ 0.02 S is a sulfide-based inclusion in a steel sheet containing a large amount of Mn, but the inclusion expanded after rolling causes deterioration of the ductility of the steel sheet. 0.02%.

【００１７】Ａｌ：０．０１≦Ａｌ≦０．１０ Ａｌは脱酸のために添加し、０．０１％以上が必要であ
るが、０．１０％以上添加してもその効果が飽和するた
め、下限を０．０１％、上限を０．１０％とする。Al: 0.01 ≦ Al ≦ 0.10 Al is added for deoxidation and needs to be added in an amount of 0.01% or more. However, even if added in an amount of 0.10% or more, the effect is saturated. , The lower limit is 0.01%, and the upper limit is 0.10%.

【００１８】Ｎ：Ｎ≦０．００４ ＮはＴｉ添加鋼中ではＴｉと結合してＴｉＮを形成する
が、ＴｉＮは加工性劣化の原因となるためできるだけ低
減することが望ましく、その上限を０．００４％とす
る。N: N ≦ 0.004 N combines with Ti in Ti-added steel to form TiN. However, since TiN causes deterioration of workability, it is desirable to reduce TiN as much as possible. 004%.

【００１９】Ｔｉ：０．０１５≦Ｔｉ≦０．０６０ Ｎｂ：０．００５≦Ｎｂ≦０．０４０ 深絞り性の劣化を招く固溶Ｎ，Ｃ低減のため、Ｔｉを少
なくとも０．０１５％、Ｎｂを少なくとも０．００５％
添加することが必要である。一方、過剰な添加は鋼板の
特性劣化を招くので、Ｔｉの上限は０．０６０％、Ｎｂ
の上限は０．０４０％とする必要がある。さらに、これ
ら固溶元素低減効果を専らＴｉにより現出させようとす
ると、Ｐ存在下ではＦｅＴｉＰの析出により深絞り性の
劣化を招き、一方過剰なＮｂの添加は再結晶温度上昇に
より延性、深絞り性の劣化を招く。これらおよび耐二次
加工脆性を改善する観点から、Ｔｉ，Ｎｂの含有量は下
記式(3) を満足することが必要である。 ０．５×Ｔｉ−０．０１≦Ｎｂ≦０．５×Ｔｉ＋０．０２ ……式(3) Ti: 0.015 ≦ Ti ≦ 0.060 Nb: 0.005 ≦ Nb ≦ 0.040 At least 0.015% of Ti and Nb to reduce solid solution N and C which cause deterioration of deep drawability. At least 0.005%
It is necessary to add. On the other hand, excessive addition causes deterioration of the properties of the steel sheet.
Must be 0.040%. Further, if the effect of reducing the solute elements is to be exhibited solely by Ti, in the presence of P, precipitation of FeTiP causes deterioration of deep drawability. On the other hand, excessive addition of Nb increases ductility and depth due to a rise in recrystallization temperature. This causes deterioration of the drawability. From these viewpoints and from the viewpoint of improving the resistance to secondary working brittleness, the contents of Ti and Nb need to satisfy the following expression (3). 0.5 × Ti−0.01 ≦ Nb ≦ 0.5 × Ti + 0.02 (3)

【００２０】Ｂ：０．０００３≦Ｂ≦０．００２０ Ｂは耐二次加工脆性および深絞り性改善のため０．００
０３％以上添加する。しかし０．００２０％を超えて添
加してもその効果は飽和するため、添加範囲を０．００
０３％〜０．００２０％とする。B: 0.0003 ≦ B ≦ 0.0020 B is 0.00% for improving secondary work brittleness and deep drawability.
Add at least 03%. However, even if added over 0.0020%, the effect is saturated.
03% to 0.0020%.

【００２１】本発明の冷延鋼板は、上記成分のほか、残
部実質的にＦｅで形成される。また、上記成分系よりな
る冷延鋼板の製造法は常法に従えばよく、焼鈍はバッチ
焼鈍、連続焼鈍の如何を問わない。また、本発明の冷延
鋼板は、深絞り用高強度溶融亜鉛めっき鋼板等の素材鋼
板として好適であり、インライン焼鈍方式の溶融亜鉛め
っき、合金化溶融亜鉛めっきを施しても良い。また、本
発明の冷延鋼板の表面に、電気メッキおよび各種化成処
理を施しても、本発明の特長を損ねるものではない。The cold-rolled steel sheet of the present invention is substantially formed of Fe in addition to the above components. The method for producing a cold-rolled steel sheet comprising the above-described components may be in accordance with a conventional method, and the annealing may be any of batch annealing and continuous annealing. Further, the cold-rolled steel sheet of the present invention is suitable as a material steel sheet such as a high-strength hot-dip galvanized steel sheet for deep drawing, and may be subjected to in-line annealing hot-dip galvanizing or alloyed hot-dip galvanizing. Further, even if the surface of the cold rolled steel sheet of the present invention is subjected to electroplating and various chemical conversion treatments, the features of the present invention are not spoiled.

【００２２】[0022]

【実施例】〔実施例１〕表１に示す成分からなる鋼を常
法により鋳造した後、仕上温度８９０℃で３．２ｍｍ厚
に熱間圧延後、３０℃／ｓで冷却し、６００℃で巻取
後、酸洗、７５％の圧下率で冷延を行い、さらに８３０
℃×６０秒の条件にて焼鈍を行い、伸び率０．８％の調
質圧延を施した。その後ＪＩＳ５号試験片による引張試
験、ｒ値測定および延性脆性遷移温度（ＤＢＴＴ）の測
定を行った。EXAMPLES Example 1 A steel having the components shown in Table 1 was cast by a conventional method, hot-rolled to a thickness of 3.2 mm at a finishing temperature of 890 ° C., cooled at 30 ° C./s, and cooled to 600 ° C. After picking up, pickling and cold rolling at a rolling reduction of 75% were carried out.
Annealing was performed under the conditions of ℃ 60 seconds, and temper rolling at an elongation of 0.8% was performed. Thereafter, a tensile test using a JIS No. 5 test piece, measurement of an r value, and measurement of a ductile brittle transition temperature (DBTT) were performed.

【００２３】ｒ値は、圧延方向に対して０，４５，９０
度方向に採取したＪＩＳ５号引張試験片の１０％変形時
の板幅歪みと板厚歪みの対数比をそれぞれｒ０，ｒ４
５，ｒ９０として下記式(4) により求めた。 ｒ＝（１／４）ｒ０＋（１／２）ｒ４５＋（１／４）ｒ９０ ……(4) 延性脆性遷移温度（ＤＢＴＴ）は、ブランクを絞り比
２．５で２５ｍｍ径のカップに成形し、頂角３０゜の円
錐ポンチを１．５ｔの加重で開口部より圧下したときの
破壊形態を各温度で調査して求めた。The r value is 0, 45, 90 with respect to the rolling direction.
The logarithmic ratio of the sheet width distortion and the sheet thickness distortion at the time of 10% deformation of the JIS No. 5 tensile test specimen taken in the degree direction was r0, r4, respectively.
5, r90 was determined by the following equation (4). r = (1/4) r0 + (1/2) r45 + (1/4) r90 (4) The ductile brittle transition temperature (DBTT) is obtained by molding a blank into a 25 mm diameter cup at a drawing ratio of 2.5. The fracture mode when a conical punch having a vertex angle of 30 ° was pressed down from the opening with a load of 1.5 t was determined at each temperature.

【００２４】これらの調査結果を表１に併せて示す。な
お、表１中、「Ｎｂ下限」、「Ｎｂ上限」の値は、前記
式(3) の下限値（％）、上限値（％）を示す。また、表
中の下線した値は発明範囲外（「Ｎｂ下限」、「Ｎｂ上
限」の場合は、Ｎｂ含有量が下限値未満あるいは上限値
超）であることを示す。The results of these investigations are also shown in Table 1. In Table 1, the values of “Nb lower limit” and “Nb upper limit” indicate the lower limit (%) and the upper limit (%) of the formula (3). The underlined values in the table indicate that the Nb content is outside the range of the invention (in the case of “Nb lower limit” and “Nb upper limit”, the Nb content is less than the lower limit or exceeds the upper limit).

【００２５】[0025]

【表１】 [Table 1]

【００２６】表１より、本発明の成分範囲を外れた試料
について、Ｔｉ量の少ないNo. １及び６において、強度
を勘案した場合のｒ値が劣化している。またＮｂ量の少
ないNo. ３，５では延性脆性遷移温度が上昇している。
一方、Ｔｉまたは／およびＮｂ添加量が過剰なNo. １
０，１５，１６，１９，２０については、いずれもＥｌ
の劣化が見られ、ｒ値も低下している。これら以外の本
発明例については、良好な強度延性バランス、ｒ値およ
び延性脆性遷移温度を示している。From Table 1, it can be seen that, for samples out of the component range of the present invention, the r values of Nos. 1 and 6 with small amounts of Ti in consideration of the strength are deteriorated. In Nos. 3 and 5 where the Nb content is small, the ductile brittle transition temperature is increased.
On the other hand, No. 1 with an excessive amount of Ti and / or Nb added
0, 15, 16, 19 and 20 are all El.
, And the r value is also reduced. Other examples of the present invention show good strength-ductility balance, r-value and ductile brittle transition temperature.

【００２７】〔実施例２〕表２に示す成分からなる鋼を
常法により鋳造した後、仕上温度９００℃で３．２ｍｍ
厚に熱間圧延後２０℃／ｓで冷却し、５８０℃で巻取
後、酸洗、７５％の圧下率で冷延を行い、さらに８５０
℃×６０秒の条件にて焼鈍を行い、伸び率０．８％の調
質圧延を施した。その後ＪＩＳ５号試験片による引張試
験、ｒ値測定および延性脆性遷移温度（ＤＢＴＴ）の測
定を行った。各測定方法は前述同様である。結果を表２
に併せて示す。なお、表２中、「Ｃ上限」の値は、前記
式(1)の上限値（％）を示す。また、表中の下線した値
は発明範囲外（「Ｃ上限」の場合は、Ｃ含有量が上限値
超）であることを示す。Example 2 After a steel having the components shown in Table 2 was cast by a conventional method, a finishing temperature of 900 ° C. was 3.2 mm.
After hot rolling to a thickness, cooling at 20 ° C / s, winding at 580 ° C, pickling, cold rolling at a reduction of 75%, and further 850
Annealing was performed under the conditions of ℃ 60 seconds, and temper rolling at an elongation of 0.8% was performed. Thereafter, a tensile test using a JIS No. 5 test piece, measurement of an r value, and measurement of a ductile brittle transition temperature (DBTT) were performed. Each measuring method is the same as described above. Table 2 shows the results
Are shown together. In Table 2, the value of "C upper limit" indicates the upper limit (%) of the above formula (1). The underlined values in the table indicate that the C content is outside the range of the invention (in the case of "C upper limit", the C content exceeds the upper limit value).

【００２８】[0028]

【表２】 [Table 2]

【００２９】表２より、総Ｃ量の不足している試料No.
２２〜２４では延性脆性遷移温度が上昇している。ま
た、有効Ｔｉ，Ｎｂ量に対してＣ量が過剰であるNo. ２
１，２６，３１，３２，３５，３６では、延性脆性遷移
温度の上昇とともに機械的性質の劣化も見られる。これ
ら以外の本発明鋼については、良好な機械的性質、ｒ値
および延性脆性遷移温度を示す。From Table 2, it can be seen that the sample Nos.
In Nos. 22 to 24, the ductile brittle transition temperature increases. No. 2 in which the amount of C is excessive with respect to the amounts of effective Ti and Nb.
In Nos. 1, 26, 31, 32, 35, and 36, the mechanical properties are also deteriorated with an increase in the ductile brittle transition temperature. Other steels of the invention exhibit good mechanical properties, r-values and ductile brittle transition temperatures.

【００３０】〔実施例３〕表３に示す成分からなる鋼を
常法により鋳造した後、仕上温度８８０℃で３．２ｍｍ
厚に熱間圧延後４０℃／ｓで冷却し、５４０℃で巻取
後、酸洗、７５％の圧下率で冷延を行い、さらに８６０
℃×６０秒の条件にて焼鈍を行い、伸び率０．５％の調
質圧延を施した。その後ＪＩＳ５号試験片による引張試
験、ｒ値測定および延性脆性遷移温度の測定を行った。
各測定方法は前述同様である。結果を表３に併せて示
す。なお、表３中、「Ｐ下限」、「Ｐ上限」の値は、前
記式(2)の下限値（％）、上限値（％）を示す。また、
表中の下線した値は発明範囲外（「Ｐ下限」、「Ｐ上
限」の場合は、Ｐ含有量が下限値未満あるいは上限値
超）であることを示す。Example 3 After a steel having the components shown in Table 3 was cast by a conventional method, a finishing temperature of 880 ° C. was 3.2 mm.
After hot rolling to a thickness, cooling at 40 ° C / s, winding at 540 ° C, pickling, cold rolling at a rolling reduction of 75%, and further 860
Annealing was carried out under the conditions of ° C. × 60 seconds, and temper rolling at an elongation of 0.5% was performed. Thereafter, a tensile test, a measurement of an r value, and a measurement of a ductile brittle transition temperature were performed using a JIS No. 5 test piece.
Each measuring method is the same as described above. The results are shown in Table 3. In Table 3, the values of “P lower limit” and “P upper limit” indicate the lower limit (%) and the upper limit (%) of the formula (2). Also,
The underlined values in the table indicate that the P content is outside the range of the invention (in the case of “P lower limit” and “P upper limit”, the P content is less than the lower limit or exceeds the upper limit).

【００３１】[0031]

【表３】 [Table 3]

【００３２】表３より、試料No. ３９，４０，５３は
Ｐ，Ｍｎの添加量が不足しており、高強度鋼板となって
いない。さらに、No. ５３については、Ｐ，Ｍｎを所定
量含有した鋼種と異なり、Ｂ添加によりｒ値が劣化して
いることが、No. ３９，４０との比較で明らかである。
またNo. ３９〜５２のＢ無添加鋼は全般に機械的性質が
優れず、延性脆性遷移温度も高くなっている。一方、Ｂ
添加鋼であるNo. ５３〜６６においても、Ｍｎ，Ｐ添加
量が過剰なNo. ５８，５９，６６およびＭｎ，Ｐ添加バ
ランスに問題のあるNo. ５６，６１，６３，６５につい
ては、機械的性質または耐二次加工脆性の劣化が生じて
いる。これら以外の本発明例については、所定量のＭ
ｎ，Ｐ含有時にＢ添加の複合効果が現れており、耐二次
加工脆性を満足しつつ、加工性も良好なものとなってい
る。From Table 3, it can be seen that Samples Nos. 39, 40 and 53 lack the added amounts of P and Mn, and are not high strength steel sheets. Furthermore, it is clear from the comparison with Nos. 39 and 40 that the r-value of No. 53 is different from the steel type containing a predetermined amount of P and Mn, and the r value is deteriorated by the addition of B.
In addition, the B-free steels of Nos. 39 to 52 generally do not have excellent mechanical properties and have a high ductile brittle transition temperature. On the other hand, B
Also in Nos. 53 to 66, which are added steels, Nos. 58, 59, and 66 with excessive amounts of Mn and P additions and Nos. 56, 61, 63, and 65 with a problem in Mn and P addition balance are mechanically Of the mechanical properties or the resistance to secondary working brittleness. For other examples of the present invention, a predetermined amount of M
When n and P are contained, the combined effect of the addition of B appears, and the workability is also good while satisfying the secondary work brittleness resistance.

【００３３】[0033]

【発明の効果】本発明の高強度冷延鋼板によれば、耐二
次加工脆性および深絞り性に優れるため、プレス成形用
高強度冷延鋼板として好適であり、自動車用内外板等、
加工性に対する要求が厳しく、かつ軽量化のために強度
も要求される工業分野における素材鋼板として最適であ
る。According to the high-strength cold-rolled steel sheet of the present invention, since it has excellent secondary work brittleness resistance and deep drawability, it is suitable as a high-strength cold-rolled steel sheet for press forming.
It is most suitable as a raw steel sheet in the industrial field where the demand for workability is severe and strength is also required for weight reduction.

Claims (1)

【特許請求の範囲】[Claims] 【請求項１】 質量％で、 Ｃ ： ０．００１０≦Ｃ ≦０．００４０、 Ｓｉ： Ｓｉ ≦１．０、 Ｍｎ： ０．５ ≦Ｍｎ ≦２．０、 Ｐ ： ０．０３ ≦Ｐ ≦０．１２、 Ｓ ： Ｓ ≦０．０２、 Ａｌ： ０．０１ ≦Ａｌ ≦０．１０、 Ｎ ： Ｎ ≦０．００４、 Ｔｉ： ０．０１５ ≦Ｔｉ ≦０．０６０、 Ｎｂ： ０．００５ ≦Ｎｂ ≦０．０４０、 Ｂ ： ０．０００３≦Ｂ ≦０．００２０ かつ、下記式(1) 、(2) および(3) を満足する各元素を
含有し、残部がＦｅ及び不可避的不純物よりなる耐二次
加工脆性および深絞り性に優れた高強度冷延鋼板。 Ｃ≦｛Ｔｉ−（４８／１４）Ｎ＋（４８／９３）Ｎｂ｝／１０……式(1) ０．０５×Ｍｎ−０．０２≦Ｐ≦０．１×Ｍｎ＋０．０２ ……式(2) ０．５×Ｔｉ−０．０１≦Ｎｂ≦０．５×Ｔｉ＋０．０２ ……式(3)1. In mass%, C: 0.0010 ≦ C ≦ 0.0040, Si: Si ≦ 1.0, Mn: 0.5 ≦ Mn ≦ 2.0, P: 0.03 ≦ P ≦ 0 .12, S: S ≦ 0.02, Al: 0.01 ≦ Al ≦ 0.10, N: N ≦ 0.004, Ti: 0.015 ≦ Ti ≦ 0.060, Nb: 0.005 ≦ Nb ≦ 0.040, B: 0.0003 ≦ B ≦ 0.0020, and contains each element satisfying the following formulas (1), (2) and (3), with the balance being Fe and unavoidable impurities. High strength cold rolled steel sheet with excellent secondary work brittleness and deep drawability. C ≦ {Ti− (48/14) N + (48/93) Nb} / 10 Formula (1) 0.05 × Mn−0.02 ≦ P ≦ 0.1 × Mn + 0.02 Formula (2) ) 0.5 × Ti−0.01 ≦ Nb ≦ 0.5 × Ti + 0.02 (3)