JP6684905B2 - High-strength cold-rolled steel sheet excellent in shear workability and method for producing the same - Google Patents

High-strength cold-rolled steel sheet excellent in shear workability and method for producing the same Download PDF

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JP6684905B2
JP6684905B2 JP2018525787A JP2018525787A JP6684905B2 JP 6684905 B2 JP6684905 B2 JP 6684905B2 JP 2018525787 A JP2018525787 A JP 2018525787A JP 2018525787 A JP2018525787 A JP 2018525787A JP 6684905 B2 JP6684905 B2 JP 6684905B2
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steel sheet
rolled steel
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shear workability
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JP2018538441A (en
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ソン−イル キム、
ソン−イル キム、
ソク−ジョン ソ、
ソク−ジョン ソ、
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Posco Holdings Inc
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Description

本発明は、剪断加工性に優れた高強度冷延鋼板及びその製造方法に関する。   The present invention relates to a high-strength cold-rolled steel sheet excellent in shear workability and a method for manufacturing the same.

自動車用の自動変速機における摩擦板向けに用いるためには、剪断加工による亀裂の発生が少ないだけでなく、摩擦熱による亀裂伝播が抑制される必要があり、高強度及び高硬度が要求される。   In order to use it for a friction plate in an automatic transmission for automobiles, not only the occurrence of cracks due to shearing must be small, but also crack propagation due to frictional heat must be suppressed, and high strength and high hardness are required. .

従来の摩擦板用または硬度保証用の高強度冷延鋼板は、特許文献１に記載されているように、中炭素鋼または様々な合金元素を含む鋼に対して回復焼鈍法を用いることで、冷間圧延後に焼鈍熱処理をする技術が適用されている。また、高炭素鋼に対して球状化熱処理工程を行う方法が一般的に使われており、特許文献２を参照すると、冷間圧延−焼鈍−冷間圧延という２回にわたって冷間圧延を行う技術が提案されている。   As described in Patent Document 1, a conventional high-strength cold-rolled steel sheet for friction plates or for hardness assurance uses a recovery annealing method for medium carbon steel or steel containing various alloy elements. A technique of applying annealing heat treatment after cold rolling is applied. Further, a method of performing a spheroidizing heat treatment step on high carbon steel is generally used, and referring to Patent Document 2, a technique of performing cold rolling twice, cold rolling-annealing-cold rolling. Is proposed.

しかし、回復焼鈍法を用いた高強度鋼板には高強度を有する鋼を製造することが難しいという問題があり、高炭素鋼を用いて球状化熱処理を行う技術及び２回にわたって冷間圧延する技術には製造コストが多くかかるという問題点がある。   However, the high-strength steel sheet using the recovery annealing method has a problem that it is difficult to produce a steel having high strength, and the technology of performing spheroidizing heat treatment using high-carbon steel and the technology of cold rolling twice Has a problem of high manufacturing cost.

また、冷間圧延された高強度鋼板を製造するために主に活用されるＣ、Ｓｉ、Ｍｎ、Ｍｏ、Ｃｒなどの合金成分は、固溶強化の効果により鋼板の強度を向上させるのに効果的であるが、必要以上添加されると、合金成分の偏析及び微細組織の不均一をもたらす。特に、冷却時の鋼の硬化能が増加し、フェライトの相変態が大幅に遅延され、低温相（マルテンサイトとオーステナイト）が発生して結晶粒界が不均一となって剪断加工時の亀裂発生が増加するようになり、使用中に摩擦熱が発生すると、亀裂が簡単に伝播されて欠陥が生じるようになる。   In addition, alloying components such as C, Si, Mn, Mo, and Cr that are mainly used to produce cold-rolled high-strength steel sheets are effective in improving the strength of steel sheets by the effect of solid solution strengthening. However, if added more than necessary, it causes segregation of alloy components and nonuniformity of the microstructure. In particular, the hardening ability of steel during cooling is increased, the phase transformation of ferrite is significantly delayed, the low temperature phase (martensite and austenite) is generated, and the grain boundaries become non-uniform, causing cracking during shearing. When the frictional heat is generated during use, cracks are easily propagated to cause defects.

また、強度をさらに向上させるために活用されるＴｉ、Ｎｂ、Ｖなどの合金成分が不適切に添加されると、結晶粒界で粗大な炭化物、窒化物、及び析出物が形成されて剪断加工時の亀裂発生量が増加し、剪断加工時に簡単に亀裂が伝播されるという問題がある。尚、剪断加工された部位には、使用中に摩擦熱が発生した場合、亀裂伝播がさらに容易に発生するという問題がある。   In addition, if alloying elements such as Ti, Nb, and V that are utilized to further improve strength are improperly added, coarse carbides, nitrides, and precipitates are formed at grain boundaries, and shearing is performed. There is a problem that the amount of cracks generated at that time increases and cracks easily propagate during shearing. In addition, there is a problem that crack propagation occurs more easily at the sheared portion when frictional heat is generated during use.

出願番号 ＫＲ １９９８−００５９８０９Application number KR 1998-0059809 出願番号 ＤＥ １０−２００５０３１４６２Application number DE 10-20050031462

本発明は、剪断加工による亀裂や摩擦熱による亀裂を抑制することができる剪断加工性に優れた高強度冷延鋼板及びその製造方法を提供することを目的とする。   An object of the present invention is to provide a high-strength cold-rolled steel sheet excellent in shear workability capable of suppressing cracks due to shearing and cracks due to frictional heat, and a method for producing the same.

一方、本発明の課題は、上述した内容に限定されない。本発明の課題は、本明細書の内容全般から理解されることができ、本発明が属する技術分野において通常の知識を有する者であれば、本発明の追加的な課題を明確に理解するものである。   On the other hand, the subject of the present invention is not limited to the above contents. The problems of the present invention can be understood from the entire content of the present specification, and those having ordinary knowledge in the technical field to which the present invention belongs clearly understand the additional problems of the present invention. Is.

本発明の一側面は、重量％で、Ｃ：０．０５〜０．１０％、Ｓｉ：０．０１〜０．５％、Ｍｎ：１．２〜２．０％、Ａｌ：０．０１〜０．１％、Ｃｒ：０．００５〜０．３％、Ｂ：０．０００３〜０．００１０％、Ｍｏ：０．００５〜０．２％、Ｐ：０．００１〜０．０５％、Ｓ：０．００１〜０．０１％、Ｎ：０．００１〜０．０１％、Ｎｂ：０．００５〜０．０８％、Ｔｉ：０．００５〜０．１３％、Ｖ：０．００５〜０．２％、残りＦｅ及び不可避不純物を含み、下記関係式（１）及び下記関係式（２）を満たし、炭化物、窒化物、及び炭窒化物のうち１以上を含む剪断加工性に優れた高強度冷延鋼板に関するものである。   One aspect of the present invention is, by weight%, C: 0.05 to 0.10%, Si: 0.01 to 0.5%, Mn: 1.2 to 2.0%, Al: 0.01 to. 0.1%, Cr: 0.005-0.3%, B: 0.0003-0.0010%, Mo: 0.005-0.2%, P: 0.001-0.05%, S : 0.001-0.01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005-0 0.2%, remaining Fe and unavoidable impurities, satisfying the following relational expression (1) and the following relational expression (2), containing one or more of carbide, nitride, and carbonitride, and having excellent shear workability. It relates to a strength cold rolled steel sheet.

本発明の他の一側面は、重量％で、Ｃ：０．０５〜０．１０％、Ｓｉ：０．０１〜０．５％、Ｍｎ：１．２〜２．０％、Ａｌ：０．０１〜０．１％、Ｃｒ：０．００５〜０．３％、Ｂ：０．０００３〜０．００１０％、Ｍｏ：０．００５〜０．２％、Ｐ：０．００１〜０．０５％、Ｓ：０．００１〜０．０１％、Ｎ：０．００１〜０．０１％、Ｎｂ：０．００５〜０．０８％、Ｔｉ：０．００５〜０．１３％、Ｖ：０．００５〜０．２％、残りＦｅ及び不可避不純物を含み、下記関係式（１）及び下記関係式（２）を満たす鋼スラブを１２００〜１３５０℃に加熱する段階と、前記加熱された鋼スラブを８５０〜１１５０℃の範囲の温度で熱間圧延する段階と、前記熱間圧延後に５５０〜７５０℃の範囲の温度まで冷却し、巻き取る段階と、前記巻取後に酸洗し、冷間圧下率６０〜７０％で冷間圧延する段階と、を含む剪断加工性に優れた高強度冷延鋼板の製造方法に関するものである。
関係式（１）：２．０≦［Ｍｎ］＋２．５［Ｍｏ］＋１．５［Ｃｒ］＋３００［Ｂ］≦２．５
関係式（２）：０．２≦（［Ｎｂ］／９３＋［Ｔｉ］／４８＋［Ｖ］／５１）／（［Ｃ］／１２＋［Ｎ］／１４）≦０．５
（但し、前記関係式（１）及び（２）において、各元素記号は該当合金元素の重量％を示す。） Another aspect of the present invention is, by weight%, C: 0.05 to 0.10%, Si: 0.01 to 0.5%, Mn: 1.2 to 2.0%, Al: 0. 01-0.1%, Cr: 0.005-0.3%, B: 0.0003-0.0010%, Mo: 0.005-0.2%, P: 0.001-0.05% , S: 0.001-0.01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005 ˜0.2%, the remaining Fe and unavoidable impurities, and heating the steel slab satisfying the following relational expressions (1) and (2) to 1200 to 1350 ° C., and the heated steel slab 850 Hot rolling at a temperature in the range of ˜1150 ° C., cooling to a temperature in the range of 550 to 750 ° C. after the hot rolling, and winding. Pickling after Kimakito, a process for producing a high-strength cold-rolled steel sheet excellent in shearing resistance comprising the steps of cold rolling at a cold reduction ratio 60% to 70%, a.
Relational expression (1): 2.0 ≦ [Mn] +2.5 [Mo] +1.5 [Cr] +300 [B] ≦ 2.5
Relational expression (2): 0.2 ≦ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≦ 0.5
(However, in the relational expressions (1) and (2), each element symbol represents the weight% of the corresponding alloy element.)

尚、上記した課題の解決手段は、本発明の特徴をすべて列挙したものではない。本発明の様々な特徴とそれに伴う長所及び効果は、以下の具体的な実施形態を参照してより詳細に理解することができる。   The means for solving the above-mentioned problems do not enumerate all the features of the present invention. Various features of the present invention and advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.

本発明によると、高強度及び高硬度を確保することができることは言うまでもなく、剪断加工による亀裂や摩擦熱による亀裂を抑制することができる剪断加工性に優れた高強度冷延鋼板及びその製造方法を提供することができるという効果を奏する。   According to the present invention, needless to say that high strength and high hardness can be ensured, and a high-strength cold-rolled steel sheet excellent in shear workability capable of suppressing cracks due to shearing and cracks due to frictional heat and a method for producing the same The effect of being able to provide.

実施例の関係式（１）及び関係式（２）の値を示したグラフである。It is a graph which showed the value of relational expression (1) and relational expression (2) of an example.

以下、本発明の好ましい実施形態を説明する。しかし、本発明の実施形態は、いくつかの他の形態に変形することができ、本発明の範囲が以下説明する実施形態に限定されるものではない。また、本発明の実施形態は、当該技術分野において平均的な知識を有する者に本発明をさらに完全に説明するために提供されるものである。   Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into some other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more fully explain the present invention to a person having average knowledge in the art.

以下、本発明による剪断加工性に優れた高強度冷延鋼板について詳細に説明する。このとき、合金組成の単位は重量％であることに留意する必要がある。   Hereinafter, the high-strength cold-rolled steel sheet excellent in shear workability according to the present invention will be described in detail. At this time, it should be noted that the unit of the alloy composition is% by weight.

本発明による剪断加工性に優れた高強度冷延鋼板は、重量％で、Ｃ：０．０５〜０．１０％、Ｓｉ：０．０１〜０．５％、Ｍｎ：１．２〜２．０％、Ａｌ：０．０１〜０．１％、Ｃｒ：０．００５〜０．３％、Ｂ：０．０００３〜０．００１０％、Ｍｏ：０．００５〜０．２％、Ｐ：０．００１〜０．０５％、Ｓ：０．００１〜０．０１％、Ｎ：０．００１〜０．０１％、Ｎｂ：０．００５〜０．０８％、Ｔｉ：０．００５〜０．１３％、Ｖ：０．００５〜０．２％、残りＦｅ及び不可避不純物を含み、下記関係式（１）及び下記関係式（２）を満たし、炭化物、窒化物、及び炭窒化物のうち１以上を含む。   The high-strength cold-rolled steel sheet excellent in shear workability according to the present invention is, by weight%, C: 0.05 to 0.10%, Si: 0.01 to 0.5%, Mn: 1.2 to 2. 0%, Al: 0.01-0.1%, Cr: 0.005-0.3%, B: 0.0003-0.0010%, Mo: 0.005-0.2%, P: 0. 0.001-0.05%, S: 0.001-0.01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13 %, V: 0.005 to 0.2%, the balance Fe and unavoidable impurities are contained, and the following relational expressions (1) and (2) are satisfied, and one or more of carbide, nitride, and carbonitride including.

Ｃ：０．０５〜０．１０％
上記Ｃは鋼を強化させるのに最も経済的且つ効果的な元素である。Ｃの添加量が増加すると、析出強化の効果またはベイナイト相分率が増加し、引張強度が増加するようになる。Ｃの含有量が０．０５％未満である場合には、Ｔｉ、Ｎｂ、及びＶなどと析出物を形成する反応が少ないため析出強化の効果が低い。これに対し、上記炭素の含有量が０．１０重量％を超えると、結晶粒界で粗大な炭化物が発生しやすくなり、剪断加工時に粗大な炭化物の界面で微細亀裂が発生するため、剪断加工性が劣位になる。したがって、上記Ｃの含有量は、０．０５〜０．１０重量％含まれることが好ましい。 C: 0.05 to 0.10%
C is the most economical and effective element for strengthening steel. When the amount of C added increases, the effect of precipitation strengthening or the bainite phase fraction increases, and the tensile strength increases. When the content of C is less than 0.05%, the effect of precipitation strengthening is low because there are few reactions to form precipitates with Ti, Nb, V and the like. On the other hand, when the carbon content exceeds 0.10% by weight, coarse carbides are likely to be generated at the grain boundaries, and fine cracks are generated at the interface of the coarse carbides during shearing. Sex becomes inferior. Therefore, the content of C is preferably 0.05 to 0.10% by weight.

Ｓｉ：０．０１〜０．５％
上記Ｓｉは、溶鋼を脱酸させ、固溶強化の効果があり、粗大な炭化物の形成を遅延させて成形性を向上させるのに有利である。しかし、Ｓｉの含有量が０．０１％未満である場合には炭化物の形成を遅延させる効果が少ないため、成形性を向上させることが難しくなる。これに対し、０．５％を超えると、熱間圧延時の鋼板表面にＳｉによる赤スケールが形成されて鋼板の表面品質が非常に悪くなるだけでなく、延性及び溶接性も低下するという問題がある。したがって、上記Ｓｉの含有量は、０．０１〜０．５％含まれることが好ましい。 Si: 0.01 to 0.5%
The above Si has the effect of deoxidizing molten steel and strengthening solid solution, and is advantageous in delaying the formation of coarse carbide and improving formability. However, when the Si content is less than 0.01%, the effect of delaying the formation of the carbide is small, and it is difficult to improve the formability. On the other hand, if it exceeds 0.5%, a red scale due to Si is formed on the surface of the steel sheet during hot rolling, which not only deteriorates the surface quality of the steel sheet, but also reduces ductility and weldability. There is. Therefore, the Si content is preferably 0.01 to 0.5%.

Ｍｎ：１．２〜２．０％
上記Ｍｎは、Ｓｉと同様に鋼を固溶強化させるのに効果的な元素であり、鋼の硬化能を増加させることで、溶接後の溶接熱影響部におけるベイナイト相の形成を容易にする。しかし、Ｍｎの含有量が１．２％未満である場合には上記効果を十分に得ることができない。これに対し、Ｍｎの含有量が２．０％を超えると、硬化能が大幅に増加してフェライト相変態が遅延されて析出強化の効果も減少するようになり、連続鋳造工程におけるスラブ鋳造時の厚さ中心部で偏析部が大きく発達し、熱間圧延後の冷却時に微細組織が厚さ方向において不均一に形成されて剪断加工時に亀裂発生が大幅に増加するようになる。したがって、上記Ｍｎの含有量は、１．２〜２．０％含まれることが好ましい。 Mn: 1.2-2.0%
Like Mn, Mn is an element effective for solid solution strengthening steel, and increases the hardening ability of steel to facilitate the formation of the bainite phase in the weld heat affected zone after welding. However, if the Mn content is less than 1.2%, the above effect cannot be sufficiently obtained. On the other hand, when the Mn content exceeds 2.0%, the hardenability is greatly increased, the ferrite phase transformation is delayed, and the effect of precipitation strengthening is also reduced. During slab casting in the continuous casting process. A large segregation portion develops in the central part of the thickness, and the microstructure is nonuniformly formed in the thickness direction during cooling after hot rolling, and the crack generation greatly increases during shearing. Therefore, the Mn content is preferably 1.2 to 2.0%.

Ｍｏ：０．００５〜０．２％
上記Ｍｏは、鋼を固溶強化させ、鋼の硬化能を増加させて鋼の強度を高める。しかし、Ｍｏの含有量が０．００５％未満である場合には、添加による上記効果を得ることができず、０．２％を超えると、過度な焼入性増加が原因でフェライト相変態が遅延され、析出強化の効果も減少するようになる。また、経済的にも不利であり、溶接性にも有害である。したがって、上記Ｍｏの含有量は、０．００５〜０．２％に制限することが好ましい。
Mo: 0.005-0.2%
The Mo solid-solution strengthens the steel, increases the hardening ability of the steel, and enhances the strength of the steel. However, if the Mo content is less than 0.005%, the above effect due to addition cannot be obtained, and if it exceeds 0.2%, ferrite phase transformation is caused due to an excessive increase in hardenability. It will be delayed and the effect of precipitation strengthening will be reduced. In addition, it is economically disadvantageous and harmful to weldability. Therefore, the Mo content is preferably limited to 0.005 to 0.2%.

Ｃｒ：０．００５〜０．３％
上記Ｃｒは、鋼を固溶強化させ、鋼の硬化能を増加させて鋼の強度を高める。しかし、Ｃｒの含有量が０．００５％未満である場合には、添加による上記効果を得ることができず、０．３％を超えると、フェライト変態を過度に遅延させるため、マルテンサイト相が形成されて伸びが低減され、析出強化の効果も減少するようになる。また、Ｍｎと同様に厚さ中心部で偏析部が大きく発達し、微細組織が厚さ方向において不均一になって剪断加工性が劣位になる。したがって、上記Ｃｒの含有量は、０．００５〜０．３％に制限することが好ましい。 Cr: 0.005-0.3%
The above Cr solid-solution strengthens the steel, increases the hardening ability of the steel, and increases the strength of the steel. However, if the Cr content is less than 0.005%, the above effect due to the addition cannot be obtained, and if it exceeds 0.3%, the ferrite transformation is excessively delayed, so that the martensite phase is formed. When formed, the elongation is reduced and the effect of precipitation strengthening is also reduced. Further, as with Mn, a segregation portion develops greatly in the central portion of the thickness, and the fine structure becomes nonuniform in the thickness direction, resulting in poor shearing workability. Therefore, the Cr content is preferably limited to 0.005 to 0.3%.

Ｂ：０．０００３〜０．００１０％
Ｂは、鋼中に少量添加しても硬化能が向上する元素である。Ｂの含有量が０．０００３％以上添加される場合には、高温でオーステナイト粒界に偏析されて結晶粒界を安定化させ、耐衝撃性を向上させることができる。一方、０．０００３％未満であればその効果を得るには十分ではない。これに対し、Ｂの含有量が０．００１０％を超えて添加されると、熱間圧延中に再結晶を遅延させて延伸された結晶粒が増加し、冷却中のフェライト相変態を遅延させて微細組織が不均一になる。また、析出強化の効果も減少して、所望する強度を得ることが難しく、初期熱間圧延板の微細組織の不均一性は、冷間圧延時の局部的な応力集中の原因となるため本発明において不利である。したがって、上記Ｂの含有量は、０．０００３〜０．００１０％に制限することが好ましい。 B: 0.0003 to 0.0010%
B is an element whose hardening ability is improved even when added in a small amount to steel. When the content of B is 0.0003% or more, it segregates to austenite grain boundaries at high temperature to stabilize the crystal grain boundaries and improve impact resistance. On the other hand, if it is less than 0.0003%, it is not sufficient to obtain the effect. On the other hand, when the content of B exceeds 0.0010%, recrystallization is delayed during hot rolling to increase the number of crystal grains stretched, which delays the ferrite phase transformation during cooling. The microstructure becomes uneven. Also, the effect of precipitation strengthening is reduced, and it is difficult to obtain the desired strength, and the non-uniformity of the microstructure of the initial hot-rolled sheet causes local stress concentration during cold rolling. It is disadvantageous in the invention. Therefore, the content of B is preferably limited to 0.0003 to 0.0010%.

Ｐ：０．００１〜０．０５％
上記Ｐは、Ｓｉと同様に固溶強化及びフェライト変態の促進効果をともに有する。しかし、Ｐの含有量が０．００１％未満である場合には、製造コストが多くかかり経済的に不利であり、強度を得るにも不十分である。これに対し、Ｐの含有量が０．０５％を超えると、粒界偏析による脆化が発生し、剪断加工時に微細な亀裂が発生しやすくなり、延性及び耐衝撃特性を大きく悪化させる。したがって、上記Ｐは０．００１〜０．０５％に制限することが好ましい。 P: 0.001-0.05%
Similar to Si, P has the effects of solid solution strengthening and promoting ferrite transformation. However, when the content of P is less than 0.001%, the manufacturing cost is high, it is economically disadvantageous, and the strength is insufficient. On the other hand, if the content of P exceeds 0.05%, embrittlement due to grain boundary segregation occurs, fine cracks are likely to occur during shearing, and ductility and impact resistance are greatly deteriorated. Therefore, it is preferable to limit P to 0.001 to 0.05%.

Ｓ：０．００１〜０．０１％
上記Ｓは、鋼中に存在する不純物である。Ｓの含有量が０．０１％を超えると、Ｍｎなどと結合して非金属介在物を形成し、その結果、鋼の切断加工時に、微細な亀裂が発生しやすくなり、伸びフランジ性及び耐衝撃性を大きく低下させるという問題がある。これに対し、Ｓの含有量を０．００１％未満添加して製造する場合には、製鋼操業時に時間が多くかかり、生産性が落ちることになる。したがって、Ｓの含有量を０．００１〜０．０１％に制限することが好ましい。 S: 0.001-0.01%
The S is an impurity present in steel. If the content of S exceeds 0.01%, it binds to Mn and the like to form non-metallic inclusions, and as a result, fine cracks tend to occur during the cutting of steel, and stretch flangeability and resistance to There is a problem that the impact resistance is greatly reduced. On the other hand, when the content of S is less than 0.001% and the steel is manufactured, it takes a lot of time during the steelmaking operation and the productivity is lowered. Therefore, it is preferable to limit the S content to 0.001 to 0.01%.

Ａｌ：０．０１〜０．１％
上記Ａｌは、主に脱酸のために添加する成分である。Ａｌの含有量が０．０１％未満である場合にはその添加効果が不足する。これに対し、Ａｌの含有量が０．１％を超えると、窒素と結合してＡｌＮが形成されて連続鋳造時のスラブにコーナークラックが発生しやすくなり、熱間圧延板のエッジ（Ｅｄｇｅ）部に介在物形成による欠陥が発生しやすくなる。また、熱間圧延後の冷間圧延時に、表面欠陥が発生して表面品質が低下するという問題が生じ得る。したがって、Ａｌの含有量を０．０１〜０．１％に制限することが好ましい。 Al: 0.01 to 0.1%
The Al is a component added mainly for deoxidation. If the Al content is less than 0.01%, the effect of addition is insufficient. On the other hand, when the Al content exceeds 0.1%, AlN is formed by combining with nitrogen, and a corner crack is likely to occur in the slab during continuous casting, resulting in an edge of the hot rolled plate (Edge). Defects due to inclusion formation tend to occur in the portion. In addition, during cold rolling after hot rolling, surface defects may occur and surface quality may deteriorate. Therefore, it is preferable to limit the Al content to 0.01 to 0.1%.

Ｎ：０．００１〜０．０１％
上記Ｎは、Ｃとともに代表的な固溶強化元素であり、Ｔｉ、Ａｌなどと同様に粗大な析出物を形成する。一般に、Ｎの固溶強化の効果は、炭素よりも優れているが、鋼中にＮの量が増加すればするほど靭性が大きく低下するという問題がある。また、Ｎの含有量を０．００１％未満添加して製造するためには、製鋼操業時に時間が多くかかり、生産性が落ちることになる。したがって、本発明では、Ｎの含有量を０．００１〜０．０１％に制限することが好ましい。 N: 0.001-0.01%
N is a typical solid solution strengthening element together with C, and forms coarse precipitates like Ti and Al. Generally, the effect of solid solution strengthening of N is superior to that of carbon, but there is a problem that as the amount of N in steel increases, the toughness decreases significantly. Further, in order to manufacture by adding the content of N less than 0.001%, it takes a lot of time during the steelmaking operation, and the productivity is lowered. Therefore, in the present invention, the N content is preferably limited to 0.001 to 0.01%.

Ｔｉ：０．００５〜０．１３％
上記Ｔｉは、Ｎｂ、Ｖとともに代表的な析出強化元素であり、Ｎとの強い親和力で鋼中に粗大なＴｉＮを形成する。ＴｉＮは、熱間圧延のための加熱過程で結晶粒が成長することを抑制するという効果がある。また、窒素と反応して残ったＴｉが鋼中に固溶されて炭素と結合することによりＴｉＣの析出物が形成されて鋼の強度を向上させる有用な成分である。Ｔｉの含有量が０．００５％未満である場合には上記の効果を得ることができず、Ｔｉの含有量が０．１３％を超えると粗大なＴｉＮの発生が原因で剪断加工時の剪断加工性を劣位にするという問題がある。したがって、本発明では、Ｔｉの含有量を０．００５〜０．１３％に制限することが好ましい。 Ti: 0.005-0.13%
The Ti is a typical precipitation strengthening element together with Nb and V, and forms a coarse TiN in steel with a strong affinity with N. TiN has the effect of suppressing the growth of crystal grains during the heating process for hot rolling. Further, Ti remaining after reacting with nitrogen is solid-solved in the steel and is bonded to carbon to form a TiC precipitate, which is a useful component for improving the strength of the steel. If the Ti content is less than 0.005%, the above effects cannot be obtained, and if the Ti content exceeds 0.13%, shearing during shearing is caused due to the generation of coarse TiN. There is a problem of degrading workability. Therefore, in the present invention, the Ti content is preferably limited to 0.005 to 0.13%.

Ｎｂ：０．００５〜０．０８％
上記Ｎｂは、Ｔｉ、Ｖとともに代表的な析出強化元素であり、熱間圧延中に析出して再結晶遅延による結晶粒微細化効果があるため鋼の強度及び衝撃靭性の向上に有効である。しかし、Ｎｂの含有量が０．００５％未満である場合には上記の効果を十分に得ることができず、Ｎｂの含有量が０．０８％を超えると、熱間圧延中における過度な再結晶遅延により、延伸された結晶粒及び粗大な複合析出物が形成されて剪断加工性が劣位になるという問題がある。したがって、本発明では、Ｎｂの含有量を０．００５〜０．０８％に制限することが好ましい。 Nb: 0.005-0.08%
Nb is a typical precipitation strengthening element together with Ti and V, and it is effective in improving the strength and impact toughness of steel because it precipitates during hot rolling and has a grain refining effect by delaying recrystallization. However, when the Nb content is less than 0.005%, the above effect cannot be sufficiently obtained, and when the Nb content exceeds 0.08%, excessive re-rolling during hot rolling is performed. Due to the crystal retardation, there is a problem that stretched crystal grains and coarse composite precipitates are formed, resulting in poor shear workability. Therefore, in the present invention, the Nb content is preferably limited to 0.005 to 0.08%.

Ｖ：０．００５〜０．２％
上記Ｖは、Ｎｂ、Ｔｉとともに代表的な析出強化元素である。巻取後に、析出物を形成して鋼の強度を向上させるのに有効である。Ｖの含有量が０．００５％未満である場合には上記の効果を十分に得ることができず、０．２％を超えると、粗大な複合析出物が形成されて剪断加工性が劣位になり、経済的にも不利である。したがって、本発明では、Ｖの含有量を０．００５〜０．２％に制限することが好ましい。 V: 0.005-0.2%
V is a typical precipitation strengthening element together with Nb and Ti. After winding, it is effective in forming precipitates and improving the strength of steel. When the V content is less than 0.005%, the above effect cannot be sufficiently obtained, and when it exceeds 0.2%, a coarse composite precipitate is formed and shear workability becomes poor. It is also economically disadvantageous. Therefore, in the present invention, it is preferable to limit the V content to 0.005 to 0.2%.

本発明の他の成分は鉄（Ｆｅ）である。但し、通常の製造過程では、原料や周囲の環境から意図しない不純物が必然的に混入される可能性があるため、これを排除することはできない。これらの不純物は、通常の製造過程における技術者であれば誰でも分かるものであるため、そのすべての内容を具体的に言及しない。   Another component of the present invention is iron (Fe). However, in a normal manufacturing process, unintended impurities may inevitably be mixed in from the raw materials and the surrounding environment, and thus they cannot be excluded. All of these impurities are not specifically mentioned because they can be known by a person skilled in the art in a normal manufacturing process.

本発明では、上記合金組成が下記関係式（１）及び下記関係式（２）を満たす必要がある。これにより、熱間圧延後に鋼の微細組織が均一に形成されて、冷間圧延後の剪断加工時の亀裂発生を抑制することができる。
関係式（１）：２．０≦［Ｍｎ］＋２．５［Ｍｏ］＋１．５［Ｃｒ］＋３００［Ｂ］≦２．５
関係式（２）：０．２≦（［Ｎｂ］／９３＋［Ｔｉ］／４８＋［Ｖ］／５１）／（［Ｃ］／１２＋［Ｎ］／１４）≦０．５
（但し、上記関係式（１）及び（２）において、各元素記号は該当合金元素の重量％を示す。） In the present invention, the alloy composition must satisfy the following relational expressions (1) and (2). Thereby, the microstructure of the steel is uniformly formed after the hot rolling, and it is possible to suppress the crack generation during the shearing process after the cold rolling.
Relational expression (1): 2.0 ≦ [Mn] +2.5 [Mo] +1.5 [Cr] +300 [B] ≦ 2.5
Relational expression (2): 0.2 ≦ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≦ 0.5
(However, in the above relational expressions (1) and (2), each element symbol represents the weight% of the corresponding alloy element.)

関係式（１）は、鋼の焼入性及び偏析に関するものであって、鋼の固溶強化の効果及び微細組織の不均一性を考慮したものである。
関係式（１）が２．０未満である場合には、鋼の固溶強化の効果が不十分であり、十分な高強度を得ることができないという問題点がある。これに対し、関係式（１）が２．５を超えると、鋼の微細組織が厚さ方向において不均一に形成され、フェライト相変態を遅延させて鋼の析出強化の効果を減少させるという問題がある。
したがって、関係式（１）が２．０〜２．５となるように制御することが好ましい。 The relational expression (1) relates to the hardenability and segregation of steel, and takes into consideration the effect of solid solution strengthening of steel and the nonuniformity of the microstructure.
When the relational expression (1) is less than 2.0, there is a problem that the effect of solid solution strengthening of steel is insufficient and sufficient high strength cannot be obtained. On the other hand, when the relational expression (1) exceeds 2.5, the microstructure of the steel is unevenly formed in the thickness direction, which delays the ferrite phase transformation and reduces the effect of precipitation strengthening of the steel. There is.
Therefore, it is preferable to control the relational expression (1) to be 2.0 to 2.5.

関係式（２）は、鋼の析出物の形成に関連する成分を制限したものであって、析出物の形成が上記組成のＴｉ、Ｎｂ、Ｖ及びＣ、Ｎの含有量と関係があるため、Ｔｉ、Ｎｂ、Ｖの合金元素の添加量をＣ、Ｎの含有量に適するように設定するためのものである。
関係式（２）が０．２未満である場合には、析出強化の効果が大幅に減少して所望する強度及び硬度値を得ることができず、０．５を超えると、多量の微細な析出物が形成されて、降伏強度が大幅に増加し、冷間圧延性が劣位になる。また、板厚方向に析出物が不均一に形成されて冷間圧延後の剪断加工時の亀裂発生が激しくなるという問題がある。
したがって、関係式（２）が０．２〜０．５となるように制御することが好ましい。 The relational expression (2) limits the components related to the formation of the precipitate of steel, and the formation of the precipitate is related to the contents of Ti, Nb, V and C, N of the above composition. , Ti, Nb, and V are added in order to set the addition amount of the alloying elements to be suitable for the C and N contents.
When the relational expression (2) is less than 0.2, the effect of precipitation strengthening is significantly reduced and desired strength and hardness values cannot be obtained. Precipitates are formed, yield strength is greatly increased, and cold rolling property is deteriorated. Further, there is a problem in that precipitates are formed nonuniformly in the plate thickness direction, and cracking becomes more intense during shearing after cold rolling.
Therefore, it is preferable to control the relational expression (2) to be 0.2 to 0.5.

上記合金組成を満たすように制御することにより、高強度及び高硬度を確保することができることは言うまでもなく、剪断加工による亀裂や摩擦熱による亀裂を抑制することができる剪断加工性に優れた高強度冷延鋼板を得ることができる。   It is needless to say that high strength and high hardness can be secured by controlling so as to satisfy the above alloy composition, and high strength excellent in shear workability capable of suppressing cracks due to shearing and cracks due to frictional heat. A cold rolled steel plate can be obtained.

本発明による冷延鋼板は、フェライトと微細なパーライトの微細組織を有する熱間圧延板を冷間圧延して得られるため、圧延方向に激しく変形された微細組織（Ｆｕｌｌ Ｈａｒｄの微細組織）を有する。このとき、冷間圧延された鋼板の微細組織において、それぞれの相を特定することはできないが、冷間圧延前の熱間圧延された鋼板は、面積分率で、フェライト相が９０％以上であり、微細なパーライト相が５％未満であり、その他に、ベイナイト相が不可避に含まれることができる。   Since the cold-rolled steel sheet according to the present invention is obtained by cold rolling a hot-rolled sheet having a fine structure of ferrite and fine pearlite, it has a fine structure that is severely deformed in the rolling direction (Full Hard's fine structure). . At this time, although each phase cannot be specified in the microstructure of the cold rolled steel sheet, the hot rolled steel sheet before cold rolling has an area fraction of 90% or more in the ferrite phase. Yes, the fine pearlite phase is less than 5%, and in addition, the bainite phase can be unavoidably included.

本発明による剪断加工性に優れた高強度冷延鋼板は、炭化物、窒化物、及び炭窒化物のうち１以上を含む。例えば、ＴｉＮ、ＴｉＣ、ＮｂＣ、ＮｂＮ、（Ｔｉ，Ｎｂ）（Ｃ，Ｎ）、（Ｔｉ，Ｍｏ，Ｎｂ）（Ｃ，Ｎ）、及び（Ｆｅ，Ｍｎ）３Ｃ、（Ｆｅ，Ｍｎ，Ｍｏ）Ｃのうち１以上を含むことができる。 The high-strength cold-rolled steel sheet excellent in shear workability according to the present invention contains at least one of carbide, nitride, and carbonitride. For example, TiN, TiC, NbC, NbN, (Ti, Nb) (C, N), (Ti, Mo, Nb) (C, N), and (Fe, Mn) 3 C, (Fe, Mn, Mo). One or more of C may be included.

このとき、上記炭化物、窒化物、及び炭窒化物の平均サイズは、１０〜５０ｎｍであることが好ましい。
その平均サイズが１０ｎｍ未満である場合には、熱間圧延板の降伏強度が過度に上昇し、冷間圧延時に局部的な加工硬化の偏差が発生しやすくなり、冷間圧延板の剪断加工や熱処理時にクラックが発生しやすくなるという問題がある。
これに対し、その平均サイズが５０ｎｍを超えると、目標とする引張強度及び硬度値を得ることが難しいという問題がある。 At this time, it is preferable that the carbides, nitrides, and carbonitrides have an average size of 10 to 50 nm.
If the average size is less than 10 nm, the yield strength of the hot-rolled sheet is excessively increased, and local work-hardening deviation is likely to occur during cold rolling. There is a problem that cracks are likely to occur during heat treatment.
On the other hand, if the average size exceeds 50 nm, it is difficult to obtain the target tensile strength and hardness values.

一方、上記冷延鋼板は、引張強度が１２００ＭＰａ以上であり、硬度値（Ｍｉｃｒｏ−Ｖｉｃｋｅｒｓ）が３４０Ｈｖ以上であることができる。かかる引張強度及び硬度値を満たすことにより、自動車用の自動変速機における摩擦板向けに好ましく適用することができる。   On the other hand, the cold rolled steel sheet may have a tensile strength of 1200 MPa or more and a hardness value (Micro-Vickers) of 340 Hv or more. By satisfying such tensile strength and hardness values, it can be preferably applied to a friction plate in an automatic transmission for automobiles.

また、上記冷延鋼板を剪断加工する際に発生する亀裂は、最大亀裂の長さが１ｍｍ以下であることが好ましい。
上記最大亀裂の長さは、直径１０ｍｍの円形金型を用いて、Ｃｌｅａｒａｎｃｅ ６％の条件でパンチングし、２００℃で１時間熱処理した後、断面で発生した最大亀裂の長さを測定した結果である。
最大亀裂の長さが１ｍｍを超えると、亀裂の発生量が増加し、剪断加工時の亀裂が容易に伝播される可能性があり、摩擦熱によって温度が上昇した場合、亀裂がさらに容易に伝播されるという問題がある。 Moreover, it is preferable that the maximum crack length of the cracks generated when the cold-rolled steel sheet is sheared is 1 mm or less.
The length of the maximum crack is the result of measuring the length of the maximum crack generated in the cross section after punching under the condition of Clearance 6% and heat treatment at 200 ° C. for 1 hour using a circular mold having a diameter of 10 mm. is there.
If the maximum crack length exceeds 1 mm, the amount of cracks will increase and the cracks during shearing may easily propagate. If the temperature rises due to frictional heat, the cracks will propagate more easily. There is a problem that is.

以下、本発明の他の一側面である剪断加工性に優れた高強度冷延鋼板の製造方法について詳細に説明する。   The method for producing a high-strength cold-rolled steel sheet having excellent shearing workability, which is another aspect of the present invention, will be described in detail below.

本発明の他の一側面による剪断加工性に優れた高強度冷延鋼板の製造方法は、上述した合金組成を満たす鋼スラブを１２００〜１３５０℃に加熱する段階と、上記加熱された鋼スラブを８５０〜１１５０℃の範囲の温度で熱間圧延する段階と、上記熱間圧延後に５５０〜７５０℃の範囲の温度まで冷却し、巻き取る段階と、上記巻取後に酸洗し、冷間圧下率５６〜７０％で冷間圧延する段階と、を含む。
According to another aspect of the present invention, a method for producing a high-strength cold-rolled steel sheet having excellent shear workability includes a step of heating a steel slab satisfying the above-described alloy composition to 1200 to 1350 ° C., and the heated steel slab. Hot rolling at a temperature in the range of 850 to 1150 ° C., cooling to a temperature in the range of 550 to 750 ° C. after the hot rolling, and winding, and pickling after the winding and cold reduction. in 56 to 70% comprising the steps of cold rolling, the.

「加熱段階」
上述した合金組成を満たす鋼スラブを１２００〜１３５０℃に加熱する。
加熱温度が１２００℃未満である場合には、析出物が十分に再固溶されず、熱間圧延以降の工程で析出物の形成が減少して、粗大なＴｉＮが残存することになる。一方、加熱温度が１３５０℃を超えると、オーステナイト結晶粒の異常粒成長によって強度が低下するため、上記再加熱温度は１２００〜１３５０℃に制限することが好ましい。 "Heating stage"
A steel slab satisfying the above alloy composition is heated to 1200 to 1350 ° C.
When the heating temperature is less than 1200 ° C., the precipitates are not sufficiently re-dissolved, the formation of the precipitates is reduced in the steps after the hot rolling, and coarse TiN remains. On the other hand, if the heating temperature exceeds 1350 ° C., the strength decreases due to abnormal grain growth of austenite crystal grains, so the reheating temperature is preferably limited to 1200 to 1350 ° C.

このとき、上記鋼スラブは、連続鋳造工程と熱延工程が直結化された工程で生産されたものであればよい。
ＴｉＮ、ＴｉＣ、ＮｂＣ、ＮｂＮ、（Ｔｉ，Ｎｂ）（Ｃ，Ｎ）、（Ｔｉ，Ｍｏ，Ｎｂ）（Ｃ，Ｎ）の析出物の再固溶のために、鋼スラブの温度を１２００〜１３５０℃としているため、上記のような連続鋳造工程と熱延工程が直結化された工程にも好ましく適用することができる。 At this time, the steel slab may be produced by a process in which the continuous casting process and the hot rolling process are directly connected.
The temperature of the steel slab is 1200 to 1350 for the re-solution of precipitates of TiN, TiC, NbC, NbN, (Ti, Nb) (C, N), (Ti, Mo, Nb) (C, N). Since the temperature is set to 0 ° C, it can be preferably applied to a process in which the continuous casting process and the hot rolling process are directly connected.

「熱間圧延段階」
上記加熱された鋼スラブを８５０〜１１５０℃の範囲の温度で熱間圧延する。
１１５０℃よりも高い温度で熱間圧延を開始すると、熱延鋼板の温度が高くなるため、結晶粒サイズが粗大となって熱延鋼板の表面品質が劣位になる可能性がある。また、熱間圧延を８５０℃よりも低い温度で終了すると、過度な再結晶遅延により、延伸された結晶粒が発達し、高降伏比が得られるため冷間圧延性が劣位になって剪断加工性も悪くなることがある。 "Hot rolling stage"
The heated steel slab is hot rolled at a temperature in the range of 850 to 1150 ° C.
If hot rolling is started at a temperature higher than 1150 ° C., the temperature of the hot rolled steel sheet rises, so that the crystal grain size becomes coarse and the surface quality of the hot rolled steel sheet may deteriorate. Further, when hot rolling is completed at a temperature lower than 850 ° C., excessive recrystallization delay develops stretched crystal grains, and a high yield ratio is obtained, so cold rolling property becomes inferior and shearing is performed. The sex may also deteriorate.

「冷却及び巻取段階」
上記熱間圧延後に、５５０〜７５０℃の範囲の温度まで冷却し、巻き取る。
５５０℃以下に冷却してから巻き取ると、鋼中にベイナイト相とマルテンサイト相が形成されて鋼の材質が劣位になる可能性があり、７５０℃以上で冷却してから巻き取ると、粗大なフェライト結晶粒が形成され、粗大な炭化物と窒化物が形成されやすくなるため、鋼の材質が劣位になるおそれがある。 "Cooling and winding stage"
After the hot rolling, it is cooled to a temperature in the range of 550 to 750 ° C. and wound.
If it is cooled to 550 ° C or lower and wound up, bainite phase and martensite phase may be formed in the steel and the material of the steel may be inferior. Since large ferrite crystal grains are formed and coarse carbides and nitrides are easily formed, the material of steel may be inferior.

このとき、平均冷却速度１０〜７０℃／ｓで冷却することができる。
冷却時の平均冷却速度が１０℃／ｓ未満である場合には、粗大なフェライト結晶粒が形成されるため微細組織が不均一になる可能性があり、平均冷却速度が７０℃／ｓを超えると、ベイナイト相が形成されやすくなり、板の微細組織も厚さ方向において不均一になって鋼の剪断加工性が劣位になるおそれがある。 At this time, cooling can be performed at an average cooling rate of 10 to 70 ° C./s.
When the average cooling rate during cooling is less than 10 ° C./s, coarse ferrite crystal grains are formed, so that the fine structure may become nonuniform, and the average cooling rate exceeds 70 ° C./s. If so, the bainite phase is likely to be formed, and the microstructure of the plate becomes non-uniform in the thickness direction, which may deteriorate the shear workability of the steel.

「冷間圧延段階」
上記巻取後に、酸洗してから冷間圧下率５６〜７０％で冷間圧延する。
冷間圧下率が５６％未満である場合には、十分な加工硬化効果が得られず、鋼の強度及び硬度を確保することが難しい。これに対し、冷間圧下率が７０％を超えると、鋼のエッジ部の品質が悪くなり、剪断加工性が劣位になることがある。
"Cold rolling stage"
After the winding, it is pickled and cold-rolled at a cold reduction of 56 to 70%.
If the cold reduction is less than 56 %, a sufficient work hardening effect cannot be obtained, and it is difficult to secure the strength and hardness of the steel. On the other hand, if the cold reduction exceeds 70%, the quality of the edge portion of the steel deteriorates and the shear workability may deteriorate.

上記の製造方法で製造された冷延鋼板は、高強度及び高硬度を確保することができることは言うまでもなく、剪断加工による亀裂や摩擦熱による亀裂を抑制することができる。   It goes without saying that the cold-rolled steel sheet manufactured by the above manufacturing method can secure high strength and high hardness, and can also suppress cracks due to shearing and cracks due to frictional heat.

一方、上記の製造方法で製造された冷延鋼板は、炭化物、窒化物、及び炭窒化物のうち１以上を含み、炭化物、窒化物、及び炭窒化物の平均サイズは１０〜５０ｎｍであることができる。また、引張強度が１２００ＭＰａ以上であり、硬度値が３４０Ｈｖ以上であることができ、剪断加工時に発生する亀裂は、最大亀裂の長さが１ｍｍ以下であることができる。   On the other hand, the cold-rolled steel sheet manufactured by the above manufacturing method contains one or more of carbide, nitride, and carbonitride, and the average size of carbide, nitride, and carbonitride is 10 to 50 nm. You can Further, the tensile strength may be 1200 MPa or more, the hardness value may be 340 Hv or more, and the crack generated during shearing may have a maximum crack length of 1 mm or less.

以下、実施例を挙げて本発明をより具体的に説明する。但し、下記の実施例は、本発明を例示してより詳細に説明するためのものに過ぎず、本発明の権利範囲を限定するためのものではないということに留意すべきである。これは、本発明の権利範囲が特許請求の範囲に記載の事項とこれから合理的に類推される事項によって決定されるものであるためである。   Hereinafter, the present invention will be described more specifically with reference to examples. However, it should be noted that the following examples are merely for illustrating the present invention in more detail and not for limiting the scope of rights of the present invention. This is because the scope of rights of the present invention is determined by the matters described in the claims and the matters reasonably inferred from them.

下記表１に示した成分組成を有する鋼スラブを１２５０℃に加熱し、下記表２に示した製造条件を適用して冷延鋼板を製造した。このとき、熱間圧延後の冷却速度は２０〜３０℃／ｓとした。   A steel slab having the composition shown in Table 1 below was heated to 1250 ° C., and the cold rolling steel sheet was manufactured by applying the manufacturing conditions shown in Table 2 below. At this time, the cooling rate after hot rolling was 20 to 30 ° C./s.

また、下記表２は、比較例及び発明例に対して関係式（１）及び関係式（２）の値を計算して示したものである。ここで、ＦＤＴ及びＣＴはそれぞれ、熱間圧延時の仕上げ圧延終了温度及び巻取温度を意味する。   Further, Table 2 below shows calculated values of the relational expressions (1) and (2) for the comparative example and the invention example. Here, FDT and CT mean the finish rolling end temperature and the winding temperature during hot rolling, respectively.

また、下記表３は、発明例及び比較例の機械的性質と微細組織の観察結果を示したものである。下記表３において、ＴＳ及びＨｖはそれぞれ、冷間圧延板の引張強度及びＭｉｃｒｏ−Ｖｉｃｋｅｒｓの硬度値を意味する。また、最大亀裂の長さは、直径１０ｍｍの円形金型を用いて、Ｃｌｅａｒａｎｃｅ ６％の条件でパンチングし、２００℃で１時間熱処理した後、断面で発生した最大亀裂の長さを測定した結果である。亀裂の長さは、光学顕微鏡（１００倍率）の観察結果から測定した。   Further, Table 3 below shows the observation results of the mechanical properties and the microstructures of the invention example and the comparative example. In Table 3 below, TS and Hv mean the tensile strength and the Micro-Vickers hardness value of the cold rolled plate, respectively. The length of the maximum crack was measured by using a circular mold having a diameter of 10 mm, punching it under the condition of Clearance 6%, heat treating at 200 ° C. for 1 hour, and measuring the length of the maximum crack generated in the cross section. Is. The length of the crack was measured from the observation result of an optical microscope (100 magnification).

鋼中に形成された炭化物、窒化物、及び炭窒化物のサイズは、冷間圧延前の熱間圧延板に対して分析を行うことで得られる。鋼中に形成された平均サイズ１０〜５０ｎｍの炭化物、窒化物、及び炭窒化物は、冷間圧延によってそのサイズと分率が変化するものではないが、冷間圧延後に激しく変形された微細組織ではそのサイズと分率を正確に観察することが難しいという問題があるため、熱間圧延板に対して分析を行った。炭化物、窒化物、及び炭窒化物の平均サイズは、透過電子顕微鏡を用いて測定した結果から決定した。平均サイズ１００ｎｍ以上の炭化物及び窒化物は５０，０００倍率の測定結果を用いており、平均サイズ１００ｎｍ以下の析出物は１００，０００倍率の測定結果を用いた。引張試験は、圧延板材の圧延方向に対して０°方向を基準にＪＩＳ５号規格に基づいて採取された試験片とした。   The sizes of the carbides, nitrides, and carbonitrides formed in the steel can be obtained by performing analysis on the hot-rolled sheet before cold rolling. Carbides, nitrides, and carbonitrides having an average size of 10 to 50 nm formed in steel do not change in size and fraction by cold rolling, but have a microstructure that is severely deformed after cold rolling. However, there is a problem that it is difficult to accurately observe the size and the fraction, so an analysis was performed on the hot-rolled sheet. The average size of carbides, nitrides, and carbonitrides was determined from the results measured using a transmission electron microscope. For the carbides and nitrides having an average size of 100 nm or more, the measurement results at 50,000 magnification were used, and for the precipitates having an average size of 100 nm or less, the measurement results at 100,000 magnification were used. The tensile test was a test piece sampled in accordance with JIS No. 5 standard with reference to the 0 ° direction with respect to the rolling direction of the rolled plate material.

Figure 0006684905
Figure 0006684905

Figure 0006684905
Figure 0006684905

Figure 0006684905
Figure 0006684905

比較例１及び２は関係式（１）及び関係式（２）の両方を満たせず、比較例１の場合、Ｃの含有量も発明の範囲を満たしていなかった。比較例１及び２は、ともに十分な固溶強化の効果が得られず、比較的低いＣの含有量及び比較的過度なＴｉ、Ｎｂ、Ｖが原因で関係式（２）の上限を超えた。その結果、鋼中に形成された炭化物、窒化物、及び析出物のサイズは微細であるものの、鋼の強度を十分に確保することはできなかった。また、比較例２は、冷間圧下率が本発明で制御した範囲を超えているため、パンチング加工後の剪断加工面における亀裂がやや激しく発生して剪断加工面の品質が劣位であることが確認できた。   Comparative Examples 1 and 2 did not satisfy both the relational expression (1) and the relational expression (2), and in the case of Comparative Example 1, the content of C did not satisfy the scope of the invention. In Comparative Examples 1 and 2, the effect of sufficient solid solution strengthening was not obtained, and the upper limit of the relational expression (2) was exceeded due to the relatively low C content and the relatively excessive Ti, Nb, and V. . As a result, although the sizes of carbides, nitrides, and precipitates formed in the steel were minute, the strength of the steel could not be sufficiently secured. Further, in Comparative Example 2, since the cold rolling reduction exceeds the range controlled by the present invention, cracks on the sheared surface after punching are rather severe and the quality of the sheared surface is inferior. It could be confirmed.

比較例３及び５は関係式（１）を満たしていない場合である。比較例３は、関係式（１）の発明の範囲を超えているため、鋼の中心部において偏析の発生が増加し、剪断加工部における品質が劣位であった。また、比較例５は、Ｍｎ、Ｃｒ、Ｂの含有量などが少ないため偏析の発生が少なく、剪断加工面における品質は非常に良好であったが、十分な固溶強化の効果が得られず、目標とした強度及び硬度値は得られなかった。   Comparative examples 3 and 5 are cases where the relational expression (1) is not satisfied. In Comparative Example 3, which exceeds the range of the invention of the relational expression (1), the occurrence of segregation in the central portion of the steel was increased, and the quality in the sheared portion was inferior. Further, in Comparative Example 5, since the content of Mn, Cr, B, etc. was small, segregation was less likely to occur, and the quality on the sheared surface was very good, but a sufficient solid solution strengthening effect was not obtained. However, the target strength and hardness values were not obtained.

比較例４及び６は関係式（２）を満たしていない場合である。比較例４は、過剰のＣが残留して粗大な析出物及び炭化物を形成し、析出強化の効果が不足して目標とした強度及び硬度値が得られなかった。
比較例６は、関係式（２）の発明の範囲を超えているため、微細な析出物が多量形成され、高強度を得ることができたが、剪断加工部における亀裂発生が激しかった。 Comparative examples 4 and 6 are cases where the relational expression (2) is not satisfied. In Comparative Example 4, excessive C remained to form coarse precipitates and carbides, and the effect of precipitation strengthening was insufficient, so that the target strength and hardness values could not be obtained.
Since Comparative Example 6 exceeds the range of the invention of the relational expression (2), a large amount of fine precipitates were formed and high strength could be obtained, but cracking in the sheared portion was severe.

比較例７は、関係式１を満たしていなかったが、高冷間圧下率により目標とした物性を確保した。しかし、高冷間圧下率が原因で剪断加工部における亀裂発生がやや激しかった。比較例９は、関係式（１）及び（２）を満たしたが、剪断加工部における品質が劣位であった。比較例１０は、関係式（１）及び（２）をともに満たしていない場合であって、剪断加工部における品質が劣位であった。
 The ratio Comparative Examples 7, which did not satisfy the relational expression 1, to ensure a targeted physical properties by the high cold rolling reduction. However, due to the high cold reduction, the cracking in the sheared part was rather severe. Comparative Example 9 is filled with related engaging formula (1) and (2), the quality of the pruning sectional processed portion was inferior. In Comparative Example 10, the relational expressions (1) and (2) were not both satisfied, and the quality in the sheared portion was inferior.

これに対し、発明例は、本発明で提案された成分範囲及び製造条件並びに関係式（１）、（２）をすべて満たしているため、目標とした物性を確保することができ、剪断加工部における品質にも優れていることが確認できる。   On the other hand, since the invention examples satisfy all the ranges of components and manufacturing conditions proposed in the present invention and the relational expressions (1) and (2), the target physical properties can be secured, and the sheared portion It can be confirmed that the quality is excellent.

一方、図１には、発明例及び比較例の関係式（１）、関係式（２）の値が示されている。図１において、斜線領域が本発明の範囲に該当する。 On the other hand, FIG. 1 shows the values of the relational expressions (1) and (2) of the invention example and the comparative example. In FIG. 1, the shaded area corresponds to the scope of the present invention.

以上、本発明の実施形態について詳細に説明したが、本発明の権利範囲はこれに限定されず、請求範囲に記載された本発明の技術的思想から外れない範囲内で多様な修正及び変形が可能であるということは、当技術分野の通常の知識を有する者には明らかである。   Although the embodiments of the present invention have been described in detail above, the scope of rights of the present invention is not limited thereto, and various modifications and variations can be made without departing from the technical idea of the present invention described in the claims. It is obvious to a person of ordinary skill in the art that it is possible.

Claims (10)

重量％で、Ｃ：０．０５〜０．１０％、Ｓｉ：０．０１〜０．５％、Ｍｎ：１．２〜２．０％、Ａｌ：０．０１〜０．１％、Ｃｒ：０．００５〜０．３％、Ｂ：０．０００３〜０．００１０％、Ｍｏ：０．００５〜０．２％、Ｐ：０．００１〜０．０５％、Ｓ：０．００１〜０．０１％、Ｎ：０．００１〜０．０１％、Ｎｂ：０．００５〜０．０８％、Ｔｉ：０．００５〜０．１３％、Ｖ：０．００５〜０．２％、残りＦｅ及び不可避不純物を含み、
下記関係式（１）及び下記関係式（２）を満たし、
炭化物、窒化物、及び炭窒化物のうち１以上を含む、剪断加工性に優れた高強度冷延鋼板。
関係式（１）：２．０≦［Ｍｎ］＋２．５［Ｍｏ］＋１．５［Ｃｒ］＋３００［Ｂ］≦２．５
関係式（２）：０．２≦（［Ｎｂ］／９３＋［Ｔｉ］／４８＋［Ｖ］／５１）／（［Ｃ］／１２＋［Ｎ］／１４）≦０．５
（但し、前記関係式（１）及び（２）において、各元素記号は該当合金元素の重量％を示す。） % By weight, C: 0.05 to 0.10%, Si: 0.01 to 0.5%, Mn: 1.2 to 2.0%, Al: 0.01 to 0.1%, Cr: 0.005 to 0.3%, B: 0.0003 to 0.0010%, Mo: 0.005 to 0.2%, P: 0.001 to 0.05%, S: 0.001 to 0. 01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005-0.2%, remaining Fe and Contains unavoidable impurities,
The following relational expression (1) and the following relational expression (2) are satisfied,
A high-strength cold-rolled steel sheet that contains one or more of carbides, nitrides, and carbonitrides and that has excellent shear workability.
Relational expression (1): 2.0 ≦ [Mn] +2.5 [Mo] +1.5 [Cr] +300 [B] ≦ 2.5
Relational expression (2): 0.2 ≦ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≦ 0.5
(However, in the relational expressions (1) and (2), each element symbol represents the weight% of the corresponding alloy element.) 前記炭化物、窒化物、及び炭窒化物の平均サイズは１０〜５０ｎｍである、請求項１に記載の剪断加工性に優れた高強度冷延鋼板。   The high-strength cold-rolled steel sheet excellent in shear workability according to claim 1, wherein the carbides, nitrides, and carbonitrides have an average size of 10 to 50 nm. 前記冷延鋼板は、引張強度が１２００ＭＰａ以上であり、硬度値が３４０Ｈｖ以上である、請求項１に記載の剪断加工性に優れた高強度冷延鋼板。   The high-strength cold-rolled steel sheet having excellent shear workability according to claim 1, wherein the cold-rolled steel sheet has a tensile strength of 1200 MPa or more and a hardness value of 340 Hv or more. 剪断加工時に発生する亀裂は最大亀裂の長さが１ｍｍ以下である、請求項１に記載の剪断加工性に優れた高強度冷延鋼板。   The high-strength cold-rolled steel sheet excellent in shear workability according to claim 1, wherein the crack generated during shearing has a maximum crack length of 1 mm or less. 前記冷延鋼板は、冷間圧延前の微細組織が、面積分率で、フェライト相が９０％以上であり、微細なパーライト相が５％未満であり、その他に、ベイナイト相が必然的に含まれる、請求項１に記載の剪断加工性に優れた高強度冷延鋼板。   In the cold rolled steel sheet, the fine structure before cold rolling has an area fraction of 90% or more of ferrite phase, less than 5% of fine pearlite phase, and inevitably contains bainite phase. The high-strength cold-rolled steel sheet having excellent shear workability according to claim 1. 重量％で、Ｃ：０．０５〜０．１０％、Ｓｉ：０．０１〜０．５％、Ｍｎ：１．２〜２．０％、Ａｌ：０．０１〜０．１％、Ｃｒ：０．００５〜０．３％、Ｂ：０．０００３〜０．００１０％、Ｍｏ：０．００５〜０．２％、Ｐ：０．００１〜０．０５％、Ｓ：０．００１〜０．０１％、Ｎ：０．００１〜０．０１％、Ｎｂ：０．００５〜０．０８％、Ｔｉ：０．００５〜０．１３％、Ｖ：０．００５〜０．２％、残りＦｅ及び不可避不純物を含み、下記関係式（１）及び下記関係式（２）を満たす鋼スラブを１２００〜１３５０℃に加熱する段階と、
前記加熱された鋼スラブを８５０〜１１５０℃の範囲の温度で熱間圧延する段階と、
前記熱間圧延後に５５０〜７５０℃の範囲の温度まで冷却し、巻き取る段階と、
前記巻取後に酸洗し、冷間圧下率５６〜７０％で冷間圧延する段階と、を含む、剪断加工性に優れた高強度冷延鋼板の製造方法。
関係式（１）：２．０≦［Ｍｎ］＋２．５［Ｍｏ］＋１．５［Ｃｒ］＋３００［Ｂ］≦２．５
関係式（２）：０．２≦（［Ｎｂ］／９３＋［Ｔｉ］／４８＋［Ｖ］／５１）／（［Ｃ］／１２＋［Ｎ］／１４）≦０．５
（但し、前記関係式（１）及び（２）において、各元素記号は該当合金元素の重量％を示す。） % By weight, C: 0.05 to 0.10%, Si: 0.01 to 0.5%, Mn: 1.2 to 2.0%, Al: 0.01 to 0.1%, Cr: 0.005 to 0.3%, B: 0.0003 to 0.0010%, Mo: 0.005 to 0.2%, P: 0.001 to 0.05%, S: 0.001 to 0. 01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005-0.2%, remaining Fe and Heating a steel slab containing inevitable impurities and satisfying the following relational expressions (1) and (2) to 1200 to 1350 ° C .;
Hot rolling the heated steel slab at a temperature in the range of 850 to 1150 ° C.,
Cooling to a temperature in the range of 550 to 750 ° C. after the hot rolling, and winding up;
A method for producing a high-strength cold-rolled steel sheet excellent in shear workability, comprising the step of pickling after winding and cold rolling at a cold reduction of 56 to 70%.
Relational expression (1): 2.0 ≦ [Mn] +2.5 [Mo] +1.5 [Cr] +300 [B] ≦ 2.5
Relational expression (2): 0.2 ≦ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≦ 0.5
(However, in the relational expressions (1) and (2), each element symbol represents the weight% of the corresponding alloy element.) 前記鋼スラブは連続鋳造工程によって生産される、請求項６に記載の剪断加工性に優れた高強度冷延鋼板の製造方法。   The method for producing a high-strength cold-rolled steel sheet having excellent shear workability according to claim 6, wherein the steel slab is produced by a continuous casting process. 前記冷却は平均冷却速度１０〜７０℃／ｓで行う、請求項６に記載の剪断加工性に優れた高強度冷延鋼板の製造方法。   The method for producing a high-strength cold-rolled steel sheet having excellent shear workability according to claim 6, wherein the cooling is performed at an average cooling rate of 10 to 70 ° C / s. 前記冷延鋼板は、炭化物、窒化物、及び炭窒化物のうち１以上を含み、炭化物、窒化物、及び炭窒化物の平均サイズは１０〜５０ｎｍである、請求項６に記載の剪断加工性に優れた高強度冷延鋼板の製造方法。   The shear workability according to claim 6, wherein the cold-rolled steel sheet contains one or more of a carbide, a nitride, and a carbonitride, and an average size of the carbide, the nitride, and the carbonitride is 10 to 50 nm. A method for producing a high-strength cold-rolled steel sheet which is excellent in 前記冷延鋼板は、引張強度が１２００ＭＰａ以上であり、硬度値が３４０Ｈｖ以上である、請求項６に記載の剪断加工性に優れた高強度冷延鋼板の製造方法。   The method for producing a high-strength cold-rolled steel sheet excellent in shear workability according to claim 6, wherein the cold-rolled steel sheet has a tensile strength of 1200 MPa or more and a hardness value of 340 Hv or more.
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