JP2009179851A - Method for producing cold-rolled steel sheet - Google Patents
Method for producing cold-rolled steel sheet Download PDFInfo
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本発明は、自動車部品等に使用される、冷延鋼板の製造方法に関し、特に、440MPa以上の高い引張強度と0.85以上の高い降伏比を有する高降伏比高張力冷延鋼板の製造方法に関するものである。 The present invention relates to a method for producing a cold-rolled steel sheet used for automobile parts and the like, and more particularly to a method for producing a high-yield ratio high-tensile cold-rolled steel sheet having a high tensile strength of 440 MPa or more and a high yield ratio of 0.85 or more. It is.
自動車の車体は、燃費改善や運動性能向上の観点から、軽量化が強く要求されている。また、衝突時の安全性確保の観点から、高強度化も必要であり、部品素材として高張力鋼板が多く適用されている。特に、車体の骨格を形成する強度部品に対しては、乗員保護の観点から、衝突時の変形を最小限に抑え、かつ変形時に吸収できるエネルギーを高めることが求められており、このような部品には、降伏強度の高い高張力鋼板を素材として使用することが望ましい。 There is a strong demand for weight reduction of automobile bodies from the viewpoint of improving fuel efficiency and athletic performance. In addition, from the viewpoint of ensuring safety at the time of collision, it is necessary to increase the strength, and many high-tensile steel plates are used as component materials. In particular, from the viewpoint of occupant protection, strength parts that form the skeleton of a vehicle body are required to minimize deformation during a collision and increase energy that can be absorbed during deformation. For this, it is desirable to use a high-tensile steel plate having a high yield strength as a material.
このような中で、自動車の車体部品には、主として板厚の薄い冷延鋼板が使用されている。また、強度部品では、少なくとも引張強度が440MPa以上の高張力鋼板が必要とされている。ただし、あまりに強度の高い鋼板では、部品への成形加工が困難となるため、強度部品の素材には、440MPa級以上、好ましくは540MPa級以上、より好ましくは590MPa級程度の適度な引張強度水準であり、かつ、降伏強度が高い、すなわち降伏比の高い高張力冷延鋼板が適当である。
引張強度が440MPa以上となるように冷延鋼板を高強度化するには、固溶強化に加えて組織強化を併用することが最も一般的な手法である。ただし、硬質相としてマルテンサイトを利用する場合には、鋼板の降伏比が低下しやすい。
一方、降伏比を高める効果的な強化手法としては、析出強化がある。しかし、冷延鋼板の通常の製造プロセスにおいて、再結晶焼鈍後の冷延鋼板中に微細な析出物を存在させることは難しい。熱延後の冷却過程において鋼板中に析出物が微細に析出しても、冷延後の焼鈍時の昇温過程で析出物は成長し易く、強化能の高い微細粒子のまま析出物を焼鈍後まで残存させることは困難だからである。そのため、冷延鋼板では析出強化を有効に利用することができず、降伏比の高い高張力冷延鋼板を得ることは容易ではない。
Under such circumstances, a cold-rolled steel sheet having a thin plate thickness is mainly used as a body part of an automobile. In addition, a high-strength steel sheet having a tensile strength of at least 440 MPa is required for strength parts. However, if the steel sheet is too strong, it will be difficult to form the part.Therefore, the material of the strong part should have an appropriate tensile strength level of 440 MPa class or higher, preferably 540 MPa class or higher, more preferably about 590 MPa class. A high-tensile cold-rolled steel sheet having a high yield strength, that is, a high yield ratio is suitable.
In order to increase the strength of a cold-rolled steel sheet so that the tensile strength is 440 MPa or more, it is most common to use structure strengthening in addition to solid solution strengthening. However, when martensite is used as the hard phase, the yield ratio of the steel sheet tends to decrease.
On the other hand, precipitation strengthening is an effective strengthening technique for increasing the yield ratio. However, in a normal manufacturing process of a cold-rolled steel sheet, it is difficult for fine precipitates to be present in the cold-rolled steel sheet after recrystallization annealing. Even if precipitates are finely precipitated in the steel sheet during the cooling process after hot rolling, the precipitates easily grow in the temperature rising process during annealing after cold rolling, and the precipitates are annealed as fine particles with high strengthening ability. This is because it is difficult to leave it later. For this reason, precipitation strengthening cannot be used effectively with cold-rolled steel sheets, and it is not easy to obtain high-tensile cold-rolled steel sheets with a high yield ratio.
降伏比の高い高張力冷延鋼板を得る手段として、例えば、特許文献1には、NbおよびTiを添加した中炭素鋼において、鋼板組織をマルテンサイト相やベイナイト相のない非複合組織とすることにより、引張強度が45kgf/mm2以上（440MPa以上）で降伏比が80%以上の高強度高降伏比型溶融亜鉛めっき鋼板を得る技術が開示されている。
また、特許文献2には、TiあるいはNbを含有させた中炭素鋼で、鋼組織を平均粒径が1〜4μmのフェライトおよびベイナイトを80%以上含有する組織とし、フェライトおよびベイナイト粒内の析出物の粒径と個数を所定の範囲に制御した、引張強度が700MPa以上かつ降伏比が0.7以上の高強度冷延鋼板が提案されている。
さらに、特許文献3には、Ti、Nb、Mo、Bの添加量を狭い範囲で厳密に管理することにより、高降伏比かつ良延性を確保した、高降伏比高強度冷延鋼板に関する技術が記載されている。
Further, Patent Document 2 is a medium carbon steel containing Ti or Nb, in which the steel structure is a structure containing 80% or more of ferrite and bainite having an average particle diameter of 1 to 4 μm, and precipitation in ferrite and bainite grains. A high-strength cold-rolled steel sheet having a tensile strength of 700 MPa or more and a yield ratio of 0.7 or more, in which the grain size and number of objects are controlled within a predetermined range, has been proposed.
Furthermore, Patent Document 3 discloses a technique related to a high yield ratio high strength cold-rolled steel sheet that ensures high yield ratio and good ductility by strictly controlling the addition amount of Ti, Nb, Mo, and B in a narrow range. Are listed.
しかしながら、特許文献１では、微細なフェライトとパーライトの組織として、組織制御により高降伏比を得ようとしている。そのため、焼鈍後の冷却中に515〜600℃という狭い温度域に保持する必要があり、冷却条件のバラツキによってはマルテンサイトやベイナイトなどが形成される場合がある。したがって、冷却条件のバラツキによる材質への影響が大きいという問題がある。
また、特許文献２では引張強度が700MPa以上、特許文献３では引張強度が780MPa級の高張力鋼板を主たる対象としており、自動車車体の部品としては、適用可能な範囲が限定されるという問題がある。
However, Patent Document 1 attempts to obtain a high yield ratio by microstructure control as a fine ferrite and pearlite structure. Therefore, it is necessary to hold | maintain in the narrow temperature range of 515-600 degreeC during cooling after annealing, and a martensite, a bainite, etc. may be formed depending on the variation in cooling conditions. Therefore, there is a problem that the influence on the material due to the variation in the cooling condition is large.
Further, Patent Document 2 mainly targets high-tensile steel sheets having a tensile strength of 700 MPa or more, and Patent Document 3 has a tensile strength of 780 MPa class, and there is a problem that the applicable range is limited as parts of an automobile body. .
本発明は、かかる事情に鑑み、自動車車体の強度部品にも適用可能な、440MPa以上の引張強度と0.85以上の高い降伏比を有する冷延鋼板の製造方法を提供することを目的とする。 In view of such circumstances, an object of the present invention is to provide a method for producing a cold-rolled steel sheet having a tensile strength of 440 MPa or more and a high yield ratio of 0.85 or more, which can be applied to a strength part of an automobile body.
発明者らは、上記問題点を解決するため、鋼の成分組成と鋼板の製造条件が鋼板の降伏比に及ぼす影響について、鋭意研究調査を重ねた。
その結果、所定の成分組成を有し、Nbを含有する冷延鋼板に対して、所定のオーステナイト単相域温度に保持することでNb析出物を一部分解し、その後の冷却過程において微細再析出の促進処理を施すことで、高張力冷延鋼板に高い降伏比特性を付与できることを見出した。
本発明は、以上の知見に基づいてなされたものであり、その要旨は以下のとおりである。
［１］質量%で、C：0.03〜0.15%、Si：1.0%以下、Mn：0.5〜2.5%、P：0.10%以下、S：0.01%以下、Al：0.01〜0.10%、N：0.005%以下、Nb：0.02〜0.20%を含み、残部はFeおよび不可避的不純物からなる成分組成を有する鋼スラブを、1100〜1300℃の温度に再加熱し、Ar3変態点以上の仕上温度で熱間圧延し、700℃以下の温度で巻き取って熱延鋼板とし、次いで、該熱延鋼板を酸洗、冷間圧延した後に、（Ac3変態点）〜（Ac3変態点+200）℃の温度で30s以上加熱保持し、次いで、10℃/s以上の冷却速度で冷却し、500〜700℃の温度で60s以上保持した後、再度冷却することを特徴とする冷延鋼板の製造方法。
［２］質量%で、C：0.03〜0.15%、Si：1.0%以下、Mn：0.5〜2.5%、P：0.10%以下、S：0.01%以下、Al：0.01〜0.10%、N：0.005%以下、Nb：0.02〜0.20%を含み、残部はFeおよび不可避的不純物からなる成分組成を有する鋼スラブを、1100〜1300℃の温度に再加熱し、Ar3変態点以上の仕上温度で熱間圧延し、700℃以下の温度で巻き取って熱延鋼板とし、次いで、該熱延鋼板を酸洗、冷間圧延した後に、（Ac3変態点）〜（Ac3変態点+200）℃の温度に30s以上加熱保持し、次いで、650〜750℃の急冷開始温度まで10〜30℃/sの冷却速度で冷却し、次いで、前記急冷開始温度から450℃以下の急冷停止温度まで30℃/sを超える冷却速度で急冷し、次いで、500〜700℃の温度に再加熱し、60s以上保持した後、再度冷却することを特徴とする冷延鋼板の製造方法。
［３］前記［１］または［２］に記載の成分組成として、さらに、下記式（１）を満足するようにTiを含有することを特徴とする冷延鋼板の製造方法。
3.5≦［Ti］/［N］≦7.0 ‥‥‥ （1）
ただし、［Ti］、［N］はそれぞれTi、Nの含有量（質量%）、
［４］前記［１］〜［３］のいずれかに記載の成分組成として、さらに、質量%で、Cr：0.05〜0.5%、Mo：0.05〜0.5%、Cu：0.05〜0.5%、Ni：0.05〜0.5%の中から選ばれた1種または2種以上の元素を含有することを特徴とする冷延鋼板の製造方法。
なお、本明細書において、鋼の成分を示す％は、すべて質量％である。また、本発明において、「高降伏比高張力冷延鋼板」とは、降伏比が0.85以上であり引張強度が440MPa以上である冷延鋼板である。
In order to solve the above-mentioned problems, the inventors have conducted intensive research and investigation on the influence of the composition of steel and the production conditions of the steel sheet on the yield ratio of the steel sheet.
As a result, Nb precipitates are partially decomposed by maintaining a predetermined austenite single phase temperature for cold rolled steel sheets having a predetermined composition and containing Nb, and fine reprecipitation in the subsequent cooling process. It has been found that a high yield ratio characteristic can be imparted to a high-tensile cold-rolled steel sheet by performing the acceleration treatment.
This invention is made | formed based on the above knowledge, The summary is as follows.
[1] By mass%, C: 0.03-0.15%, Si: 1.0% or less, Mn: 0.5-2.5%, P: 0.10% or less, S: 0.01% or less, Al: 0.01-0.10%, N: 0.005% Hereinafter, a steel slab containing Nb: 0.02 to 0.20%, with the balance being composed of Fe and inevitable impurities, is reheated to a temperature of 1100 to 1300 ° C, and hot at a finishing temperature not lower than the Ar 3 transformation point. Rolled and wound at a temperature of 700 ° C. or less to form a hot rolled steel sheet, and then pickling and cold rolling the hot rolled steel sheet, then (Ac 3 transformation point) to (Ac 3 transformation point +200) ° C. A method for producing a cold-rolled steel sheet, comprising heating and holding at a temperature for 30 seconds or more, then cooling at a cooling rate of 10 ° C / s or more, holding at a temperature of 500 to 700 ° C for 60s or more, and then cooling again.
[2] By mass%, C: 0.03-0.15%, Si: 1.0% or less, Mn: 0.5-2.5%, P: 0.10% or less, S: 0.01% or less, Al: 0.01-0.10%, N: 0.005% Hereinafter, a steel slab containing Nb: 0.02 to 0.20%, with the balance being composed of Fe and inevitable impurities, is reheated to a temperature of 1100 to 1300 ° C, and hot at a finishing temperature not lower than the Ar 3 transformation point. Rolled and wound at a temperature of 700 ° C. or less to form a hot rolled steel sheet, and then pickling and cold rolling the hot rolled steel sheet, then (Ac 3 transformation point) to (Ac 3 transformation point +200) ° C. Held at a temperature for 30 s or more, then cooled to a quenching start temperature of 650 to 750 ° C. at a cooling rate of 10 to 30 ° C./s, then from the quenching start temperature to a quenching stop temperature of 450 ° C. or less at 30 ° C. / A method for producing a cold-rolled steel sheet, characterized by quenching at a cooling rate exceeding s, then reheating to a temperature of 500 to 700 ° C., holding for 60 s or more, and then cooling again.
[3] A method for producing a cold-rolled steel sheet, wherein the component composition according to [1] or [2] further contains Ti so as to satisfy the following formula (1).
3.5 ≦ [Ti] / [N] ≦ 7.0 (1)
However, [Ti] and [N] are the contents of Ti and N (% by mass),
[4] As the component composition according to any one of [1] to [3], Cr: 0.05 to 0.5%, Mo: 0.05 to 0.5%, Cu: 0.05 to 0.5%, Ni: A method for producing a cold-rolled steel sheet, comprising one or more elements selected from 0.05 to 0.5%.
In addition, in this specification,% which shows the component of steel is mass% altogether. In the present invention, the “high yield ratio high tensile cold-rolled steel sheet” is a cold-rolled steel sheet having a yield ratio of 0.85 or more and a tensile strength of 440 MPa or more.
本発明によれば、高い降伏比を有する高張力冷延鋼板が得られる。また、本発明では、再析出促進処理での保持時間が長いため、その他の冷却条件の制約が少なく、冷却条件のバラツキによる材質への影響の問題が回避できる。
本発明により得られる鋼板は、自動車部品素材として十分な基本的成形性を維持しつつ、高い降伏比特性を具備しているため、自動車車体の強度部品等の素材として好適に使用される。
According to the present invention, a high-tensile cold-rolled steel sheet having a high yield ratio can be obtained. Further, in the present invention, since the retention time in the reprecipitation promotion treatment is long, there are few restrictions on other cooling conditions, and the problem of influence on the material due to variations in cooling conditions can be avoided.
The steel sheet obtained by the present invention has a high yield ratio characteristic while maintaining sufficient basic formability as an automobile part material, and therefore is suitably used as a material for a strength part of an automobile body.
以下、本発明を詳細に説明する。
まず、本発明に用いる鋼スラブの成分組成の限定理由について説明する。
Ｃ：0.03〜0.15%
Cは、鋼の高強度化に必要な元素であり、析出強化を通じて鋼板の高降伏比化にも大きな役割を果たす。これらの所望の鋼板特性を得るためには、Cを0.03%以上含有することが必要である。ただし、Cの含有量が0.15%を超えると、鋼板の溶接性が大きく低下する。よって、Cの含有量は0.03％以上0.15%以下とする。好ましいCの含有量は0.03％以上0.10%以下であり、さらに好ましくは0.03％以上0.07%以下である。
Hereinafter, the present invention will be described in detail.
First, the reason for limiting the component composition of the steel slab used in the present invention will be described.
C: 0.03-0.15%
C is an element necessary for increasing the strength of steel and plays a major role in increasing the yield ratio of steel sheets through precipitation strengthening. In order to obtain these desired steel sheet characteristics, it is necessary to contain 0.03% or more of C. However, if the C content exceeds 0.15%, the weldability of the steel sheet is greatly reduced. Therefore, the C content is 0.03% or more and 0.15% or less. The C content is preferably 0.03% or more and 0.10% or less, more preferably 0.03% or more and 0.07% or less.
Si：1.0%以下
Siは、固溶強化により鋼の強度を高める作用を有する元素である。しかし、Siの含有量が1.0%を超えると、鋼板の表面性状が顕著に劣化し、めっき性にも悪影響を及ぼす。そのため、Siの含有量は1.0%以下とする。なお、鋼板に溶融亜鉛めっきを施す場合には、Siの含有量は0.5%以下とするのが好ましく、より好ましくは0.1%以下である。なお、本発明においては、Siは積極的に含有する必要はなく、含有しなくても（0％であっても）良い。
Si: 1.0% or less
Si is an element having an effect of increasing the strength of steel by solid solution strengthening. However, if the Si content exceeds 1.0%, the surface properties of the steel sheet are remarkably deteriorated and the plating properties are also adversely affected. Therefore, the Si content is 1.0% or less. In addition, when hot dip galvanizing is performed on the steel sheet, the Si content is preferably 0.5% or less, more preferably 0.1% or less. In the present invention, Si does not need to be positively contained, and may not be contained (may be 0%).
Mn：0.5〜2.5%
Mnは、固溶強化により鋼の強度を増す作用を有する元素であり、所望の鋼板強度を得るためには0.5%以上を含有させる。しかし、過度のMnの含有は、鋼板の成形性やめっき性を低下させるので、Mn含有量の上限は2.5%とする。好ましくは、1.5％以上2.5%以下である。
Mn: 0.5-2.5%
Mn is an element having an action of increasing the strength of the steel by solid solution strengthening, and 0.5% or more is contained in order to obtain a desired steel plate strength. However, excessive Mn content decreases the formability and plating properties of the steel sheet, so the upper limit of the Mn content is 2.5%. Preferably, it is 1.5% or more and 2.5% or less.
P：0.10%以下
Pは、固溶強化により鋼を高強度化する元素であり、所望の鋼板強度を確保するためには0.01%以上の含有が好ましい。一方、多量のPの添加は、鋼板の溶接性やめっき性を低下させる。よって、Pの含有量は0.10%以下とする必要がある。なお、鋼板に溶融亜鉛めっきを施す場合には、Pの含有量は0.05%以下とするのが好ましい。
P: 0.10% or less
P is an element that increases the strength of the steel by solid solution strengthening, and is preferably contained in an amount of 0.01% or more in order to ensure the desired strength of the steel sheet. On the other hand, the addition of a large amount of P decreases the weldability and plating properties of the steel sheet. Therefore, the P content needs to be 0.10% or less. In addition, when hot dip galvanizing is applied to the steel sheet, the P content is preferably 0.05% or less.
S：0.01%以下
Sは、鋼中に不純物として存在する元素である。多量のSの含有は、鋼板の成形性や溶接性を低下させる。よって、Sの含有量は0.01%以下とする。
S: 0.01% or less
S is an element present as an impurity in steel. Inclusion of a large amount of S decreases the formability and weldability of the steel sheet. Therefore, the S content is 0.01% or less.
Al：0.01〜0.10%
Alは、鋼の脱酸のために添加される元素である。Alの含有量が0.01%未満では十分な脱酸効果が得られない場合がある。一方、Alの含有量が0.10%を越えると、前記脱酸効果は飽和する上、鋼中介在物の増加によって鋼板の表面欠陥や内部欠陥が増加する。よって、Alの含有量は0.01％以上0.10%以下とする。好ましくは、0.01％以上0.05%以下である。
Al: 0.01-0.10%
Al is an element added for deoxidation of steel. If the Al content is less than 0.01%, a sufficient deoxidation effect may not be obtained. On the other hand, when the Al content exceeds 0.10%, the deoxidation effect is saturated, and the surface defects and internal defects of the steel sheet increase due to the increase of inclusions in the steel. Therefore, the Al content is 0.01% or more and 0.10% or less. Preferably, it is 0.01% or more and 0.05% or less.
N：0.005%以下
Nは、鋼中に不純物として存在する元素である。多量のNの含有は、鋼板の成形性を低下させる。よって、Nの含有量は0.005%以下とする。好ましくは0.003％以下である。
N: 0.005% or less
N is an element present as an impurity in steel. A large amount of N decreases the formability of the steel sheet. Therefore, the N content is 0.005% or less. Preferably it is 0.003% or less.
Nb：0.02〜0.20%
Nbは、本発明において最も重要な元素である。Nbは、炭化物や炭窒化物を形成し、鋼中に析出して鋼を析出強化し、鋼板を高強度化および高降伏比化する作用がある。また、結晶粒を微細化し、高温加熱時の結晶粒粗大化を抑制する効果も有する。このような効果を十分に得るためには、Nbを0.02%以上含有させる必要がある。一方、過度に多量のNbの含有は、鋼板の製造性を悪化させるので、Nbの含有量は0.20%以下とする。良好な製造性を保つためには、Nb含有量は0.15%以下とするのが好ましい。なお、本発明において、Nb析出物とは、Nb炭化物およびNb炭窒化物を指す。ただし、冷間圧延後の加熱保持により一部分解し、冷却過程で再析出させるには、鋼中への溶解度が小さいNb炭化物のほうが好適である。
Nb: 0.02 to 0.20%
Nb is the most important element in the present invention. Nb forms carbides and carbonitrides, precipitates in the steel, strengthens the steel, and has the effect of increasing the strength and yield ratio of the steel sheet. In addition, it has the effect of miniaturizing crystal grains and suppressing coarsening of crystal grains during high-temperature heating. In order to obtain such effects sufficiently, it is necessary to contain 0.02% or more of Nb. On the other hand, an excessively large amount of Nb deteriorates the productivity of the steel sheet, so the Nb content is 0.20% or less. In order to maintain good manufacturability, the Nb content is preferably 0.15% or less. In the present invention, the Nb precipitate refers to Nb carbide and Nb carbonitride. However, Nb carbide having a low solubility in steel is more suitable for partial decomposition by heating and holding after cold rolling and reprecipitation in the cooling process.
また、本発明では、鋼スラブに下記式（１）の範囲でTiを含有させることができる。
Ti：3.5≦［Ti］/［N］≦7.0 ‥‥‥ （1）
TiはNとの親和性が強く、窒化物を形成する作用が強力な元素である。好適なNb析出物を得るために、鋼中のNを全量固定するためには、N含有量との関係式で、［Ti］/［N］≧3.5とする必要がある。一方、［Ti］/［N］＞7.0となるようにTiを添加してもNの固定効果は飽和する。よって、Tiを含有する場合は上記式（1）を満足させるように含有する。Ti窒化物は高温でも安定であるため、TiによるNの析出固定には、高温加熱時の結晶粒粗大化防止効果も期待される。なお、鋼スラブがTiを含有する場合には、Nb析出物に若干のTiが固溶することもあるが、本発明の範囲内ならば特段の問題はない。
Moreover, in this invention, Ti can be contained in the range of following formula (1) to steel slab.
Ti: 3.5 ≦ [Ti] / [N] ≦ 7.0 (1)
Ti is an element that has a strong affinity for N and a strong action to form nitrides. In order to fix the total amount of N in the steel in order to obtain a suitable Nb precipitate, it is necessary that [Ti] / [N] ≧ 3.5 in the relational expression with the N content. On the other hand, even if Ti is added so that [Ti] / [N]> 7.0, the N fixing effect is saturated. Therefore, when it contains Ti, it contains so that the said Formula (1) may be satisfied. Since Ti nitride is stable even at high temperatures, the effect of preventing grain coarsening during high-temperature heating is also expected for the precipitation and fixation of N by Ti. When the steel slab contains Ti, some Ti may be dissolved in the Nb precipitate, but there is no particular problem within the scope of the present invention.
本発明に用いる鋼スラブの化学組成は、上記した成分元素の他は、残部Feおよび不可避的不純物からなる。ただし、これらの成分元素に加えて、以下の合金元素を必要に応じて含有することができる。 The chemical composition of the steel slab used in the present invention is composed of the remaining Fe and unavoidable impurities in addition to the above-described component elements. However, in addition to these component elements, the following alloy elements can be contained as required.
Cr：0.05〜0.5%、Mo：0.05〜0.5%、Cu：0.05〜0.5%、Ni：0.05〜0.5%の中から選ばれた1種または2種以上
Cr、Mo、Cu、Niは、それぞれ固溶強化により鋼の強度を増す作用を有する元素であり、鋼板強度を高めるためには、いずれの元素の場合も0.05%以上を含有させる必要がある。一方、過度の含有は、鋼板の表面性状の悪化やめっき性の低下を招き、経済的にも不利である。よって、それぞれの元素を含有する場合の各々の元素含有量は0.05％以上0.5％以下とする。また、Cr、Mo、Cu、Niのうちの2種以上を含有する場合には、それらの含有量の合計は1.0%以下とすることが好ましい。
One or more selected from Cr: 0.05 to 0.5%, Mo: 0.05 to 0.5%, Cu: 0.05 to 0.5%, Ni: 0.05 to 0.5%
Cr, Mo, Cu, and Ni are elements that have the effect of increasing the strength of the steel by solid solution strengthening, and in order to increase the strength of the steel sheet, it is necessary to contain 0.05% or more for any of the elements. On the other hand, excessive inclusion causes deterioration of the surface properties of the steel sheet and deterioration of the plating property, which is disadvantageous economically. Therefore, the content of each element in the case of containing each element is set to 0.05% to 0.5%. Further, when two or more of Cr, Mo, Cu, and Ni are contained, the total content thereof is preferably 1.0% or less.
次に、本発明の製造条件の限定理由について説明する。
本発明における冷延鋼板は、前記成分組成を有する鋼スラブを、1100〜1300℃の温度に再加熱し、Ar3変態点以上の仕上温度で熱間圧延し、700℃以下の温度で巻き取って熱延鋼板とし、次いで、該熱延鋼板を酸洗、冷間圧延した後に、（Ac3変態点）〜（Ac3変態点＋200）℃の温度で30s以上加熱保持し、次いで、10℃/s以上の冷却速度で冷却し、500〜700℃の温度で60s以上保持した後、再度冷却することにより製造される。または、前記、（Ac3変態点）〜（Ac3変態点＋200）℃の温度に30s以上加熱保持後、650〜750℃の急冷開始温度まで10〜30℃/sの冷却速度で冷却し、次いで、前記急冷開始温度から450℃以下の急冷停止温度まで30℃/sを超える冷却速度で急冷し、次いで、500〜700℃の温度に再加熱し、60s以上保持した後、再度冷却することにより製造される。
なお、その他の製造条件は、通常行われている公知の方法で行うことができる。詳細には以下の通りである。
Next, the reasons for limiting the manufacturing conditions of the present invention will be described.
The cold-rolled steel sheet in the present invention is a steel slab having the above component composition, reheated to a temperature of 1100 to 1300 ° C, hot-rolled at a finishing temperature not lower than the Ar 3 transformation point, and wound at a temperature of 700 ° C or lower. Then, after hot-rolling the steel sheet, pickling and cold-rolling the hot-rolled steel sheet, it is heated and held at a temperature of (Ac 3 transformation point) to (Ac 3 transformation point +200) ° C. for 30 seconds or more, and then 10 ° C. It is manufactured by cooling at a cooling rate of not less than / s, holding at a temperature of 500 to 700 ° C. for not less than 60 s, and then cooling again. Alternatively, after heating and holding at a temperature of (Ac 3 transformation point) to (Ac 3 transformation point +200) ° C. for 30 seconds or more, cooling to a rapid cooling start temperature of 650 to 750 ° C. at a cooling rate of 10 to 30 ° C./s, Next, quench from the quenching start temperature to a quenching stop temperature of 450 ° C. or less at a cooling rate exceeding 30 ° C./s, then reheat to a temperature of 500 to 700 ° C., hold for 60s or more, and then cool again. Manufactured by.
In addition, other manufacturing conditions can be performed by the well-known method normally performed. Details are as follows.
本発明鋼板の素材となる鋼スラブは、前記の成分組成を有する鋼を転炉法により溶製し、連続鋳造法により鋳造してスラブとすることが、生産性ならびにスラブ品質の観点からは好ましいが、その他の手段を用いて製造しても構わない。また、必要に応じて、溶銑予備処理や脱ガス処理に代表される各種予備処理や二次精錬、表面欠陥防止のためのスラブ手入等を実施することが好ましい。 It is preferable from the viewpoint of productivity and slab quality that the steel slab used as the material of the steel sheet of the present invention is produced by melting the steel having the above composition by a converter method and casting it by a continuous casting method to form a slab. However, you may manufacture using another means. Moreover, it is preferable to implement various pretreatments represented by hot metal pretreatment and degassing treatment, secondary refining, and slab care for preventing surface defects, as necessary.
スラブ再加熱温度（SRT）：1100〜1300℃
鋼スラブの再加熱温度は、1100℃以上1300℃以下の範囲とする。再加熱温度が1300℃を超えると、鋼板の表面性状の劣化を招く上、加熱に要するエネルギーの点からも好ましくない。一方、再加熱温度が1100℃未満になると、鋼スラブ中の析出物の分解が不十分となり、鋼板に必要な強度および特性を付与し難くなる。より好ましくは、1150〜1250℃である。
なお、鋼スラブの再加熱においては、常温まで冷却した冷スラブを再加熱してもよいし、鋳造後に降温中の温スラブを直接加熱炉に装入して再加熱してもよい。
Slab reheating temperature (SRT): 1100-1300 ° C
The reheating temperature of the steel slab is in the range of 1100 ° C to 1300 ° C. When the reheating temperature exceeds 1300 ° C., the surface properties of the steel sheet are deteriorated, and it is not preferable from the viewpoint of energy required for heating. On the other hand, when the reheating temperature is less than 1100 ° C., the decomposition of precipitates in the steel slab becomes insufficient, and it becomes difficult to impart the necessary strength and characteristics to the steel sheet. More preferably, it is 1150-1250 degreeC.
In the reheating of the steel slab, the cold slab cooled to room temperature may be reheated or the temperature slab whose temperature is lowered after casting may be directly charged into a heating furnace and reheated.
仕上温度（FT）：Ar3変態点以上
熱間圧延の仕上温度がAr3変態点未満の場合には、鋼板の組織が不均一となり、十分な成形性が得られなくなる。そのため、仕上温度はAr3変態点以上とする。ただし、仕上温度が（Ar3変態点＋100℃）を超えると、結晶粒が粗大化しやすく、成形性や表面性状の劣化を招きやすい。したがって、仕上温度は（Ar3変態点＋100℃）以下とすることが望ましい。
なお、所定の仕上温度を確保するために、エッヂヒーターあるいはバーヒーター等のシートバー加熱装置を利用してもよい。また、複数のシートバーを接合し、連続して仕上圧延を行ってもよい。
ここで、Ar3変態点は熱収縮測定による実測あるいは鋼の成分組成からの計算等により求めることができる。
Finishing temperature (FT): finishing temperature of Ar 3 between transformation point or more heat rolling in the case of less than Ar 3 transformation point, the tissue of the steel sheet becomes uneven, not sufficient formability can not be obtained. Therefore, the finishing temperature is set to the Ar 3 transformation point or higher. However, when the finishing temperature exceeds (Ar 3 transformation point + 100 ° C.), the crystal grains are likely to be coarsened, and formability and surface properties are liable to deteriorate. Therefore, it is desirable that the finishing temperature be (Ar 3 transformation point + 100 ° C.) or less.
In order to secure a predetermined finishing temperature, a sheet bar heating device such as an edge heater or a bar heater may be used. Further, a plurality of sheet bars may be joined and finish rolling may be performed continuously.
Here, the Ar 3 transformation point can be obtained by actual measurement by heat shrinkage measurement or calculation from the component composition of steel.
巻取温度：700℃以下
熱間圧延後の巻取温度が700℃を超える場合には、巻取後の徐冷過程において鋼中析出物が粗大化してしまい、冷間圧延後の高温保持による再分解を経て冷延鋼板中に微細に再析出させることが困難になる。そのため、熱延後の巻取温度は700℃以下に限定する。巻取温度の下限は、特に限定するものではないが、鋼板の形状確保や均一冷却の観点から400℃以上とするのが好ましい。
Winding temperature: 700 ° C or less When the coiling temperature after hot rolling exceeds 700 ° C, precipitates in the steel become coarse during the slow cooling process after winding, and the high temperature is maintained after cold rolling. It becomes difficult to reprecipitate finely in the cold-rolled steel sheet through re-decomposition. Therefore, the coiling temperature after hot rolling is limited to 700 ° C. or less. The lower limit of the coiling temperature is not particularly limited, but is preferably 400 ° C. or higher from the viewpoint of securing the shape of the steel sheet and uniform cooling.
酸洗、冷間圧延
上記により得た熱延鋼板は、常法に従い、酸洗を行い、鋼板表面に形成されているスケールを除去し、次いで、冷間圧延する。
酸洗条件は特に限定しない。通常行われている方法を用いることができる。
冷間圧延の圧下率は特に限定はしないが、結晶粒粗大化の抑制および圧延負荷の増大回避のため、30〜80％程度とするのが好ましい。
Pickling and cold rolling The hot-rolled steel sheet obtained as described above is pickled according to a conventional method to remove scales formed on the surface of the steel sheet, and then cold-rolled.
The pickling conditions are not particularly limited. Conventional methods can be used.
The rolling reduction of cold rolling is not particularly limited, but is preferably about 30 to 80% in order to suppress grain coarsening and avoid an increase in rolling load.
加熱（一次加熱）：（Ac3変態点）〜（Ac3変態点+200）℃の範囲の温度に30s以上保持
冷延鋼板を析出強化して降伏比を高めるためには、冷間圧延後の一次加熱時に、熱延後の冷却中に析出したNb析出物を分解し、その後の冷却過程で再度微細に析出させる必要がある。そのため、冷間圧延後の一次加熱の際には、十分な量のNb析出物が分解する温度まで加熱することが必須となる。一次加熱温度がAc3変態点以上であると、鋼組織のオーステナイト単相化によるC固溶限の拡大に伴い、Nb析出物の分解が促進される。また、オーステナイト変態により、鋼中に残存する未再結晶フェライトが消滅する。よって、一次加熱温度はAc3変態点以上とする。一方、加熱温度が高すぎると、結晶粒の粗大化を招いて鋼板の成形性低下を招く。そのため、一次加熱温度の上限は（Ac3変態点+200）℃とする。
ここで、Ac3変態点は熱膨張測定による実測あるいは鋼の成分組成からの計算等により求めることができる。
また、保持温度が30ｓ未満ではNb析出物の分解が十分に進まない場合がある。
Heating (primary heating): (Ac 3 transformation point) to (Ac 3 transformation point +200) In order to increase the yield ratio by precipitation strengthening cold rolled steel sheet retained for 30s or more after cold rolling, At the time of primary heating, it is necessary to decompose Nb precipitates precipitated during cooling after hot rolling and to finely precipitate again in the subsequent cooling process. Therefore, in the primary heating after cold rolling, it is essential to heat to a temperature at which a sufficient amount of Nb precipitates decomposes. When the primary heating temperature is equal to or higher than the Ac 3 transformation point, the decomposition of Nb precipitates is promoted with the expansion of the C solid solubility limit due to the austenite single phase of the steel structure. In addition, the non-recrystallized ferrite remaining in the steel disappears due to the austenite transformation. Therefore, the primary heating temperature is set to the Ac 3 transformation point or higher. On the other hand, if the heating temperature is too high, the crystal grains become coarse and the formability of the steel sheet is lowered. Therefore, the upper limit of the primary heating temperature is (Ac 3 transformation point +200) ° C.
Here, the Ac 3 transformation point can be obtained by actual measurement by thermal expansion measurement or calculation from the component composition of steel.
Further, when the holding temperature is less than 30 s, the decomposition of Nb precipitates may not sufficiently proceed.
一次加熱後の冷却速度：10℃/s以上
一次加熱温度から下記保持温度（500〜700℃）までの冷却速度が小さすぎると、冷却中の高温域でNb析出物が析出して粗大化し易く、所望の強化効果が得られない。そのため、一次加熱後の冷却速度は10℃/s以上とする。冷却速度の上限は、特に限定するものではないが、鋼板の形状確保の観点から100℃/s以下とするのが好ましい。
Cooling rate after primary heating: 10 ° C / s or more If the cooling rate from the primary heating temperature to the following holding temperature (500 to 700 ° C) is too small, Nb precipitates precipitate in the high temperature range during cooling and are likely to become coarse The desired reinforcing effect cannot be obtained. Therefore, the cooling rate after primary heating is set to 10 ° C./s or more. The upper limit of the cooling rate is not particularly limited, but is preferably 100 ° C./s or less from the viewpoint of securing the shape of the steel sheet.
保持温度：500〜700℃
一次加熱時に分解したNb析出物を再度微細に析出させるためには、一次加熱後の冷却中に適切な温度域に鋼板を保持し、再析出を促進させる必要がある。この保持温度が500℃未満では、析出が十分な速度で進行しない。一方、保持温度が700℃を超える場合には、析出物が粗大化してしまい、所望の強化能を維持できない。よって、一次加熱後の保持温度は500℃以上700℃以下の範囲とする。好ましくは、550〜650℃である。
また、前記保持温度での保持時間が60s未満では、十分な析出促進効果が得られない。よって、保持時間は60s以上とする。好ましくは120s以上である。なお、保持時間が過度に長い場合には生産性の大幅な低下を招くので、保持時間は600s以下とするのが望ましい。
Holding temperature: 500-700 ° C
In order to make the Nb precipitate decomposed at the time of primary heating fine again, it is necessary to keep the steel sheet in an appropriate temperature range during the cooling after the primary heating to promote the reprecipitation. When this holding temperature is less than 500 ° C., precipitation does not proceed at a sufficient rate. On the other hand, when the holding temperature exceeds 700 ° C., the precipitate becomes coarse, and the desired strengthening ability cannot be maintained. Therefore, the holding temperature after the primary heating is in the range of 500 ° C. or higher and 700 ° C. or lower. Preferably, it is 550-650 degreeC.
Further, if the holding time at the holding temperature is less than 60 s, a sufficient precipitation promoting effect cannot be obtained. Therefore, the holding time is 60 seconds or longer. Preferably it is 120 s or more. Note that if the holding time is excessively long, the productivity is greatly reduced, and therefore the holding time is preferably 600 s or less.
保持後は、再度適宜冷却する。 After holding, cool again as appropriate.
なお、本発明の製造方法においては、Nb析出物の再析出促進を目的として行われる一次加熱後の保持工程を、急冷後再加熱に替えることができる。急冷後再加熱の場合には、一次加熱後の冷却過程での析出挙動を制御するため、以下の方法で冷却再加熱する必要がある。 In the production method of the present invention, the holding step after the primary heating performed for the purpose of promoting the reprecipitation of the Nb precipitate can be replaced with the reheating after the rapid cooling. In the case of reheating after quenching, in order to control the precipitation behavior in the cooling process after the primary heating, it is necessary to reheat and reheat by the following method.
一次加熱後の冷却速度：10〜30℃/s
一次加熱温度から急冷開始温度までの冷却速度が小さすぎると、冷却中の高温域でNb析出物が析出して粗大化し易く、所望の強化効果が得られない。そのため、一次加熱後の冷却速度は10℃/s以上とする。一方、一次加熱温度から急冷開始温度までの冷却速度が30℃/sを超えると、フェライト変態の進行が遅滞し、所望の鋼板特性が得られない。よって、一次加熱後急冷開始温度までの冷却速度は10℃/s以上30℃/s以下とする。
Cooling rate after primary heating: 10-30 ° C / s
If the cooling rate from the primary heating temperature to the rapid cooling start temperature is too small, Nb precipitates are likely to precipitate and coarsen in the high temperature region during cooling, and the desired strengthening effect cannot be obtained. Therefore, the cooling rate after primary heating is set to 10 ° C./s or more. On the other hand, when the cooling rate from the primary heating temperature to the rapid cooling start temperature exceeds 30 ° C./s, the progress of the ferrite transformation is delayed and the desired steel sheet characteristics cannot be obtained. Therefore, the cooling rate from the primary heating to the rapid cooling start temperature is 10 ° C./s to 30 ° C./s.
急冷開始温度：650〜750℃
一次加熱後の急冷は、650〜750℃の範囲の温度で開始する必要がある。急冷開始温度が750℃より高いと、フェライト変態が抑制され、所望の鋼板特性が得られない。一方、急冷開始温度が650℃より低い場合には、析出物の粗大化を招きやすく、所望の強化効果が得られない。よって、一次加熱後の急冷開始温度は650℃以上750℃以下とする。
Rapid cooling start temperature: 650-750 ° C
The rapid cooling after the primary heating needs to start at a temperature in the range of 650-750 ° C. When the quenching start temperature is higher than 750 ° C., ferrite transformation is suppressed and desired steel sheet characteristics cannot be obtained. On the other hand, when the rapid cooling start temperature is lower than 650 ° C., the precipitate is likely to be coarsened, and a desired strengthening effect cannot be obtained. Therefore, the rapid cooling start temperature after primary heating is set to 650 ° C. or higher and 750 ° C. or lower.
急冷開始温度から450℃以下の急冷停止温度まで冷却速度：30℃/s超え
一次加熱後の保持工程に代えて、急冷後の再加熱を実施する場合には、急冷開始温度から450℃以下の急冷停止温度まで、30℃/sを超える冷却速度で急冷する。前記温度範囲での急冷速度が30℃/s以下の場合には、析出物の粗大化を招きやすく、所望の強化効果が得難くなる。冷却速度の上限については、特に制限する必要はなく、水焼入のように非常に冷却速度の高い冷却方法を採用してもよい。急冷停止温度が450℃以下であれば、前記した析出物の粗大化は回避できる。好ましい急冷停止温度は300℃以下である。
Cooling rate from the rapid cooling start temperature to the rapid cooling stop temperature of 450 ° C or lower: Over 30 ° C / s When replacing the holding process after primary heating and performing reheating after rapid cooling, the cooling rate is 450 ° C or lower from the rapid cooling start temperature. Rapid cooling to a quenching stop temperature at a cooling rate exceeding 30 ° C / s. When the rapid cooling rate in the temperature range is 30 ° C./s or less, the precipitates are liable to be coarsened, making it difficult to obtain a desired strengthening effect. The upper limit of the cooling rate is not particularly limited, and a cooling method having a very high cooling rate such as water quenching may be employed. If the quenching stop temperature is 450 ° C. or less, the above-described coarsening of the precipitate can be avoided. A preferred quench stop temperature is 300 ° C. or lower.
上記急冷後再加熱を施す。
再加熱温度：500〜700℃
一次加熱時に分解したNb析出物を上記急冷後再度微細に析出させるためには、再加熱して再析出反応を促進させる必要がある。この再加熱温度が500℃未満では、析出反応が十分な速度で進行しない。一方、再加熱温度が700℃を超える場合には、析出物が粗大化してしまい所望の強化能を維持できない。よって、急冷後の再加熱温度は500℃以上700℃以下の範囲とする。好ましくは、550℃以上650℃以下である。
また、前記再加熱温度での保持時間が60s未満では、十分な析出促進効果が得られない。よって、上記再加熱温度での保持時間は60s以上とする。なお、保持時間が過度に長い場合には生産性の低下を招くので、保持時間は600s以下とするのが好ましい。
保持後は、適宜冷却する。
Reheating is performed after the rapid cooling.
Reheating temperature: 500-700 ° C
In order to cause the Nb precipitate decomposed during the primary heating to be finely precipitated again after the rapid cooling, it is necessary to reheat to promote the reprecipitation reaction. When this reheating temperature is less than 500 ° C., the precipitation reaction does not proceed at a sufficient rate. On the other hand, when the reheating temperature exceeds 700 ° C., the precipitate becomes coarse and the desired strengthening ability cannot be maintained. Therefore, the reheating temperature after rapid cooling is set to a range of 500 ° C. or more and 700 ° C. or less. Preferably, they are 550 degreeC or more and 650 degrees C or less.
Further, if the holding time at the reheating temperature is less than 60 s, a sufficient precipitation promoting effect cannot be obtained. Therefore, the holding time at the reheating temperature is 60 s or longer. Note that if the holding time is excessively long, the productivity is lowered, so the holding time is preferably 600 s or less.
After holding, cool appropriately.
上記の冷延鋼板に施す熱処理工程については、連続ラインで実施すること、および冷間圧延後の再結晶焼鈍工程に兼ねて実施することが、生産性の観点から好ましい。ただし、再結晶焼鈍後に別途実施することも可能である。 About the heat treatment process given to said cold-rolled steel plate, it is preferable from a viewpoint of productivity to implement in a continuous line and to carry out together with the recrystallization annealing process after cold rolling. However, it can also be performed separately after recrystallization annealing.
上記熱処理（焼鈍）後の冷延鋼板は、溶融めっきまたは電気めっきを施して亜鉛めっき鋼板とすることもでき、亜鉛めっき鋼板としても十分な発明効果が得られる。亜鉛めっきとしては、合金化亜鉛めっきや純亜鉛めっきが挙げられる。なお、冷延鋼板に合金化溶融亜鉛めっき処理を施す場合には、上記した析出促進のための急冷後再加熱工程を合金化工程に兼ねて実施することが、生産性の観点から好ましい。熱処理後あるいはめっき処理後の鋼板には、形状矯正や表面粗度の調整のための調質圧延を加えても良い。また、本発明による鋼板は、亜鉛以外の金属めっきや種々の塗装、潤滑被覆等の各種表面処理を施すことも可能である。 The cold-rolled steel sheet after the heat treatment (annealing) can be subjected to hot dip plating or electroplating to obtain a galvanized steel sheet, and a sufficient invention effect can be obtained as a galvanized steel sheet. Examples of zinc plating include alloyed zinc plating and pure zinc plating. In addition, when subjecting a cold-rolled steel sheet to an alloying hot dip galvanizing treatment, it is preferable from the viewpoint of productivity that the reheating step after the rapid cooling for promoting the precipitation is also performed as the alloying step. The steel plate after heat treatment or plating treatment may be subjected to temper rolling for shape correction or surface roughness adjustment. Further, the steel sheet according to the present invention can be subjected to various surface treatments such as metal plating other than zinc, various coatings, and lubricating coating.
表1に示す成分元素を含有し、残部がFeおよび不可避的不純物よりなる鋼片を、表2に示す条件で熱間圧延して板厚3mmの熱延鋼板を得た。次いで、得られた熱延鋼板を酸洗してデスケーリングした後、冷間圧延して板厚１.2mmの冷延鋼板とした。さらに、得られた冷延鋼板を、表２に示す条件で熱処理（焼鈍、冷却）した。なお、一部鋼板については、一次加熱後の急冷後に溶融亜鉛めっき処理を施し、急冷後再加熱工程を合金化工程に兼ねて、合金化溶融亜鉛めっき鋼板とした。
また、表2中のAr3変態点およびAc3変態点は、下記式により鋼の化学組成から算出して得た値である。
Ar3（℃）＝Kr−203［C］1/2＋44.7［Si］−15［Mn］＋350［P］＋200［Al］＋200［Ti］−10［Cu］−15.2［Ni］−5.5［Cr］＋31.5［Mo］
ただし、［C］、［Si］、［Mn］、［P］、［Al］、［Ti］、［Cu］、［Ni］、［Cr］、［Mo］は、それぞれC、Si、Mn、P、Al、Ti、Cu、Ni、Cr、Moの含有量（質量%）。
Krは、Cu、Ni、Cr、Moのいずれか1種以上を含有する場合はKr＝820、
これ以外はKr＝825。
Ac3（℃）＝900−203［C］1/2＋44.7［Si］−15［Mn］＋350［P］＋200［Al］＋200［Ti］−10［Cu］−15.2［Ni］−5.5［Cr］＋31.5［Mo］
ただし、［C］、［Si］、［Mn］、［P］、［Al］、［Ti］、［Cu］、［Ni］、［Cr］、［Mo］は、それぞれC、Si、Mn、P、Al、Ti、Cu、Ni、Cr、Moの含有量（質量%）。
このようにして得られた冷延鋼板に対して、伸長率0.5%の調質圧延を施した後、下記の要領で鋼板の引張特性を測定、評価した。
Steel strips containing the component elements shown in Table 1 and the balance consisting of Fe and unavoidable impurities were hot-rolled under the conditions shown in Table 2 to obtain hot-rolled steel sheets having a thickness of 3 mm. Next, the obtained hot-rolled steel sheet was pickled and descaled, and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.2 mm. Furthermore, the obtained cold-rolled steel sheet was heat-treated (annealed and cooled) under the conditions shown in Table 2. In addition, about some steel plates, the hot-dip galvanization process was performed after the rapid cooling after primary heating, and the reheating process after the rapid cooling was combined with the alloying process, and it was set as the alloyed hot-dip galvanized steel plate.
The Ar 3 transformation point and Ac 3 transformation point in Table 2 are values obtained by calculating from the chemical composition of the steel according to the following formula.
Ar 3 (° C.) = Kr−203 [C] 1/2 +44.7 [Si] −15 [Mn] +350 [P] +200 [Al] +200 [Ti] −10 [Cu] −15.2 [Ni] −5.5 [Cr] +31.5 [Mo]
However, [C], [Si], [Mn], [P], [Al], [Ti], [Cu], [Ni], [Cr], [Mo] are C, Si, Mn, Content of P, Al, Ti, Cu, Ni, Cr, Mo (% by mass).
If Kr contains one or more of Cu, Ni, Cr, Mo, Kr = 820,
Otherwise, Kr = 825.
Ac 3 (° C.) = 900−203 [C] 1/2 +44.7 [Si] −15 [Mn] +350 [P] +200 [Al] +200 [Ti] −10 [Cu] −15.2 [Ni] −5.5 [Cr] +31.5 [Mo]
However, [C], [Si], [Mn], [P], [Al], [Ti], [Cu], [Ni], [Cr], [Mo] are C, Si, Mn, Content of P, Al, Ti, Cu, Ni, Cr, Mo (% by mass).
The cold-rolled steel sheet thus obtained was subjected to temper rolling with an elongation of 0.5%, and then the tensile properties of the steel sheet were measured and evaluated in the following manner.
引張特性
試験方向が圧延方向と直角になるように採取した日本工業規格JIS Z 2201に規定の5号試験片を用いて、同じくJIS Z 2241に規定の方法に準拠し、引張強度（TS）、降伏応力（YS）、破断伸び（El）を測定し、降伏比（YR）を求めた。なお、ここでの降伏応力には下降伏応力あるいは0.2％耐力の値を採用した。
以上により得られた結果を条件と併せて表２に示す。
Tensile properties
Using the No. 5 test piece specified in Japanese Industrial Standard JIS Z 2201 collected so that the test direction is perpendicular to the rolling direction, the tensile strength (TS) and yield stress are also in accordance with the method specified in JIS Z 2241. (YS) and elongation at break (El) were measured to determine the yield ratio (YR). Here, the yield stress or the value of 0.2% proof stress was adopted as the yield stress.
The results obtained as described above are shown in Table 2 together with the conditions.
表２より、本発明例の各鋼板は、440MPa以上の引張強度を有し、0.85以上の高い降伏比を示している。
一方、鋼組成あるいは熱処理条件が本発明の範囲を外れる比較例の各鋼板は、降伏比が所望の水準に達しておらず、高降伏比型高張力冷延鋼板としては不適当である。
From Table 2, each steel plate of the present invention example has a tensile strength of 440 MPa or more and a high yield ratio of 0.85 or more.
On the other hand, each steel plate of the comparative example whose steel composition or heat treatment condition falls outside the scope of the present invention does not reach the desired level, and is unsuitable as a high yield ratio type high-tensile cold-rolled steel plate.
本発明による鋼板は、自動車部品を中心に、高い降伏比と高強度を必要とする各種電気機器などの部品に対して好適に使用できる。 The steel sheet according to the present invention can be suitably used for parts such as various electric devices that require a high yield ratio and high strength, centering on automobile parts.
Claims (4)
次いで、該熱延鋼板を酸洗、冷間圧延した後に、（Ac3変態点）〜（Ac3変態点+200）℃の温度で30s以上加熱保持し、次いで、10℃/s以上の冷却速度で冷却し、500〜700℃の温度で60s以上保持した後、再度冷却することを特徴とする冷延鋼板の製造方法。 In mass%, C: 0.03-0.15%, Si: 1.0% or less, Mn: 0.5-2.5%, P: 0.10% or less, S: 0.01% or less, Al: 0.01-0.10%, N: 0.005% or less, Nb : A steel slab containing 0.02 to 0.20%, with the balance consisting of Fe and inevitable impurities, reheated to a temperature of 1100 to 1300 ° C, hot-rolled at a finishing temperature not lower than the Ar 3 transformation point, Winding at a temperature of 700 ° C or less to make a hot-rolled steel sheet,
Next, the hot-rolled steel sheet is pickled and cold-rolled, and then heated and held at a temperature of (Ac 3 transformation point) to (Ac 3 transformation point +200) ° C. for 30 seconds or more, and then cooled to 10 ° C./s or more. A method for producing a cold-rolled steel sheet, wherein the method is cooled at a speed, held at a temperature of 500 to 700 ° C. for 60 seconds or more, and then cooled again.
次いで、該熱延鋼板を酸洗、冷間圧延した後に、（Ac3変態点）〜（Ac3変態点+200）℃の温度に30s以上加熱保持し、次いで、650〜750℃の急冷開始温度まで10〜30℃/sの冷却速度で冷却し、次いで、前記急冷開始温度から450℃以下の急冷停止温度まで30℃/sを超える冷却速度で急冷し、次いで、500〜700℃の温度に再加熱し、60s以上保持した後、再度冷却することを特徴とする冷延鋼板の製造方法。 In mass%, C: 0.03-0.15%, Si: 1.0% or less, Mn: 0.5-2.5%, P: 0.10% or less, S: 0.01% or less, Al: 0.01-0.10%, N: 0.005% or less, Nb : A steel slab containing 0.02 to 0.20%, with the balance consisting of Fe and inevitable impurities, reheated to a temperature of 1100 to 1300 ° C, hot-rolled at a finishing temperature not lower than the Ar 3 transformation point, Winding at a temperature of 700 ° C or less to make a hot-rolled steel sheet,
Next, the hot-rolled steel sheet is pickled and cold-rolled, and then heated and held at a temperature of (Ac 3 transformation point) to (Ac 3 transformation point +200) ° C. for 30 s or more, and then rapidly cooled to 650 to 750 ° C. Cooling to a temperature at a cooling rate of 10-30 ° C./s, then quenching at a cooling rate exceeding 30 ° C./s from the quenching start temperature to a quenching stop temperature of 450 ° C. or less, and then a temperature of 500-700 ° C. A method for producing a cold-rolled steel sheet, wherein the steel sheet is re-heated and held for 60 seconds or more, and then cooled again.
3.5≦［Ti］/［N］≦7.0 ‥‥‥ （1）
ただし、［Ti］、［N］はそれぞれTi、Nの含有量（質量%） A method for producing a cold-rolled steel sheet, further comprising Ti as a component composition according to claim 1 or 2 so as to satisfy the following formula (1).
3.5 ≦ [Ti] / [N] ≦ 7.0 (1)
However, [Ti] and [N] are Ti and N contents (mass%), respectively.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2006152362A (en) * | 2004-11-29 | 2006-06-15 | Jfe Steel Kk | High-strength steel plate having excellent rigidity and production method thereof |
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| JP2006152362A (en) * | 2004-11-29 | 2006-06-15 | Jfe Steel Kk | High-strength steel plate having excellent rigidity and production method thereof |
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