JP2007100114A - Method for producing high-tensile cold-rolled steel sheet - Google Patents
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 46
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 19
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 75
- 239000010959 steel Substances 0.000 claims abstract description 75
- 238000010791 quenching Methods 0.000 claims abstract description 51
- 238000000137 annealing Methods 0.000 claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 24
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 23
- 238000005496 tempering Methods 0.000 claims abstract description 9
- 238000005097 cold rolling Methods 0.000 claims abstract description 6
- 230000000171 quenching effect Effects 0.000 claims description 48
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 44
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 229910000734 martensite Inorganic materials 0.000 description 20
- 238000001816 cooling Methods 0.000 description 10
- 230000009466 transformation Effects 0.000 description 9
- 238000004088 simulation Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 239000003562 lightweight material Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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Abstract
Description
本発明は、水焼入れを行う連続焼鈍プロセスにより引張強さ１１８０ＭＰａ級の高張力冷延鋼板を製造するのに好適な冷延鋼板の製造方法に関する。 The present invention relates to a method for producing a cold-rolled steel sheet suitable for producing a high-tensile cold-rolled steel sheet having a tensile strength of 1180 MPa class by a continuous annealing process in which water quenching is performed.
近年、自動車における安全性向上及び軽量化による燃費向上が今まで以上に要求されるようになってきており、高強度且つ軽量な材料に対する要求が強まっている。このような状況にあって、１１８０ＭＰａ（１２０ｋｇｆ／ｍｍ２）級の高張力冷延鋼板を、例えば自動車のインパクトビームのような単純な筒形状の部品だけでなく、複雑なプレス加工やロールフォーミングなどにより製造されるような補強部品に対してもその適応範囲を拡大しようとしている。この場合、機械加工する際に用いられる加工設備に鋼板を装入する際の妨げとならないように、また、加工後の製品形状の精度を阻害することがないように、加工前の鋼板の形状は良好であること、つまり、例えば反りの高さが１０ｍｍ以下であることが必要とされる。 In recent years, there has been an increasing demand for improved safety and lighter fuel consumption in automobiles than ever, and there is an increasing demand for high-strength and lightweight materials. Under such circumstances, a 1180 MPa (120 kgf / mm 2 ) -class high-tensile cold-rolled steel sheet is used not only for simple cylindrical parts such as automobile impact beams, but also for complex pressing and roll forming. It is trying to expand the range of application to reinforcement parts such as those manufactured by the company. In this case, the shape of the steel plate before processing is not disturbed when the steel plate is inserted into the processing equipment used for machining, and the accuracy of the product shape after processing is not hindered. Needs to be good, that is, for example, the height of warpage is 10 mm or less.
しかし、通常の水焼入れを行う連続焼鈍プロセスにより、１１８０ＭＰａ級以上の高張力を有する冷延鋼板を製造した場合には、その鋼板には大きな反り、例えば２０ｍｍ〜４０ｍｍ程度の反りが発生する場合がある。このような大きな反りが発生すると、歩留が低下し、あるいは反りを矯正する工程を追加することによるコストアップが問題となっていた。 However, when a cold-rolled steel sheet having a high tension of 1180 MPa class or higher is produced by a continuous annealing process in which normal water quenching is performed, the steel sheet may undergo a large warp, for example, a warp of about 20 mm to 40 mm. is there. When such a large warp occurs, the yield decreases, or a cost increase due to the addition of a process for correcting the warp has been a problem.
特開平４−２８９１２０号公報（特許文献１）には、引張強度が１４７０ＭＰａ（１５０ｋｇｆ／ｍｍ２）〜１９６０ＭＰａ（２００ｋｇｆ／ｍｍ２）級の鋼板に対する反り高さと、鋼板中のマルテンサイト体積率との関係が述べられている。そして、その中で、特定成分の鋼を熱延板において組織を均一微細化し、続く連続焼鈍でマルテンサイト体積率が８０〜９７％で残部がフェライトからなる微細な２相組織とすることにより、成形性とストリップ形状の良好な超高強度冷延鋼板が製造できるとしている。 The JP-A 4-289120 (Patent Document 1), tensile strength 1470MPa (150kgf / mm 2) ~1960MPa and warp height for (200 kgf / mm 2) grade steel, the volume fraction of martensite in the steel sheet The relationship is stated. And in that, by making the structure of the steel of the specific component uniform in the hot-rolled sheet, and making it a fine two-phase structure consisting of ferrite with the remainder of the martensite volume fraction of 80-97% by continuous annealing, It is said that an ultra-high-strength cold-rolled steel sheet with good formability and strip shape can be produced.
また、特開２００４−４３８７８号公報（特許文献２）には、４９０ＭＰａ（５０ｋｇｆ／ｍｍ２）〜１４７０ＭＰａ（１５０ｋｇｆ／ｍｍ２）級の鋼板に対し、焼入れ時の鋼板の温度を搬送方向位置での２回微分した微分係数の最大値が、あらかじめ定められた許容最大反り量に対応する微分係数値以下となるように鋼板の焼入れを行う高強度冷延鋼板の製造方法について記載されている。ここでは、このような方法を用いることで、形状不良を生じさせることなく高強度の冷延鋼板が安定して製造できるとしている。
しかし、上記特許文献１に開示されている鋼板の反り高さと、鋼板中のマルテンサイト体積率との関係を１１８０ＭＰａ級の冷延鋼板にそのまま適用することはできない。これは、特許文献１は１４７０ＭＰａ級以上の超高強度冷延鋼板を対象としており、鋼板の降伏応力が高いためにマルテンサイト変態膨張応力と冷却収縮応力よる変形が発生しにくいと考えられるからである。 However, the relationship between the warp height of the steel sheet disclosed in Patent Document 1 and the martensite volume ratio in the steel sheet cannot be applied as it is to a 1180 MPa grade cold-rolled steel sheet. This is because Patent Document 1 is intended for ultra-high-strength cold-rolled steel sheets of 1470 MPa class or higher, and it is considered that deformation due to martensitic transformation expansion stress and cooling shrinkage stress is unlikely to occur because the yield stress of the steel sheet is high. is there.
また、上記特許文献２に記載の方法は、要するに水焼入れによる冷却速度を低くすることを意図したものであるが、これを１１８０ＭＰａ級の鋼板に適用した場合、鋼板の冷却速度不足による強度低下の影響が発生し、１１８０ＭＰａ級の冷延鋼板を安定して製造することが難しいという問題がある。 In addition, the method described in Patent Document 2 is intended to reduce the cooling rate by water quenching, but when this is applied to a 1180 MPa grade steel plate, the strength is reduced due to the insufficient cooling rate of the steel plate. There is a problem that it is difficult to stably produce a 1180 MPa grade cold-rolled steel sheet.
そこで、本発明は、１１８０ＭＰａ級の冷延鋼板を製造した場合においても、反り量が少なく、形状の良好な高張力冷延鋼板を安定して製造することが可能な高張力冷延鋼板の製造方法を提供することを目的とする。 Therefore, the present invention provides a high-tensile cold-rolled steel sheet that can stably produce a high-strength cold-rolled steel sheet with a small amount of warpage and a good shape even when a 1180 MPa-class cold-rolled steel sheet is manufactured. It aims to provide a method.
上記課題を解決するために、本発明は以下のような特徴を有する。
［１］冷間圧延後の鋼板に対し、連続焼鈍プロセスにより焼鈍し、水焼入れし、過時効処理を行う引張強さ１１８０ＭＰａ級の高張力冷延鋼板の製造方法であって、
水焼入れ前の鋼板中のオーステナイト体積率が７０％未満となる温度から水焼入れを行うとともに、鋼板の引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満となるように焼鈍温度および焼戻温度を調節することを特徴とする高張力冷延鋼板の製造方法。
［２］質量％で、Ｃ：０．０５〜０．２％、Ｓｉ：２．５％以下、Ｍｎ：３．０％以下、Ｐ：０．３％以下、Ｓ：０．０３％以下、Ｓｏｌ．Ａｌ：０．１％以下を含有し、さらに必要に応じてＮｂ：０．１％以下、Ｔｉ：０．２％以下、Ｂ：０．０１％以下、Ｓｂ：０．１％以下、Ｖ：０．１％以下、Ｃｒ：０．３％以下、Ｍｏ：０．３％以下、Ｎｉ：０．３％以下の１種または２種以上を含有し、残部Ｆｅおよび不可避的不純物からなる鋼を、熱間圧延し、酸洗し、冷間圧延した後、引き続き連続焼鈍プロセスにより焼鈍し、水焼入れし、過時効処理を行う引張強さ１１８０ＭＰａ級の高張力冷延鋼板の製造方法であって、
水焼入れ前の鋼板中のオーステナイト体積率が７０％未満となる温度から水焼入れを行うとともに、鋼板の引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満となるように焼鈍温度および焼戻温度を調節することを特徴とする高張力冷延鋼板の製造方法。
［３］上記［２］において、鋼は、下記（１）式で示される炭素当量Ｃｅｑが０．４８以上であることを特徴とする高張力冷延鋼板の製造方法。
Ｃｅｑ＝Ｃ＋Ｓｉ／２４＋Ｍｎ／６＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４ ・・・（１）
但し、上記（１）式中の元素記号は各元素の含有量（質量％）を表す。
In order to solve the above problems, the present invention has the following features.
[1] A method for producing a high-tensile cold-rolled steel sheet having a tensile strength of 1180 MPa, in which the steel sheet after cold rolling is annealed by a continuous annealing process, water-quenched, and subjected to overaging treatment,
Water quenching is performed from the temperature at which the austenite volume fraction in the steel sheet before water quenching is less than 70%, and the annealing temperature and tempering temperature are adjusted so that the tensile strength of the steel sheet is 1180 MPa or more and less than 1470 MPa. A method for producing a high-tensile cold-rolled steel sheet.
[2] In mass%, C: 0.05 to 0.2%, Si: 2.5% or less, Mn: 3.0% or less, P: 0.3% or less, S: 0.03% or less, Sol. Al: 0.1% or less, further Nb: 0.1% or less, Ti: 0.2% or less, B: 0.01% or less, Sb: 0.1% or less, V: A steel containing one or more of 0.1% or less, Cr: 0.3% or less, Mo: 0.3% or less, Ni: 0.3% or less, the balance being Fe and inevitable impurities A method for producing a high-strength cold-rolled steel sheet having a tensile strength of 1180 MPa, which is hot-rolled, pickled, cold-rolled, subsequently annealed by a continuous annealing process, water-quenched, and over-aged. ,
Water quenching is performed from the temperature at which the austenite volume fraction in the steel sheet before water quenching is less than 70%, and the annealing temperature and tempering temperature are adjusted so that the tensile strength of the steel sheet is 1180 MPa or more and less than 1470 MPa. A method for producing a high-tensile cold-rolled steel sheet.
[3] The method for producing a high-tensile cold-rolled steel sheet according to [2], wherein the steel has a carbon equivalent Ceq represented by the following formula (1) of 0.48 or more.
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (1)
However, the element symbol in the above formula (1) represents the content (% by mass) of each element.
なお、本発明において、１１８０ＭＰａ級高張力冷延鋼板とは、引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満の冷延鋼板を意味するものとする。 In the present invention, the 1180 MPa class high-tensile cold-rolled steel sheet means a cold-rolled steel sheet having a tensile strength of 1180 MPa or more and less than 1470 MPa.
本発明によれば、１１８０ＭＰａ級の冷延鋼板を製造した場合においても、反り量が１０ｍｍ以下と少なく、形状の良好な高張力冷延鋼板を安定して製造することが可能な高張力冷延鋼板の製造方法が提供される。 According to the present invention, even when a 1180 MPa grade cold-rolled steel sheet is manufactured, the amount of warping is as small as 10 mm or less, and a high-tensile cold-rolled steel sheet that can stably manufacture a high-tensile cold-rolled steel sheet having a good shape can be obtained. A method for manufacturing a steel sheet is provided.
以下、本発明を実施するための最良の形態の一例を説明する。 Hereinafter, an example of the best mode for carrying out the present invention will be described.
本発明にかかる高張力冷延鋼板の製造方法は、冷間圧延後の鋼板に対し、連続焼鈍プロセスにより焼鈍し、水焼入れし、過時効処理を行うに際し、水焼入れ前の鋼板中のオーステナイト体積率が７０％未満となる温度から、水焼入れを行うことを特徴とするものである。 The method for producing a high-strength cold-rolled steel sheet according to the present invention is a steel sheet after cold rolling, which is annealed by a continuous annealing process, water-quenched, and subjected to overaging treatment, and the austenite volume in the steel sheet before water quenching. Water quenching is performed from a temperature at which the rate is less than 70%.
ここで、本発明が対象とする高張力冷延鋼板とは、引張強さ１１８０ＭＰａ級の高張力冷延鋼板であり、具体的には、引張強さ１１８０ＭＰａ以上１４７０ＭＰａ未満のものが対象となる。したがって、本発明では、連続焼鈍プロセスにおいて、鋼板の引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満となるように焼鈍温度および焼戻温度を調節する。 Here, the high-tensile cold-rolled steel sheet targeted by the present invention is a high-tensile cold-rolled steel sheet having a tensile strength of 1180 MPa, and specifically, has a tensile strength of 1180 MPa or more and less than 1470 MPa. Therefore, in this invention, in a continuous annealing process, an annealing temperature and a tempering temperature are adjusted so that the tensile strength of a steel plate may be 1180 MPa or more and less than 1470 MPa.
なお、前記連続焼鈍プロセスにおける温度調節により前記引張強さを確保することができれば、特に成分は限定されるものではないが、例えば、質量％で、Ｃ：０．０５〜０．２％、Ｓｉ：２．５％以下、Ｍｎ：３．０％以下、Ｐ：０．３％以下、Ｓ：０．０３％以下、Ｓｏｌ．Ａｌ：０．１％以下を含有し、さらに必要に応じてＮｂ：０．１％以下、Ｔｉ：０．２％以下、Ｂ：０．０１％以下、Ｓｂ：０．１％以下、Ｖ：０．１％以下、Ｃｒ：０．３％以下、Ｍｏ：０．３％以下、Ｎｉ：０．３％以下の１種または２種以上を含有し、残部Ｆｅおよび不可避的不純物からなる鋼が、好適に用いられる。また、下記（１）式で示される炭素当量Ｃｅｑが０．４８以上である鋼がより好ましい。
Ｃｅｑ＝Ｃ＋Ｓｉ／２４＋Ｍｎ／６＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４ ・・・（１）
但し、上記（１）式中の元素記号は各元素の含有量（質量％）を表す。
In addition, if the said tensile strength can be ensured by the temperature control in the said continuous annealing process, although a component will not be specifically limited, For example, by mass%, C: 0.05-0.2%, Si : 2.5% or less, Mn: 3.0% or less, P: 0.3% or less, S: 0.03% or less, Sol. Al: 0.1% or less, further Nb: 0.1% or less, Ti: 0.2% or less, B: 0.01% or less, Sb: 0.1% or less, V: A steel containing one or more of 0.1% or less, Cr: 0.3% or less, Mo: 0.3% or less, Ni: 0.3% or less, the balance being Fe and inevitable impurities. Are preferably used. Moreover, the steel whose carbon equivalent Ceq shown by following (1) Formula is 0.48 or more is more preferable.
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (1)
However, the element symbol in the above formula (1) represents the content (% by mass) of each element.
上記成分の鋼を用い、焼鈍温度、焼入温度、焼戻温度を最適化することにより、水焼入れ前の鋼板中のオーステナイト体積率を７０％未満とし、且つ得られる冷延鋼板の引張強さを１１８０ＭＰａ級とすることができる。さらに、炭素当量Ｃｅｑが０．４８以上の場合、焼鈍温度、焼入温度、焼戻温度を最適化することにより、水焼入れ前の鋼板中のオーステナイト体積率を７０％未満、且つ得られる冷延鋼板の引張強さ１１８０ＭＰａ級とすることが容易となる。 By using the steels of the above components and optimizing the annealing temperature, quenching temperature, and tempering temperature, the austenite volume fraction in the steel sheet before water quenching is less than 70%, and the tensile strength of the resulting cold-rolled steel sheet Can be set to 1180 MPa class. Further, when the carbon equivalent Ceq is 0.48 or more, by optimizing the annealing temperature, quenching temperature, and tempering temperature, the austenite volume fraction in the steel sheet before water quenching is less than 70%, and the cold rolling obtained It becomes easy to set the tensile strength of the steel sheet to 1180 MPa class.
本発明者等は、連続焼鈍プロセスにより高張力冷延鋼板を製造した場合に、水焼入れ時に発生する形状不良、例えば反りについて、それがどのように発生するのかについて検討を行った。 The inventors of the present invention have studied how shape defects such as warpage occur during water quenching when a high-tensile cold-rolled steel sheet is manufactured by a continuous annealing process.
鋼板に作用する応力としては、焼鈍プロセス中における水焼入れの際の急冷に伴う冷却収縮応力と、オーステナイトからマルテンサイトへの変態に伴う変態膨張応力とが考えられる。そこで、焼鈍プロセス中における水焼入れの際の前記鋼板にかかる応力のシミュレーションを行った。 As stress acting on the steel sheet, cooling shrinkage stress accompanying rapid cooling during water quenching during the annealing process and transformation expansion stress accompanying transformation from austenite to martensite are considered. Therefore, the stress applied to the steel sheet during water quenching during the annealing process was simulated.
図１及び図２に、水焼入れの際の鋼板にかかる応力のシミュレーション結果を示す。図１は、前記鋼板長手方向及び鋼板幅方向の応力分布と応力の働く方向を示した図、図２は、水焼入れ時の鋼板にかかる応力による変形（反り）の状態をシミュレーションした結果を示した斜視図である。 The simulation result of the stress concerning the steel plate in the case of water quenching is shown in FIG.1 and FIG.2. FIG. 1 is a diagram showing the stress distribution in the longitudinal direction and the width direction of the steel plate and the direction in which the stress acts. FIG. 2 shows the result of simulating the state of deformation (warpage) due to the stress applied to the steel plate during water quenching. FIG.
水焼入れによってマルテンサイトを生成させる場合、水焼入れ時にオーステナイトからマルテンサイトへ変態する変態膨張応力と水により急冷される冷却収縮応力の相反する方向の力が瞬時に段階的に鋼板幅方向にかかることがわかる。そして、水焼入れ時に発生する変態膨張応力と冷却収縮応力による応力が鋼板の降伏応力より低い場合には鋼板の幅方向の変形（反り）は発生せず、前記変態膨張応力と冷却収縮応力による応力が鋼板の降伏応力を上回った場合には図２に示すように鋼板の幅方向の変形（反り）が発生する。つまり、オーステナイト体積率が高い場合には、オーステナイトからマルテンサイトへ変態する際の変態膨張応力が大きくなり変形（反り）が発生すると考えられる。 When martensite is generated by water quenching, the forces in the opposite directions of the transformation expansion stress that transforms from austenite to martensite and the cooling shrinkage stress that is quenched by water are instantaneously and gradually applied in the width direction of the steel sheet. I understand. When the stress due to transformation expansion stress and cooling shrinkage stress generated during water quenching is lower than the yield stress of the steel plate, deformation (warp) in the width direction of the steel plate does not occur, and stress due to the transformation expansion stress and cooling shrinkage stress. 2 exceeds the yield stress of the steel plate, deformation (warpage) in the width direction of the steel plate occurs as shown in FIG. That is, when the volume ratio of austenite is high, it is considered that the transformation expansion stress at the time of transformation from austenite to martensite increases and deformation (warpage) occurs.
図３に、水焼入れ前の鋼板温度を変更することにより水焼入れ直前のオーステナイト体積率（％）を変化させた場合における、製品のマルテンサイト体積率（％）と反り量（ｍｍ）を測定した結果を示す。ここで、水焼入れ直前のオーステナイトはすべてマルテンサイトへ変態したと仮定し、製品のマルテンサイト体積率の測定値＝水焼入れ直前のオーステナイト体積率と考える。また、前記測定には、後述する表１における成分Ｂの組成を有する１１８０ＭＰａ級高張力冷延鋼板を用いて行った。 In FIG. 3, the martensite volume ratio (%) and warpage amount (mm) of the product when the austenite volume ratio (%) immediately before water quenching was changed by changing the steel plate temperature before water quenching were measured. Results are shown. Here, it is assumed that all austenite immediately before water quenching has transformed into martensite, and the measured value of the martensite volume fraction of the product = the austenite volume fraction just prior to water quenching. Moreover, the said measurement was performed using the 1180 MPa class high tension cold-rolled steel plate which has a composition of the component B in Table 1 mentioned later.
図３に示すように、鋼板中のマルテンサイト体積率が７０％を境としてそれ以上において反り量が大きく増えることがわかる。つまり、水焼入れ前の鋼板中のオーステナイト体積率を７０％未満として水焼入れを行うことにより、反り量が１０ｍｍ以下の良好な形状の鋼板が得られる。 As shown in FIG. 3, it can be seen that the amount of warpage greatly increases when the martensite volume ratio in the steel plate is 70% or more. That is, by performing water quenching with the austenite volume fraction in the steel plate before water quenching being less than 70%, a steel plate having a good shape with a warp amount of 10 mm or less is obtained.
上述した特許文献１には、引張強度が１４７０ＭＰａ（１５０ｋｇｆ／ｍｍ２）以上の冷延鋼板はマルテンサイト体積率が８０〜９７％で、良好なストリップ形状が得られるとしているが、これは引張強度が１４７０ＭＰａ級以上の場合、鋼板の強度が高いためオーステナイト体積率が７０％以上でも変態膨張応力と冷却収縮応力が鋼板の降伏応力を上回らないので、変形（反り）が発生しないためと考えられる。 In Patent Document 1 described above, a cold-rolled steel sheet having a tensile strength of 1470 MPa (150 kgf / mm 2 ) or more has a martensite volume ratio of 80 to 97%, and a good strip shape is obtained. Is 1470 MPa class or more, the strength of the steel sheet is high, so even if the volume ratio of austenite is 70% or more, the transformation expansion stress and the cooling shrinkage stress do not exceed the yield stress of the steel sheet, so that deformation (warpage) does not occur.
ここで、前記水焼入れ前における鋼板中のオーステナイト体積率を制御する方法としては、例えば、水焼入れ前の鋼板温度をコントロールすることにより行うことができる。 Here, as a method of controlling the volume ratio of austenite in the steel plate before water quenching, for example, it can be performed by controlling the steel plate temperature before water quenching.
図４は、後述する表１における成分Ｂの組成を有する鋼板を、Ａｃ３点よりも高い８３０℃で焼鈍した場合における、焼入温度（水焼入れ直前の鋼板温度（℃））と製品のマルテンサイト体積率（％）（つまり、水焼入れ直前のオーステナイト体積率（％））との関係を示したものである。図４より、これを６９０℃以下まで冷却した後、水焼入れを行うことにより、水焼入れ直前の鋼板のオーステナイト体積率を７０％未満とすることができることがわかる。 FIG. 4 shows the quenching temperature (steel plate temperature (° C.) just before water quenching) and product martensite when a steel plate having the composition of component B in Table 1 described later is annealed at 830 ° C. higher than the Ac3 point. It shows the relationship with the volume ratio (%) (that is, the austenite volume ratio (%) immediately before water quenching). FIG. 4 shows that the austenite volume ratio of the steel sheet immediately before water quenching can be made less than 70% by performing water quenching after cooling to 690 ° C. or less.
以上より、本発明の１１８０ＭＰａ級高張力冷延鋼板の製造方法は、水焼入れ前の鋼板中のオーステナイト体積率が７０％未満となる温度から水焼入れを行うとともに、鋼板の引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満となるように焼鈍温度および焼戻温度を調節する。これにより、反り量が１０ｍｍ以下の形状良好な１１８０ＭＰａ級高張力冷延鋼板を安定して製造することができる。 As mentioned above, the manufacturing method of the 1180 MPa class high-tensile cold-rolled steel sheet of the present invention performs water quenching from a temperature at which the austenite volume fraction in the steel sheet before water quenching is less than 70%, and the tensile strength of the steel sheet is 1180 MPa or more. The annealing temperature and tempering temperature are adjusted to be less than 1470 MPa. Thereby, the 1180 MPa class high-tensile cold-rolled steel sheet having a good shape with a warp amount of 10 mm or less can be stably produced.
水焼入れを行う連続焼鈍プロセスにおいて、下記表１に示す成分（単位は質量％）を有し、残部Ｆｅおよび不可避的不純物からなる鋼板Ａ，Ｂ，Ｃについて、熱間圧延および冷間圧延を施した後、連続焼鈍プロセスにおいて下記表２に示す温度条件で高張力冷延鋼板の製造を行った。製品サイズは、板厚１．２ｍｍ、板幅１１００ｍｍである。なお、表２には、得られた製品のマルテンサイト体積率（つまり、水焼入れ直前のオーステナイト体積率（％））、引張強さ（ＭＰａ）、反り量（ｍｍ）をあわせて示す。 In the continuous annealing process in which water quenching is performed, hot rolling and cold rolling are performed on the steel sheets A, B, and C having the components shown in Table 1 below (unit: mass%) and the balance Fe and inevitable impurities. Then, a high-tensile cold-rolled steel sheet was manufactured under the temperature conditions shown in Table 2 below in a continuous annealing process. The product size is a plate thickness of 1.2 mm and a plate width of 1100 mm. Table 2 also shows the martensite volume fraction (that is, austenite volume fraction (%) immediately before water quenching), tensile strength (MPa), and warpage (mm) of the obtained product.
表２に示すように、鋼成分が本発明の好ましい範囲を外れる成分Ａの鋼を用いたＮｏ．１〜４の場合、焼鈍プロセスにおける温度条件を種々変更しても、マルテンサイト体積率を７０％未満とし、且つ引張強度１１８０ＭＰａ級の冷延鋼板は得られていない。 As shown in Table 2, No. 1 using a steel of component A whose steel component deviates from the preferred range of the present invention. In the case of 1-4, even if the temperature conditions in the annealing process are variously changed, a cold-rolled steel sheet having a martensite volume fraction of less than 70% and a tensile strength of 1180 MPa class has not been obtained.
成分Ｂおよび成分Ｃの鋼を用いた場合、マルテンサイト体積率が７０％未満且つ鋼板の引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満となるように連続焼鈍プロセスにおける温度条件を適切に調節したＮｏ．９〜１２においては、反り量が１０ｍｍ以下となった。一方、Ｎｏ．５，６は所望の引張強さが得られず、また、Ｎｏ．７，８はマルテンサイト体積率が７０％以上であり、反り量が２５ｍｍ以上となった。 When steels of component B and component C were used, the temperature conditions in the continuous annealing process were appropriately adjusted so that the martensite volume fraction was less than 70% and the tensile strength of the steel sheet was 1180 MPa or more and less than 1470 MPa. In 9-12, the curvature amount became 10 mm or less. On the other hand, no. Nos. 5 and 6 do not provide the desired tensile strength. Nos. 7 and 8 had a martensite volume ratio of 70% or more and a warpage amount of 25 mm or more.
Claims (3)
水焼入れ前の鋼板中のオーステナイト体積率が７０％未満となる温度から水焼入れを行うとともに、鋼板の引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満となるように焼鈍温度および焼戻温度を調節することを特徴とする高張力冷延鋼板の製造方法。 A method for producing a high-tensile cold-rolled steel sheet with a tensile strength of 1180 MPa, which is annealed by a continuous annealing process, water-quenched, and subjected to an overaging treatment on a steel sheet after cold rolling,
Water quenching is performed from the temperature at which the austenite volume fraction in the steel sheet before water quenching is less than 70%, and the annealing temperature and tempering temperature are adjusted so that the tensile strength of the steel sheet is 1180 MPa or more and less than 1470 MPa. A method for producing a high-tensile cold-rolled steel sheet.
水焼入れ前の鋼板中のオーステナイト体積率が７０％未満となる温度から水焼入れを行うとともに、鋼板の引張強さが１１８０ＭＰａ以上１４７０ＭＰａ未満となるように焼鈍温度および焼戻温度を調節することを特徴とする高張力冷延鋼板の製造方法。 In mass%, C: 0.05 to 0.2%, Si: 2.5% or less, Mn: 3.0% or less, P: 0.3% or less, S: 0.03% or less, Sol. Al: 0.1% or less, further Nb: 0.1% or less, Ti: 0.2% or less, B: 0.01% or less, Sb: 0.1% or less, V: A steel containing one or more of 0.1% or less, Cr: 0.3% or less, Mo: 0.3% or less, Ni: 0.3% or less, the balance being Fe and inevitable impurities A method for producing a high-strength cold-rolled steel sheet having a tensile strength of 1180 MPa, which is hot-rolled, pickled, cold-rolled, subsequently annealed by a continuous annealing process, water-quenched, and over-aged. ,
Water quenching is performed from the temperature at which the austenite volume fraction in the steel sheet before water quenching is less than 70%, and the annealing temperature and tempering temperature are adjusted so that the tensile strength of the steel sheet is 1180 MPa or more and less than 1470 MPa. A method for producing a high-tensile cold-rolled steel sheet.
Ｃｅｑ＝Ｃ＋Ｓｉ／２４＋Ｍｎ／６＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４ ・・・（１）
但し、上記（１）式中の元素記号は各元素の含有量（質量％）を表す。
The method for producing a high-tensile cold-rolled steel sheet according to claim 2, wherein the steel has a carbon equivalent Ceq represented by the following formula (1) of 0.48 or more.
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (1)
However, the element symbol in the above formula (1) represents the content (% by mass) of each element.
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