JP3520119B2 - High-strength hot-rolled thin steel sheet excellent in workability, fatigue properties and low-temperature toughness, and method for producing the same - Google Patents
High-strength hot-rolled thin steel sheet excellent in workability, fatigue properties and low-temperature toughness, and method for producing the sameInfo
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- JP3520119B2 JP3520119B2 JP23994594A JP23994594A JP3520119B2 JP 3520119 B2 JP3520119 B2 JP 3520119B2 JP 23994594 A JP23994594 A JP 23994594A JP 23994594 A JP23994594 A JP 23994594A JP 3520119 B2 JP3520119 B2 JP 3520119B2
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- weight
- ferrite
- strength
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- thin steel
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Description
【０００１】[0001]
【産業上の利用分野】本発明は自動車、産業用機械等に
使用することを企図した加工性、疲労特性及び低温靭性
に優れた高強度熱延薄鋼板及びその製造方法に関するも
のである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength hot-rolled steel sheet excellent in workability, fatigue characteristics and low temperature toughness intended for use in automobiles, industrial machines and the like, and a method for producing the same.
【０００２】[0002]
【従来の技術】自動車用薄鋼板の軽量化と衝突時の安全
確保を主な背景として高強度薄鋼板の需要が増大してお
り、ＴＳ５９０MPa 級鋼が広く使用されるに到ってい
る。さらに昨今では、ＴＳ＞５９０MPa の要求が強まっ
ており、また、要求特性は単にＴＳのみならず、加工性
（高ＴＳ×Ｔ．Ｅｌ、低ＹＲ、高ｄ／ｄ0 ）、溶接性等
々多岐にわたっている。特に高強度熱延薄鋼板の場合、
用途として使用状況が苛酷であるロード・ホイール等の
足廻り部材に用いられることが多いため、加工性、溶接
性のみならず、十分な疲労特性及び低温靭性を有するこ
とが要求される。しかるに従来の薄鋼板ではＴＳ＞５９
０MPa という高強度特性と加工性（高ＴＳ×Ｔ．Ｅｌ、
低ＹＲ、高ｄ／ｄ0 ）、疲労特性（高疲労限度比）及び
低温靭性を両立させたものがないのが実状である。2. Description of the Related Art The demand for high-strength thin steel sheets is increasing mainly due to the weight reduction of thin steel sheets for automobiles and ensuring safety in the event of a collision, and TS590 MPa class steel has come into wide use. Furthermore, in recent years, the demand for TS> 590 MPa is increasing, and the required properties are not only TS, but also workability (high TS × T.El, low YR, high d / d 0 ), weldability, etc. There is. Especially in the case of high strength hot rolled thin steel sheet,
Since it is often used as an underbody member such as a road wheel, which is used severely as an application, it is required to have sufficient fatigue characteristics and low temperature toughness as well as workability and weldability. However, TS> 59 for conventional thin steel sheets.
High strength property of 0 MPa and workability (high TS × T.El,
The reality is that there is no one that combines low YR, high d / d 0 ), fatigue characteristics (high fatigue limit ratio) and low temperature toughness.
【０００３】[0003]
【発明が解決しようとする課題】本発明は上記した従来
技術が持つ問題点を解消し、高強度特性（ＴＳ＞５９０
MPa)と優れた加工性（降伏比（ＹＲ）≦７０％、強度−
延性バランス（引張強さ×全伸び）≧１８０００(MPa・
％）、穴拡げ比（ｄ／ｄ0 ）≧１．２）、優れた疲労特
性（疲労限度比≧０．４０）及び優れた低温靭性（破面
遷移温度≦−４０℃）を合わせ持つ高強度熱延薄鋼板と
その製造方法を提供することを課題としている。DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and has high strength characteristics (TS> 590).
MPa) and excellent workability (yield ratio (YR) ≤ 70%, strength-
Ductility balance (tensile strength x total elongation) ≧ 18000 (MPa ・
%), Hole expansion ratio (d / d 0 ) ≧ 1.2), excellent fatigue properties (fatigue limit ratio ≧ 0.40) and excellent low temperature toughness (fracture transition temperature ≦ −40 ° C.). It is an object to provide a high-strength hot-rolled thin steel sheet and a manufacturing method thereof.
【０００４】[0004]
【課題を解決するための手段】本発明は上記した課題を
達成するため、以下に示す構成を手段とする。
（１）化学成分として、Ｃ＝０．０４〜０．１５重量
％、Ｓｉ＝１．０〜５重量％、Ｍｎ＝１．０〜３重量
％、Ｎｂ＝０．００５〜０．０５０重量％、Ａｌ＝０．
００５〜０．１０重量％、Ｓ≦０．０１重量％、残部Ｆ
ｅ及び不可避的不純物からなり、ミクロ組織として主に
フェライト、マルテンサイトで構成され、フェライト占
積率（ＶF ）＞５０％、前記２相以外の組織は５％未満
であり、かつフェライト平均粒径（ｄF ）≦５μｍかつ
マルテンサイト平均粒径（ｄM ）≦５μｍであり、特性
として引張強さ（ＴＳ）＞５９０MPa 、降伏比（ＹＲ）
≦７０％、強度−延性バランス（引張強さ×全伸び）≧
１８０００(MPa・％）、穴拡げ比（ｄ／ｄ0 ）≧１．
２、疲労限度比≧０．４０、破面遷移温度≦−４０℃を
具備することを特徴とする加工性、疲労特性及び低温靭
性に優れた高強度熱延薄鋼板。In order to achieve the above-mentioned object, the present invention has the following constitution. (1) As chemical components, C = 0.04 to 0.15 wt%, Si = 1.0 to 5 wt%, Mn = 1.0 to 3 wt%, Nb = 0.005 to 0.050 wt% , Al = 0.
005 to 0.10% by weight, S ≦ 0.01% by weight, balance F
e and unavoidable impurities , mainly composed of ferrite and martensite as a microstructure, ferrite space factor (V F )> 50% , and the structure other than the above two phases is less than 5%
And the average ferrite grain size (d F ) ≦ 5 μm and the average martensite grain size (d M ) ≦ 5 μm. Tensile strength (TS)> 590 MPa and yield ratio (YR) as characteristics.
≦ 70%, strength-ductility balance (tensile strength × total elongation) ≧
18000 (MPa ·%), hole expansion ratio (d / d 0 ) ≧ 1.
2. A high-strength hot-rolled thin steel sheet having excellent workability, fatigue characteristics, and low-temperature toughness, characterized by having a fatigue limit ratio ≧ 0.40 and a fracture surface transition temperature ≦ −40 ° C.
【０００５】（２）さらに、Ｃａ＝０．０００５〜０．
０１重量％またはＲＥＭ＝０．００５〜０．０５重量％
を含有することを特徴とする（１）に記載の加工性、疲
労特性及び低温靭性に優れた高強度熱延薄鋼板。
（３）さらに、Ｃｒ＝０．０１〜１重量％を含有するこ
とを特徴とする（１）または（２）に記載の加工性、疲
労特性及び低温靭性に優れた高強度熱延薄鋼板。(2) Further, Ca = 0.005 to 0.
01 wt% or REM = 0.005-0.05 wt%
A high-strength hot-rolled thin steel sheet having excellent workability, fatigue characteristics, and low-temperature toughness as described in (1), which comprises: (3) The high-strength hot-rolled thin steel sheet excellent in workability, fatigue characteristics, and low-temperature toughness according to (1) or (2) , further containing Cr = 0.01 to 1 % by weight.
【０００６】（４）化学成分として、Ｃ＝０．０４〜
０．１５重量％、Ｓｉ＝１．０〜５重量％、Ｍｎ＝１．
０〜３重量％、Ｎｂ＝０．００５〜０．０５０重量％、
Ａｌ＝０．００５〜０．１０重量％、Ｓ≦０．０１重量
％、残部Ｆｅ及び不可避的不純物からなる鋼を鋳造して
得た鋼片を用いて、８００℃以上で仕上げ圧延を完了し
た後、ホットランテーブルにて２５℃／秒未満の冷却速
度で３秒以上緩冷却し、５５０℃以上で該緩冷却を完了
した後、２５℃／秒以上の冷却速度で急冷却し、巻取を
３５０℃未満で実施することを特徴とするミクロ組織と
して主にフェライト、マルテンサイトで構成され、フェ
ライト占積率（ＶF ）＞５０％かつフェライト平均粒径
（ｄF ）≦５μｍかつマルテンサイト平均粒径（ｄM ）
≦５μｍであり、特性として引張強さ（ＴＳ）＞５９０
MPa 、降伏比（ＹＲ）≦７０％、強度−延性バランス
（引張強さ×全伸び）≧１８０００(MPa・％）、穴拡げ
比（ｄ／ｄ0 ）≧１．２、疲労限度比≧０．４０、破面
遷移温度≦−４０℃を具備する加工性、疲労特性及び低
温靭性に優れた高強度熱延薄鋼板の製造方法。(4) As a chemical component, C = 0.04-
0.15% by weight, Si = 1.0 to 5 % by weight, Mn = 1.
0 to 3 % by weight, Nb = 0.005 to 0.050 % by weight,
Finish rolling was completed at 800 ° C. or higher using a steel piece obtained by casting a steel consisting of Al = 0.005 to 0.10% by weight, S ≦ 0.01% by weight, the balance Fe and inevitable impurities . After that, gentle cooling was performed on the hot run table at a cooling rate of less than 25 ° C./sec for 3 seconds or more, and after completion of the gentle cooling at 550 ° C. or more, rapid cooling was performed at a cooling rate of 25 ° C./sec or more, and winding was performed. The microstructure characterized by being performed at less than 350 ° C. is mainly composed of ferrite and martensite, and has a ferrite space factor (V F )> 50% and a ferrite average grain size (d F ) ≦ 5 μm and a martensite average. Particle size (d M )
≦ 5 μm, and the characteristic is tensile strength (TS)> 590
MPa, yield ratio (YR) ≤ 70%, strength-ductility balance (tensile strength x total elongation) ≥ 18000 (MPa ·%), hole expansion ratio (d / d 0 ) ≥ 1.2, fatigue limit ratio ≥ 0 40, a fracture surface transition temperature ≤ -40 ° C, and a method for producing a high-strength hot-rolled thin steel sheet excellent in workability, fatigue characteristics, and low-temperature toughness.
【０００７】（５）化学成分として、Ｃ＝０．０４〜
０．１５重量％、Ｓｉ＝１．０〜５重量％、Ｍｎ＝１．
０〜３重量％、Ｎｂ＝０．００５〜０．０５０重量％、
Ａｌ＝０．００５〜０．１０重量％、Ｓ≦０．０１重量
％、残部Ｆｅ及び不可避的不純物からなる鋼を鋳造して
得た鋼片を用いて、８００℃以上で仕上げ圧延を完了し
た後、ホットランテーブルにて２５℃／秒以上の冷却速
度で８００℃〜５５０℃に急冷却し、該温度範囲内にて
２５℃／秒未満の冷却速度で３秒以上緩冷却し、５５０
℃以上で該緩冷却を完了した後、再び２５℃／秒以上の
冷却速度で急冷却し、巻取を３５０℃未満で実施するこ
とを特徴とするミクロ組織として主にフェライト、マル
テンサイトで構成され、フェライト占積率（ＶF ）＞５
０％かつフェライト平均粒径（ｄF ）≦５μｍかつマル
テンサイト平均粒径（ｄM ）≦５μｍであり、特性とし
て引張強さ（ＴＳ）＞５９０MPa 、降伏比（ＹＲ）≦７
０％、強度−延性バランス（引張強さ×全伸び）≧１８
０００(MPa・％）、穴拡げ比（ｄ／ｄ0 ）≧１．２、疲
労限度比≧０．４０、破面遷移温度≦−４０℃を具備す
る加工性、疲労特性及び低温靭性に優れた高強度熱延薄
鋼板の製造方法。(5) As a chemical component, C = 0.04-
0.15% by weight, Si = 1.0 to 5 % by weight, Mn = 1.
0 to 3 % by weight, Nb = 0.005 to 0.050 % by weight,
Finish rolling was completed at 800 ° C. or higher using a billet obtained by casting a steel consisting of Al = 0.005 to 0.10% by weight, S ≦ 0.01% by weight , the balance Fe and unavoidable impurities . After that, it is rapidly cooled to 800 ° C. to 550 ° C. at a cooling rate of 25 ° C./sec or more in a hot run table, and slowly cooled to 3 seconds or more at a cooling rate of less than 25 ° C./sec within the temperature range of 550.
After the slow cooling is completed at ℃ or more, it is rapidly cooled again at a cooling rate of 25 ℃ / s or more, and the winding is performed at less than 350 ℃, mainly composed of ferrite and martensite. And the ferrite space factor (V F )> 5
0% and ferrite average particle size (d F ) ≦ 5 μm and martensite average particle size (d M ) ≦ 5 μm, and tensile strength (TS)> 590 MPa and yield ratio (YR) ≦ 7 as characteristics.
0%, strength-ductility balance (tensile strength x total elongation) ≧ 18
000 (MPa ·%), hole expansion ratio (d / d 0 ) ≧ 1.2, fatigue limit ratio ≧ 0.40, fracture transition temperature ≦ −40 ° C. Excellent workability, fatigue characteristics and low temperature toughness Method for producing high strength hot rolled thin steel sheet.
【０００８】（６）さらに、Ｃａ＝０．０００５〜０．
０１重量％またはＲＥＭ＝０．００５〜０．０５重量％
を含有することを特徴とする（４）または（５）に記載
の加工性、疲労特性及び低温靭性に優れた高強度熱延薄
鋼板の製造方法。
（７）さらに、Ｃｒ＝０．０１〜１重量％を含有するこ
とを特徴とする（４）乃至（６）のいずれかに記載の加
工性、疲労特性及び低温靭性に優れた高強度熱延薄鋼板
の製造方法。(6) Further, Ca = 0.005 to 0.
01 wt% or REM = 0.005-0.05 wt%
The method for producing a high-strength hot-rolled thin steel sheet having excellent workability, fatigue characteristics, and low-temperature toughness according to (4) or (5) , characterized by containing. (7) High strength hot rolling excellent in workability, fatigue characteristics and low temperature toughness according to any one of (4) to (6), further containing Cr = 0.01 to 1 % by weight. Manufacturing method of thin steel sheet.
【０００９】[0009]
【作用】以下、本発明について詳細に説明する。まず、
化学成分の特徴及び制限理由を説明する。Ｃはマルテン
サイトの確保のために、０．０４重量％（以下重量％を
％と略）以上添加するが、溶接部の脆化を防止して、最
良なスポット溶接性を得、さらにｄ／ｄ0 ≧１．２以上
の優れた穴拡げ性を得るために、その添加上限を０．１
５％以下とする。Ｓｉ，Ｍｎは強化元素である。また、
Ｓｉはフェライトの生成を促進し、炭化物の生成を抑制
することにより、マルテンサイトを確保する作用があ
り、Ｍｎは焼き入れ性を向上してマルテンサイトを確保
する作用がある。その作用を十分に発揮させるために
は、Ｓｉ，Ｍｎの各々の単独の添加下限量は１．０％以
上である。The present invention will be described in detail below. First,
The characteristics of the chemical components and the reasons for limitation are explained. C is added in an amount of 0.04 wt% or more (hereinafter, wt% is abbreviated as%) in order to secure martensite, but prevents embrittlement of the welded portion to obtain the best spot weldability, and further d / In order to obtain excellent hole expandability of d 0 ≧ 1.2 or more, the upper limit of addition is 0.1.
5% or less. Si and Mn are strengthening elements. Also,
Si has the effect of securing the martensite by promoting the formation of ferrite and suppressing the formation of carbides, and Mn has the action of improving the hardenability and securing martensite. In order to bring out the effect sufficiently, the lower limit of addition of each of Si and Mn is 1.0% or more.
【００１０】特にＳｉは加工性を劣化させずに高強度と
高疲労特性を得るために有効であり、１．５％以上の添
加が好ましい。一方、Ｓｉ，Ｍｎの添加上限量は、熱間
圧延性の劣化等の製造上の観点からＳｉ≦５％、フェラ
イト占積率確保の観点からＭｎ≦３％が好ましい。Particularly, Si is effective for obtaining high strength and high fatigue characteristics without deteriorating workability, and addition of 1.5% or more is preferable. On the other hand, the upper limit of addition of Si and Mn is preferably Si ≦ 5% from the viewpoint of manufacturing such as deterioration of hot rolling property, and Mn ≦ 3% from the viewpoint of securing the ferrite space factor.
【００１１】Ｎｂは本発明のポイントとなる元素であ
り、フェライト及びマルテンサイトの微細化に寄与し、
優れた低温靭性を発揮させるとともに、疲労特性向上に
も寄与する。その作用を十分に発揮させるためには添加
下限量は０．００５％以上である。その効果の飽和か
ら、添加上限量は０．０５０％が好ましい。Ｓは硫化物
系介在物により、穴拡げ性が劣化するのを防ぐため、そ
の上限量を０．０１％、好ましくは０．００２％以下と
する。Ａｌは脱酸とＡｌＮによるオーステナイトの細粒
化を経たフェライト占積率の増加、フェライトの細粒
化、マルテンサイトの確保、細粒化を目的に０．００５
％以上添加する。脱酸効果の飽和から０．１０％を添加
上限とするが、フェライト占積率の増加、フェライトの
細粒化、マルテンサイトの確保、細粒化の観点から３％
まで添加してもよい。Nb is an element which is a key point of the present invention, and contributes to miniaturization of ferrite and martensite,
It exerts excellent low temperature toughness and contributes to the improvement of fatigue characteristics. The lower limit of addition is 0.005% or more in order to sufficiently exhibit the action. From the viewpoint of saturation of the effect, the upper limit of addition is preferably 0.050%. The upper limit of S is 0.01%, preferably 0.002% or less, in order to prevent the hole expandability from being deteriorated by sulfide inclusions. Al is 0.005 for the purpose of increasing the space factor of ferrite through deoxidation and austenite grain refinement by AlN, grain refinement of ferrite, securing martensite, and grain refinement.
% Or more. From the viewpoint of saturation of deoxidation effect, the upper limit of addition is 0.10%, but 3% from the viewpoint of increasing ferrite space factor, ferrite grain refinement, securing martensite, and grain refinement.
May be added up to.
【００１２】Ｃａは硫化物系介在物の形状制御（球状
化）により、穴拡げ性をより向上させるために０．００
０５％以上添加するが、効果の飽和さらには介在物の増
加による逆効果（穴拡げ性の劣化）の点からその上限を
０．０１％、好ましくは０．００１０〜０．００５０％
とする。また、ＲＥＭも同様の理由からその添加量を
０．００５〜０．０５％とする。[0012] Ca is 0.00 to improve the hole expandability by controlling the shape (spherical shape) of sulfide inclusions.
Although it is added in an amount of not less than 05%, its upper limit is 0.01%, preferably 0.0010 to 0.0050%, from the viewpoint of saturation of the effect and adverse effect due to increase of inclusions (deterioration of hole expandability).
And Further, the addition amount of REM is set to 0.005 to 0.05% for the same reason.
【００１３】Ｃｒは強化元素であり、また、Ｓｉ，Ｍｎ
添加によるマルテンサイトを確保する作用をより高める
効果を有する。その効果を発揮させるためには添加下限
量は０．０１％以上である。フェライト占積率確保の観
点から添加上限量は１％以下が好ましい。また、同様の
観点からＭｎとの合計量は３％以下が好ましい。Cr is a strengthening element, and Si, Mn
It has the effect of further increasing the action of securing martensite by the addition. In order to exert the effect, the lower limit of addition is 0.01% or more. From the viewpoint of ensuring the ferrite space factor, the upper limit of addition is preferably 1% or less. From the same viewpoint, the total amount with Mn is preferably 3% or less.
【００１４】以上が本発明の主たる成分の添加理由であ
るが、強度確保、細粒化を目的に特性を劣化させない範
囲でＴｉ，Ｃｕ，Ｎｉ，Ｖ，Ｂ，Ｍｏを１種または２種
以上添加してもよい。また、ＰはＳｉやＡｌと同様の作
用を有するため添加してもよいが、２次加工性、靭性、
溶接性の観点から、好ましくは上限量を０．０２％とす
る。The above is the reason for adding the main components of the present invention. One or more of Ti, Cu, Ni, V, B and Mo are added within the range of not deteriorating the characteristics for the purpose of ensuring strength and fine graining. You may add. Further, P may be added because it has the same effect as Si and Al, but secondary workability, toughness,
From the viewpoint of weldability, the upper limit is preferably 0.02%.
【００１５】次に、ミクロ組織の特徴及び制限理由を以
下に説明する。
主にフェライト、マルテンサイトの２相で構成されて
おり、フェライト占積率（ＶF ）が５０％超であり、そ
の他組織（ベイナイト、パーライト、残留オーステナイ
トの１種または２種以上）は５％未満であること。フ
ェライト平均粒径（ｄF ）≦５μｍかつマルテンサイト
平均粒径（ｄM ）≦５μｍであること。かつを満た
すことができない場合、材質特性の劣化を生ずる。すな
わち、引張強さ（ＴＳ）＞５９０MPa かつ降伏比（Ｙ
Ｒ）≦７０％かつ強度−延性バランス（引張強さ×全伸
び）≧１８０００(MPa・％）かつ穴拡げ比（ｄ／ｄ0 ）
≧１．２、疲労限度比≧０．４０かつ破面遷移温度≦−
４０℃を満足することができない。なお、高強度特性、
高加工性、高疲労特性の両立という観点から、フェライ
トは硬質であることが好ましく、ビッカース硬度でフェ
ライト硬さ＞１５０、さらに好ましくはフェライト硬さ
＞２００が望まれる。Next, the features of the microstructure and the reasons for limitation will be described below. Primarily ferrite, is composed of two phases of martensite, ferrite space factor (V F) is 50 percent, and other tissues (bainite, pearlite, one or more residual austenite) 5% Be less than. Ferrite average particle size (d F ) ≦ 5 μm and martensite average particle size (d M ) ≦ 5 μm. If the above condition cannot be satisfied, deterioration of material characteristics occurs. That is, tensile strength (TS)> 590 MPa and yield ratio (Y
R) ≦ 70% and strength-ductility balance (tensile strength × total elongation) ≧ 18000 (MPa ·%) and hole expansion ratio (d / d 0 ).
≥1.2, fatigue limit ratio ≥0.40 and fracture surface transition temperature ≤-
40 ° C cannot be satisfied. In addition, high strength characteristics,
From the viewpoint of achieving both high workability and high fatigue properties, ferrite is preferably hard, and ferrite hardness of Vickers hardness> 150, more preferably ferrite hardness> 200 is desired.
【００１６】さらに、前記したミクロ組織を如何に達成
するかという観点から圧延規制、冷却規制、巻取規制等
の値とその制限理由を説明する。仕上げ圧延終了温度
（ＦＴ７）の下限は加工組織（加工フェライト）・層状
組織の出現による特性の劣化を防ぐため、８００℃、好
ましくは８５０℃とする。なお、組織微細化の観点から
９５０℃を上限とすることが望ましい。次にホットラン
テーブルでの冷却及び巻取について述べる。冷却は図１
に示す２つのパターン（パターンＡ及びパターンＢ）に
よる。Further, from the viewpoint of how to achieve the above-mentioned microstructure, the values of rolling regulation, cooling regulation, winding regulation and the like and the reasons for the limitation will be explained. The lower limit of the finish rolling end temperature (FT7) is 800 ° C., preferably 850 ° C., in order to prevent deterioration of properties due to appearance of a worked structure (worked ferrite) / layered structure. From the viewpoint of micronization of the structure, it is desirable to set the upper limit to 950 ° C. Next, cooling and winding on the hot run table will be described. Figure 1 for cooling
2 patterns (pattern A and pattern B) shown in FIG.
【００１７】パターンＡにおいては、まず、図３に示す
如くフェライト占積率５０％以上の増加効果を得るた
め、２５℃／秒未満の冷却速度で３秒以上緩冷却し、７
５％以上のフェライト占積率を得るためには８秒以上の
緩冷却を行い、パーライトかつまたはベイナイトの生成
防止のため、該緩冷却を５５０℃以上で完了した後、２
５℃／秒以上の冷却速度で急冷却し、巻取はパーライト
かつまたはベイナイトかつまたは残留オーステナイトが
５％以上生成することを防止するため３５０℃未満とす
る。In the pattern A, as shown in FIG. 3, first, in order to obtain the effect of increasing the ferrite space factor of 50% or more, the cooling rate of less than 25 ° C./second is slowly cooled for 3 seconds or more.
To obtain a ferrite space factor of 5% or more, gentle cooling is performed for 8 seconds or more, and in order to prevent the formation of pearlite and / or bainite, the gentle cooling is completed at 550 ° C. or more, and then 2
The material is rapidly cooled at a cooling rate of 5 ° C./second or more, and the winding is performed at less than 350 ° C. in order to prevent generation of 5% or more of pearlite and / or bainite and / or retained austenite.
【００１８】パターンＢにおいては、まず、フェライト
の細粒化効果を高めるため２５℃／秒以上の冷却速度で
８００℃〜５５０℃に急冷却する。８００℃超ではフェ
ライトの細粒化効果が得られず、５５０℃未満ではパー
ライトかつまたはベイナイトが５％以上生成する。次
に、フェライト占積率の増加効果を得るため該温度範囲
内にて２５℃／秒未満の冷却速度で３秒以上（好ましく
は８秒以上）緩冷却する。In the pattern B, first, in order to enhance the effect of grain refining of ferrite, it is rapidly cooled to 800 ° C. to 550 ° C. at a cooling rate of 25 ° C./sec or more. If it exceeds 800 ° C, the grain refining effect of ferrite cannot be obtained, and if it is less than 550 ° C, 5% or more of pearlite and / or bainite is formed. Next, in order to obtain the effect of increasing the ferrite space factor, slow cooling is performed within the temperature range at a cooling rate of less than 25 ° C./sec for 3 seconds or more (preferably 8 seconds or more).
【００１９】さらに、パーライトかつまたはベイナイト
の生成防止のため、該緩冷却を５５０℃以上で完了した
後、２５℃／秒以上の冷却速度で急冷却し、巻取はパー
ライトかつまたはベイナイトかつまたは残留オーステナ
イトが５％以上生成することを防止するため３５０℃未
満とする。また、フェライト占積率の増加効果、フェラ
イト及びマルテンサイトの細粒化効果、さらにはホット
ランテーブル長の低減を狙って、圧延直後急冷を行って
もよい。Furthermore, in order to prevent the formation of pearlite and / or bainite, after the slow cooling is completed at 550 ° C. or higher, rapid cooling is performed at a cooling rate of 25 ° C./sec or more, and winding is perlite and / or bainite and / or residual. The temperature is lower than 350 ° C. in order to prevent generation of 5% or more of austenite. Further, rapid cooling may be performed immediately after rolling for the purpose of increasing the ferrite space factor, reducing the grain size of ferrite and martensite, and reducing the hot run table length.
【００２０】以上が本発明の製造方法の規制理由である
が、フェライト占積率の増加効果、フェライト及びマル
テンサイトの細粒化効果を高めるため、加熱温度上限
を１１５０℃とする、仕上げ圧延の開始温度（ＦＴ
０）を１０００℃以下とする、仕上げ圧延の全圧下率
を７５％以上とする等の手段を単独ないしは複合で行っ
てもよい。なお、圧延に供する鋼片はいわゆる冷片再加
熱、ＨＣＲ，ＨＤＲのいずれであってもかまわない。ま
た、いわゆる薄肉連続鋳造による鋼片であってもかまわ
ない。また、本発明による熱延薄鋼板をめっき原板とし
てもよい。The reasons for restricting the production method of the present invention are as described above. In order to enhance the effect of increasing the ferrite space factor and the effect of refining ferrite and martensite, the upper limit of the heating temperature is set to 1150 ° C. for finish rolling. Start temperature (FT
0) may be 1000 ° C. or less, and the total reduction ratio of finish rolling may be 75% or more. The steel pieces to be rolled may be so-called cold piece reheating, HCR, or HDR. Further, it may be a steel piece produced by so-called thin wall continuous casting. Further, the hot-rolled thin steel sheet according to the present invention may be used as the original plating plate.
【００２１】[0021]
【実施例】供試鋼のＦｅ以外の化学成分を表１に示す。
また、本発明例及び比較例の熱延薄鋼板の製造条件を表
２に、材質特性値及びミクロ組織を表３に示す。また、
フェライト占積率と疲労限度比との関係を図２に、フェ
ライト占積率と緩冷却時間との関係を図３に示す。引張
試験はＪＩＳ−５にて、穴拡げ試験はクリアランス１０
％にて打ち抜いた２０φの穴をバリを外側にして３０度
円錐ポンチにて押し拡げて実施した。疲労特性は受入れ
ままの表面状態で完全両振りの平面曲げ疲労試験を行
い、疲労限度比＝２００万回疲労強度／引張強さを求め
た。[Examples] Table 1 shows the chemical composition of the sample steel other than Fe.
Table 2 shows manufacturing conditions of the hot-rolled thin steel sheets of the present invention and comparative examples, and Table 3 shows material characteristic values and microstructures. Also,
The relationship between the ferrite space factor and the fatigue limit ratio is shown in FIG. 2, and the relationship between the ferrite space factor and the slow cooling time is shown in FIG. Tensile test is JIS-5, hole expansion test is clearance 10
A hole of 20φ punched out with the burrs was pushed out with a 30 ° conical punch with the burr on the outside. Regarding the fatigue characteristics, a plane bending fatigue test of complete swinging was performed on the as-received surface state, and the fatigue limit ratio = 2 million times fatigue strength / tensile strength was determined.
【００２２】また、遷移温度ｖＴｒｓは１／４サブサイ
ズのシャルピー衝撃試験片を用いて、＋２０℃〜−６０
℃の範囲にて２０℃ピッチで実施して求めた破面率５０
％の遷移温度である。なお、フェライト占積率ＶF 、マ
ルテンサイト占積率ＶM 、フェライト平均粒径ｄF 及び
マルテンサイト平均粒径ｄM は１０００倍の光学顕微鏡
写真から求めた。フェライト硬さは１０ｇのマイクロビ
ッカース試験機により求めた。The transition temperature vTrs is + 20 ° C. to −60 using a Charpy impact test piece of ¼ subsize.
Fracture surface ratio 50 obtained by carrying out at 20 ° C pitch in the range of 0 ° C
% Transition temperature. The ferrite space factor V F , the martensite space factor V M , the ferrite average particle size d F, and the martensite average particle size d M were obtained from an optical microscope photograph of 1000 times. The ferrite hardness was obtained by a 10-g micro Vickers tester.
【００２３】[0023]
【表１】 [Table 1]
【００２４】[0024]
【表２】 [Table 2]
【００２５】[0025]
【表３】 [Table 3]
【００２６】本発明例であるNo．１〜No．３及びNo．５
〜No．１０はミクロ組織としてフェライトとマルテンサ
イトで構成され、フェライト平均粒径（ｄF ）≦５μｍ
かつマルテンサイト平均粒径（ｄM ）≦５μｍであり、
特性として引張強さ（ＴＳ）＞５９０MPa 、降伏比（Ｙ
Ｒ）≦７０％、強度−延性バランス（引張強さ×全伸
び）≧１８０００(MPa・％）、穴拡げ比（ｄ／ｄ0 ）≧
１．２、疲労限度比≧０．４０、破面遷移温度≦−４０
℃を具備しており、加工性、疲労特性及び低温靭性に優
れた高強度熱延薄鋼板が得られている。また異方性も小
さい。なお、フェライト硬さはＤ鋼が２５０、Ａ，Ｂ，
Ｃ，Ｅ鋼は２００〜２５０であった。比較例であるNo．
４はＮｂを含有していないためにフェライト平均粒径が
大きくなり、破面遷移温度が著しく劣化しており、低温
靭性が不良である。No. 1, which is an example of the present invention. 1-No. 3 and No. 5
~ No. 10 is composed of ferrite and martensite as a microstructure, and has an average ferrite particle size (d F ) ≦ 5 μm.
And the martensite average particle size (d M ) ≦ 5 μm,
Tensile strength (TS)> 590MPa, Yield ratio (Y
R) ≦ 70%, strength-ductility balance (tensile strength × total elongation) ≧ 18000 (MPa ·%), hole expansion ratio (d / d 0 ) ≧
1.2, fatigue limit ratio ≧ 0.40, fracture surface transition temperature ≦ −40
A high-strength hot-rolled thin steel sheet having a temperature of ℃ and excellent in workability, fatigue characteristics, and low-temperature toughness is obtained. The anisotropy is also small. The ferrite hardness is 250 for D steel, A, B,
The C and E steels were 200 to 250. No. which is a comparative example.
Since No. 4 does not contain Nb, the average ferrite grain size is large, the fracture surface transition temperature is significantly deteriorated, and the low temperature toughness is poor.
【００２７】なお、特に重要な特性である疲労限度比
は、図２に示すようにフェライト占積率＞５０％で０．
４０以上、フェライト占積率＞７５％で０．４５以上と
いう優れた特性を示す。その制御については、図３に示
すように緩冷時間の制御が重要である。The fatigue limit ratio, which is a particularly important characteristic, as shown in FIG.
It exhibits excellent characteristics of 0.45 or more at 40 or more and a ferrite space factor> 75%. Regarding the control, it is important to control the slow cooling time as shown in FIG.
【００２８】[0028]
【発明の効果】本発明により従来にない複合特性を合わ
せ持つ熱延高強度薄鋼板、すなわち高強度特性（ＴＳ＞
５９０MPa)と、優れた加工性（降伏比（ＹＲ）≦７０
％、強度−延性バランス（引張強さ×全伸び）≧１８０
００(MPa・％）、穴拡げ比（ｄ／ｄ0 ≧１．２）、優れ
た疲労特性（疲労限度比≧０．４０）及び優れた低温靭
性（破面遷移温度≦−４０℃）を合わせ持つ高強度熱延
薄鋼板とその製造方法を低コストかつ安定的に提供する
ことが可能となったため、使用用途・使用条件が格段に
広がり、工業上、経済上の効果は非常に大きい。EFFECTS OF THE INVENTION According to the present invention, a hot-rolled high-strength steel sheet having unprecedented composite characteristics, that is, high strength characteristics (TS>
590 MPa) and excellent workability (yield ratio (YR) ≦ 70
%, Strength-ductility balance (tensile strength x total elongation) ≧ 180
00 (MPa ·%), hole expansion ratio (d / d 0 ≧ 1.2), excellent fatigue properties (fatigue limit ratio ≧ 0.40) and excellent low temperature toughness (fracture transition temperature ≦ -40 ° C) Since it has become possible to provide a high-strength hot-rolled thin steel sheet and a method for producing the same that can be combined at a low cost and in a stable manner, the applications and conditions of use are dramatically expanded, and the industrial and economic effects are extremely large.
【図１】ａ，ｂは冷却テーブルでの冷却方法を示す図表
である。1A and 1B are tables showing a cooling method on a cooling table.
【図２】フェライト占積率と疲労限度比の関係を示す図
表である。FIG. 2 is a table showing a relationship between a ferrite space factor and a fatigue limit ratio.
【図３】フェライト占積率と緩冷時間の関係を示す図表
である。FIG. 3 is a chart showing a relationship between a ferrite space factor and a slow cooling time.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭57−104650（ＪＰ，Ａ) 特開 昭60−145355（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 - 38/60 C21D 8/00 - 8/04 C21D 9/46 - 9/48 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-104650 (JP, A) JP-A-60-145355 (JP, A) (58) Fields investigated (Int.Cl. 7 , DB name) C22C 38/00-38/60 C21D 8/00-8/04 C21D 9/46-9/48
Claims (7)
成され、フェライト占積率（ＶF ）＞５０％、前記２相
以外の組織は５％未満であり、かつフェライト平均粒径
（ｄF ）≦５μｍかつマルテンサイト平均粒径（ｄM ）
≦５μｍであり、特性として引張強さ（ＴＳ）＞５９０
MPa 、降伏比（ＹＲ）≦７０％、強度−延性バランス
（引張強さ×全伸び）≧１８０００(MPa・％）、穴拡げ
比（ｄ／ｄ0 ）≧１．２、疲労限度比≧０．４０、破面
遷移温度≦−４０℃を具備することを特徴とする加工
性、疲労特性及び低温靭性に優れた高強度熱延薄鋼板。1. C = 0.04 to 0.15% by weight, Si = 1.0 to 5 % by weight, Mn = 1.0 to 3 % by weight, Nb = 0.005 to 0.050 % by weight, Al = 0.005 to 0.10 wt%, S ≦ 0.01 wt%, and the balance Fe and unavoidable impurities, primarily ferrite, is composed of martensite as microstructure, ferrite space factor (V F)> 50% , the two phases
Other than 5%, the average grain size of ferrite (d F ) ≦ 5 μm, and the average grain size of martensite (d M ).
≦ 5 μm, and the characteristic is tensile strength (TS)> 590
MPa, yield ratio (YR) ≤ 70%, strength-ductility balance (tensile strength x total elongation) ≥ 18000 (MPa ·%), hole expansion ratio (d / d 0 ) ≥ 1.2, fatigue limit ratio ≥ 0 40, a fracture surface transition temperature ≤ -40 ° C, which is a high-strength hot-rolled thin steel sheet excellent in workability, fatigue characteristics, and low-temperature toughness.
重量％またはＲＥＭ＝０．００５〜０．０５重量％を含
有することを特徴とする請求項１に記載の加工性、疲労
特性及び低温靭性に優れた高強度熱延薄鋼板。2. Further, Ca = 0.005-0.01.
%, Or REM = 0.005-0.05% by weight, The high-strength hot-rolled thin steel sheet having excellent workability, fatigue characteristics, and low-temperature toughness according to claim 1.
有することを特徴とする請求項１または２に記載の加工
性、疲労特性及び低温靭性に優れた高強度熱延薄鋼板。3. A high-strength hot-rolled thin steel sheet having excellent workability, fatigue properties and low-temperature toughness according to claim 1 or 2 , further containing Cr = 0.01 to 1 % by weight.
鋼片を用いて、８００℃以上で仕上げ圧延を完了した
後、ホットランテーブルにて２５℃／秒未満の冷却速度
で３秒以上緩冷却し、５５０℃以上で該緩冷却を完了し
た後、２５℃／秒以上の冷却速度で急冷却し、巻取を３
５０℃未満で実施し、ミクロ組織として主にフェライ
ト、マルテンサイトで構成され、フェライト占積率（Ｖ
F ）＞５０％かつフェライト平均粒径（ｄF ）≦５μｍ
かつマルテンサイト平均粒径（ｄM ）≦５μｍであり、
特性として引張強さ（ＴＳ）＞５９０MPa 、降伏比（Ｙ
Ｒ）≦７０％、強度−延性バランス（引張強さ×全伸
び）≧１８０００(MPa・％）、穴拡げ比（ｄ／ｄ0 ）≧
１．２、疲労限度比≧０．４０、破面遷移温度≦−４０
℃を具備することを特徴とする加工性、疲労特性及び低
温靭性に優れた高強度熱延薄鋼板の製造方法。4. C = 0.04 to 0.15% by weight, Si = 1.0 to 5 % by weight, Mn = 1.0 to 3 % by weight, Nb = 0.005 to 0.050 % by weight, Al = 0.005 to 0.10% by weight, S ≤ 0.01% by weight, using a billet obtained by casting a steel consisting of balance Fe and unavoidable impurities , after finishing rolling at 800 ° C or higher. , Slow cooling at a cooling rate of less than 25 ° C./sec for 3 seconds or more on the hot run table, complete the gentle cooling at 550 ° C. or more, then rapidly cool at a cooling rate of 25 ° C./sec or more, and wind 3
Conducted at a temperature of less than 50 ° C, the microstructure is mainly composed of ferrite and martensite, and the ferrite space factor (V
F )> 50% and average ferrite grain size (d F ) ≦ 5 μm
And the martensite average particle size (d M ) ≦ 5 μm,
Tensile strength (TS)> 590MPa, Yield ratio (Y
R) ≦ 70%, strength-ductility balance (tensile strength × total elongation) ≧ 18000 (MPa ·%), hole expansion ratio (d / d 0 ) ≧
1.2, fatigue limit ratio ≧ 0.40, fracture surface transition temperature ≦ −40
A method for producing a high-strength hot-rolled thin steel sheet having excellent workability, fatigue characteristics, and low-temperature toughness, which is characterized by having a temperature of ℃.
後、ホットランテーブルにて２５℃／秒以上の冷却速度
で８００℃〜５５０℃に急冷却し、該温度範囲内にて２
５℃／秒未満の冷却速度で３秒以上緩冷却し、５５０℃
以上で該緩冷却を完了した後、再び２５℃／秒以上の冷
却速度で急冷却し、巻取を３５０℃未満で実施し、ミク
ロ組織として主にフェライト、マルテンサイトで構成さ
れ、フェライト占積率（ＶF ）＞５０％かつフェライト
平均粒径（ｄF ）≦５μｍかつマルテンサイト平均粒径
（ｄM ）≦５μｍであり、特性として引張強さ（ＴＳ）
＞５９０MPa 、降伏比（ＹＲ）≦７０％、強度−延性バ
ランス（引張強さ×全伸び）≧１８０００(MPa・％）、
穴拡げ比（ｄ／ｄ0 ）≧１．２、疲労限度比≧０．４
０、破面遷移温度≦−４０℃を具備することを特徴とす
る請求項４記載の加工性、疲労特性及び低温靭性に優れ
た高強度熱延薄鋼板の製造方法。5. After finishing rolling is completed at 800 ° C. or higher, it is rapidly cooled to 800 ° C. to 550 ° C. at a cooling rate of 25 ° C./sec or more on a hot run table, and 2 within the temperature range.
Slow cooling for 3 seconds or more at a cooling rate of less than 5 ° C / sec, 550 ° C
After the slow cooling is completed as described above, it is rapidly cooled again at a cooling rate of 25 ° C./sec or more, and winding is performed at less than 350 ° C. The microstructure is mainly composed of ferrite and martensite. Ratio (V F )> 50%, ferrite average grain size (d F ) ≦ 5 μm and martensite average grain size (d M ) ≦ 5 μm, and tensile strength (TS) is a characteristic.
> 590 MPa, Yield ratio (YR) ≤ 70%, Strength-ductility balance (tensile strength x total elongation) ≥ 18000 (MPa ·%),
Hole expansion ratio (d / d 0 ) ≧ 1.2, fatigue limit ratio ≧ 0.4
5. The method for producing a high-strength hot-rolled thin steel sheet having excellent workability, fatigue characteristics, and low-temperature toughness according to claim 4, wherein the fracture surface transition temperature is ≤ -40 ° C.
重量％またはＲＥＭ＝０．００５〜０．０５重量％を含
有することを特徴とする請求項４または５に記載の加工
性、疲労特性及び低温靭性に優れた高強度熱延薄鋼板の
製造方法。6. Further, Ca = 0.005 to 0.01
% Or REM = 0.005-0.05 wt% is contained, The manufacturing method of the high-strength hot-rolled thin steel sheet excellent in workability, fatigue characteristics, and low temperature toughness according to claim 4 or 5 , .
有することを特徴とする請求項４乃至６のいずれかに記
載の加工性、疲労特性及び低温靭性に優れた高強度熱延
薄鋼板の製造方法。7. A high-strength hot-rolled sheet having excellent workability, fatigue characteristics and low-temperature toughness according to any one of claims 4 to 6, which further contains Cr = 0.01 to 1 % by weight. Manufacturing method of thin steel sheet.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23994594A JP3520119B2 (en) | 1993-10-04 | 1994-10-04 | High-strength hot-rolled thin steel sheet excellent in workability, fatigue properties and low-temperature toughness, and method for producing the same |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5-248019 | 1993-10-04 | ||
| JP24801993 | 1993-10-04 | ||
| JP23994594A JP3520119B2 (en) | 1993-10-04 | 1994-10-04 | High-strength hot-rolled thin steel sheet excellent in workability, fatigue properties and low-temperature toughness, and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07150294A JPH07150294A (en) | 1995-06-13 |
| JP3520119B2 true JP3520119B2 (en) | 2004-04-19 |
Family
ID=26534507
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP23994594A Expired - Fee Related JP3520119B2 (en) | 1993-10-04 | 1994-10-04 | High-strength hot-rolled thin steel sheet excellent in workability, fatigue properties and low-temperature toughness, and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3520119B2 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BR9806204A (en) * | 1997-09-11 | 2000-02-15 | Kawasaki Heavy Ind Ltd | Hot-rolled steel sheet with fine grains with improved formability, production of hot-rolled or cold-rolled steel sheet. |
| JP4577999B2 (en) * | 2001-01-25 | 2010-11-10 | 新日本製鐵株式会社 | Low C-Mn ultrafine grain steel and method for producing the same |
| TWI467028B (en) | 2011-09-30 | 2015-01-01 | Nippon Steel & Sumitomo Metal Corp | High-strength hot-dip galvanized steel sheet with excellent impact resistance and its manufacturing method and high-strength alloyed hot-dip galvanized steel sheet and manufacturing method thereof |
| CN102534383B (en) * | 2012-03-01 | 2013-11-27 | 首钢总公司 | High-tenacity steel plate for oceengineering and manufacturing method thereof |
-
1994
- 1994-10-04 JP JP23994594A patent/JP3520119B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH07150294A (en) | 1995-06-13 |
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