JPH04276024A - Manufacture of high strength hot rolled steel sheet excellent in stretch-flanging property - Google Patents
Manufacture of high strength hot rolled steel sheet excellent in stretch-flanging propertyInfo
- Publication number
- JPH04276024A JPH04276024A JP5839291A JP5839291A JPH04276024A JP H04276024 A JPH04276024 A JP H04276024A JP 5839291 A JP5839291 A JP 5839291A JP 5839291 A JP5839291 A JP 5839291A JP H04276024 A JPH04276024 A JP H04276024A
- Authority
- JP
- Japan
- Prior art keywords
- strength
- temperature
- stretch flangeability
- ferrite
- rolled steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 60
- 239000010959 steel Substances 0.000 title claims abstract description 60
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 15
- 238000001816 cooling Methods 0.000 claims abstract description 36
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 34
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 21
- 238000005098 hot rolling Methods 0.000 claims abstract description 21
- 238000005096 rolling process Methods 0.000 claims abstract description 17
- 239000002131 composite material Substances 0.000 claims description 9
- 238000000034 method Methods 0.000 claims description 9
- 238000004804 winding Methods 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract 1
- 229910006639 Si—Mn Inorganic materials 0.000 abstract 1
- 229910052799 carbon Inorganic materials 0.000 abstract 1
- 239000000463 material Substances 0.000 description 17
- 230000000052 comparative effect Effects 0.000 description 14
- 238000005728 strengthening Methods 0.000 description 9
- 239000000203 mixture Substances 0.000 description 8
- 229910001562 pearlite Inorganic materials 0.000 description 8
- 230000000694 effects Effects 0.000 description 7
- 238000005516 engineering process Methods 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 5
- 229910000734 martensite Inorganic materials 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 241000219307 Atriplex rosea Species 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
【０００１】0001
【産業上の利用分野】本発明は、ロアアームなどの自動
車足廻り部品等に好適に使用される、成形性（とくに伸
びフランジ性）・溶接性・疲労特性に優れる高強度熱延
鋼板の製造方法に関する。[Industrial Application Field] The present invention is a method for producing high-strength hot-rolled steel sheets with excellent formability (especially stretch flangeability), weldability, and fatigue properties, which are suitably used for automobile suspension parts such as lower arms. Regarding.
【０００２】0002
【従来の技術】近年、地球環境保護の運動が高まる中で
自動車は排ガス対策や省エネルギーのための燃費低減が
これまで以上に強く求められている。そのための有力な
対策の一つとして車体の軽量化があり、又、車体の安全
性向上を図ることともあわせて、使用する鋼板を高強度
化・薄肉化する努力が続けられている。その中でも、ロ
アアームなどの自動車足廻り部品に使用される熱延鋼板
は、伸びフランジ成形を主体とする過酷な成形を受け、
且つ製品としては重要保安部品としての高い部品強度が
必要とされる。従って、優れたプレス成形性、とくに良
好な伸びフランジ性を有する高強度鋼板の要求が高まっ
ている。BACKGROUND OF THE INVENTION In recent years, with the growing movement to protect the global environment, there has been a stronger demand than ever for automobiles to take measures against exhaust gases and reduce fuel consumption in order to save energy. One of the effective measures to achieve this is to reduce the weight of the car body, and in addition to improving the safety of the car body, efforts are being made to make the steel plates used higher in strength and thinner. Among these, hot-rolled steel sheets used for automobile suspension parts such as lower arms undergo severe forming, mainly stretch flange forming.
Moreover, the product requires high component strength as an important safety component. Therefore, there is an increasing demand for high-strength steel sheets having excellent press formability, especially good stretch flangeability.
【０００３】これらの要求に対応するかのように従来も
自動車の安全性向上やオイルショックを契機とした省エ
ネルギーのための車体軽量化ニーズに応えるため、析出
強化・固溶強化・変態組織強化などさまざまの強化手段
を駆使して各種の自動車用高強度熱延鋼板が提案されて
いる。[0003] In response to these demands, precipitation strengthening, solid solution strengthening, transformed structure strengthening, etc. have been developed in order to meet the needs for lighter vehicle bodies to improve automobile safety and save energy in the wake of the oil crisis. Various high-strength hot-rolled steel sheets for automobiles have been proposed by making full use of various strengthening methods.
【０００４】■ そのうちプレス成形性、とりわけ伸
びフランジ性の優れた高強度熱延鋼板の製造法に関する
ものとしては、例えば、固溶強化を主体としてフェライ
ト・パーライト組織を基本とする技術（特公昭６４−１
０５６３）がある。[0004] Among these, methods for manufacturing high-strength hot-rolled steel sheets with excellent press formability, particularly stretch flangeability, include, for example, technology based on ferrite-pearlite structure mainly based on solid solution strengthening (Japanese Patent Publication No. 64 -1
0563).
【０００５】■ 又、パーライトよりも強化能が大き
い変態組織強化を利用する例として、ベイナイト単相組
織を基本とする技術（特公昭６３−３７１６６）がある
。[0005] Furthermore, as an example of utilizing transformation structure strengthening which has a stronger strengthening ability than pearlite, there is a technology based on a bainite single phase structure (Japanese Patent Publication No. 63-37166).
【０００６】■ 更に、フェライトとベイナイトから
なる複合組織鋼（特公昭６２−３７０８９、同じく特公
平１−４６５８３、同じく特公平２−４８６０８、以上
３件の製造法に係る特許、及び特公昭６１−９６０５７
の鋼板に関する特許）がある。[0006] Furthermore, composite structure steel consisting of ferrite and bainite (Japanese Patent Publication No. 62-37089, also Patent Publication No. 1-46583, also Patent Publication No. 2-48608, patents related to the above three manufacturing methods, and Patent Publication No. 1986-46589, Patent Publication No. 1-46583, Patent Publication No. 2-48608) 96057
There are patents related to steel plates.
【０００７】■ 一方、類似の特許として、フェライ
ト・ベイナイト・マルテンサイトの三相組織を基本とす
る技術（特公平１−４３００５、特開昭６０−１８１２
３２、以上２件の製造法に関する特許、及び特公平１−
３３５４３の鋼板に関する特許）もある。[0007] On the other hand, similar patents include technology based on a three-phase structure of ferrite, bainite, and martensite (Japanese Patent Publication No. 1-43005, Japanese Patent Application Laid-open No. 1812-1983)
32. Patents related to the above two manufacturing methods and Patent Publication No. 1-
There is also a patent related to steel plate No. 33543).
【０００８】[0008]
【発明が解決しようとする課題】自動車足廻りの部品な
どの用途に適用される高強度熱延鋼板としては、前述し
たように優れたプレス成形性、とくに優れた伸びフラン
ジ性を有することが必須で、且つ良好な強度・延性バラ
ンスを有することも必要である。又、同時に、強度レベ
ルについては降伏点設計された所定の部品機能を確実且
つ安定して確保するために、単なるＴＳの高強度のみで
なく降伏比についても適正な範囲に管理することが求め
られている。即ち、降伏比が低すぎると必要な部品強度
が実質的に確保できなくなり、逆に降伏比が高すぎると
成形時のスプリングバックが大きく所定の形状寸法が得
にくい問題が生ずる。[Problems to be Solved by the Invention] As mentioned above, it is essential for high-strength hot-rolled steel sheets to be used in applications such as automobile suspension parts to have excellent press formability, especially excellent stretch flangeability. It is also necessary to have a good strength/ductility balance. At the same time, regarding the strength level, in order to reliably and stably ensure the function of the specified parts designed for the yield point, it is necessary to manage not only the high strength of the TS but also the yield ratio within an appropriate range. ing. That is, if the yield ratio is too low, the required part strength cannot be substantially ensured, and conversely, if the yield ratio is too high, the problem arises that springback during molding is large and it is difficult to obtain a predetermined shape and size.
【０００９】以上の要求特性の観点から上記■〜■の技
術を再検討してみると、これらの高強度熱延鋼板製造技
術では、プレス成形性（伸びフランジ性、延性）及び降
伏比といった最も重要且つ基本的な特性に関して、最近
の非常に厳しい、且つ今後ますます高度になると予測さ
れる自動車業界をはじめとするユーザーの要求に応えら
れない問題があった。[0009] Re-examining the above-mentioned technologies ① to ② from the viewpoint of the above-mentioned required properties, these high-strength hot-rolled steel sheet manufacturing technologies have the most Regarding important and basic characteristics, there has been a problem in that they cannot meet the demands of users, including those in the automobile industry, which have recently become very strict and are expected to become even more sophisticated in the future.
【００１０】即ち、■の技術では、パーライトの強化能
が小さいため強度レベルの割に比較的多量のＣ量が必要
であり、得られる伸びフランジ性のレベルには限界があ
る（ＴＳ×λ＜４０００ｋｇｆ／ｍｍ２・％）。That is, in the technique (2), since the reinforcing ability of pearlite is small, a relatively large amount of C is required in relation to the strength level, and there is a limit to the level of stretch flangeability that can be obtained (TS×λ< 4000kgf/mm2・%).
【００１１】又、■の技術では、軟質・高延性なフェラ
イトを含まないため得られる延性レベルには限界があっ
た（ＴＳ×Ｅｌ＜１６００ｋｇｆ／ｍｍ２・％）。[0011] Furthermore, in the technique (2), since soft and highly ductile ferrite is not included, there is a limit to the level of ductility that can be obtained (TS×El<1600 kgf/mm2·%).
【００１２】更に、■の技術では、降伏強度（又は降伏
比）の下限を管理して適用部品の強度機能（静的に耐変
形強度や疲労強度特性）を確実に確保するという思想は
全く見られない。従ってこれらの従来技術では通常の場
合、降伏比は０．５〜０．６程度であり、補助的強化手
段としてＮｂ，Ｔｉ，Ｖ，Ｚｒなどの析出強化元素を添
加した場合には、降伏比を０．８程度まで高められるが
、この場合は強度・延性バランスの劣化が避けられない
。又、ベイナイトの体積率が高い場合にも高い降伏比が
得られる場合があるが、この場合には良好な成形性を安
定して維持することが難しいという問題があった。Furthermore, in the technique (2), there is no concept of controlling the lower limit of yield strength (or yield ratio) to ensure the strength function (static deformation resistance and fatigue strength characteristics) of the applied parts. I can't do it. Therefore, in these conventional techniques, the yield ratio is usually about 0.5 to 0.6, and when precipitation strengthening elements such as Nb, Ti, V, and Zr are added as an auxiliary strengthening means, the yield ratio increases. can be increased to about 0.8, but in this case, deterioration of the strength/ductility balance is unavoidable. A high yield ratio may also be obtained when the volume fraction of bainite is high, but in this case there is a problem in that it is difficult to stably maintain good formability.
【００１３】一方、■の技術は、微量のマルテンサイト
導入による低降伏比化を主たる目標の一つとして開発さ
れたもので、基本的な技術思想や手段が全く異なり、こ
の場合の対象材の降伏比はほとんどが０．６５未満であ
る。
一部の比較的に降伏比の高いケースでも降伏比は０．７
５未満である。On the other hand, the technology (2) was developed with one of the main goals being to lower the yield ratio by introducing a small amount of martensite, and the basic technical idea and means are completely different. Most yield ratios are less than 0.65. Even in some cases with a relatively high yield ratio, the yield ratio is 0.7
Less than 5.
【００１４】本発明は、以上ような観点から、従来技術
で達成されなかった総合特性バランスの優れた高強度熱
延鋼板を、低コストで、且つ安定して製造できるように
するもので、そのような高強度熱延鋼板としては、上述
のような目的・用途に対して最も好適な総合特性を具備
するものであって、具体的にはＴＳ ５０〜６０ｋｇｆ
／ｍｍ２、降伏比０．７５〜０．８５であって、且つ極
めて優れた強度・伸びフランジ性バランス、及び良好な
強度・延性バランスを有するほか、溶製性や疲労特性に
も優れていなければならない。ここで、伸びフランジ性
のレベルについては穴拡げ率（λ：％）で評価した場合
、ＴＳ×λの値で９０００ｋｇｆ／ｍｍ２・％以上を極
めて良好なレベルとするものであり、又、延性のレベル
についてはＴＳ×Ｅｌの値で１６００ｋｇｆ／ｍｍ２・
％以上のレベルを指す。[0014] From the viewpoints described above, the present invention enables the stable production of high-strength hot-rolled steel sheets with an excellent balance of overall properties, which has not been achieved with the prior art, at low cost. A high-strength hot-rolled steel sheet such as
/mm2, a yield ratio of 0.75 to 0.85, an extremely good balance of strength and stretch flangeability, and a good balance of strength and ductility, as well as excellent meltability and fatigue properties. It won't happen. Here, when evaluating the level of stretch flangeability using the hole expansion ratio (λ:%), a value of TS×λ of 9000 kgf/mm2・% or more is considered to be an extremely good level, and the ductility Regarding the level, the value of TS x El is 1600 kgf/mm2・
% or higher level.
【００１５】[0015]
【問題点を解決するための手段】本発明者等は、上述の
ような観点から、従来材・従来法にみられる問題点を解
決し、特に伸びフランジ性の見地から、従来材・従来法
を凌駕する性能を具備した熱延鋼板を低コストで、安定
して製造する方法を検討した結果、まず比較的低炭素を
ベースとするＣ−Ｓｉ−Ｍｎ鋼において平均粒径５μｍ
以下の如く極めて微細なフェライトとベイナイトの混合
組織とし、且つ適度なスキンパス圧延を付加することに
より、従来にない優れたプレス成形性、とりわけ伸びフ
ランジ性と強度とのバランスが達成できることがわかっ
た。[Means for Solving the Problems] From the above-mentioned viewpoints, the present inventors solved the problems seen in conventional materials and conventional methods, and in particular from the viewpoint of stretch flangeability, As a result of considering a method to stably produce hot-rolled steel sheets with performance exceeding
It has been found that by creating an extremely fine mixed structure of ferrite and bainite as shown below and adding appropriate skin pass rolling, it is possible to achieve unprecedented excellent press formability, especially a balance between stretch flangeability and strength.
【００１６】本発明は、上記知見に基づいてなされたも
のであり、その骨子は次の通りである。The present invention has been made based on the above findings, and its gist is as follows.
【００１７】即ち、重量％でＣ：０．０４〜０．０８％
、Ｓｉ：０．１０〜０．５０％、Ｍｎ：１．００〜１．
８０％、Ｓ：０．０００２〜０．００１０％、Ａｌ：０
．００５〜０．０５０％、Ｎ：０．００１０〜０．００
３０％を含み、残部Ｆｅ及び他の不可避的不純物より成
る成分組成の鋼を熱延により製造する。この熱延はＡｒ
３〜（Ａｒ３＋４０℃）を仕上温度とし、且つ仕上温度
〜（仕上温度＋５０℃）の間で７０〜９０％の圧下率に
より熱間圧延を行う。続いて冷却処理を行うが、熱間圧
延終了後直ちに１２０〜２００℃／Ｓの冷却速度で６２
０〜６８０℃の温度域に冷却すると共に、その後３〜７
秒保持し又は空冷し、次いで５０〜１５０℃／Ｓの冷却
速度で４００〜４５０℃の温度に冷却して巻取る。
更に伸長率１．５〜３．０％の範囲でスキンパスを行う
。これらの工程を経て、極めて微細なフェライト相とベ
イナイト相の複合組織からなる伸びフランジ性に優れた
高強度熱延鋼板が得られることになる。ここで得られる
熱延鋼板は、平均粒径が５μｍ以下のような微細なフェ
ライトと、ベイナイトからなる混合組織を呈し、強度が
５０〜６０ｋｇｆ／ｍｍ２級であり、強度−伸びフラン
ジ性バランス（ＴＳ×λ）が９０００ｋｇｆ／ｍｍ２・
％以上で、且つ強度−伸びバランス（ＴＳ×Ｅｌ）が１
６００ｋｇｆ／ｍｍ２・％以上を具備する伸びフランジ
性の優れたものである。ここではＴＳは引張強度、λは
穴拡げ率、Ｅｌは伸びを示す。That is, C: 0.04 to 0.08% by weight
, Si: 0.10-0.50%, Mn: 1.00-1.
80%, S: 0.0002-0.0010%, Al: 0
．． 005-0.050%, N: 0.0010-0.00
A steel having a composition containing 30% Fe and the balance consisting of Fe and other unavoidable impurities is produced by hot rolling. This hot rolling is made of Ar
3 to (Ar3 + 40°C) as the finishing temperature, and hot rolling is performed at a rolling reduction rate of 70 to 90% between the finishing temperature and (finishing temperature + 50°C). Subsequently, a cooling treatment is performed, and immediately after the hot rolling is completed, the cooling process is performed at a cooling rate of 62°C to 200°C/S.
Cool to a temperature range of 0 to 680°C, and then 3 to 7
It is held for seconds or air cooled, then cooled to a temperature of 400 to 450°C at a cooling rate of 50 to 150°C/S and wound up. Furthermore, a skin pass is performed at an elongation rate in the range of 1.5 to 3.0%. Through these steps, a high-strength hot-rolled steel sheet with excellent stretch flangeability consisting of a composite structure of extremely fine ferrite and bainite phases is obtained. The hot rolled steel sheet obtained here exhibits a mixed structure consisting of fine ferrite with an average grain size of 5 μm or less and bainite, has a strength of 50 to 60 kgf/mm2 class, and has a strength-stretch flangeability balance (TS ×λ) is 9000kgf/mm2・
% or more, and the strength-elongation balance (TS x El) is 1
It has excellent stretch flangeability with 600 kgf/mm2·% or more. Here, TS represents tensile strength, λ represents hole expansion rate, and El represents elongation.
【００１８】又、第２発明では上記構成に加えて、その
鋼組成中にＲＥＭ，Ｃａ，Ｍｇ等の選択的添加元素を含
むもので、上記第１発明の鋼成分組成を有する他、ＲＥ
Ｍ：０．００５〜０．１％、Ｃａ：０．０００５〜０．
０１％、Ｍｇ：０．０００５〜０．０１％のうち１種乃
至２種以上を含むものである。Further, in the second invention, in addition to the above structure, the steel composition contains selectively added elements such as REM, Ca, Mg, etc. In addition to having the steel composition of the first invention, RE
M: 0.005-0.1%, Ca: 0.0005-0.
01%, Mg: 0.0005 to 0.01%.
【００１９】これらの発明は、鋼成分・熱間圧延条件・
スキンパス伸長率の各製造因子を総て適正に制御しては
じめて達成されるものであり、以下、本発明について詳
細に説明する。[0019] These inventions are based on steel composition, hot rolling conditions,
This can only be achieved by properly controlling all of the manufacturing factors of the skin pass elongation rate, and the present invention will be described in detail below.
【００２０】（Ａ） 本発明の成分系
Ｃは、ベイナイトを生成させ目標とする強度を確保する
ために必須な元素である。本発明で対象とする５０〜６
０ｋｇｆ／ｍｍ２の強度を得るには、０．０４％が必要
であり、これを下限とする。一方、Ｃをいたずらに増加
させるとベイナイトを硬化させることにより、伸びフラ
ンジ性が劣化するため０．０８％を上限とする。(A) Component system C of the present invention is an essential element for producing bainite and securing the target strength. 50 to 6 targeted by the present invention
To obtain a strength of 0 kgf/mm2, 0.04% is required, and this is taken as the lower limit. On the other hand, if C is increased unnecessarily, the stretch flangeability deteriorates by hardening bainite, so the upper limit is set at 0.08%.
【００２１】Ｓｉは、フェライトの生成を促進し、本鋼
板のフェライトとベイナイトの複合組織化に不可欠で、
且つ強度上昇や延性を与えるのに好適な元素であり、０
．１０％以上の添加が必要である。しかし、その含有量
が高くなると鋼板表面に赤スケールが生成し、表面性状
が劣化するため、０．５０％をＳｉ量の上限と定めた。[0021]Si promotes the formation of ferrite and is essential for the composite structure of ferrite and bainite in this steel sheet.
It is also an element suitable for increasing strength and imparting ductility, and has 0
．． It is necessary to add 10% or more. However, if the Si content becomes high, red scale is generated on the surface of the steel sheet and the surface quality deteriorates, so 0.50% was set as the upper limit of the Si content.
【００２２】Ｍｎは、ベイナイト組織形成に不可欠の元
素であり、本発明の強度レベルを確保するためには、１
．００％以上の添加が必要であり、これを下限とした。
一方、Ｍｎ量が多すぎると溶接性と加工性が悪化するの
で、上限を１．８０％とした。Mn is an essential element for the formation of bainite structure, and in order to ensure the strength level of the present invention, 1.
．． It is necessary to add 00% or more, and this was set as the lower limit. On the other hand, if the amount of Mn is too large, weldability and workability deteriorate, so the upper limit was set at 1.80%.
【００２３】Ｓは、鋼中のＭｎと結合しＡ系介在物（Ｍ
ｎＳ系介在物）を生じ、伸びフランジ性を低下させる不
純物元素であるので、極力低減することが望ましい。本
発明者等は、引張強さ５０ｋｇｆ／ｍｍ２級の熱延鋼板
を用いてＳ量と穴拡げ率の関係を調べ、図１に示す結果
を得た。Ｓ量が０．００１０％以下になると穴拡げ率が
急激に上昇するため、これを上限とした。又、製鋼での
経済性を考慮して下限は０．０００２％とした。[0023] S combines with Mn in the steel and forms A-based inclusions (M
Since it is an impurity element that causes nS-based inclusions and reduces stretch flangeability, it is desirable to reduce it as much as possible. The present inventors investigated the relationship between the amount of S and the hole expansion ratio using a hot-rolled steel plate with a tensile strength of 50 kgf/mm2 class, and obtained the results shown in FIG. 1. When the amount of S becomes 0.0010% or less, the hole expansion rate increases rapidly, so this was set as the upper limit. Further, in consideration of economic efficiency in steel manufacturing, the lower limit was set to 0.0002%.
【００２４】Ａｌは、脱酸元素として不可欠であり、そ
の効果が期待でき、且つ連続鋳造が実施できる添加量と
しては０．００５％が限度であるので、０．００５％を
その下限とした。一方０．０５０％を超える範囲では脱
酸効果が飽和することになるので、０．０５０％をその
上限とした。[0024] Al is essential as a deoxidizing element, and the upper limit of the amount of addition that can be expected to be effective and that allows continuous casting to be performed is 0.005%, so 0.005% was set as the lower limit. On the other hand, if the content exceeds 0.050%, the deoxidizing effect will be saturated, so 0.050% was set as the upper limit.
【００２５】Ｎは、伸びフランジ性を劣化させる不純物
であり減ずる必要があるので、悪影響が顕著となる０．
００３０％を上限とした。一方、極低Ｎ化するためには
製鋼での余分のコストアップとなるため製鋼での経済性
から下限を０．００１０％とした。[0025] N is an impurity that deteriorates stretch flangeability and must be reduced.
The upper limit was set at 0.0030%. On the other hand, in order to achieve extremely low N content, the cost in steel manufacturing would increase, so the lower limit was set at 0.0010% from the economical point of view of steel manufacturing.
【００２６】ＲＥＭ，Ｃａ及びＭｇの各元素は、Ａ系介
在物（Ａｌ２Ｏ３系介在物）の形態制御（球状化）によ
り、伸びフランジ性を改善できる元素である。このため
第２発明ではその１種又は２種以上を添加することとし
ているが、添加量が多すぎると介在物量が増加し、却っ
て、伸びフランジ性が劣化するため、これらの上限をＲ
ＥＭ，Ｃａ，Ｍｇにつき夫々０．１％、０．０１％、０
．０１％とした。一方、下限は介在物形態制御効果が期
待できる添加量として夫々０．００５％、０．０００５
％、０．０００５％とした。The elements REM, Ca, and Mg are elements that can improve stretch flangeability by controlling the morphology (spheroidization) of A-based inclusions (Al2O3-based inclusions). For this reason, in the second invention, one or more of these are added, but if the amount added is too large, the amount of inclusions will increase, and on the contrary, the stretch flangeability will deteriorate, so the upper limit of these is set to R.
0.1%, 0.01%, 0 for EM, Ca, Mg respectively
．． It was set as 01%. On the other hand, the lower limit is 0.005% and 0.0005%, respectively, as the addition amount that can be expected to have an inclusion form control effect.
%, 0.0005%.
【００２７】（Ｂ） 熱延条件
イ． 熱間仕上圧延条件
まず微細なフェライト相とベイナイト相からなる複合相
を得るため、オーステナイトの微細化とオーステナイト
の加工によるフェライト変態の促進を図る必要がある。
そのためＡｒ３〜（Ａｒ３＋４０℃）の温度範囲で圧延
を仕上げ、且つ仕上温度〜（仕上温度＋５０℃）の温度
範囲で合計７０〜９０％の圧下率を採る必要がある。(B) Hot rolling conditions a. Hot finish rolling conditions First, in order to obtain a composite phase consisting of a fine ferrite phase and a bainite phase, it is necessary to promote ferrite transformation by refining the austenite and processing the austenite. Therefore, it is necessary to finish the rolling in the temperature range of Ar3 to (Ar3+40°C) and to achieve a total reduction rate of 70 to 90% in the temperature range of the finishing temperature to (finishing temperature +50°C).
【００２８】以上の圧延条件のうち圧延仕上温度が（Ａ
ｒ３＋４０℃）より高温の場合、オーステナイトの微細
化が十分でないため微細なフェライトとベイナイトの複
合組織が得られなくなり、伸びフランジ性が低下する。Among the above rolling conditions, the finishing temperature of rolling is (A
If the temperature is higher than (r3+40°C), the austenite is not sufficiently refined and a fine composite structure of ferrite and bainite cannot be obtained, resulting in poor stretch flangeability.
【００２９】一方、Ａｒ３点以下の仕上温度では、生成
したフェライトが加工され、却って延性、伸びフランジ
性が劣化することになる。On the other hand, if the finishing temperature is lower than 3 Ar points, the produced ferrite will be processed, and the ductility and stretch flangeability will deteriorate.
【００３０】更に、図２に、下記表１に示すＡ鋼を用い
て実験を行った時に得られた仕上温度〜（仕上温度＋５
０℃）の間の圧下率と穴拡げ率（λ値）及びフェライト
粒径の関係を示す。尚、その他の熱延・冷却・スキンパ
ス条件は、本発明の規定条件内のものとした。Furthermore, FIG. 2 shows the finishing temperature ~ (finishing temperature + 5
0°C), the relationship between the rolling reduction rate, hole expansion rate (λ value), and ferrite grain size is shown. Note that other hot rolling, cooling, and skin pass conditions were within the specified conditions of the present invention.
【００３１】[0031]
【表１】[Table 1]
【００３２】同図からも明らかなように、７０％以上の
圧下率で、非常に優れたλ値が得られており、その際の
組織は極めて微細になっている。従って、圧下率の下限
を７０％とした。これに対し、９０％を超える圧下はミ
ル能力からみて困難であり、実用的ではないのでこれを
上限とした。As is clear from the figure, an extremely excellent λ value is obtained at a reduction rate of 70% or more, and the structure at that time becomes extremely fine. Therefore, the lower limit of the rolling reduction rate was set to 70%. On the other hand, a reduction exceeding 90% is difficult in terms of mill capacity and is not practical, so this was set as the upper limit.
【００３３】ロ． 仕上圧延終了直後の急冷条件次に変
態点（Ａｒ３点）直上での大圧下による微細なオーステ
ナイトから微細なフェライトを析出させ、且つ約８０％
以上のフェライトを熱延ランナウト・テーブル上で短時
間に変態させるためには、仕上圧延後６２０〜６８０℃
の範囲の温度まで、１２０〜２００℃／Ｓの平均冷却速
度で冷却する必要がある。このような構成は本発明者等
の次のような実験結果から得られたものである。B. Rapid cooling conditions immediately after finish rolling, followed by large reduction just above the transformation point (Ar 3 point) to precipitate fine ferrite from fine austenite, and approximately 80%
In order to transform the above ferrite on the hot rolling runout table in a short time, the temperature must be 620 to 680°C after finish rolling.
It is necessary to cool down to a temperature in the range of , at an average cooling rate of 120-200°C/S. This configuration was obtained from the following experimental results by the inventors.
【００３４】図３は、前記表１中のＢ鋼を用いて、熱延
仕上後の冷却速度を種々変えることにより（他の条件は
本発明条件として）、板厚２．６ｍｍの熱延鋼板のλ値
とフェライト粒径との関係を求めたものである。FIG. 3 shows hot-rolled steel sheets with a thickness of 2.6 mm obtained by using steel B in Table 1 and varying the cooling rate after hot-rolling (other conditions being the conditions of the present invention). The relationship between the λ value and the ferrite grain size is determined.
【００３５】同図から、伸びフランジ性の優れるフェラ
イト平均粒径５μｍ以下のような微細組織とするには、
仕上圧延後の冷却速度は１２０℃／Ｓ以上とする必要が
あることがわかる。即ち、１２０℃／Ｓ未満の冷却では
、微細なフェライトとベイナイトからなる組織は得られ
ず、優れたλ値は得られないことになる。一方、冷却速
度の上限は実験設備での制御性から２００℃／Ｓとした
。From the same figure, in order to obtain a fine structure with a ferrite average grain size of 5 μm or less, which has excellent stretch flangeability,
It can be seen that the cooling rate after finish rolling needs to be 120°C/S or more. That is, if the cooling temperature is less than 120° C./S, a structure consisting of fine ferrite and bainite cannot be obtained, and an excellent λ value cannot be obtained. On the other hand, the upper limit of the cooling rate was set to 200° C./S from the viewpoint of controllability in experimental equipment.
【００３６】ハ． 中間温度域での保持又は空冷本発明
で６２０〜６８０℃までの急冷に続き、３〜７秒の保持
又は空冷を行うこととしているが、その理由としては、
フェライト変態を短時間に起こさせ、約８０％以上の適
正なフェライトを変態させるためである。そのうち保持
又は空冷の時間が３秒未満ではフェライトの生成量が不
十分であるため、３秒をその下限とする。一方、上限は
パーライトが生成しない条件で制限されるべきであるが
、実際には実機での操業面、生産性の点などから７秒と
した。これはフェライトの生成量からみても十分な時間
である。C. Holding in intermediate temperature range or air cooling In the present invention, quenching to 620 to 680°C is followed by holding or air cooling for 3 to 7 seconds, and the reason is as follows.
This is to cause ferrite transformation to occur in a short time and to transform approximately 80% or more of proper ferrite. If the holding or air cooling time is less than 3 seconds, the amount of ferrite produced is insufficient, so 3 seconds is the lower limit. On the other hand, the upper limit should be set under conditions that do not produce pearlite, but in reality it is set to 7 seconds from the viewpoint of operation in actual equipment and productivity. This is a sufficient time considering the amount of ferrite produced.
【００３７】ニ． 保持又は空冷から巻取り温度までの
冷却速度
この工程の急冷により最終的な微細フェライトとベイナ
イトの複合組織が得られるが、この際の冷却速度の下限
はパーライトの生成を避けることから規定される。つま
り５０℃／Ｓ未満ではパーライトノーズにかかり、適正
な複合組織とならないため、優れた伸びフランジ性が達
成できないことになる。一方、１５０℃／Ｓを超えると
、次の巻取り温度の制御性が低下し材質の安定性を低下
させるため、これを上限とした。D. Cooling rate from holding or air cooling to coiling temperature The final composite structure of fine ferrite and bainite is obtained by rapid cooling in this step, but the lower limit of the cooling rate is determined in order to avoid the formation of pearlite. In other words, if it is less than 50° C./S, the pearlite nose will form and an appropriate composite structure will not be obtained, making it impossible to achieve excellent stretch flangeability. On the other hand, if it exceeds 150° C./S, the controllability of the next winding temperature decreases and the stability of the material decreases, so this was set as the upper limit.
【００３８】ホ． 巻取り温度
本来、硬質のベイナイト自体に適度の延性を付与させる
ため４００〜４５０℃で巻取る必要がある。図４に巻取
り温度による穴拡げ率（λ）及びＴＳの変化を示した。
この時使用した供試材はＳ：０．０５％、Ｓ：０．５０
％、Ｍｎ：１．４５％の鋼を１２００℃に加熱し、８３
０℃で仕上圧延を終了して二段冷却後巻取り温度を変化
させて得た種々の鋼板である。
尚、他の熱延条件、冷却条件及びスキンパス条件は本発
明で規定された条件内である。同図から４００〜４５０
℃の温度域で伸びフランジ性の最良域が存在することが
わかる。一方、これより低温の巻取りの場合は硬質のベ
イナイトやマルテンサイトが生成するため、高強度には
なるが伸びフランジ性を低下させることになる。これに
より高温の巻取りでは、パーライトが生成し伸びフラン
ジ性が低下することになる。[0038] E. Winding temperature It is necessary to wind at a temperature of 400 to 450°C in order to impart appropriate ductility to bainite itself, which is originally hard. FIG. 4 shows changes in hole expansion ratio (λ) and TS depending on the winding temperature. The test materials used at this time were S: 0.05% and S: 0.50.
%, Mn: 1.45% steel was heated to 1200°C, 83
These are various steel plates obtained by finishing finish rolling at 0°C, cooling in two stages, and then changing the coiling temperature. Note that other hot rolling conditions, cooling conditions, and skin pass conditions are within the conditions specified in the present invention. 400-450 from the same figure
It can be seen that the best range of stretch flangeability exists in the temperature range of °C. On the other hand, in the case of winding at a lower temperature than this, hard bainite and martensite are produced, which results in high strength but a decrease in stretch flangeability. As a result, during high-temperature winding, pearlite is produced and stretch flangeability is reduced.
【００３９】ヘ． スキンパス伸長率
図５に、前記表１に示された本発明のＢ鋼を用いて、本
発明の熱延条件及び冷却条件で製造した板厚２．９ｍｍ
の熱延鋼板を供試材とし、これにスキンパスを行った時
の穴拡げ率、伸びに及ぼすスキンパス伸長率の影響を示
している。この図からスキンパス伸長率を１．５〜３．
０％の範囲でとることにより、穴拡げ率が最高の領域に
入ることが明らかである。適正なスキンパスの付与は本
発明の重要な要素の一つであり、これまでに示された成
分と熱延条件の適正化で得られる伸びフランジ性を更に
向上させるために必要な製造因子である。しかし、伸長
率が１．５％未満ではスキンパスによる伸びフランジ性
改善効果は小さく、そのため１．５％を下限とした。一
方、３．０％を超えると伸びフランジ性は劣化するので
３．０％を上限とした。このスキンパスによる伸びフラ
ンジ性改善効果の本質的な原因は必ずしも明確ではない
が、適正なスキンパスによりサブ組織の均一化が働いて
いるように思われる。F. Skin pass elongation rate Figure 5 shows a sheet with a thickness of 2.9 mm produced using the B steel of the present invention shown in Table 1 and under the hot rolling conditions and cooling conditions of the present invention.
This figure shows the effect of the skin pass elongation rate on the hole expansion rate and elongation when a skin pass is performed on a hot rolled steel sheet as a test material. From this figure, the skin pass elongation rate is 1.5 to 3.
It is clear that the hole expansion rate is in the highest range by setting it within the range of 0%. Providing an appropriate skin pass is one of the important elements of the present invention, and is a necessary manufacturing factor to further improve the stretch flangeability obtained by optimizing the components and hot rolling conditions shown so far. . However, if the elongation rate is less than 1.5%, the effect of improving stretch flangeability by the skin pass is small, and therefore 1.5% was set as the lower limit. On the other hand, if it exceeds 3.0%, stretch flangeability deteriorates, so 3.0% was set as the upper limit. Although the essential cause of this effect of improving stretch flangeability due to the skin pass is not necessarily clear, it seems that the uniformity of the substructure is worked by an appropriate skin pass.
【００４０】[0040]
【実施例】〈実施例１〉本発明者等は、まず前記表１に
示す成分組成を有する１０種の鋼を溶製した。このうち
鋼Ａ〜Ｅが本発明規定成分を満足する鋼であり、又、鋼
Ｆ〜Ｊは比較鋼である。このうち表１の鋼Ａ〜Ｊを用い
、熱延・冷却・スキンパスを下記表２に示す各条件（本
発明で規定された範囲内）で行い、板厚２．６ｍｍの熱
延鋼板を製造した。こうして得られた鋼板の機械的性質
を調べるために、引張試験と伸びフランジ性の指標とな
る「穴拡げ試験」による穴拡げ率を測定し、同表に併せ
て示した。尚、「穴拡げ率」は前記熱延鋼板に直径１０
ｍｍの円形打ち抜き穴を形成した後、該穴に６０°円錐
ポンチを押し当て穴拡げ加工を行い、穴縁に亀裂を生じ
た時点の穴の拡大率で示した。[Example] <Example 1> The present inventors first melted ten types of steel having the compositions shown in Table 1 above. Of these, steels A to E are steels that satisfy the specified composition of the present invention, and steels F to J are comparative steels. Using steels A to J in Table 1, hot rolling, cooling, and skin passing were performed under the conditions shown in Table 2 below (within the range specified by the present invention) to produce hot rolled steel sheets with a thickness of 2.6 mm. did. In order to investigate the mechanical properties of the steel sheets obtained in this way, the hole expansion ratio was measured by a tensile test and a "hole expansion test" which is an indicator of stretch flangeability, and is also shown in the table. In addition, the "hole expansion rate" refers to the diameter of 10 mm in the hot rolled steel plate.
After forming a circular punched hole of mm in size, a 60° conical punch was pressed against the hole to enlarge the hole, and the enlargement rate of the hole at the time when a crack was generated at the edge of the hole was shown.
【００４１】[0041]
【表２】[Table 2]
【００４２】同表から本発明で規定された成分組成を有
するＡ〜Ｅの鋼では、強度−延性バランスを示す「ＴＳ
×Ｅｌ」の値が１６００以上で且つ降伏比ＹＲが０．７
５以上を満たすと共に、強度−伸びフランジ性バランス
を示す「ＴＳ×λ」の値が９０００以上の高い値を有す
る５０〜６０ｋｇｆ／ｍｍ２級の強度レベルの伸びフラ
ンジ性に極めて優れた熱延鋼板が安定して得られること
がわかる。特に鋼ＥのＣａ添加鋼を用いた本発明鋼５に
よって得られた熱延鋼板は、より優れた伸びフランジ性
を示すことが明らかとなった。From the same table, steels A to E having the composition specified in the present invention have "TS" which indicates the strength-ductility balance.
×El” value is 1600 or more and yield ratio YR is 0.7
5 or more, and has a high value of 9000 or more for "TS x λ" indicating the strength-stretch flangeability balance, and has extremely excellent stretch flangeability at a strength level of 50 to 60 kgf/mm2 class. It can be seen that the results are stable. In particular, it became clear that the hot-rolled steel sheet obtained by Inventive Steel 5 using Ca-added steel of Steel E exhibits better stretch flangeability.
【００４３】これに対して、鋼の組成が本発明から外れ
ている鋼Ｆ〜Ｊの比較鋼６〜１０の熱延鋼板は、「ＴＳ
×λ」が高々６０００程度であって伸びフランジ性が良
くない。これは微細なフェライトとベイナイトからなる
最適な組織が得られていないためである。On the other hand, the hot rolled steel sheets of Comparative Steels 6 to 10 of Steels F to J whose steel compositions deviate from the present invention are
×λ” is about 6000 at most, and the stretch flangeability is not good. This is because an optimal structure consisting of fine ferrite and bainite is not obtained.
【００４４】〈実施例２〉前記した表１のＡ〜Ｄ鋼を用
いて、下記表３に示すように熱延・冷却・スキンパスの
各条件を種々変化させて、板厚２．６ｍｍの熱延鋼板を
製造した。得られた機械試験値をこの表３に併せて示し
た。
尚、同表では、穴拡げ試験で機械的特性を評価している
。<Example 2> Using the steels A to D shown in Table 1 above, hot rolling, cooling, and skin pass conditions were variously changed as shown in Table 3 below, and a sheet thickness of 2.6 mm was heated. A rolled steel plate was manufactured. The obtained mechanical test values are also shown in Table 3. In addition, in the same table, mechanical properties are evaluated by a hole expansion test.
【００４５】[0045]
【表３】[Table 3]
【００４６】本発明法の熱延・冷却・スキンパスの各条
件のいずれかを満足していない比較材１１〜２１のＴＳ
×λは高々５２００程度で、いずれも本発明でいう組織
の適正化が達成されないことから本発明の９０００以上
の優れた強度−伸びフランジ性バランス（ＴＳ×λ）は
得られていない。TS of comparative materials 11 to 21 that do not satisfy any of the hot rolling, cooling, and skin pass conditions of the method of the present invention
×λ is about 5200 at most, and the optimization of the structure as defined in the present invention is not achieved in either case, so the excellent strength-stretch flangeability balance (TS×λ) of 9000 or more of the present invention is not obtained.
【００４７】即ち、比較材１１では、熱延仕上温度ＦＴ
が上限（Ａｒ３＋４０℃）を超えており、又、比較材１
２では、仕上温度から「仕上温度＋５０℃」での圧下率
が７０％未満のため、オーステナイトの微細化が不十分
になることから、適正フェライト量の確保とフェライト
の微細化が不十分となり、優れた伸びフランジ性は得ら
れない。That is, in comparative material 11, the hot rolling finishing temperature FT
exceeds the upper limit (Ar3+40℃), and comparative material 1
In 2, since the reduction ratio from the finishing temperature to "finishing temperature + 50 ° C" is less than 70%, the refinement of austenite is insufficient, so securing the appropriate amount of ferrite and refining the ferrite are insufficient. Excellent stretch flangeability cannot be obtained.
【００４８】比較材１３は、熱延仕上後の急冷の冷却速
度が小さいため細粒フェライトが得られず、目標特性に
到達しなかったものである。[0048] Comparative material 13 did not achieve the target properties because the cooling rate during the rapid cooling after hot rolling was low, so fine grain ferrite could not be obtained.
【００４９】比較材１４は、中間保持温度が高すぎる場
合であり、反対に比較材１５は、中間保持温度が低すぎ
る場合であって、いずれもフェライト量が不十分なため
、伸びフランジ性は良好ではない。Comparative material 14 is a case where the intermediate holding temperature is too high, and comparative material 15 is a case where the intermediate holding temperature is too low.In both cases, the amount of ferrite is insufficient, so the stretch flangeability is poor. Not good.
【００５０】比較材１６は、圧延直後の冷却に続く空冷
（中間保持）時間が０．５秒と短いため、フェライト量
が少なく伸びフランジ性が悪い。Comparative material 16 has a small amount of ferrite and poor stretch flangeability because the air cooling (intermediate holding) time following cooling immediately after rolling is as short as 0.5 seconds.
【００５１】比較材１７は、中間保持後の急冷の冷却速
度が遅い場合であり、又、比較材１８は、巻取り温度が
６００℃と高いため、いずれも鋼板冷却中にパーライト
が生成し低い伸びフランジ性しか示さない。Comparative material 17 has a slow cooling rate during rapid cooling after intermediate holding, and comparative material 18 has a high coiling temperature of 600°C, so pearlite is generated during cooling of the steel sheet and the temperature is low. Shows only stretch flangeability.
【００５２】比較材１９は、巻取り温度が１８０℃と低
いため、第２相がマルテンサイトとなり、強度は高いも
のの、伸びフランジ性は低く、ＴＳ×λの値も４７０３
と低い。Comparative material 19 has a low winding temperature of 180°C, so the second phase becomes martensite, and although its strength is high, its stretch flangeability is low, and the value of TS×λ is also 4703.
and low.
【００５３】比較材２０は、スキンパス伸長率が０．５
％の場合、一方、比較材２１は、スキンパス伸長率が４
．０％と本発明の規定の範囲外であり、優れた伸びフラ
ンジ性は得られていない。Comparative material 20 has a skin pass elongation rate of 0.5.
%, on the other hand, comparative material 21 has a skin pass elongation rate of 4
．． 0%, which is outside the specified range of the present invention, and excellent stretch flangeability is not obtained.
【００５４】[0054]
【発明の効果】以上説明したように、この本発明によれ
ば、現行の熱間圧延工程に格別な変更を加えることなく
、しかも格別に高価な素材を使用せずに伸びフランジ性
に優れた熱延高強度鋼板を低コストで、且つ安定して製
造することができるなど、工業的に非常に有用な効果が
得られる。[Effects of the Invention] As explained above, according to the present invention, excellent stretch flangeability can be achieved without making any special changes to the current hot rolling process and without using particularly expensive materials. Industrially very useful effects can be obtained, such as being able to stably produce hot-rolled high-strength steel sheets at low cost.
【図１】鋼中のＳ量と伸びフランジ性（穴拡げ率）の関
係を示すグラフである。FIG. 1 is a graph showing the relationship between the amount of S in steel and stretch flangeability (hole expansion rate).
【図２】仕上温度〜（仕上温度＋５０℃）の間の圧下率
とフェライトの平均粒径及び伸びフランジ性（穴拡げ率
）の関係を示すグラフである。FIG. 2 is a graph showing the relationship between the rolling reduction rate between the finishing temperature and (finishing temperature + 50° C.), the average grain size of ferrite, and stretch flangeability (hole expansion rate).
【図３】仕上圧延後の冷却速度とフェライトの平均粒径
及び伸びフランジ性（穴拡げ率）との関係を示すグラフ
である。FIG. 3 is a graph showing the relationship between the cooling rate after finish rolling, the average grain size of ferrite, and stretch flangeability (hole expansion ratio).
【図４】巻取り温度と強度及び伸びフランジ性（穴拡げ
率）との関係を示すグラフである。FIG. 4 is a graph showing the relationship between winding temperature, strength, and stretch flangeability (hole expansion ratio).
【図５】スキンパス伸長率と伸びフランジ性（穴拡げ率
）及び延性（伸び）との関係を示すグラフである。FIG. 5 is a graph showing the relationship between skin pass elongation rate, stretch flangeability (hole expansion rate), and ductility (elongation).
Claims (2)
Ｓｉ：０．１０〜０．５０％、Ｍｎ：１．００〜１．８
０％、Ｓ：０．０００２〜０．００１０％、Ａｌ：０．
００５〜０．０５０％、Ｎ：０．００１０〜０．００３
０％を含有し、残部Ｆｅ及び他の不可避的不純物からな
る鋼に対し、Ａｒ３〜（Ａｒ３＋４０℃）を仕上温度と
し、且つ仕上温度〜（仕上温度＋５０℃）の間で７０〜
９０％の圧下率により熱間圧延を行い、続いて直ちに１
２０〜２００℃／Ｓの冷却速度で６２０〜６８０℃の温
度域に冷却すると共に、その後３〜７秒保持し又は空冷
し、次いで５０〜１５０℃／Ｓの冷却速度で４００〜４
５０℃の温度に冷却して巻取り、更に伸長率１．５〜３
．０％の範囲でスキンパスを行うことを特徴とする極め
て微細なフェライト相とベイナイト相の複合組織からな
る伸びフランジ性に優れた高強度熱延鋼板の製造方法。Claim 1: C: 0.04 to 0.08% by weight,
Si: 0.10-0.50%, Mn: 1.00-1.8
0%, S: 0.0002-0.0010%, Al: 0.
005-0.050%, N: 0.0010-0.003
For steel containing 0% Fe and other unavoidable impurities, the finishing temperature is Ar3 ~ (Ar3 + 40°C), and the finishing temperature is 70 ~ (finishing temperature + 50°C).
Hot rolling is carried out with a rolling reduction of 90%, followed immediately by 1
Cool to a temperature range of 620 to 680°C at a cooling rate of 20 to 200°C/S, then hold for 3 to 7 seconds or air cool, then cool to 400 to 400°C at a cooling rate of 50 to 150°C/S.
It is cooled to a temperature of 50°C, wound, and further elongated at a rate of 1.5 to 3.
．． A method for producing a high-strength hot-rolled steel sheet with excellent stretch flangeability consisting of an extremely fine composite structure of ferrite and bainite phases, characterized by performing a skin pass in the range of 0%.
Ｓｉ：０．１０〜０．５０％、Ｍｎ：１．００〜１．８
０％、Ｓ：０．０００２〜０．００１０％、Ａｌ：０．
００５〜０．０５０％、Ｎ：０．００１０〜０．００３
０％を含み、更にＲＥＭ：０．００５〜０．１％、Ｃａ
：０．０００５〜０．０１％及びＭｇ：０．０００５〜
０．０１％のうち１種乃至２種以上の元素を含有し、残
部Ｆｅ及び他の不可避的不純物からなる鋼に対し、Ａｒ
３〜（Ａｒ３＋４０℃）を仕上温度とし、且つ仕上温度
〜（仕上温度＋５０℃）の間で７０〜９０％の圧下率に
より熱間圧延を行い、続いて直ちに１２０〜２００℃／
Ｓの冷却速度で６２０〜６８０℃の温度域に冷却すると
共に、その後３〜７秒保持し又は空冷し、次いで５０〜
１５０℃／Ｓの冷却速度で４００〜４５０℃の温度に冷
却して巻取り、更に伸長率１．５〜３．０％の範囲でス
キンパスを行うことを特徴とする極めて微細なフェライ
ト相とベイナイト相の複合組織からなる伸びフランジ性
に優れた高強度熱延鋼板の製造方法。[Claim 2] C: 0.04 to 0.08% by weight;
Si: 0.10-0.50%, Mn: 1.00-1.8
0%, S: 0.0002-0.0010%, Al: 0.
005-0.050%, N: 0.0010-0.003
0%, further REM: 0.005-0.1%, Ca
:0.0005~0.01% and Mg:0.0005~
Ar
3~(Ar3+40℃) is the finishing temperature, and hot rolling is carried out at a reduction rate of 70~90% between the finishing temperature and (finishing temperature +50℃), followed immediately by 120~200℃/
Cool to a temperature range of 620 to 680 °C at a cooling rate of S, then hold for 3 to 7 seconds or air cool, then cool to 50 to 680 °C
Extremely fine ferrite phase and bainite characterized by cooling to a temperature of 400 to 450 °C at a cooling rate of 150 °C/S, winding, and further skin pass at an elongation rate of 1.5 to 3.0%. A method for manufacturing high-strength hot-rolled steel sheets with excellent stretch flangeability consisting of a composite structure of phases.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5839291A JPH0826407B2 (en) | 1991-02-28 | 1991-02-28 | Method for manufacturing high strength hot rolled steel sheet with excellent stretch flangeability |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5839291A JPH0826407B2 (en) | 1991-02-28 | 1991-02-28 | Method for manufacturing high strength hot rolled steel sheet with excellent stretch flangeability |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04276024A true JPH04276024A (en) | 1992-10-01 |
| JPH0826407B2 JPH0826407B2 (en) | 1996-03-13 |
Family
ID=13083079
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5839291A Expired - Fee Related JPH0826407B2 (en) | 1991-02-28 | 1991-02-28 | Method for manufacturing high strength hot rolled steel sheet with excellent stretch flangeability |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0826407B2 (en) |
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| JP2005281764A (en) * | 2004-03-29 | 2005-10-13 | Jfe Steel Kk | Production method of low yield ratio high strength hot-rolled steel strip |
| CN100439542C (en) * | 2004-01-29 | 2008-12-03 | 杰富意钢铁株式会社 | High strength steel sheet and method for manufacturing same |
| WO2009028515A1 (en) * | 2007-08-24 | 2009-03-05 | Jfe Steel Corporation | Process for manufacturing high-strength hot-rolled steel sheet |
| WO2012020847A1 (en) * | 2010-08-10 | 2012-02-16 | Ｊｆｅスチール株式会社 | High-strength hot-rolled steel sheet having excellent workability, and a method for producing same |
| WO2012128206A1 (en) * | 2011-03-18 | 2012-09-27 | 新日本製鐵株式会社 | Hot-rolled steel sheet exhibiting exceptional press-molding properties and method for manufacturing same |
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1991
- 1991-02-28 JP JP5839291A patent/JPH0826407B2/en not_active Expired - Fee Related
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| JP2005281764A (en) * | 2004-03-29 | 2005-10-13 | Jfe Steel Kk | Production method of low yield ratio high strength hot-rolled steel strip |
| WO2009028515A1 (en) * | 2007-08-24 | 2009-03-05 | Jfe Steel Corporation | Process for manufacturing high-strength hot-rolled steel sheet |
| JP2009052065A (en) * | 2007-08-24 | 2009-03-12 | Jfe Steel Kk | Method for producing high strength hot rolled steel sheet |
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| WO2012020847A1 (en) * | 2010-08-10 | 2012-02-16 | Ｊｆｅスチール株式会社 | High-strength hot-rolled steel sheet having excellent workability, and a method for producing same |
| JP2012057250A (en) * | 2010-08-10 | 2012-03-22 | Jfe Steel Corp | High strength hot-rolled steel sheet excellent in workability, and manufacturing method therefor |
| CN103080359A (en) * | 2010-08-10 | 2013-05-01 | 杰富意钢铁株式会社 | High-strength hot-rolled steel sheet having excellent workability, and a method for producing same |
| WO2012128206A1 (en) * | 2011-03-18 | 2012-09-27 | 新日本製鐵株式会社 | Hot-rolled steel sheet exhibiting exceptional press-molding properties and method for manufacturing same |
| US10428409B2 (en) | 2011-03-18 | 2019-10-01 | Nippon Steel Corporation | Hot-rolled steel sheet with excellent press formability and production method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0826407B2 (en) | 1996-03-13 |
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