JPH04228517A - Manufacture of hot rolled high strength steel sheet excellent in workability - Google Patents
Manufacture of hot rolled high strength steel sheet excellent in workabilityInfo
- Publication number
- JPH04228517A JPH04228517A JP10765291A JP10765291A JPH04228517A JP H04228517 A JPH04228517 A JP H04228517A JP 10765291 A JP10765291 A JP 10765291A JP 10765291 A JP10765291 A JP 10765291A JP H04228517 A JPH04228517 A JP H04228517A
- Authority
- JP
- Japan
- Prior art keywords
- cooling
- temperature
- steel
- rolling
- ferrite
- 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 45
- 239000010959 steel Substances 0.000 title claims abstract description 45
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 20
- 238000001816 cooling Methods 0.000 claims abstract description 48
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 43
- 238000005096 rolling process Methods 0.000 claims abstract description 42
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 35
- 230000000717 retained effect Effects 0.000 claims abstract description 24
- 229910001568 polygonal ferrite Inorganic materials 0.000 claims abstract description 15
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 11
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 10
- 229910052742 iron Inorganic materials 0.000 claims abstract description 6
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 229910052799 carbon Inorganic materials 0.000 abstract description 7
- 238000005098 hot rolling Methods 0.000 abstract description 3
- 230000001105 regulatory effect Effects 0.000 abstract description 3
- 230000000694 effects Effects 0.000 description 11
- 230000009466 transformation Effects 0.000 description 11
- 238000004804 winding Methods 0.000 description 9
- 238000000034 method Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000014759 maintenance of location Effects 0.000 description 6
- 229910001562 pearlite Inorganic materials 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 239000000126 substance Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 230000002301 combined effect Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000000879 optical micrograph Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000007668 thin rolling process Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
Abstract
Description
【０００１】0001
【産業上の利用分野】この発明は自動車、産業用機械等
に使用することを目的とした高延性を有する加工性に優
れた熱延高強度鋼板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 method for producing hot rolled high strength steel sheets having high ductility and excellent workability for use in automobiles, industrial machinery, etc.
【０００２】0002
【従来の技術】自動車用鋼板の軽量化と衝突時の安全確
保を主な背景として鋼板の高強度化の要請は強い。しか
し、高強度鋼板といえどもその加工性に対する要求は高
く、強度と加工性を両立させる鋼板が必要とされている
。従来、良好な延性を必要とする用途に供される熱延鋼
板として、フェライトとマルテンサイトにより構成され
るＤｕａｌ ｐｈａｓｅ鋼（以下ＤＰ鋼と称す。）が
ある。このＤＰ鋼は固溶強化型高強度鋼板、析出強化型
高強度鋼板よりすぐれた強度・延性バランスを示すこと
が知られている。しかし、その強度・延性バランスの限
界はＴＳ×Ｔ．Ｅｌ≦２０００であり、より厳しい要求
には耐えられないのが現状である。[Prior Art] There is a strong demand for higher strength steel plates for automobiles, mainly to reduce the weight of steel plates and ensure safety in the event of a collision. However, even high-strength steel sheets have high demands on their workability, and there is a need for steel sheets that have both strength and workability. BACKGROUND ART Dual phase steel (hereinafter referred to as DP steel) composed of ferrite and martensite has conventionally been used as a hot rolled steel sheet for applications requiring good ductility. This DP steel is known to exhibit a better balance of strength and ductility than solid solution strengthened high strength steel plates and precipitation strengthened high strength steel plates. However, the limit of strength/ductility balance is TS×T. El≦2000, and the current situation is that it cannot withstand more stringent requirements.
【０００３】この現状を打破してＴＳ×Ｔ．Ｅｌ＞２０
００が得られるシーズとして残留オーステナイトの利用
がある。その一例としてＡｒ３ 〜Ａｒ３ ＋５０℃で
熱間圧延後、鋼板を４５０〜６５０℃の温度範囲で４〜
２０秒保持し、次いで３５０℃以下で捲き取り、残留オ
ーステナイトを有する鋼板を製造する方法（特開昭６０
−４３４２５）、更に他の例として仕上温度８５０℃以
上で全圧下率８０％以上かつ最終３パスの合計圧下率６
０％以上、最終パス圧下率２０％以上の大圧下圧延を行
い、続いて５０℃／ｓ以上の冷却速度で３００℃以下ま
で冷却し、残留オーステナイトを有する鋼板を製造する
方法（特開昭６０−１６５３２０）等が示されている。[0003] Breaking away from this current situation, TS×T. El>20
One of the seeds for obtaining 00 is the use of retained austenite. As an example, after hot rolling at Ar3 ~ Ar3 +50℃, the steel plate is rolled in a temperature range of 450~650℃.
A method for manufacturing a steel plate with retained austenite by holding it for 20 seconds and then rolling it up at 350°C or less
-43425), and as another example, the finishing temperature is 850°C or higher, the total rolling reduction is 80% or more, and the total rolling reduction of the final three passes is 6.
A method of producing a steel sheet with retained austenite by performing large reduction rolling with a final pass reduction rate of 0% or more and a final pass reduction rate of 20% or more, followed by cooling to 300°C or less at a cooling rate of 50°C/s or more (Japanese Patent Application Laid-Open No. 1983-1993) -165320) etc. are shown.
【０００４】しかしながら、省エネルギー、生産性向上
の点からすると、冷却途中、４５０〜６５０℃での４〜
２０秒の保持、および３５０℃以下の低温捲取あるいは
大圧下圧延等を必要とする従来方法は操業上好ましくな
い。それにもかかわらず、これらの方法によって得られ
た鋼板の加工性はＴＳ×Ｔ．Ｅｌ＜２４００であり、か
ならずしも使用者側の要求レベルをすべて満たしている
とは言い難い。より高いＴＳ×Ｔ．Ｅｌ値（望ましくは
２４００以上）を持つ鋼板、およびより生産性の高いそ
の製造方法が求められていた。However, from the point of view of energy saving and productivity improvement, it is difficult to
Conventional methods that require holding for 20 seconds, low-temperature winding at 350° C. or lower, large reduction rolling, etc. are unfavorable from an operational point of view. Nevertheless, the workability of the steel sheets obtained by these methods is TS×T. Since El<2400, it is difficult to say that it necessarily satisfies all the levels required by the user. Higher TS×T. There has been a need for a steel plate with an El value (preferably 2400 or more) and a manufacturing method thereof with higher productivity.
【０００５】[0005]
【発明が解決しようとする課題】従来技術の限界を超え
てＴＳ×Ｔ．Ｅｌ≧２０００を得るには、本願発明者達
の各種の実験結果によると、後述する実施例のＡ鋼を対
象とし図１に示す如く少なくとも５％以上の残留オース
テナイトを含有することが必要であり、これによって前
記したＤＰ鋼レベルのＴＳ×Ｔ．Ｅｌがほぼ２０００は
確実に凌駕できる。また、ＴＳ×Ｔ．Ｅｌの向上代は一
様伸びの向上に大きく基づいており、２０％以上の一様
伸びを有している。本発明はこの知見をもとに経済的に
５％以上の残留オーステナイトを含有する加工性に優れ
た熱延高強度鋼板を安定、確実に製造する方法を提供す
るものである。Problem to be Solved by the Invention: TS×T. In order to obtain El≧2000, according to various experimental results by the inventors of the present invention, it is necessary to contain at least 5% or more retained austenite as shown in FIG. , thereby achieving the TS x T. of the DP steel level described above. You can definitely surpass El of almost 2000. Also, TS×T. The improvement in El is largely based on the improvement in uniform elongation, and has a uniform elongation of 20% or more. Based on this knowledge, the present invention provides an economical method for stably and reliably producing hot-rolled high-strength steel sheets containing 5% or more retained austenite and excellent workability.
【０００６】[0006]
【課題を解決するための手段】上記、問題点を解決する
ために本発明は次の構成を手段とするものである。[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention has the following configuration.
【０００７】１． 重量％で、Ｃ：０．１５超〜０．
３％未満、Ｓｉ：０．５〜２．０％、Ｍｎ：０．５〜２
．０％、残部が鉄および不可避的不純物からなる鋼を、
全圧下率が８０％以上の熱間仕上圧延を行い、その圧延
終了温度をＡｒ３ ＋５０℃超とし、該温度から４０℃
／ｓ未満の冷却速度で冷却を開始し、その鋼のＡｒ３
以下でＡｒ１ 超となる温度範囲内の任意の温度Ｔで前
記冷却を終了し、続けて冷却温度４０℃／ｓ以上で冷却
して３５０〜５００℃で捲き取り、ポリゴナルフェライ
ト占積率ＶＰＦ（％）とポリゴナルフェライト平均粒径
ｄＰＦ（μｍ ）の比ＶＰＦ／ｄＰＦが７以上でかつ残
留オーステナイトを体積比で５％以上含むフェライト、
ベイナイトおよび残留オーステナイトの組織から構成さ
れ、強度−延性バランスＴＳ×Ｔ．Ｅｌで２０００ｋｇ
ｆ／ｍｍ２ ・％以上であることを特徴とする加工性に
優れた熱延高強度鋼板の製造方法。1. In weight%, C: more than 0.15 to 0.
Less than 3%, Si: 0.5-2.0%, Mn: 0.5-2
．． 0%, the balance is iron and unavoidable impurities,
Perform hot finish rolling with a total reduction ratio of 80% or more, set the rolling end temperature to Ar3 +50℃, and reduce the temperature by 40℃ from this temperature.
Cooling is started at a cooling rate of less than /s, and the Ar3 of the steel is
Below, the cooling is finished at an arbitrary temperature T within the temperature range exceeding Ar1, and then the cooling is continued at a cooling temperature of 40°C/s or more and rolled up at 350 to 500°C, and the polygonal ferrite space factor VPF ( %) and polygonal ferrite average grain size dPF (μm) VPF/dPF is 7 or more and contains retained austenite in a volume ratio of 5% or more,
It is composed of a structure of bainite and retained austenite, and has a strength-ductility balance of TS×T. 2000kg with El
A method for producing a hot-rolled high-strength steel sheet with excellent workability, characterized in that f/mm2.% or more.
【０００８】２． 重量％で、Ｃ：０．１５超〜０．
３％未満、Ｓｉ：０．５〜２．０％、Ｍｎ：０．５〜２
．０％に加えて、Ｃａ：０．０００５〜０．０１００％
、ＲＥＭ：０．００５〜０．０５０％のどちらか１種を
含有し、かつ、Ｓ：０．０１０％以下に制限し、残部が
鉄および不可避的不純物からな鋼を、全圧下率が８０％
以上の熱間仕上圧延を行い、その圧延終了温度をＡｒ３
＋５０℃超とし、該温度から４０℃／ｓ未満の冷却速
度で冷却を開始し、その鋼のＡｒ３ 以下でＡｒ１ 超
となる温度範囲内の任意の温度Ｔで前記冷却を終了し、
続けて冷却温度４０℃／ｓ以上で冷却して３５０〜５０
０℃で捲き取り、ポリゴナルフェライト占積率ＶＰＦ（
％）とポリゴナルフェライト平均粒径ｄＰＦ（μｍ ）
の比ＶＰＦ／ｄＰＦが７以上でかつ残留オーステナイト
を体積比で５％以上含むフェライト、ベイナイトおよび
残留オーステナイトの組織から構成され、強度−延性バ
ランスＴＳ×Ｔ．Ｅｌで２０００ｋｇｆ／ｍｍ２ ・％
以上であることを特徴とする加工性に優れた熱延高強度
鋼板の製造方法。2. In weight%, C: more than 0.15 to 0.
Less than 3%, Si: 0.5-2.0%, Mn: 0.5-2
．． In addition to 0%, Ca: 0.0005-0.0100%
, REM: 0.005 to 0.050%, and S: limited to 0.010% or less, with the remainder being iron and unavoidable impurities, with a total reduction rate of 80%. %
Perform the above hot finish rolling, and set the rolling end temperature to Ar3
+50° C. or above, and start cooling from that temperature at a cooling rate of less than 40° C./s, and end the cooling at an arbitrary temperature T within a temperature range of Ar3 or below and Ar1 above the steel,
Continue to cool at a cooling temperature of 40℃/s or higher to 350~50℃.
Rolled up at 0℃, polygonal ferrite space factor VPF (
%) and polygonal ferrite average grain size dPF (μm)
It is composed of a structure of ferrite, bainite, and retained austenite with a ratio VPF/dPF of 7 or more and a volume ratio of 5% or more of retained austenite, and has a strength-ductility balance TS×T. 2000kgf/mm2・% at El
A method for producing a hot-rolled high-strength steel sheet with excellent workability, characterized by the above.
【０００９】[0009]
【作用】以下、本発明の構成要件について説明を行う。
まず、本発明に用いる鋼の化学的成分の限定理由を説明
する。Ｃは鋼の強化に不可欠な元素であり、０．１５％
（ｗｔ％以下同じ）以下では本発明鋼の延性を向上させ
ている残留オーステナイトが充分に得られない。また、
０．３％以上では溶接性を劣化させ、鋼を脆化させる。
そこで０．１５超〜０．３％未満とした。[Operation] The constituent elements of the present invention will be explained below. First, the reasons for limiting the chemical composition of the steel used in the present invention will be explained. C is an essential element for strengthening steel, and 0.15%
(The same applies below wt%), the retained austenite which improves the ductility of the steel of the present invention cannot be sufficiently obtained. Also,
If it exceeds 0.3%, weldability deteriorates and the steel becomes brittle. Therefore, the content was set at more than 0.15% and less than 0.3%.
【００１０】Ｓｉはその含有量の増加により、延性向上
に寄与するフェライトの生成、純化に有利であり、また
、Ｃを未変態オーステナイト中へ濃化させて、残留オー
ステナイトを得るのに有利となる。この効果は０．５％
未満では充分に発揮されず、また、２％をこえるとその
効果は飽和し、かえってスケール性状、溶接性を劣化さ
せる。そこで０．５〜２．０％とした。[0010] Increased Si content is advantageous for the generation and purification of ferrite that contributes to improving ductility, and is also advantageous for enriching C in untransformed austenite to obtain retained austenite. . This effect is 0.5%
If it is less than 2%, the effect will not be fully exhibited, and if it exceeds 2%, the effect will be saturated and the scale properties and weldability will deteriorate. Therefore, it was set at 0.5 to 2.0%.
【００１１】Ｍｎはよく知られている通りオーステナイ
トの安定化元素としてオーステナイトの残留に寄与する
。その効果は０．５％未満では充分に発揮されず、また
２％をこえるとその効果は飽和し、かえって溶接性を劣
化等の悪い影響を発生する。そこで０．５〜２．０％と
した。Ｓは穴拡げ性に有害な元素であり、０．０１０％
をこえると穴拡げ性を劣化させる。そこで０．０１０％
以下とした。なお、好ましくは０．００１％以下とする
ことが望ましい。As is well known, Mn contributes to the retention of austenite as an austenite stabilizing element. If the content is less than 0.5%, the effect will not be sufficiently exhibited, and if it exceeds 2%, the effect will be saturated, and on the contrary, adverse effects such as deterioration of weldability will occur. Therefore, it was set at 0.5 to 2.0%. S is an element harmful to hole expandability, and 0.010%
Exceeding this will deteriorate the hole expandability. So 0.010%
The following was made. Note that the content is preferably 0.001% or less.
【００１２】また、穴拡げ性向上のためにはＳを減らし
硫化物系介在物を減らすとともに、その球状化が有効で
ある。球状化にはＣａもしくはＲＥＭを添加することが
有効である。それぞれ０．０００５％、０．００５０％
未満では球状化の効果は少なく、それぞれ、０．０１０
０％、０．０５０％超では球状化の効果が飽和し、むし
ろ介在物を増加させて逆効果となるため、それぞれ０．
０００５〜０．０１００％、０．００５〜０．０５０％
とした。[0012] Furthermore, in order to improve the hole expandability, it is effective to reduce S and sulfide inclusions, as well as to make them spheroidal. Adding Ca or REM is effective for spheroidization. 0.0005% and 0.0050% respectively
Below 0.010, the effect of spheroidization is small.
If it exceeds 0% or 0.050%, the effect of spheroidization will be saturated, and if anything, it will increase inclusions and have the opposite effect.
0005~0.0100%, 0.005~0.050%
And so.
【００１３】次に本発明の組織上の制限とその理由を説
明する。後述する実施例におけるＡ鋼をベースにして前
記の課題を解決するための手段としての各種製造方法お
よびその製造条件の付近で製造された鋼板を整理、検討
した結果、次のことを確認した。Next, the organizational limitations of the present invention and their reasons will be explained. As a result of organizing and examining various manufacturing methods and steel plates manufactured around the manufacturing conditions as a means to solve the above problems based on Steel A in Examples described later, the following was confirmed.
【００１４】本発明において鋼板の延性を向上させるた
めには５％以上の残留オーステナイトを生じせしめるこ
とが必須で、そのためにはオーステナイトがＣ等の元素
の濃化により安定化されることが望まれる。このために
は■フェライトを生成させることによりオーステナイト
中へのＣ等の元素の濃化を促進させ、オーステナイトの
残留に寄与せしめること、■ベイナイト変態の進行に伴
い、オーステナイト中へのＣ等の元素の濃化を促進させ
、オーステナイトの残留に寄与せしめることが必要であ
る。In the present invention, in order to improve the ductility of the steel sheet, it is essential to generate 5% or more retained austenite, and for this purpose, it is desirable that the austenite be stabilized by enriching elements such as C. . To do this, ■ Promote the concentration of elements such as C in austenite by generating ferrite, contributing to the retention of austenite; ■ As the bainite transformation progresses, elements such as C in austenite It is necessary to promote the concentration of austenite and contribute to the retention of austenite.
【００１５】フェライトの生成によりオーステナイト中
へのＣ等の元素の濃化を促進させ、オーステナイトの残
留に寄与せしめようとする場合、フェライト占積率を増
加させ、フェライト粒を微細化することが必要である。
なぜならばＣ濃度が最も高く、オーステナイトとして残
留しやすい箇所はフェライトと未変態オーステナイトの
界面であり、その界面はフェライト占積率の増加とフェ
ライト粒の微細化により増加するからである。[0015] In order to promote the concentration of elements such as C in austenite through the formation of ferrite and contribute to the retention of austenite, it is necessary to increase the ferrite space factor and refine the ferrite grains. It is. This is because the location where the C concentration is highest and where it tends to remain as austenite is at the interface between ferrite and untransformed austenite, and this interface increases due to an increase in the ferrite space factor and the refinement of ferrite grains.
【００１６】図１と同じ条件の実験結果を整理した図２
に示すように少なくともＴＳ×Ｔ．Ｅｌ＞２０００を確
実に得るにはポリゴナルフェライト占積率（ＶＰＦ）％
とポリゴナルフェライト粒径（ｄＰＦ）μｍ の比：Ｖ
ＰＦ／ｄＰＦを７以上とすればよいことを見い出した。
（ポリゴナル・フェライトの占積率および平均粒径は光
学顕微鏡写真にて測定を行う。なおポリゴナル・フェラ
イトとはフェライトの内で軸比（長軸／短軸）＝１〜３
のものと定義する。）フェライト、残留オーステナイト
以外の残部組織はオーステナイト中へのＣ等の濃化に寄
与するベイナイトと（ベイナイト変態の進行により未変
態オーステナイトへＣが濃化し、オーステナイトを安定
化し、オーステナイトの残留に好ましい効果を発揮する
。）残留オーステナイト量を減少させるパーライト、マ
ルテンサイトを生成させないことが必要である。[0016] Figure 2 organizes the experimental results under the same conditions as Figure 1.
As shown in , at least TS×T. To ensure El>2000, polygonal ferrite space factor (VPF)%
and polygonal ferrite grain size (dPF) μm ratio: V
It has been found that it is sufficient to set PF/dPF to 7 or more. (The space factor and average grain size of polygonal ferrite are measured using optical micrographs. Polygonal ferrite is a type of ferrite with an axial ratio (major axis/minor axis) of 1 to 3.
Define as the thing of. ) The remaining structures other than ferrite and retained austenite consist of bainite, which contributes to the concentration of C, etc. in austenite; (as bainite transformation progresses, C is concentrated in untransformed austenite, stabilizes austenite, and has a favorable effect on the retention of austenite) ) It is necessary to prevent the formation of pearlite and martensite, which reduce the amount of retained austenite.
【００１７】次に本発明の製造工程上の制限とその理由
について説明する。フェライト占積率を増加させる（即
ちＶＰＦを大きくする）製造技術としては低温圧延、高
圧下圧延、仕上圧延後の冷却テーブル上におけるフェラ
イト変態のノーズ温度付近（Ａｒ１ 超〜Ａｒ３ ）で
の徐冷（フェライト変態のノーズ温度とは恒温フェライ
ト変態が最小時間で開始、終了する温度）が有効である
。フェライトを細粒化する（即ち、ｄＰＦを小さくする
）製造技術としては低温圧延、高圧下圧延、Ａｒ３ 変
態点近傍での急冷、フェライト変態後の急冷（粒成長を
避けるために）が有効である。従って、上記の前者の各
手段および後者のそれを組み合わせた製造方法が考えら
れる。Next, limitations in the manufacturing process of the present invention and their reasons will be explained. Manufacturing techniques for increasing the ferrite space factor (that is, increasing the VPF) include low-temperature rolling, high-reduction rolling, and slow cooling near the nose temperature of ferrite transformation (over Ar1 to Ar3) on a cooling table after finish rolling. The effective nose temperature for ferrite transformation is the temperature at which isothermal ferrite transformation starts and ends in the minimum time. Effective manufacturing techniques for refining ferrite grains (that is, reducing dPF) include low-temperature rolling, high-reduction rolling, rapid cooling near the Ar3 transformation point, and rapid cooling after ferrite transformation (to avoid grain growth). . Therefore, a manufacturing method that combines each of the above-mentioned former means and the latter means is conceivable.
【００１８】圧延温度：フェライト占積率を増し、フェ
ライトを細粒化するためには低温圧延が有効である。た
だし、Ａｒ３ −５０℃より低い温度では加工フェライ
トが増加し、延性を害する。また、Ａｒ３ ＋５０℃よ
り高い温度ではフェライトが充分生成しない。従ってＡ
ｒ３ ±５０℃が仕上圧延終了温度としては有効である
。さらに仕上圧延開始温度をＡｒ３＋１００℃以下とす
ることにより、フェライトの生成および微細化が促進さ
れる。Rolling temperature: Low temperature rolling is effective for increasing the ferrite space factor and making the ferrite grains finer. However, at temperatures lower than Ar3 -50°C, processed ferrite increases, impairing ductility. Further, at temperatures higher than Ar3 +50°C, ferrite is not sufficiently generated. Therefore A
r3 ±50°C is effective as the finish rolling finishing temperature. Further, by setting the finishing rolling start temperature to Ar3+100° C. or lower, the formation and refinement of ferrite are promoted.
【００１９】ただし、低温圧延は、薄物圧延（板厚≦２
ｍｍ）時、特に変形抵抗の高い高カーボン当量材もしく
は高合金材の圧延時には、圧延荷重の増大、形状確保の
困難等の操業上好ましからざる点がある。従って後述す
る熱間仕上圧延後の冷却テーブル上での冷却をコントロ
ールすることによってフェライトの生成および微細化を
はかることが有効である。その場合、Ａｒ３ ＋５０℃
超の熱間仕上圧延終了温度とすることが必要である。However, low-temperature rolling is thin rolling (thickness ≦2
mm), particularly when rolling high carbon equivalent materials or high alloy materials with high deformation resistance, there are unfavorable operational points such as an increase in rolling load and difficulty in securing the shape. Therefore, it is effective to generate and refine ferrite by controlling cooling on a cooling table after hot finish rolling, which will be described later. In that case, Ar3 +50℃
It is necessary to set the finishing temperature of hot finish rolling to an extremely high temperature.
【００２０】圧下率：熱間仕上圧延における合計圧下率
を８０％以上とするとフェライトの生成、微細化が促進
され、良好な材質が得られるため、下限を８０％以上と
した。Reduction ratio: If the total reduction ratio in hot finish rolling is 80% or more, the formation and refinement of ferrite will be promoted and a good material quality will be obtained, so the lower limit is set at 80% or more.
【００２１】冷却：熱間圧延後、Ａｒ３ 〜Ａｒ１ を
４０℃／ｓ以上の冷却速度で冷却してはオーステナイト
の残留に必要なフェライトの生成とＣ濃化が十分に進行
しないため、図６に示すような温度パターンに沿って圧
延後、Ｔ（Ａｒ１ ＜Ｔ≦Ａｒ３ ）まで冷却速度４０
℃／ｓ未満で冷却することが必要である。あるいは、さ
らに望ましい冷却方法として図７に示すパターンがあり
、圧延後Ｔ１ （Ａｒ１ ＜Ｔ１ ≦Ａｒ３ かつＡｒ
１ ＜Ｔ１ ＜圧延終了温度）まで冷却速度４０℃／ｓ
以上で冷却してフェライト変態により生成したフェライ
トの微細化と圧延中に生成したフェライトも含めて粒成
長の抑制をはかり、さらに続いてＴ２ （Ａｒ１ ＜Ｔ
２ ＜Ｔ１ ）まで冷却速度４０℃／ｓ未満で冷却する
ことによりフェライト変態ノーズ付近でフェライト占積
率を増加させ、より良好な材質が得られる。Cooling: After hot rolling, if Ar3 to Ar1 are cooled at a cooling rate of 40°C/s or more, the formation of ferrite and C concentration necessary for the retention of austenite will not proceed sufficiently. After rolling according to the temperature pattern shown, the cooling rate is 40 to T (Ar1 <T≦Ar3).
It is necessary to cool down at less than °C/s. Alternatively, as a more desirable cooling method, there is a pattern shown in FIG.
Cooling rate 40℃/s until 1 <T1 <rolling end temperature)
The above cooling is performed to refine the ferrite generated by ferrite transformation and to suppress grain growth, including ferrite generated during rolling, and then to T2 (Ar1 < T
2 < T1 ) at a cooling rate of less than 40° C./s, the ferrite space factor is increased near the ferrite transformation nose, and a better material quality can be obtained.
【００２２】Ａｒ３ を超える温度では冷却速度４０℃
／ｓ未満で冷却してもフェライトは生成せず、Ａｒ１
以下の温度まで冷却速度４０℃／ｓ未満で冷却するとパ
ーライトを生成するため、Ａｒ１ ＜Ｔ≦Ａｒ３ 、Ａ
ｒ１ ＜Ｔ２ ＜Ｔ１ ≦Ａｒ３ とする。その後の捲
き取り温度までの冷却速度はパーライトの生成を避け、
組織の微細化を助けるという観点から４０℃／ｓ以上と
する。[0022] At temperatures above Ar3, the cooling rate is 40°C.
Even if it is cooled at less than /s, ferrite is not generated and Ar1
Since pearlite is produced when cooling at a cooling rate of less than 40°C/s to the following temperature, Ar1 < T ≦ Ar3, A
Let r1 < T2 < T1 ≦Ar3. The subsequent cooling rate to the rolling temperature avoids the formation of pearlite.
From the viewpoint of helping to refine the structure, the temperature is set to 40° C./s or higher.
【００２３】図１と同じ条件で圧延し、冷却した後、捲
き取り温度を変えて実験した結果を図３、図４に示す。
捲取温度は５００℃をこえると捲取後ベイナイト変態が
過度に進行し、あるいはパーライトが生成し、図３に示
す如く体積比で５％以上の残留オーステナイトが得られ
なくなるため上限を５００℃以下とする。また、３５０
℃未満では図４に示す如く、マルテンサイトが生成し穴
拡げ性が劣化するため、下限を３５０℃以上とする。ま
た、過度のベイナイト変態を避けより多量のオーステナ
イトを残留させるため図３に示す如く、捲取後、水中浸
漬、ミスト噴霧等により３０℃／ｈｒ以上の冷却速度で
２００℃以下まで冷却することがより有効である。[0023] Figures 3 and 4 show the results of an experiment conducted by rolling under the same conditions as in Figure 1, cooling, and then changing the winding temperature. If the winding temperature exceeds 500°C, bainite transformation will proceed excessively after winding, or pearlite will form, making it impossible to obtain a retained austenite of 5% or more by volume as shown in Figure 3, so the upper limit should be 500°C or less. shall be. Also, 350
If the temperature is lower than 350°C, martensite is generated and the hole expandability deteriorates as shown in FIG. 4, so the lower limit is set to 350°C or higher. In addition, in order to avoid excessive bainite transformation and retain a larger amount of austenite, as shown in Figure 3, after winding, it is possible to cool down to 200°C or less by immersion in water, mist spraying, etc. at a cooling rate of 30°C/hr or more. more effective.
【００２４】以上の各製造技術の組み合わせた技術とし
て図６および図７に集約される。そして、仕上圧延終了
温度が低温範囲（Ａｒ３ ±５０℃）のものと高温範囲
（Ａｒ３ ＋５０℃以上）のものの２種類がある。さら
に上記４種類の製造方法に、熱間仕上圧延開始温度の上
限をＡｒ３ ＋１００℃以下と規制したもの、または捲
取後の冷却方法を規制したものの片方あるいは両方を組
み合わせた製造方法がある。その組み合わせを重ねる程
、効果も大きくなることは当然である。A combination of the above manufacturing techniques is summarized in FIGS. 6 and 7. There are two types of finish rolling, one in a low temperature range (Ar3 ±50°C) and one in a high temperature range (Ar3 +50°C or higher). Furthermore, in addition to the above four types of manufacturing methods, there is a manufacturing method in which the upper limit of the hot finish rolling start temperature is regulated to Ar3+100° C. or lower, or a manufacturing method in which the cooling method after winding is regulated, or a combination of both. It goes without saying that the more these combinations are combined, the greater the effect will be.
【００２５】[0025]
【実施例】本発明による実施例を以下に示す。表１に示
す化学成分を有するＡ〜Ｋの鋼を図６または図７に従っ
て表２に示す条件で鋼板を製造した。ここで鋼ＣはＣ量
が下限量を割ったものであり、鋼ＥおよびＨはそれぞれ
Ｓｉ量およびＭｎ量が下限量を割ったものである。表２
における記号を説明すると、下記のようになる。[Example] Examples according to the present invention are shown below. Steel plates A to K having the chemical components shown in Table 1 were manufactured under the conditions shown in Table 2 according to FIG. 6 or 7. Here, in steel C, the amount of C is less than the lower limit, and in steels E and H, the amount of Si and the amount of Mn are less than the lower limit, respectively. Table 2
The symbols in are explained as follows.
【００２６】ＦＴ０ は仕上圧延開始温度ＦＴ７ は仕
上圧延終了温度
ＣＴは捲取温度
ＴＳは引張強さ
Ｔ．Ｅｌは全伸び
γＲ は残留オーステナイト体積比（％）ＶＰＦはポリ
ゴナルフェライト占積率（％）ｄＰＦはポリゴナルフェ
ライト粒径（μｍ ）表１、表２の鋼のＡｒ１ 温度は
Ａ〜ＣおよびＦ〜Ｈ、Ｊが６５０℃、Ｄが６３５℃、Ｅ
が６１０℃、ＩとＫが６４０℃であり、またＡｒ３ 温
度はそれぞれ順に８００，８１０，８１５，７９０，７
８０，８１０，８１０，８２０，７９０，８０５，７９
５℃であった。FT0 is finish rolling start temperature FT7 is finish rolling end temperature CT is winding temperature TS is tensile strength T. El is the total elongation γR is the retained austenite volume ratio (%) VPF is the polygonal ferrite space factor (%) dPF is the polygonal ferrite grain size (μm) Ar1 of the steel in Tables 1 and 2 Temperatures are A to C and F ~H, J is 650℃, D is 635℃, E
is 610℃, I and K are 640℃, and the Ar3 temperatures are 800, 810, 815, 790, 7, respectively.
80,810,810,820,790,805,79
The temperature was 5°C.
【００２７】本発明法に沿うものはＮｏ．１６，１７，
１８，１９，２０，２１，２２，２４，２７，２８，２
９，３１，３３，３５，３６であり、当初ＴＳ×Ｔ．Ｅ
ｌ≧２０００をめざしたが、複合効果により、図５に示
されるようにＴＳ×Ｔ．Ｅｌ＞２４００という非常に良
好な強度・延性バランスを示す。これに対し比較例は各
々良好な延性が得られていない。The method according to the present invention is No. 16, 17,
18, 19, 20, 21, 22, 24, 27, 28, 2
9, 31, 33, 35, 36, initially TS×T. E
Although we aimed for TS×T.l≧2000, due to the combined effect, as shown in FIG. Shows a very good balance of strength and ductility with El>2400. On the other hand, in the comparative examples, good ductility was not obtained.
【００２８】[0028]
【表１】[Table 1]
【００２９】[0029]
【表２】[Table 2]
【００３０】[0030]
【表３】[Table 3]
【００３１】[0031]
【表４】[Table 4]
【００３２】[0032]
【表５】[Table 5]
【００３３】[0033]
【発明の効果】本発明によれば以上の説明から明らかな
ごとく延性の特に優れた熱延高強度鋼板（ＴＳ×Ｔ．Ｅ
ｌ≧２４００）を特別な合金元素などを必要とせずにか
つ高生産条件で製造できるため、産業上の効果は極めて
大きい。According to the present invention, as is clear from the above explanation, a hot rolled high strength steel plate (TS×T.E.
l≧2400) without the need for special alloying elements and under high production conditions, the industrial effect is extremely large.
【図１】残留オーステナイト体積比とＴＳ×Ｔ．Ｅｌの
関係を示した図。FIG. 1: Retained austenite volume ratio and TS×T. A diagram showing the relationship between El.
【図２】ＶＰＦ／ｄＰＦとＴＳ×Ｔ．Ｅｌの関係を示し
た図。FIG. 2: VPF/dPF and TS×T. A diagram showing the relationship between El.
【図３】捲取温度と残留オーステナイト体積比の関係を
示した図。FIG. 3 is a diagram showing the relationship between winding temperature and retained austenite volume ratio.
【図４】捲取温度と穴拡げ比の関係を示した図。FIG. 4 is a diagram showing the relationship between winding temperature and hole expansion ratio.
【図５】ＴＳとＴ．Ｅｌの関係を示した図。FIG. 5: TS and T.S. A diagram showing the relationship between El.
【図６】仕上圧延終了温度、冷却速度■、Ｔ、冷却速度
■の関係を示した温度パターン図。FIG. 6 is a temperature pattern diagram showing the relationship among finish rolling end temperature, cooling rate (■), T, and cooling rate (■).
【図７】仕上圧延終了温度、冷却速度■′、Ｔ１ 、冷
却速度■′、Ｔ２ 、冷却速度■′の関係を示した温度
パターン図。FIG. 7 is a temperature pattern diagram showing the relationship among finish rolling end temperature, cooling rate ■', T1, cooling rate ■', T2, and cooling rate ■'.
Claims (2)
未満、Ｓｉ：０．５〜２．０％、Ｍｎ：０．５〜２．０
％、残部が鉄および不可避的不純物からなる鋼を、全圧
下率が８０％以上の熱間仕上圧延を行い、その圧延終了
温度をＡｒ３ ＋５０℃超とし、該温度から４０℃／ｓ
未満の冷却速度で冷却を開始し、その鋼のＡｒ３ 以下
でＡｒ１ 超となる温度範囲内の任意の温度Ｔで前記冷
却を終了し、続けて冷却温度４０℃／ｓ以上で冷却して
３５０〜５００℃で捲き取り、ポリゴナルフェライト占
積率ＶＰＦ（％）とポリゴナルフェライト平均粒径ｄＰ
Ｆ（μｍ ）の比ＶＰＦ／ｄＰＦが７以上でかつ残留オ
ーステナイトを体積比で５％以上含むフェライト、ベイ
ナイトおよび残留オーステナイトの組織から構成され、
強度−延性バランスＴＳ×Ｔ．Ｅｌで２０００ｋｇｆ／
ｍｍ２ ・％以上であることを特徴とする加工性に優れ
た熱延高強度鋼板の製造方法。[Claim 1] C: more than 0.15 to 0.3% by weight
less than, Si: 0.5-2.0%, Mn: 0.5-2.0
%, the balance consists of iron and unavoidable impurities, hot finish rolling is carried out at a total reduction rate of 80% or more, the rolling end temperature is set to exceed Ar3 +50°C, and from this temperature the steel is heated at 40°C/s.
The cooling is started at a cooling rate of less than 350℃/s, and the cooling is finished at an arbitrary temperature T within the temperature range of Ar3 or less and exceeding Ar1 of the steel, and then cooling is continued at a cooling temperature of 40℃/s or more to 350 to 350℃. Rolling at 500℃, polygonal ferrite space factor VPF (%) and polygonal ferrite average grain size dP
It is composed of a structure of ferrite, bainite and retained austenite with a ratio of F (μm) VPF/dPF of 7 or more and containing retained austenite in a volume ratio of 5% or more,
Strength-ductility balance TS×T. 2000kgf/El
A method for producing a hot-rolled high-strength steel sheet with excellent workability, characterized in that the steel sheet has a hardness of at least mm2.%.
未満、Ｓｉ：０．５〜２．０％、Ｍｎ：０．５〜２．０
％に加えて、Ｃａ：０．０００５〜０．０１００％、Ｒ
ＥＭ：０．００５〜０．０５０％のどちらか１種を含有
し、かつ、Ｓ：０．０１０％以下に制限し、残部が鉄お
よび不可避的不純物からな鋼を、全圧下率が８０％以上
の熱間仕上圧延を行い、その圧延終了温度をＡｒ３ ＋
５０℃超とし、該温度から４０℃／ｓ未満の冷却速度で
冷却を開始し、その鋼のＡｒ３ 以下でＡｒ１ 超とな
る温度範囲内の任意の温度Ｔで前記冷却を終了し、続け
て冷却温度４０℃／ｓ以上で冷却して３５０〜５００℃
で捲き取り、ポリゴナルフェライト占積率ＶＰＦ（％）
とポリゴナルフェライト平均粒径ｄＰＦ（μｍ ）の比
ＶＰＦ／ｄＰＦが７以上でかつ残留オーステナイトを体
積比で５％以上含むフェライト、ベイナイトおよび残留
オーステナイトの組織から構成され、強度−延性バラン
スＴＳ×Ｔ．Ｅｌで２０００ｋｇｆ／ｍｍ２ ・％以上
であることを特徴とする加工性に優れた熱延高強度鋼板
の製造方法。[Claim 2] C: more than 0.15 to 0.3% by weight
less than, Si: 0.5-2.0%, Mn: 0.5-2.0
In addition to %, Ca: 0.0005-0.0100%, R
Steel containing one of EM: 0.005 to 0.050%, S: limited to 0.010% or less, and the remainder being iron and unavoidable impurities, with a total reduction rate of 80%. The above hot finish rolling is carried out, and the rolling end temperature is set to Ar3 +
Above 50°C, start cooling from this temperature at a cooling rate of less than 40°C/s, end the cooling at an arbitrary temperature T within the temperature range where the steel reaches Ar3 or below and exceeds Ar1, and then continue cooling. Cooling at a temperature of 40℃/s or higher to 350-500℃
Polygonal ferrite space factor VPF (%)
It is composed of a structure of ferrite, bainite, and retained austenite with a ratio of VPF/dPF of polygonal ferrite average grain size dPF (μm) of 7 or more and a volume ratio of 5% or more of retained austenite, and has a strength-ductility balance TS × T ．． A method for producing a hot-rolled high-strength steel sheet with excellent workability, characterized by an El of 2000 kgf/mm2.% or more.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10765291A JPH04228517A (en) | 1988-02-29 | 1991-05-13 | Manufacture of hot rolled high strength steel sheet excellent in workability |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63044527A JPS6479345A (en) | 1987-06-03 | 1988-02-29 | High-strength hot rolled steel plate excellent in workability and its production |
| JP10765291A JPH04228517A (en) | 1988-02-29 | 1991-05-13 | Manufacture of hot rolled high strength steel sheet excellent in workability |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP63044527A Division JPS6479345A (en) | 1987-06-03 | 1988-02-29 | High-strength hot rolled steel plate excellent in workability and its production |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04228517A true JPH04228517A (en) | 1992-08-18 |
| JPH0565566B2 JPH0565566B2 (en) | 1993-09-20 |
Family
ID=26384459
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP10765291A Granted JPH04228517A (en) | 1988-02-29 | 1991-05-13 | Manufacture of hot rolled high strength steel sheet excellent in workability |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH04228517A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000054072A (en) * | 1998-08-03 | 2000-02-22 | Kobe Steel Ltd | High strength hot rolled steel plate excellent in press formability |
| US6190469B1 (en) | 1996-11-05 | 2001-02-20 | Pohang Iron & Steel Co., Ltd. | Method for manufacturing high strength and high formability hot-rolled transformation induced plasticity steel containing copper |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999013123A1 (en) * | 1997-09-11 | 1999-03-18 | Kawasaki Steel Corporation | Hot rolled steel plate to be processed having hyper fine particles, method of manufacturing the same, and method of manufacturing cold rolled steel plate |
| JP4692018B2 (en) * | 2004-03-22 | 2011-06-01 | Ｊｆｅスチール株式会社 | High-tensile hot-rolled steel sheet with excellent strength-ductility balance and method for producing the same |
-
1991
- 1991-05-13 JP JP10765291A patent/JPH04228517A/en active Granted
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6190469B1 (en) | 1996-11-05 | 2001-02-20 | Pohang Iron & Steel Co., Ltd. | Method for manufacturing high strength and high formability hot-rolled transformation induced plasticity steel containing copper |
| JP2000054072A (en) * | 1998-08-03 | 2000-02-22 | Kobe Steel Ltd | High strength hot rolled steel plate excellent in press formability |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0565566B2 (en) | 1993-09-20 |
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