JPH06228653A - Production of high strength hot rolled steel sheet excellent in bulging property at high yield - Google Patents
Production of high strength hot rolled steel sheet excellent in bulging property at high yieldInfo
- Publication number
- JPH06228653A JPH06228653A JP1574093A JP1574093A JPH06228653A JP H06228653 A JPH06228653 A JP H06228653A JP 1574093 A JP1574093 A JP 1574093A JP 1574093 A JP1574093 A JP 1574093A JP H06228653 A JPH06228653 A JP H06228653A
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- Japan
- Prior art keywords
- cooling
- steel
- steel sheet
- hot
- high yield
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- 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.)
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- Heat Treatment Of Sheet Steel (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
Description
【0001】[0001]
【産業上の利用分野】本発明は、590N/mm2 以上の
引張強度と高い伸び特性、すなわち高い張り出し成形性
を有する熱延鋼板を高い歩留まりで製造する方法にかか
わる。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-rolled steel sheet having a tensile strength of 590 N / mm 2 or more and a high elongation property, that is, a high stretch formability with a high yield.
【0002】[0002]
【従来の技術】地球温暖化に端を発した自動車の燃料消
費規制から、自動車の軽量化が重要な課題となり、高強
度鋼板の果たす役割が従来以上に大きくなった現在、高
い加工性を有する種々の高強度鋼板が開発されつつあ
る。その中でも、変態誘起塑性による高い破断伸び特性
を示す残留オーステナイトを含む高強度鋼板は、その高
い張り出し成形性から、新しい高強度鋼板として脚光を
あびている。2. Description of the Related Art Due to the fuel consumption regulations of automobiles caused by global warming, weight reduction of automobiles has become an important issue, and the role of high-strength steel sheets has become greater than ever, and it has high workability. Various high strength steel sheets are being developed. Among them, a high-strength steel sheet containing retained austenite that exhibits high elongation at break due to transformation-induced plasticity has been highlighted as a new high-strength steel sheet because of its high stretch formability.
【0003】残留オーステナイトを含む熱延高強度鋼板
の製造技術としては例えば特開平1−79345号公
報、特開昭60−184664号公報、特開平1−15
9317号公報がある。特に、後の2つの技術は、熱延
のランアウトテーブルから巻取りにいたる工程において
限定した条件で製造する方法であり、これにより得られ
る特性は、例えば980N/mm2 級の引張強度で30%
以上の破断伸びを示す加工性に極めて優れた高強度熱延
鋼板である。As a technique for producing a hot rolled high strength steel sheet containing retained austenite, for example, JP-A-1-79345, JP-A-60-184664 and JP-A-1-15 are available.
There is a 9317 publication. In particular, the latter two technologies are methods of manufacturing under the limited conditions in the process of winding from a hot rolling runout table, and the properties obtained by this are, for example, 980 N / mm 2 class tensile strength of 30%.
It is a high-strength hot-rolled steel sheet exhibiting the above-mentioned elongation at break and having excellent workability.
【0004】[0004]
【発明が解決しようとする課題】自動車部品は、たいて
いの場合クランクプレスにより高速かつ大量に生産され
る。従って、自動車部品用の鋼帯は、高位に安定した材
質でかつ高い均一性を保っている必要がある。換言すれ
ば材質歩留まりが高ければ、材料ロスとプレストラブル
がなくなることにより、一部品当りの値段が安くなるこ
とや、計画性の高い自動車生産を行うことができるよう
になる。しかしながら、概して従来技術により熱延工程
のみで製造される残留オーステナイトを含む熱延高強度
鋼板の場合は、製造上ランアウトテーブルでの精密な冷
却制御を必要とし、特に400℃近傍なる水による冷却
の核沸騰と膜沸騰の遷移温度域で巻取ることも重なり、
この条件がばらつくことによる低い材質安定性、低い歩
留まりとなることが多く、工業生産上の大きな課題であ
った。一方、これを回避するために巻取り後に熱処理を
行う技術として特開平1−259210号公報や特開平
1−259121号公報に示された技術が提案されてい
る。これらは、歩留まりに関しては高いものが得られる
ものと判断されるが、一工程増えることによる製造原価
増は避けられない。Automobile parts are often produced at high speed and in large quantities by crank presses. Therefore, the steel strip for automobile parts needs to be made of a highly stable material and maintain high uniformity. In other words, if the material yield is high, the material loss and the press trouble are eliminated, so that the price per part can be reduced and the automobile production with high planning can be performed. However, in the case of hot-rolled high-strength steel sheet containing residual austenite, which is generally produced only by the hot-rolling process according to the conventional technique, precise cooling control at a run-out table is required in production, and particularly, cooling with water near 400 ° C. Winding in the transition temperature range of nucleate boiling and film boiling also overlaps,
Due to variations in these conditions, low material stability and low yield often occur, which are major problems in industrial production. On the other hand, in order to avoid this, a technique disclosed in Japanese Patent Application Laid-Open No. 1-259210 and Japanese Patent Application Laid-Open No. 1-259121 has been proposed as a technique for performing heat treatment after winding. Although it is judged that these yields high yields, an increase in manufacturing cost due to one additional process is inevitable.
【0005】[0005]
【課題を解決するための手段】本発明は、従来の高強度
熱延鋼板より高い加工性を有することから注目されてい
る残留オーステナイトを含む熱延高強度鋼板を社会の需
要にあわせるべく高い歩留まりでかつ安価に提供するこ
とを目的として発明されたものであり、その骨子とする
ところは、質量割合で、C:0.08〜0.25%、S
i:0.7〜2.5%、Mn:0.8〜3.0%、残部
実質的にFeからなる鋼を熱延するに際し、仕上圧延終
了温度をAr3 〜(Ar3 +70)℃とし、平均冷却速
度20℃/s以上で550℃以下に冷却するに際し、鋼
帯の上部からの冷却の熱伝達係数αU と鋼帯の下部から
の冷却の熱伝達係数αL の比(αU /αL )を0.8以
上1.1未満となるようにし、350〜500℃で巻取
ることにより得られる、張り出し成形性に優れた高強度
熱延鋼板を高い歩留まりで製造する方法である。The present invention provides a hot-rolled high-strength steel sheet containing retained austenite, which is attracting attention because it has higher workability than the conventional high-strength hot-rolled steel sheet, and has a high yield to meet the needs of society. It was invented for the purpose of providing it at low cost, and the main point is that C: 0.08-0.25%, S
i: 0.7 to 2.5%, Mn: 0.8 to 3.0%, and the balance of finish rolling is Ar 3 to (Ar 3 +70) ° C. when hot-rolling steel consisting essentially of Fe. When cooling at an average cooling rate of 20 ° C./s or more to 550 ° C. or less, the ratio of the heat transfer coefficient α U of cooling from the upper part of the steel strip to the heat transfer coefficient α L of cooling from the lower part of the steel strip (α U / α L ) to be 0.8 or more and less than 1.1, and a method for producing a high-strength hot-rolled steel sheet excellent in stretch formability, which is obtained by winding at 350 to 500 ° C. with a high yield. is there.
【0006】[0006]
【作用】次に、本発明の各要件の作用および数値限定理
由について述べる。 C:本発明鋼は、実質上残留オーステナイトを残留させ
ることにより高い成形性を有する高強度鋼板とする。特
に本発明のようにオーステンパーによりオーステナイト
を残留させる場合、残留オーステナイト中には一般にC
が1.0〜1.6%ほど濃化しているといわれている。
本発明者らの測定結果でも1.0〜1.2%のC濃度を
有している。このような残留オーステナイトを体積率で
例えば5%以上確保させるためには、少なくとも0.0
5%以上のCが必要となる。さらに、不可避的に形成さ
れる微細な鉄炭化物の生成も考慮に入れると0.08%
のCが必要である。従って、本発明では0.08%をC
の下限値とした。当然、到達させる引張強度レベルに応
じてC量を変更すればよい。上限は、スポット溶接性を
考慮し、0.25%とした。これ以上のCが鋼中に含有
されると、スポット溶接部のナゲット内破断が避けられ
ない。好ましいCの含有範囲は、0.1〜0.2%であ
る。Next, the function of each requirement of the present invention and the reason for limiting numerical values will be described. C: The steel of the present invention is a high-strength steel sheet having high formability by substantially remaining retained austenite. In particular, when austenite is retained by austempering as in the present invention, C is generally contained in the retained austenite.
Is said to be about 1.0 to 1.6% thicker.
The measurement results of the present inventors also have a C concentration of 1.0 to 1.2%. In order to secure such retained austenite in a volume ratio of, for example, 5% or more, at least 0.0
5% or more of C is required. In addition, 0.08% when the generation of inevitable fine iron carbide is taken into consideration.
C is required. Therefore, in the present invention, 0.08% is C
The lower limit of Of course, the amount of C may be changed according to the tensile strength level to be reached. The upper limit was set to 0.25% in consideration of spot weldability. If more C is contained in the steel, fracture in the nugget of the spot welded portion cannot be avoided. A preferred C content range is 0.1 to 0.2%.
【0007】Si:Siは、本発明においては仕上圧延
終了からランアウトテーブルでの冷却途中過程における
ポリゴナルフェライトの生成と、冷却途中過程からの巻
取り後の徐冷過程におけるオーステンパーにおいて未変
態オーステナイト中の炭化物生成の抑制という役割を果
たす。この効果を発揮させるためには少なくとも0.7
%のSiの含有が必要である。上限は、コストの観点と
転炉での溶製の観点から2.5%とした。好ましいSi
の含有範囲は1.0〜2.2%である。In the present invention, Si is an untransformed austenite in the austemper in the austemper in the process of cooling from the end of finish rolling to the process of cooling on the run-out table and in the process of slow cooling after winding from the process of cooling. It plays a role of suppressing the formation of carbide in the inside. To achieve this effect, at least 0.7
% Si content is required. The upper limit was set to 2.5% from the viewpoint of cost and melting in the converter. Preferred Si
The content range of is 1.0 to 2.2%.
【0008】Mn:Mnは、オーステナイトの安定化を
もたらすとともに鋼帯の引張強度を高める。本発明鋼に
おいては、これらを有効に発揮させるためにMnを含有
させる。これらの効果を発揮させるためには少なくとも
0.8%のMnの含有が必要である。狙いとする引張強
度に応じてMnレベルは下限値以上で変更すればよい。
上限は、コストの観点と転炉での溶製の観点から3.0
%とした。好ましいMnの含有範囲は1.0〜2.0%
である。Mn: Mn brings about stabilization of austenite and also enhances the tensile strength of the steel strip. In the steel of the present invention, Mn is contained in order to effectively exhibit these. In order to exert these effects, the content of Mn of at least 0.8% is required. The Mn level may be changed to be equal to or higher than the lower limit value according to the desired tensile strength.
The upper limit is 3.0 from the viewpoint of cost and melting in the converter.
%. The preferable Mn content range is 1.0 to 2.0%.
Is.
【0009】S,Ca:伸びフランジ性を劣化させたく
ない場合には、MnSの形成を回避するためにSを徹底
的に下げることが有効であることが多くの公知例から明
らかであり、本発明においてこれを採用しても何等効果
をなくすものではない。その場合、0.005%以下の
含有であることが好ましい。さらに不可避的に残留する
SをCaSとして固定することも明らかとなっており、
この場合も本発明の効力をなくすものではなく、0.0
03%程度以下の含有とすることが好ましい。 Al:Alは、脱酸を目的として使用されることが多
く、MnやSiの転炉での溶製上の歩留まりを向上させ
る意味も含め本発明で用いることができる。その場合
は、0.01〜0.1%の含有範囲であればよく、好ま
しくは0.02〜0.05%程度でよい。S, Ca: It is clear from many publicly known examples that it is effective to thoroughly reduce S in order to avoid the formation of MnS when it is not desired to deteriorate the stretch flangeability. Even if this is adopted in the invention, the effect is not lost. In that case, the content is preferably 0.005% or less. Furthermore, it has been clarified that S that remains inevitable is fixed as CaS,
Even in this case, the effect of the present invention is not lost, and 0.0
It is preferable that the content be about 03% or less. Al: Al is often used for the purpose of deoxidation, and can be used in the present invention including the meaning of improving the yield of Mn and Si during melting in a converter. In that case, the content range is 0.01 to 0.1%, and preferably about 0.02 to 0.05%.
【0010】次に、本発明における熱延方法の数値限定
理由について述べる。 仕上圧延終了温度:仕上圧延終了温度は、熱間圧延中の
オーステナイトの粒径を決定する。オーステナイトの粒
径は、その後のランアウトテーブルにおける冷却過程に
おいてポリゴナルフェライトの生成を左右するものであ
り、本発明においてする必要がある。すなわち、本発明
は冷却制御性をよくするためにランアウトテーブルの前
半部分で冷却を開始させることを意図することから、あ
まり冷却開始までの空冷時間をとりたくない。一方、残
留オーステナイトを得るための第1段階として未変態オ
ーステナイトへのCの濃化を十分に行わせるためにポリ
ゴナルフェライトを生成させる必要がある。従って、こ
の両者を実現させるために成分上の考慮と仕上圧延温度
の考慮が必要である。前者についてはSiの限定理由で
述べた通りである。後者については仕上圧延温度はAr
3 変態点直上であることが必要である。工業的な製造を
考慮にいれ、本発明においては仕上圧延終了温度をAr
3 〜(Ar3 +70)℃とした。これを超える仕上圧延
終了温度となると、ポリゴナルフェライトが生成しにく
くなり生成させるための特別の考慮が必要となる。Next, the reasons for limiting the numerical values of the hot rolling method according to the present invention will be described. Finish rolling end temperature: The finish rolling end temperature determines the grain size of austenite during hot rolling. The grain size of austenite influences the formation of polygonal ferrite in the subsequent cooling process on the run-out table, and is required in the present invention. That is, since the present invention intends to start cooling in the first half of the runout table in order to improve the cooling controllability, it is not necessary to take an air cooling time until the start of cooling. On the other hand, as the first step for obtaining retained austenite, it is necessary to generate polygonal ferrite in order to sufficiently enrich C in untransformed austenite. Therefore, in order to realize both of these, it is necessary to consider the composition and the finish rolling temperature. The former is as described in the reason for limiting Si. For the latter, the finish rolling temperature is Ar
3 Must be directly above the transformation point. In consideration of industrial production, the finish rolling end temperature is set to Ar in the present invention.
The temperature was set to 3 to (Ar 3 +70) ° C. If the finish rolling finish temperature exceeds this, it is difficult to form polygonal ferrite, and special consideration is required to form it.
【0011】ランアウトテーブルにおける冷却条件と冷
却方法:冷却条件は、平均冷却速度20℃/s以上で5
50℃以下まで冷却する。平均冷却速度の下限値20℃
/sは、これ未満であるとパーライトまたは粗大な鉄炭
化物を含むベイナイトの生成が避けられないためにこれ
を定めた。上限は特に定めるものではないが、冷却終了
温度の制御性から現状の技術では150℃/s程度まで
と考えられる。好ましい冷却速度の範囲は、30〜10
0℃/sである。また、550℃以下までの冷却につい
ては、これを超える冷却終了であるとこれもパーライト
または粗大な鉄炭化物を含むベイナイトの生成が避けら
れないためにこれを定めた。もちろん、下限値は巻取温
度となる。しかしながら、冷却制御性のことを考慮に入
れると好ましい冷却終了温度範囲は550〜450℃で
ある。これは水による冷却の核沸騰と膜沸騰の遷移温度
が380〜450℃程度にあるためであり、この温度域
を空冷とすると冷却ばらつきが小さくてすむために好ま
しい。Cooling condition and cooling method in run-out table: Cooling condition is 5 at an average cooling rate of 20 ° C./s or more.
Cool to below 50 ° C. Lower limit of average cooling rate 20 ℃
/ S is set because the production of bainite containing pearlite or coarse iron carbide is unavoidable when it is less than this. The upper limit is not particularly specified, but it is considered to be up to about 150 ° C./s in the present technology due to the controllability of the cooling end temperature. A preferable cooling rate range is 30 to 10
It is 0 ° C / s. Further, regarding cooling to 550 ° C. or lower, if the cooling exceeding this is also inevitable, the formation of bainite containing pearlite or coarse iron carbide is unavoidable. Of course, the lower limit value is the winding temperature. However, in consideration of the cooling controllability, the preferable cooling end temperature range is 550 to 450 ° C. This is because the transition temperature between the nucleate boiling and the film boiling for cooling with water is about 380 to 450 ° C., and it is preferable to use air cooling in this temperature range because the cooling variation can be small.
【0012】冷却方法は、本発明において最も重要な構
成要件である。鋼帯の上部からの冷却の熱伝達係数αU
と鋼帯の下部からの冷却の熱伝達係数αL の比(αU /
αL)を0.8以上1.1未満となるようにする必要が
ある。冷却方法は、冷却中の鋼帯の形状に大きく影響を
およぼしているようである。推定の域ではあるが、これ
は以下の理由と考えられる。すなわち、上下の冷却能力
が大きく異なると鋼帯上に圧延方向に向かって水が残る
ような形状となりこれが助長されると鋼帯が圧延方向に
対して波のような形状となる。これが、局部的に鋼帯を
冷却させるようなことになり、鋼帯の温度ばらつきが大
きくなる。その状態でさらに水冷が施されると長手方向
に大きな温度ばらつきが生じ、これが材質ばらつきを招
き、歩留まりを低下させる。The cooling method is the most important constituent element in the present invention. Heat transfer coefficient for cooling from the top of the steel strip α U
And the ratio of the heat transfer coefficient α L for cooling from the bottom of the steel strip (α U /
It is necessary to make α L ) 0.8 or more and less than 1.1. The cooling method seems to have a great influence on the shape of the steel strip during cooling. Although it is an area of estimation, this is considered to be due to the following reasons. That is, if the upper and lower cooling capacities are significantly different, the shape of water remains on the steel strip in the rolling direction, and if this is promoted, the steel strip becomes wavy in the rolling direction. This causes the steel strip to be locally cooled, and the temperature variation of the steel strip increases. If water cooling is further applied in this state, a large temperature variation occurs in the longitudinal direction, which causes a variation in material and reduces the yield.
【0013】形状不良には、仕上圧延終了後に開始する
ポリゴナルフェライトの変態による体積膨張も寄与して
いるものと推定され、部分的な変態進行は致命的な形状
不良につながるものと考えられる。このような形状不良
に起因する温度ばらつきを徹底的に少なくするために、
本発明者らが度重なる工場実験を行ったことはいうまで
もない。その結果、冷却安定性を高めるための冷却方法
は、上部からと下部からの冷却の熱伝達係数を制御する
ことにあることがわかり、本発明に至った。αU /αL
が0.8未満であっても1.1以上であっても温度ばら
つきが大きい。冷却バルブは、パイプラミナーでもスリ
ットラミナーでもさらには、スプレイノズルでも効果は
同じである。もちろん、主たる冷却のみならず、鋼帯上
に不可避的に残る水をクロススプレイやVスプレイによ
って切ることも本発明において採用すればよい。It is presumed that volume expansion due to transformation of polygonal ferrite, which starts after finishing rolling, also contributes to the shape defect, and it is considered that partial progress of transformation leads to fatal shape defect. In order to thoroughly reduce temperature variations due to such shape defects,
It goes without saying that the present inventors have conducted repeated factory experiments. As a result, it was found that the cooling method for enhancing the cooling stability is to control the heat transfer coefficient of cooling from the upper part and the lower part, and thus the present invention was completed. α U / α L
If the ratio is less than 0.8 or 1.1 or more, the temperature variation is large. The cooling valve has the same effect whether it is a pipe laminar, a slit laminar, or a spray nozzle. Of course, not only the main cooling but also cutting off the water unavoidably left on the steel strip by cross spraying or V spraying may be adopted in the present invention.
【0014】巻取温度:巻取温度は、350〜500℃
とする。これは、未変態γのオーステンパーによりベイ
ナイトフェライトのラス間や端部にCを濃化させ常温で
順安定な残留オーステナイトを生成させるために最終的
に必要な条件である。500℃を超えると実質上残留オ
ーステナイトは生成せず、350℃未満であると下部ベ
イナイトの生成により硬質になるとともに残留オーステ
ナイト量も減少する。好ましい巻取温度範囲は400〜
450℃である。さらに、鋼帯長手端部の材質を向上さ
せるために、鋼帯長手中央部よりも50〜100℃程度
巻取温度を上げることも本発明においては有効な方法で
ある。この場合も上限の巻取温度は500℃である。Winding temperature: The winding temperature is 350 to 500 ° C.
And This is a condition finally necessary to concentrate C between the laths and the ends of the bainite ferrite by the austemper of untransformed γ and to generate retained austenite that is normally stable at room temperature. If it exceeds 500 ° C., substantially no retained austenite is formed, and if it is less than 350 ° C., the lower bainite is formed to become hard and the amount of retained austenite also decreases. The preferred winding temperature range is 400-
It is 450 ° C. Further, in order to improve the material of the longitudinal end portion of the steel strip, it is also an effective method in the present invention to raise the winding temperature by about 50 to 100 ° C. above the central portion of the longitudinal length of the steel strip. Also in this case, the upper limit winding temperature is 500 ° C.
【0015】[0015]
(実施例1)表1に示す鋼Aを用い、表2に示す条件で
熱延した。表2のFT(仕上圧延終了温度)とCT(巻
取温度)は、当該コイルの実績温度範囲で示した。冷却
終了温度は、コイル長手全長についての測定機器がない
ことから、コイル長手方向中央部についての実績を示し
た。表2中の下線は、発明範囲外であることを示す。熱
延最終板厚は2.3mm、幅は1000mmである。(Example 1) Steel A shown in Table 1 was used and hot-rolled under the conditions shown in Table 2. FT (finishing rolling end temperature) and CT (winding temperature) in Table 2 are shown in the actual temperature range of the coil. Regarding the cooling end temperature, since there is no measuring device for the entire length of the coil, the actual results for the central portion in the longitudinal direction of the coil are shown. The underline in Table 2 indicates that it is outside the scope of the invention. The final hot-rolled sheet thickness is 2.3 mm and the width is 1000 mm.
【0016】[0016]
【表1】 [Table 1]
【0017】[0017]
【表2】 [Table 2]
【0018】このようにして得た熱延コイルに0.8%
の調質圧延を施した後、引張試験と残留オーステナイト
量の測定試験に供した。引張試験は、JIS Z220
1記載の5号試験片を用い、同Z2241記載の方法に
従って行い、降伏点強度YP、引張強度TS、破断伸び
Elを測定した。残留オーステナイト量は、X線回折に
より測定したα相の{100}と{211}、γ相の
{110}と{311}のX線強度から求めた。この測
定は、A−1からA−4の各熱延コイルについては長手
方向2m毎、幅方向100mm毎に行った。また、その他
のコイルについては長手方向は30m毎に行った。A鋼
は、TS≧780N/mm2 、El≧29%を目標に製造
したものであるので、これを達成した割合をその歩留ま
りとして、また平均の残留オーステナイト量をあわせて
表2に示した。表2から明らかなように、本発明方法に
よると確実に歩留まりが90%以上確保することができ
る。 (実施例2)表1のB〜D鋼を用い、仕上圧延温度、冷
却速度を発明範囲内とし、αU /αL を変更した熱延を
行った。その製造実績を表3に示した。αU /αL を変
更したので巻取温度は発明範囲外のものも発生した。こ
れにより得られた熱延コイルに0.8%の調質圧延を施
し、実施例1のA−1〜A−4の評価方法と同様に歩留
まりを算定した。なお、歩留まりの算定には各鋼のTS
とElの目標値(表3)を用いた。The hot rolled coil thus obtained has 0.8%
After the temper rolling was performed, it was subjected to a tensile test and a residual austenite amount measurement test. The tensile test is JIS Z220
The No. 5 test piece described in 1 was used, and the yield point strength YP, the tensile strength TS, and the elongation at break El were measured by the method described in Z2241. The amount of retained austenite was determined from the X-ray intensities of {100} and {211} of α phase and {110} and {311} of γ phase measured by X-ray diffraction. This measurement was performed for each of the hot-rolled coils A-1 to A-4 every 2 m in the longitudinal direction and every 100 mm in the width direction. For the other coils, the lengthwise direction was set every 30 m. Steel A was manufactured with the target of TS ≧ 780 N / mm 2 and El ≧ 29%. Therefore, the ratio of achieving this is taken as the yield, and the average amount of retained austenite is also shown in Table 2. As is clear from Table 2, according to the method of the present invention, a yield of 90% or more can be reliably ensured. (Example 2) Using the steels B to D shown in Table 1, hot rolling was performed with the finishing rolling temperature and the cooling rate set within the ranges of the invention and α U / α L changed. The manufacturing results are shown in Table 3. Since α U / α L was changed, some coiling temperatures were outside the range of the invention. The hot-rolled coil thus obtained was subjected to temper rolling of 0.8%, and the yield was calculated in the same manner as in the evaluation methods A-1 to A-4 of Example 1. For the calculation of yield, TS of each steel
And the target values for El (Table 3) were used.
【0019】[0019]
【表3】 [Table 3]
【0020】これで得られた歩留まりは、図1のように
なった。αU /αL が発明範囲内に入っている水準につ
いては高い歩留まりが維持された。The yield thus obtained is as shown in FIG. A high yield was maintained when α U / α L was within the range of the invention.
【0021】[0021]
【発明の効果】本発明によれば、高い伸び、すなわち張
り出し成形性に優れた残留オーステナイトを含む高強度
熱延鋼板が工業生産上重要な要素である高い歩留まりで
生産することができる。これは、昨今の自動車業界で重
要な課題となっている車体軽量化のための高強度鋼板の
使用に際して、単に成形性がよいという観点からの残留
オーステナイトを含む高強度鋼板の使用ということだけ
ではなく、高い製造歩留まりと材質均質性から自動車業
界にとっての素材購入の時の低コスト化、製造時のばら
つきの低減化につながり、自動車業界に対しての貢献度
は多大なものである。According to the present invention, a high-strength hot-rolled steel sheet containing retained austenite, which has high elongation, that is, is excellent in stretch formability, can be produced at a high yield, which is an important factor in industrial production. This means that when using high-strength steel sheets for weight reduction of car bodies, which has become an important issue in the automobile industry these days, it is not only the use of high-strength steel sheets containing retained austenite from the viewpoint of good formability. In addition, the high manufacturing yield and the homogeneity of the material lead to a reduction in cost at the time of purchasing a material for the automobile industry and a reduction in variation at the time of manufacture, and the contribution to the automobile industry is enormous.
【図1】歩留まりとαU /αL とのグラフである。FIG. 1 is a graph of yield and α U / α L.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 木原 茂 君津市君津1番地 新日本製鐵株式会社君 津製鐵所内 (72)発明者 上原 拓男 君津市君津1番地 新日本製鐵株式会社君 津製鐵所内 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Kihara 1 Kimitsu, Kimitsu-shi Kimitsu Works, Nippon Steel Corporation (72) Inventor Takuo Uehara 1 Kimitsu, Kimitsu-shi Kimitsu Co., Ltd. Inside the steelworks
Claims (1)
延終了温度をAr3 〜(Ar3 +70)℃とし、平均冷
却速度20℃/s以上で550℃以下に冷却するに際
し、鋼帯の上部からの冷却の熱伝達係数αU と鋼帯の下
部からの冷却の熱伝達係数αL の比(αU /αL )を
0.8以上1.1未満となるようにし、350〜500
℃で巻取ることにより得られる、張り出し成形性に優れ
た高強度熱延鋼板を高い歩留まりで製造する方法。1. By mass ratio, C: 0.08 to 0.25% Si: 0.7 to 2.5% Mn: 0.8 to 3.0% The remainder is hot-rolled steel consisting essentially of Fe. In doing so, the finish rolling finish temperature is set to Ar 3 to (Ar 3 +70) ° C., and when cooling to 550 ° C. or lower at an average cooling rate of 20 ° C./s or more, the heat transfer coefficient α U for cooling from the upper part of the steel strip is The ratio (α U / α L ) of the heat transfer coefficient α L of cooling from the lower part of the steel strip is set to 0.8 or more and less than 1.1, and 350 to 500
A method for producing a high-strength hot-rolled steel sheet excellent in stretch formability, which is obtained by winding at ℃, at a high yield.
Priority Applications (1)
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JP01574093A JP3417589B2 (en) | 1993-02-02 | 1993-02-02 | Method for producing high-strength hot-rolled steel sheet with excellent stretch formability at high yield |
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Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP01574093A JP3417589B2 (en) | 1993-02-02 | 1993-02-02 | Method for producing high-strength hot-rolled steel sheet with excellent stretch formability at high yield |
Publications (2)
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JPH06228653A true JPH06228653A (en) | 1994-08-16 |
JP3417589B2 JP3417589B2 (en) | 2003-06-16 |
Family
ID=11897164
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JP01574093A Expired - Lifetime JP3417589B2 (en) | 1993-02-02 | 1993-02-02 | Method for producing high-strength hot-rolled steel sheet with excellent stretch formability at high yield |
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2013013935A (en) * | 2011-06-07 | 2013-01-24 | Nippon Steel & Sumitomo Metal Corp | Cooling method of hot-rolled steel sheet |
US9186710B2 (en) | 2011-06-07 | 2015-11-17 | Nippon Steel & Sumitomo Metal Corporation | Method for cooling hot-rolled steel sheet |
US9211574B2 (en) | 2011-07-27 | 2015-12-15 | Nippon Steel & Sumitomo Metal Corporation | Method for manufacturing steel sheet |
US9566625B2 (en) | 2011-06-07 | 2017-02-14 | Nippon Steel & Sumitomo Metal Corporation | Apparatus for cooling hot-rolled steel sheet |
WO2018117471A1 (en) * | 2016-12-21 | 2018-06-28 | 주식회사 포스코 | High-strength and high-corrosion resistance steel wire and manufacturing method therefor |
-
1993
- 1993-02-02 JP JP01574093A patent/JP3417589B2/en not_active Expired - Lifetime
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2013013935A (en) * | 2011-06-07 | 2013-01-24 | Nippon Steel & Sumitomo Metal Corp | Cooling method of hot-rolled steel sheet |
US9186710B2 (en) | 2011-06-07 | 2015-11-17 | Nippon Steel & Sumitomo Metal Corporation | Method for cooling hot-rolled steel sheet |
US9566625B2 (en) | 2011-06-07 | 2017-02-14 | Nippon Steel & Sumitomo Metal Corporation | Apparatus for cooling hot-rolled steel sheet |
US9211574B2 (en) | 2011-07-27 | 2015-12-15 | Nippon Steel & Sumitomo Metal Corporation | Method for manufacturing steel sheet |
WO2018117471A1 (en) * | 2016-12-21 | 2018-06-28 | 주식회사 포스코 | High-strength and high-corrosion resistance steel wire and manufacturing method therefor |
Also Published As
Publication number | Publication date |
---|---|
JP3417589B2 (en) | 2003-06-16 |
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