JP3292619B2 - Manufacturing method of hot rolled steel sheet with excellent stretch flangeability - Google Patents
Manufacturing method of hot rolled steel sheet with excellent stretch flangeabilityInfo
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- JP3292619B2 JP3292619B2 JP06924095A JP6924095A JP3292619B2 JP 3292619 B2 JP3292619 B2 JP 3292619B2 JP 06924095 A JP06924095 A JP 06924095A JP 6924095 A JP6924095 A JP 6924095A JP 3292619 B2 JP3292619 B2 JP 3292619B2
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- temperature
- steel sheet
- winding
- stretch flangeability
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- Heat Treatment Of Sheet Steel (AREA)
Description
【０００１】[0001]
【産業上の利用分野】本発明は、複雑なプレス加工部品
の製造のための原板として好適に用いることができる伸
びフランジ性にすぐれる熱延鋼板に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel sheet having excellent stretch flangeability, which can be suitably used as an original sheet for producing a complicated pressed part.
【０００２】[0002]
【従来の技術】熱延鋼板の伸びフランジ性を確保するた
めには、介在物や硬質層の生成を制御し、打ち抜き断面
の亀裂やボイドの発生を抑える必要がある。例えば、５
００℃以上の温度での巻取りは、Ｐ等の粒界偏析のため
に脆化が進行し、鋼板の打抜き断面に亀裂やボイドを誘
発し、一方、未変態のオーステナイトを残存させて、５
００℃以下の温度で巻取れば、マルテンサイト等の硬質
相の生成を免れない。従って、伸びフランジ性にすぐれ
る熱延鋼板を安定して得るためには、巻取までの冷却で
変態をほぼ完了させると共に、５００℃以下で巻取るこ
とが必要である。2. Description of the Related Art In order to ensure the stretch flangeability of a hot-rolled steel sheet, it is necessary to control the formation of inclusions and hard layers to suppress the occurrence of cracks and voids in a punched cross section. For example, 5
Winding at a temperature of 00 ° C. or higher causes embrittlement to proceed due to grain boundary segregation of P and the like, and induces cracks and voids in the punched cross section of the steel sheet, while leaving untransformed austenite and causing
If it is wound at a temperature of 00 ° C. or less, the formation of a hard phase such as martensite is unavoidable. Therefore, in order to stably obtain a hot-rolled steel sheet having excellent stretch flangeability, it is necessary to substantially complete the transformation by cooling until winding, and to wind at 500 ° C. or lower.
【０００３】しかし、通常の熱延設備では、仕上温度の
維持や生産性の観点から、圧延から巻取までの間に十分
な冷却時間をとることができないので、実操業上は、巻
取までに変態を完了させることが困難である。特に、高
強度熱延鋼板では、Ｃｒ等のフェライト変態やパーライ
ト変態を強力に抑制する合金元素も添加されているの
で、巻取の後までオーステナイトが残存しやすい。そこ
で、従来、巻取時に多少のオーステナイトが残存してい
ても、伸びフランジ性にすぐれる鋼板を製造し得る方法
が強く要望されている。However, ordinary hot rolling equipment cannot provide a sufficient cooling time between rolling and winding from the viewpoint of maintenance of the finishing temperature and productivity, so that in actual operation, it is necessary to reduce the cooling time to winding. It is difficult to complete the transformation. In particular, in a high-strength hot-rolled steel sheet, since an alloying element such as Cr that strongly suppresses ferrite transformation and pearlite transformation is added, austenite tends to remain until after winding. Therefore, conventionally, there has been a strong demand for a method capable of producing a steel sheet having excellent stretch flangeability even if some austenite remains during winding.
【０００４】このような状況において、特開平４−２４
６１２７号公報には、疲労特性にすぐれる加工用熱延鋼
板の製造方法が示されているが、この方法によれば、熱
間圧延の後、７６０℃から６００℃までを冷却速度３０
℃／秒以上で冷却するので、合金元素の添加量の多い高
強度熱延鋼板の場合には、この冷却時にパーライトが十
分に析出せず、巻取まで多量のオーステナイトが残存
し、そこで、この残存オーステナイトが巻取後に変態
し、巻取温度が低いほど硬質化する。この硬質相は、プ
レス加工時にボイドの起点になりやすいので、鋼板の伸
びフランジ加工性を劣化させることとなり、好ましくな
い。In such a situation, Japanese Patent Laid-Open Publication No.
No. 6127 discloses a method for producing a hot-rolled steel sheet for processing having excellent fatigue properties. According to this method, after hot rolling, a cooling rate of 760 ° C. to 600 ° C. is 30 ° C.
Since cooling is performed at a rate of at least ° C / sec, in the case of a high-strength hot-rolled steel sheet containing a large amount of alloying elements, pearlite does not sufficiently precipitate during this cooling, and a large amount of austenite remains until winding. The remaining austenite is transformed after winding, and becomes harder as the winding temperature is lower. This hard phase is likely to be a starting point of a void during the press working, and thus deteriorates the stretch flangeability of the steel sheet, which is not preferable.
【０００５】巻取を高い温度で行なえば、巻取後に変態
しても、残存オーステナイトは変態後に著しく硬質化し
ないが、問題がある。例えば、特開平４−８８１２５号
公報には、伸びフランジ性にすぐれた自動車足回り用高
強度熱延鋼板の製造方法が記載されており、この方法に
よれば、巻取温度が５００℃以上であって、Ｐ等の粒界
偏析が進行しやすい６００℃から５００℃を徐冷するの
で、プレス前の打抜き加工断面に亀裂が生じやすく、こ
の亀裂から割れが生じ、伸びフランジ性が劣化する。巻
取後に徐冷するのは、鋼帯が円筒形のコイルになるため
である。[0005] If the winding is performed at a high temperature, the retained austenite does not harden significantly after the transformation even if it is transformed after the winding, but there is a problem. For example, Japanese Patent Application Laid-Open No. 4-88125 describes a method for producing a high-strength hot-rolled steel sheet for automobile undercarriage having excellent stretch flangeability. According to this method, a winding temperature of 500 ° C. or higher is used. Then, since the grain boundary segregation such as P is gradually cooled from 600 ° C. to 500 ° C., cracks are apt to be generated in the punched section before pressing, and cracks are generated from the cracks, and the stretch flangeability is deteriorated. The reason for the slow cooling after the winding is that the steel strip becomes a cylindrical coil.
【０００６】また、特開平４−２７６０２４号公報に
も、伸びフランジ性にすぐれた高強度熱延鋼板の製造が
記載されているが、残留オーステナイトを含んだ鋼板を
前提としている。しかし、残留オーステナイトは、不安
定であるので、安定した材質の鋼板を得るためには、室
温に冷却する過程で完全に変態させることが好ましい。
以上のように、巻取時にオーステナイトが残存する場
合、低温で巻取れば、残存オーステナイトが変態後、硬
質化し、他方、高温で巻取れば、Ｐ等の偏析による脆化
が生じることから、従来、伸びフランジ性にすぐれる高
強度熱延鋼板の製造は困難であった。Japanese Unexamined Patent Publication (Kokai) No. 4-276024 discloses the production of a high-strength hot-rolled steel sheet having excellent stretch flangeability, but presupposes a steel sheet containing retained austenite. However, since retained austenite is unstable, in order to obtain a steel plate of a stable material, it is preferable to completely transform during the process of cooling to room temperature.
As described above, when austenite remains at the time of winding, if winding at a low temperature, the remaining austenite is transformed and hardened after transformation, while if winding at a high temperature, embrittlement due to segregation of P and the like occurs. It was difficult to produce a high-strength hot-rolled steel sheet having excellent stretch flangeability.
【０００７】[0007]
【発明が解決しようとする課題】本発明は、従来の高強
度熱延鋼板の製造における上述したような問題を解決す
るためになされたものであって、巻取時のオーステナイ
ト残存量を可能な限り抑え、更に、それでも残存したオ
ーステナイトを可能な限りに無害な組織とし、低温巻取
りによって、Ｐの偏析を抑え、かくして、すぐれた伸び
フランジ性を有する熱延鋼板を製造する方法を提供する
ことを目的とする。SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in the production of a conventional high-strength hot-rolled steel sheet. To provide a method for producing a hot-rolled steel sheet having a structure in which the retained austenite is made as harmless as possible, the segregation of P is suppressed by low-temperature winding, and thus the stretch flangeability is excellent. With the goal.
【０００８】[0008]
【課題を解決するための手段】本発明による伸びフラン
ジ性にすぐれる熱延鋼板の製造方法は、重量％にて Ｃ 0.０５〜0.２０％、 Ｍｎ 0.５０〜2.００％、 Ｓｉ 0.０１〜1.５０％、 Ｐ 0.１０％以下、 Ｓ 0.００５％以下、及び Ｃｒ 0.２０〜2.００％ を含み、残部鉄及び不可避的不純物よりなる鋼をオース
テナイト域で圧延を終了し、６５０℃とパーライト変態
が停止する温度Ｔ℃の間で５秒以上保持し、更に、Ｔ℃
から５００℃の間を平均冷却速度３０℃／秒以上にて冷
却し、５００〜３００℃の範囲の温度で巻取ることを特
徴とする。The method for producing a hot-rolled steel sheet having excellent stretch flangeability according to the present invention comprises: 0.05 to 0.20% by weight of C; 0.50 to 2.00% of Mn; Steel containing 0.01-1.50% of Si, 0.10% or less of P, 0.005% of S or less, and 0.20-2.00% of Cr in the austenitic region with the balance being iron and unavoidable impurities Rolling is completed, and maintained at 650 ° C. and a temperature T ° C. at which the pearlite transformation stops for 5 seconds or more.
To 500 ° C. at an average cooling rate of 30 ° C./sec or more, and winding at a temperature in the range of 500 to 300 ° C.
【０００９】先ず、本発明の方法の基礎となった実験事
実について説明する。Ｃ0.１％、Ｍｎ1.０％、Ｓｉ0.５
％及びＣｒ0.５％なる成分を有する鋼を図１に示すよう
に、９５０℃（オーステナイト域）で５分間加熱し、７
００℃で１分間恒温保持し、更に、６８０〜４９０℃の
範囲の温度で１０秒間保持し、この後、水焼入れした。
７００℃での恒温保持は、フェライトを十分に析出させ
るためのものであって、熱延実機設備にて圧延した場
合、圧延の圧下率が非常に高く、フェライトの析出が速
いので、圧延後、急冷した場合でも、フェライトがほぼ
平衡まで析出する点を考慮したものである。First, the experimental facts underlying the method of the present invention will be described. C 0.1%, Mn 1.0%, Si 0.5
% And Cr 0.5% were heated at 950 ° C. (austenitic range) for 5 minutes as shown in FIG.
It was kept at a constant temperature of 00 ° C. for 1 minute, further kept at a temperature in the range of 680 to 490 ° C. for 10 seconds, and then water-quenched.
The constant temperature holding at 700 ° C. is for precipitating the ferrite sufficiently, and when rolling is performed by using a hot rolling equipment, the rolling reduction of the rolling is very high, and the precipitation of the ferrite is fast. This takes into account the point that ferrite precipitates to almost equilibrium even when quenched.
【００１０】６８０℃から４９０℃での恒温保持は、パ
ーライトを析出させるためのものである。図２にこの保
持温度がパーライト変態率に及ぼす結果を示す。パーラ
イトは、６５０℃から５８０℃の間でのみ、析出してい
る。但し、図２では、５％未満のパーライトは０％とし
て取り扱っている。上記実験鋼は、５８０℃以下では、
パーライト変態が進行しないので、６５０℃から５８０
℃までを徐冷しなければ、巻取後までオーステナイトが
大量に残存する。このオーステナイトは、巻取後に硬質
相となるため、図３に示すように、６５０℃から５８０
℃までの保持時間が短い程、限界穴拡げ率λ値が低い。
ここに、λ値とは、直径１０mmの穴を打ち抜いた鋼板を
６０℃の円錐ポンチで押し上げ、亀裂が生じた際の穴径
の拡張率をいう。The constant temperature holding at 680 ° C. to 490 ° C. is for precipitating pearlite. FIG. 2 shows the effect of the holding temperature on the pearlite transformation rate. Perlite precipitates only between 650 ° C and 580 ° C. However, in FIG. 2, pearlite of less than 5% is treated as 0%. At 580 ° C or lower, the experimental steel
Since pearlite transformation does not proceed, the temperature is 580 to 580 ° C.
Unless the temperature is gradually cooled down to ℃, a large amount of austenite remains after winding. Since this austenite becomes a hard phase after winding, as shown in FIG.
The shorter the holding time to ° C, the lower the critical hole expansion ratio λ value.
Here, the λ value refers to the expansion rate of the hole diameter when a steel plate punched out of a hole having a diameter of 10 mm is pushed up with a conical punch at 60 ° C. and a crack occurs.
【００１１】また、残存オーステナイトが少ない場合で
も、５８０℃から５００℃を徐冷すると、伸びフランジ
性が劣化する。即ち、図４に残存オーステナイト量１３
％（６５０℃から５８０℃までの保持時間２秒）と５％
（同８秒）の同じ鋼を種々の冷却速度で冷却した際の伸
びフランジ性を示す。いずれの場合でも、５８０℃から
５００℃を徐冷すると、λ値が劣化する。この理由は明
確ではないが、５８０℃から５００℃の間に、残存オー
ステナイトから伸びフランジ性に有害な組織が析出する
ためであると考えられる。Further, even when the amount of retained austenite is small, when the temperature is gradually cooled from 580 ° C. to 500 ° C., the stretch flangeability deteriorates. That is, FIG.
% (Holding time from 650 ° C to 580 ° C for 2 seconds) and 5%
(8 seconds) show stretch flangeability when the same steel was cooled at various cooling rates. In any case, when the temperature is gradually cooled from 580 ° C. to 500 ° C., the λ value deteriorates. Although the reason for this is not clear, it is considered that a structure harmful to stretch flangeability is precipitated from the residual austenite between 580 ° C and 500 ° C.
【００１２】５８０℃から５００℃までを急冷した場
合、残存したオーステナイトはベイナイトに変態した
が、徐冷した場合は、フェライトとマルテンサイトとが
混在した異常組織が実際にみられる。但し、５００〜５
５０℃を急冷した場合でも、残存オーステナイトが１３
％のものは、５％のものよりもλ値が著しく低い。When quenched from 580 ° C. to 500 ° C., the remaining austenite is transformed into bainite, but when cooled slowly, an abnormal structure in which ferrite and martensite are mixed is actually observed. However, 500-5
Even when the temperature is rapidly cooled to 50 ° C., the residual austenite remains 13%.
% Have significantly lower λ values than 5%.
【００１３】以上から明らかなように、上記実験鋼を用
いて伸びフランジ性にすぐれる熱延鋼板を得るために
は、パーライトの析出する６５０℃から５８０℃の間を
徐冷し、フェライト変態後に残存するオーステナイトを
できる限りにパーライトとし、且つ、５８０℃から５０
０℃を急冷して、異常組織の発生を抑え、５００℃以下
の温度で巻き取ればよいことが理解される。このよう
に、巻取温度を５００℃以下とすれば、Ｐ等の偏析によ
る打ち抜き断面の亀裂発生も少ない。As is apparent from the above, in order to obtain a hot-rolled steel sheet having excellent stretch flangeability using the above-mentioned experimental steel, the temperature is gradually cooled between 650 ° C. and 580 ° C. where pearlite is precipitated, and after the ferrite transformation, The remaining austenite is made as pearlite as possible and at 580 ° C to 50
It is understood that the temperature may be rapidly cooled to 0 ° C. to suppress the generation of abnormal tissue, and the film may be wound at a temperature of 500 ° C. or less. As described above, when the winding temperature is 500 ° C. or less, the occurrence of cracks in the punched section due to segregation of P and the like is small.
【００１４】次に、上記実験鋼以外についても研究し
た。図５にパーライト変態が停止する温度Ｔ（℃）に及
ぼすＣｒ量の影響を示すように、Ｃｒ量が多くなるほ
ど、パーライト変態が進行する下限温度が上昇する。こ
のことは、Ｃｒが多くなるにつれて、セメンタイトの析
出が抑制されるためであるとみられる。パーライトは、
オーステナイトがフェライトとセメンタイトとに分離し
たもので、この際にＣｒの分配がフェライトとセメンタ
イトの間で起こるので、パーライト析出が抑制される。
パーライト析出の上限温度は、Ｃｒ量によらず、殆ど変
化しないので、６５０℃からパーライト析出の下限温度
まで徐冷することが重要である。パーライト変態は、Ｃ
ｒ以外の置換型合金元素によっても抑制されるので、他
の合金元素でも同様のことが生じる。Next, other steels than the above-mentioned experimental steels were studied. FIG. 5 shows the effect of the amount of Cr on the temperature T (° C.) at which the pearlite transformation stops, as the Cr amount increases, the lower limit temperature at which the pearlite transformation proceeds increases. This is presumably because the precipitation of cementite is suppressed as the amount of Cr increases. Perlite is
Austenite is separated into ferrite and cementite. At this time, the distribution of Cr occurs between the ferrite and cementite, so that pearlite precipitation is suppressed.
Since the upper limit temperature of pearlite precipitation hardly changes regardless of the amount of Cr, it is important to gradually cool from 650 ° C. to the lower limit temperature of pearlite precipitation. Perlite transformation is C
Since the same is suppressed by a substitutional alloy element other than r, the same occurs with other alloy elements.
【００１５】従来、合金元素の相違によるパーライト変
態の停止温度の変化は考慮されたことがなく、合金元素
が異なる場合、十分にパーライト変態を進行させる条件
を見出すことができなかった。本発明によれば、この温
度を成分系毎に測定することによって、合金元素の異な
る場合に適応することが可能となる。本発明は、以上の
知見に基づいて完成されたものである。Conventionally, the change in the stop temperature of the pearlite transformation due to the difference in the alloying elements has not been taken into consideration, and when the alloying elements are different, it has not been possible to find the conditions for sufficiently proceeding the pearlite transformation. According to the present invention, by measuring this temperature for each component system, it is possible to adapt to the case where the alloy elements are different. The present invention has been completed based on the above findings.
【００１６】次に、本発明において、鋼の化学成分につ
いて説明する。Ｃは、鋼板の強度を確保するために必要
な元素であって、少なくとも0.０５％の添加が必要であ
り、0.１０％以上の添加が好ましい。しかし、添加量が
0.２０％を越えるときは、巻取時の残存オーステナイト
の量を低減することが困難となり、伸びフランジ性が劣
化する。好ましくは、添加量は、0.１５％以下の範囲と
する。Next, the chemical composition of steel in the present invention will be described. C is an element necessary to secure the strength of the steel sheet, and needs to be added at least 0.05%, and preferably added at 0.10% or more. However, the amount added
If it exceeds 0.20%, it becomes difficult to reduce the amount of residual austenite during winding, and the stretch flangeability deteriorates. Preferably, the amount added is in the range of 0.15% or less.
【００１７】Ｍｎも、Ｃと同様の理由によって、添加量
を0.５０〜2.００％の範囲とし、好ましくは、0.８０〜
1.５０％の範囲である。Ｓｉは、その添加量が1.５０％
を越えるときは、巻取時の残存オーステナイト量を低減
することが困難となり、伸びフランジ性が劣化する。し
かし、0.０１％よりも少なくしても、徒に製造コストの
上昇を招くのみならず、材質上の改善も特に期待できな
いので、添加量は、0.０１％以上とする。For the same reason as for C, Mn is added in an amount of 0.50 to 2.00%, preferably 0.80 to 2.00%.
It is in the range of 1.50%. Si is added at 1.50%
When the value exceeds, it becomes difficult to reduce the amount of residual austenite during winding, and the stretch flangeability deteriorates. However, if the amount is less than 0.01%, not only does the production cost increase unnecessarily, but also no improvement in material quality can be expected. Therefore, the addition amount is set to 0.01% or more.
【００１８】Ｐは、これを多量に添加するときは、脆化
による割れが生じるので、0.１０％以下とする。しか
し、0.０１％よりも少なくしても、徒に製造コストの上
昇を招くのみならず、材質上の改善も特に期待できない
ので、添加量は、0.０１％以上とする。Ｓは、ＭｎＳ等
の介在物を生成して、伸びフランジ性を劣化させるの
で、0.００５％以下とし、好ましくは、0.００２％以下
とする。When P is added in a large amount, cracking due to embrittlement occurs, so P is set to 0.10% or less. However, if the amount is less than 0.01%, not only does the production cost increase unnecessarily, but also no improvement in material quality can be expected. Therefore, the addition amount is set to 0.01% or more. Since S generates inclusions such as MnS and deteriorates stretch flangeability, S is set to 0.005% or less, and preferably 0.002% or less.
【００１９】Ｃｒは、鋼板の強度の向上に有効であり、
この効果を有効に得るには、少なくとも0.２０％の添加
を必要とする。しかし、過多に添加すれば、巻取時の残
存オーステナイト量を低減することが困難となり、伸び
フランジ性を劣化させるので、添加量は2.００％以下と
する。Cr is effective in improving the strength of the steel sheet.
To obtain this effect effectively, it is necessary to add at least 0.20%. However, if it is added excessively, it becomes difficult to reduce the amount of residual austenite at the time of winding, and the stretch flangeability is deteriorated. Therefore, the addition amount is 2.00% or less.
【００２０】本発明によれば、上記元素に加えて、Ｃｕ
1.０％以下、Ｔｉ 0.０５％以下、及びＮｂ 0.０５
％以下よりなる群から選ばれる少なくとも１種の元素を
添加することができる。According to the present invention, in addition to the above elements, Cu
1.0% or less, Ti 0.05% or less, and Nb 0.05
% Or less can be added.
【００２１】Ｃｕは、析出強化によってフェライト強度
を向上させるので、鋼板の高強度化や疲労強度の向上を
目的として添加される。しかし、多量の添加は、熱間脆
性を防止するために、同時に高価なＮｉを多量に添加し
なければならず、鋼板の製造コストを高めるので、添加
量は1.０％以下とする。本発明によれば、添加量が1.０
％以下の場合であっても、少なくともＣｕの半分程度の
Ｎｉを表面疵防止のために添加することが好ましい。Since Cu enhances the ferrite strength by precipitation strengthening, Cu is added for the purpose of increasing the strength of the steel sheet and improving the fatigue strength. However, the addition of a large amount requires the addition of a large amount of expensive Ni at the same time in order to prevent hot embrittlement and increases the manufacturing cost of the steel sheet. Therefore, the addition amount is set to 1.0% or less. According to the present invention, the amount added is 1.0.
% Or less, it is preferable to add at least about half of Cu to prevent surface flaws.
【００２２】Ｔｉ及びＮｂは、Ｃｒと同様に鋼板の高強
度化に有用である。しかし、過多に添加するときは、降
伏比が高くなり、プレス加工時の形状凍結性が悪くなる
ので、高強度化のために添加する場合も、いずれの元素
についても、その上限を0.０５％とする。Ti and Nb, like Cr, are useful for increasing the strength of a steel sheet. However, when excessively added, the yield ratio becomes high, and the shape freezing property at the time of press working deteriorates. Therefore, when adding for high strength, the upper limit of any element is 0.05. %.
【００２３】更に、本発明によれば、伸びフランジ性に
有害なＭｎＳの析出を抑えるために鋼に、Ｃａ 0.００
２０％以下、及びＲＥＭ 0.００２０％以下よりなる群
から選ばれる少なくとも１種の元素を添加することがで
きる。しかし、これらの元素も過多に添加すれば、鋼板
の製造コストを高めるのみならず、上記効果が飽和する
ので、いずれの元素についても、その添加量は0.００２
０％以下とする。Further, according to the present invention, in order to suppress the precipitation of MnS which is harmful to the stretch flangeability, Ca 0.000 is added to the steel.
At least one element selected from the group consisting of 20% or less and REM 0.0020% or less can be added. However, if these elements are added excessively, not only does the production cost of the steel sheet increase, but also the above effects are saturated. Therefore, the addition amount of each element is 0.002.
0% or less.
【００２４】本発明によれば、上記以外にも、必要に応
じて、次のような合金元素を添加することができる。特
に、Ｃｕを添加した鋼では、前述したように、表面割れ
等を防止するために、Ｎｉを添加することが好ましい。
但し、その添加量は、1.０％以下の範囲であり、これ以
上の添加は、製造費用を徒に高めるので、好ましくな
い。According to the present invention, in addition to the above, the following alloy elements can be added as required. In particular, in steel to which Cu has been added, as described above, it is preferable to add Ni in order to prevent surface cracks and the like.
However, the amount of addition is in the range of 1.0% or less, and the addition of more than that is not preferable because the production cost is unnecessarily increased.
【００２５】Ｖ及びＺｒは、鋼板の強度の向上に有効で
あるが、過多に添加しても、効果が飽和するので、上限
は、Ｖについては、0.２重量％、Ｚｒについては、0.１
％とする。Ｍｏも、Ｖと同じく、鋼板の強度の向上に有
効であるが、過多に添加しても、効果が飽和するので、
上限を1.０％とする。Ｂは、耐縦割れ性や強度の向上に
有用であり、過多に添加するときは、脆くするので、添
加量は、２０ｐｐｍを上限とする。Although V and Zr are effective in improving the strength of the steel sheet, the effect is saturated even if added in an excessive amount. Therefore, the upper limit is 0.2% by weight for V and 0% for Zr. .1
%. Mo is also effective in improving the strength of the steel sheet, like V, but even if it is added excessively, the effect is saturated.
The upper limit is set to 1.0%. B is useful for improving longitudinal cracking resistance and strength, and becomes brittle when added in excess, so the upper limit is 20 ppm.
【００２６】本発明によれば、上述したような化学成分
を有する鋼をオーステナイト域で圧延を終了し、６５０
℃とパーライト変態が停止する温度Ｔ℃の間で５秒以上
保持し、更に、Ｔ℃から５００℃の間を平均冷却速度３
０℃／秒以上にて冷却し、５００〜３００℃の範囲の温
度で巻取ることによって、伸びフランジ性にすぐれる熱
延鋼板を得ることができる。According to the present invention, the steel having the chemical composition as described above is rolled in the austenitic region, and is subjected to 650.
5 ° C. and the temperature at which the pearlite transformation stops, 5 ° C. or more, and the average cooling rate 3 between T ° C. and 500 ° C.
By cooling at 0 ° C./sec or more and winding at a temperature in the range of 500 to 300 ° C., a hot-rolled steel sheet excellent in stretch flangeability can be obtained.
【００２７】オーステナイト・フェライト域で圧延を行
なうときは、得られる鋼板が熱間強度において不安定に
なり、製品の板厚精度が著しく劣化するので、本発明に
よれば、圧延終了温度をオーステナイト域とする必要が
ある。When rolling is performed in the austenite / ferrite region, the resulting steel sheet becomes unstable in hot strength and the thickness accuracy of the product is significantly deteriorated. It is necessary to
【００２８】本発明において、パーライト析出停止温度
Ｔ（℃）は、フェライトを共析温度付近において十分に
析出させ、これを共析温度から５００℃の範囲の温度で
１０秒間保持したとき、パーライトの析出量が５％未満
である最高温度をいうものとする。高強度熱延鋼板にお
いて、伸びフランジ性にすぐれる熱延鋼板を得るために
は、フェライト変態後の残存オーステナイトをできる限
りにパーライト変態させ、更に、５５０℃から５００℃
の範囲における残存オーステナイトから有害組織が生じ
ると考えられる温度域を急冷し、５００℃以下の温度で
巻取る必要がある。In the present invention, the pearlite precipitation stop temperature T (° C.) is set to a value obtained when the ferrite is sufficiently precipitated in the vicinity of the eutectoid temperature and held at a temperature in the range from the eutectoid temperature to 500 ° C. for 10 seconds. The maximum temperature at which the amount of precipitation is less than 5%. In order to obtain a hot-rolled steel sheet having excellent stretch flangeability in a high-strength hot-rolled steel sheet, the residual austenite after the ferrite transformation is transformed into pearlite as much as possible, and further from 550 ° C to 500 ° C.
It is necessary to rapidly cool the temperature range in which a harmful structure is considered to be generated from the residual austenite in the range described above and wind it at a temperature of 500 ° C. or less.
【００２９】パーライト変態の進行の停止がみられない
鋼については、本発明の方法は適用できない。また、通
常の熱延後の冷却において、パーライトが析出しない鋼
にも、本発明の方法は適用できない。The method of the present invention cannot be applied to steel in which progress of the pearlite transformation is not stopped. In addition, the method of the present invention cannot be applied to steel in which pearlite does not precipitate during cooling after ordinary hot rolling.
【００３０】次に、本発明に従って、図３に示すよう
に、パーライトの析出する温度域で５秒程度保持すれ
ば、λ値が良好であるので、６５０℃から温度Ｔ（℃）
の間を５秒以上保持する。しかし、高強度熱延鋼板で
は、合金元素の添加量が多いので、好ましくは、７秒以
上保持する。Next, according to the present invention, as shown in FIG. 3, if the temperature is maintained for about 5 seconds in a temperature range in which pearlite is precipitated, the λ value is good.
Is maintained for 5 seconds or more. However, in a high-strength hot-rolled steel sheet, since the amount of alloying elements added is large, it is preferably maintained for 7 seconds or more.
【００３１】６５０℃からＴ（℃）までを５秒以上保持
し、オーステナイトの残存が少ない鋼でも、図４に示す
ように、５８０℃〜５００℃の範囲の温度で徐冷する
と、伸びフランジ性が劣化するので、本発明によれば、
この温度範囲を平均冷却速度３０℃／秒以上にて冷却す
る。特に、平均冷却速度４０℃／秒以上で冷却すること
か好ましい。As shown in FIG. 4, even if the steel is maintained from 650.degree. C. to T (.degree. C.) for 5 seconds or more and the austenite remains small, the steel is gradually cooled at a temperature in the range of 580.degree. Is deteriorated, so according to the present invention,
This temperature range is cooled at an average cooling rate of 30 ° C./sec or more. In particular, it is preferable to cool at an average cooling rate of 40 ° C./sec or more.
【００３２】本発明によれば、巻取後、徐冷となるの
で、温度Ｔ（℃）から５００℃を徐冷するおそれれがあ
ることと、Ｐ等の偏析による脆化を避けるために、巻取
温度を５００℃以下とする。脆化は、前述したように伸
びフランジ性を劣化させる。また、３００℃以下で巻取
るときは、残存したオーステナイトがマルテンサイトと
呼ばれる極めて硬質な相になるので、伸びフランジ性を
劣化させる。好ましくは、巻取温度は４００〜５００℃
の範囲の温度である。According to the present invention, since the temperature is gradually cooled after winding, there is a possibility that the temperature may be gradually lowered from the temperature T (° C.) to 500 ° C., and in order to avoid embrittlement due to segregation of P and the like, The winding temperature is set to 500 ° C. or less. Embrittlement deteriorates stretch flangeability as described above. When the film is wound at a temperature of 300 ° C. or lower, the remaining austenite becomes an extremely hard phase called martensite, which deteriorates stretch flangeability. Preferably, the winding temperature is 400-500 ° C
Temperature.
【００３３】[0033]
【実施例】以下に実施例を挙げて本発明を説明するが、
本発明はこれら実施例により何ら限定されるものではな
い。表１から表３に実施例を示す。表１から表３におい
て、Ｔはパーライト変態の停止温度（℃）、ｔは６５０
℃から温度Ｔ（℃）までの保持時間、相は圧延終了時の
鋼の相、ＴＳは引張強度を示す。また、冷却速度は、巻
取温度が５００℃以上であるのとき、温度Ｔ（℃）から
巻取温度までの平均冷却速度を示し、巻取温度が５００
℃以下であるとき、温度Ｔ（℃）から５００℃までの平
均冷却速度を示す。また、一般に、λは、鋼板の強度が
高い程、低下するので、引張強さ（ＴＳ）とλとの積も
併せて示す。EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples. Tables 1 to 3 show examples. In Tables 1 to 3, T is the stop temperature (° C.) of the pearlite transformation, and t is 650.
The holding time from ° C. to the temperature T (° C.), the phase indicates the steel phase at the end of rolling, and TS indicates the tensile strength. The cooling rate indicates an average cooling rate from the temperature T (° C.) to the winding temperature when the winding temperature is 500 ° C. or higher, and the cooling temperature is 500 ° C.
When it is lower than or equal to ° C., it indicates an average cooling rate from the temperature T (° C.) to 500 ° C. In general, λ decreases as the strength of the steel sheet increases, and thus the product of the tensile strength (TS) and λ is also shown.
【００３４】比較鋼のうち、Ａ１３は、圧延終了時の組
織がに２相域であるので、λ値が低い。また、巻取温度
が４００℃以下であるＡ１４や、巻取温度が５００℃以
上であるＡ１６やＡ１７も、λ値が低い。Of the comparative steels, A13 has a low λ value because the structure at the end of rolling is in the two-phase region. Also, A14 having a winding temperature of 400 ° C. or lower, and A16 and A17 having a winding temperature of 500 ° C. or higher also have low λ values.
【００３５】また、一般に、合金元素量が高くなると、
温度Ｔ（℃）が上昇する傾向にあり、６５０℃から温度
Ｔ（℃）までの範囲で保持時間を長くとることか困難と
なる。従って、本発明においては、このような観点から
は、Ｃｒ量は、1.３％以下が好ましい。Ｔｉ及びＮｂ
は、鋼板の強度を高めるうえで有効であるが、多面、Ｃ
ｒと同様に、温度Ｔを高めるので、多量に添加すること
は好ましくない。In general, when the amount of alloying elements increases,
The temperature T (° C.) tends to increase, and it is difficult to increase the holding time in the range from 650 ° C. to the temperature T (° C.). Therefore, in the present invention, from such a viewpoint, the Cr content is preferably 1.3% or less. Ti and Nb
Is effective in increasing the strength of the steel sheet,
Like r, it increases the temperature T, so it is not preferable to add a large amount.
【００３６】[0036]
【表１】 [Table 1]
【００３７】[0037]
【表２】 [Table 2]
【００３８】[0038]
【表３】 [Table 3]
【００３９】[0039]
【発明の効果】以上のように、本発明の方法によれば、
合金元素の添加量を最適に設計し、６５０℃からパーラ
イト変態が停止する温度Ｔ（℃）までの間で５秒以上保
持し、更に、温度Ｔ（℃）から５００℃の間を平均冷却
速度３０℃／秒以上にて冷却し、５００〜３００℃の範
囲の温度で巻取ることによって、巻取時のオーステナイ
ト残存量を可能な限り抑え、更に、それでも残存したオ
ーステナイトを可能な限りに無害な組織とし、低温巻取
りによって、Ｐの偏析を抑え、かくして、すぐれた伸び
フランジ性を有する熱延鋼板を得ることができる。本発
明によれば、このようにして、伸びフランジ性の指標と
して、引張強さ（ＴＳ）とλとの積（ＴＳ×λ）をとれ
ば、これが５５００以上、好ましい態様によれば、５７
００以上である熱延鋼板を得ることができる。As described above, according to the method of the present invention,
Optimum amount of alloying element is added, maintained for more than 5 seconds between 650 ° C and temperature T (° C) at which pearlite transformation stops, and average cooling rate between temperature T (° C) and 500 ° C By cooling at a rate of 30 ° C./sec or more and winding at a temperature in the range of 500 to 300 ° C., the amount of retained austenite at the time of winding is suppressed as much as possible. By forming into a structure and winding at a low temperature, segregation of P is suppressed, and thus a hot-rolled steel sheet having excellent stretch flangeability can be obtained. According to the present invention, if the product (TS × λ) of the tensile strength (TS) and λ is taken as an index of the stretch flangeability in this way, this is 5500 or more, and according to a preferred embodiment, it is 57
It is possible to obtain a hot-rolled steel sheet of not less than 00.
【００４０】このような熱延鋼板によれば、プレス原板
の薄肉化が可能となり、例えば、自動車の車体重量の軽
量化等に寄与することができる。According to such a hot-rolled steel sheet, it is possible to reduce the thickness of the original press sheet, which can contribute to, for example, reducing the weight of a vehicle body.
【図１】は、実験鋼の実験に用いた熱処理を示す温度−
時間のグラフである。FIG. 1 shows the temperature of the heat treatment used in the experiment of the experimental steel.
It is a graph of time.
【図２】は、６８０℃から４９０℃の間での保持温度が
パーライト変態率に及ぼす影響を示すグラフである。FIG. 2 is a graph showing the effect of the holding temperature between 680 ° C. and 490 ° C. on the pearlite transformation rate.
【図３】は、６５０℃から５８０℃までの間の温度での
保持時間が限界穴拡げ率λ値に及ぼす影響を示すグラフ
である。FIG. 3 is a graph showing the effect of holding time at a temperature between 650 ° C. and 580 ° C. on the critical hole expansion rate λ value.
【図４】は、５８０℃から５０℃までの冷却速度がλ値
に及ぼす影響を示すグラフである。FIG. 4 is a graph showing the effect of the cooling rate from 580 ° C. to 50 ° C. on the λ value.
【図５】は、Ｃｒ量とパーライト変態が停止する温度Ｔ
（℃）との関係を示すグラフである。FIG. 5 shows Cr content and temperature T at which pearlite transformation stops.
6 is a graph showing a relationship with (° C.).
フロントページの続き (56)参考文献 特開 平４−341523（ＪＰ，Ａ) 特開 平６−57330（ＪＰ，Ａ) 特開 昭57−137426（ＪＰ，Ａ) 特開 平４−88125（ＪＰ，Ａ) 特開 平６−264139（ＪＰ，Ａ) 特開 平７−118740（ＪＰ，Ａ) 特開 平４−246127（ＪＰ，Ａ) 特開 平４−276024（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C21D 8/02 - 8/04 C21D 9/46 - 9/48 C22C 38/00 - 38/60 Continuation of the front page (56) References JP-A-4-341523 (JP, A) JP-A-6-57330 (JP, A) JP-A-57-137426 (JP, A) JP-A-4-88125 (JP) JP-A-6-264139 (JP, A) JP-A-7-118740 (JP, A) JP-A-4-246127 (JP, A) JP-A-4-276024 (JP, A) Field surveyed (Int. Cl. 7 , DB name) C21D 8/02-8/04 C21D 9/46-9/48 C22C 38/00-38/60
Claims (7)
テナイト域で圧延を終了し、６５０℃からパーライト変
態が停止する温度Ｔ（℃）までの間で５秒以上保持し、
更に、温度Ｔ（℃）から５００℃の間を平均冷却速度３
０℃／秒以上にて冷却し、５００〜３００℃の範囲の温
度で巻取ることを特徴とする伸びフランジ性にすぐれる
熱延鋼板の製造方法。C. 0.05 to 0.20%, Mn 0.50 to 2.00%, Si 0.01 to 1.50% , P 0.10% or less, and S 0.005% by weight. % Or less, and 0.20 to 2.00% of Cr, the steel consisting of the balance iron and unavoidable impurities is rolled in the austenitic range, from 650 ° C to the temperature T (° C) at which the pearlite transformation stops. Hold for more than 5 seconds,
Further, an average cooling rate of 3 between the temperature T (° C.) and 500 ° C.
A method for producing a hot-rolled steel sheet having excellent stretch flangeability, wherein the hot-rolled steel sheet is cooled at a temperature of 0 ° C / sec or more and wound at a temperature in the range of 500 to 300 ° C.
域で圧延を終了し、６５０℃とパーライト変態が停止す
る温度Ｔ℃の間で５秒以上保持し、更に、Ｔ℃から５０
０℃の間を平均冷却速度３０℃／秒以上にて冷却し、５
００〜３００℃の範囲の温度で巻取ることを特徴とする
伸びフランジ性にすぐれる熱延鋼板の製造方法。Wherein at wt% (a) C 0.05~0.20%, Mn 0.50~2.00%, Si 0.01~1.50%, P 0.10% or less, S 0.005% or less, and Cr 0.20 to 2.00% , and (b) at least one element selected from the group consisting of 0.0020% or less Ca and 0.0020% or less REM Rolling of the steel consisting of iron and unavoidable impurities is stopped in the austenitic region, and the temperature is maintained at 650 ° C. and the temperature T ° C. at which the pearlite transformation stops for 5 seconds or more.
Cool between 0 ° C at an average cooling rate of 30 ° C / sec or more,
A method for producing a hot-rolled steel sheet having excellent stretch flangeability, comprising winding at a temperature in the range of 00 to 300 ° C.
域で圧延を終了し、６５０℃とパーライト変態が停止す
る温度Ｔ℃の間で５秒以上保持し、更に、Ｔ℃から５０
０℃の間を平均冷却速度３０℃／秒以上にて冷却し、５
００〜３００℃の範囲の温度で巻取ることを特徴とする
伸びフランジ性にすぐれる熱延鋼板の製造方法。3. At wt% (a) C 0.05~0.20%, Mn 0.50~2.00%, Si 0.01~1.50%, P 0.10% or less, S 0.005% or less, and Cr 0.20 to 2.00% , and further selected from the group consisting of: (b) Cu 1.0% or less, Ti 0.05% or less, and Nb 0.05% or less. The steel containing at least one element and the balance consisting of iron and unavoidable impurities is subjected to rolling in the austenitic region, and is maintained for 5 seconds or more between 650 ° C. and the temperature T ° C. at which the pearlite transformation stops. ℃ to 50
Cool between 0 ° C at an average cooling rate of 30 ° C / sec or more,
A method for producing a hot-rolled steel sheet having excellent stretch flangeability, comprising winding at a temperature in the range of 00 to 300 ° C.
み、 残部鉄及び不可避的不純物よりなる鋼をオーステナイト
域で圧延を終了し、６５０℃とパーライト変態が停止す
る温度Ｔ℃の間で５秒以上保持し、更に、Ｔ℃から５０
０℃の間を平均冷却速度３０℃／秒以上にて冷却し、５
００〜３００℃の範囲の温度で巻取ることを特徴とする
伸びフランジ性にすぐれる熱延鋼板の製造方法。4. At wt% (a) C 0.05~0.20%, Mn 0.50~2.00%, Si 0.01~1.50%, P 0.10% or less, S 0.005% or less, and includes a Cr from .20 to 2.00%, further at least one element selected from (b) Ca 0.0020% or less, and REM 0.0020% group consists of the following (C) steel containing at least one element selected from the group consisting of Cu 1.0% or less, Ti 0.05% or less and Nb 0.05% or less, with the balance being iron and unavoidable impurities. Rolling is completed in the austenite region, and the temperature is maintained at 650 ° C. and the temperature at which the pearlite transformation stops at T ° C. for 5 seconds or more.
Cool between 0 ° C at an average cooling rate of 30 ° C / sec or more,
A method for producing a hot-rolled steel sheet having excellent stretch flangeability, comprising winding at a temperature in the range of 00 to 300 ° C.
域で圧延を終了し、６５０℃とパーライト変態が停止す
る温度Ｔ℃の間で５秒以上保持し、更に、Ｔ℃から５０
０℃の間を平均冷却速度３０℃／秒以上にて冷却し、５
００〜３００℃の範囲の温度で巻取ることを特徴とする
伸びフランジ性にすぐれる熱延鋼板の製造方法。5. At wt% (a) C 0.05~0.20%, Mn 0.50~2.00%, Si 0.01~1.50%, P 0.10% or less, S 0.005% or less, and Cr 0.20 to 2.00% . (B) Ni 1.0% or less, V 0.2% or less, Zr 0.1% or less, Mo 1.0% Below, and B at least one element selected from the group consisting of 20 ppm or less, the steel consisting of the balance of iron and unavoidable impurities is rolled in the austenitic region, and the temperature of 650 ° C. and the temperature T ° C. at which the pearlite transformation stops. Hold for more than 5 seconds between T ° C and 50 ° C.
Cool between 0 ° C at an average cooling rate of 30 ° C / sec or more,
A method for producing a hot-rolled steel sheet having excellent stretch flangeability, comprising winding at a temperature in the range of 00 to 300 ° C.
み、 残部鉄及び不可避的不純物よりなる鋼をオーステナイト
域で圧延を終了し、６５０℃とパーライト変態が停止す
る温度Ｔ℃の間で５秒以上保持し、更に、Ｔ℃から５０
０℃の間を平均冷却速度３０℃／秒以上にて冷却し、５
００〜３００℃の範囲の温度で巻取ることを特徴とする
伸びフランジ性にすぐれる熱延鋼板の製造方法。6. At wt% (a) C 0.05~0.20%, Mn 0.50~2.00%, Si 0.01~1.50%, P 0.10% or less, S 0.005% or less, and Cr 0.20 to 2.00% . (B) Ni 1.0% or less, V 0.2% or less, Zr 0.1% or less, Mo 1.0% And at least one element selected from the group consisting of: B and 20 ppm or less; and (c) at least one element selected from the group consisting of: 0.0020% or less Ca and 0.0020% or less REM Rolling of the steel consisting of the balance of iron and unavoidable impurities is stopped in the austenitic region, and the temperature is kept at 650 ° C. and the temperature T ° C. at which the pearlite transformation stops for 5 seconds or more.
Cool between 0 ° C at an average cooling rate of 30 ° C / sec or more,
A method for producing a hot-rolled steel sheet having excellent stretch flangeability, comprising winding at a temperature in the range of 00 to 300 ° C.
み、 残部鉄及び不可避的不純物よりなる鋼をオーステナイト
域で圧延を終了し、６５０℃とパーライト変態が停止す
る温度Ｔ℃の間で５秒以上保持し、更に、Ｔ℃から５０
０℃の間を平均冷却速度３０℃／秒以上にて冷却し、５
００〜３００℃の範囲の温度で巻取ることを特徴とする
伸びフランジ性にすぐれる熱延鋼板の製造方法。7. At weight% (a) C 0.05~0.20%, Mn 0.50~2.00%, Si 0.01~1.50%, P 0.10% or less, S 0.005% or less, and Cr 0.20 to 2.00% . (B) Ni 1.0% or less, V 0.2% or less, Zr 0.1% or less, Mo 1.0% And at least one element selected from the group consisting of B and 20 ppm or less; and (c) at least one element selected from the group consisting of Ca and 0.0020% or less and REM and 0.0020% or less; d) a steel containing at least one element selected from the group consisting of Cu 1.0% or less, Ti 0.05% or less, and Nb 0.05% or less, with the balance being iron and unavoidable impurities, At 650 ° C. and at a temperature T ° C. at which the pearlite transformation stops, for 5 seconds or more.
Cool between 0 ° C at an average cooling rate of 30 ° C / sec or more,
A method for producing a hot-rolled steel sheet having excellent stretch flangeability, comprising winding at a temperature in the range of 00 to 300 ° C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP06924095A JP3292619B2 (en) | 1995-03-28 | 1995-03-28 | Manufacturing method of hot rolled steel sheet with excellent stretch flangeability |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP06924095A JP3292619B2 (en) | 1995-03-28 | 1995-03-28 | Manufacturing method of hot rolled steel sheet with excellent stretch flangeability |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08269538A JPH08269538A (en) | 1996-10-15 |
| JP3292619B2 true JP3292619B2 (en) | 2002-06-17 |
Family
ID=13397040
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP06924095A Expired - Fee Related JP3292619B2 (en) | 1995-03-28 | 1995-03-28 | Manufacturing method of hot rolled steel sheet with excellent stretch flangeability |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3292619B2 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100544746B1 (en) * | 2001-12-27 | 2006-01-24 | 주식회사 포스코 | A Method of Manufacturing Hot-Rolled Sheet Having Superior Strength and Elongation |
| WO2004059021A1 (en) * | 2002-12-24 | 2004-07-15 | Nippon Steel Corporation | High strength steel sheet exhibiting good burring workability and excellent resistance to softening in heat-affected zone and method for production thereof |
| KR100859057B1 (en) * | 2006-03-09 | 2008-09-17 | 가부시키가이샤 고베 세이코쇼 | High yield ratio and high tension steel sheet excellent in control of fatigue crack growth and toughness of weld heat-affected zone |
| CN105642675B (en) * | 2014-11-12 | 2017-08-15 | 上海梅山钢铁股份有限公司 | Prevent phosphorus Non-equilibrium Grain Boundary Segregation hot rolling technology control method |
-
1995
- 1995-03-28 JP JP06924095A patent/JP3292619B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08269538A (en) | 1996-10-15 |
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