JP3119122B2 - Manufacturing method of high strength hot rolled steel sheet - Google Patents
Manufacturing method of high strength hot rolled steel sheetInfo
- Publication number
- JP3119122B2 JP3119122B2 JP07152669A JP15266995A JP3119122B2 JP 3119122 B2 JP3119122 B2 JP 3119122B2 JP 07152669 A JP07152669 A JP 07152669A JP 15266995 A JP15266995 A JP 15266995A JP 3119122 B2 JP3119122 B2 JP 3119122B2
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- Prior art keywords
- cooling
- steel sheet
- hot
- rolled steel
- temperature
- Prior art date
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Description
【０００１】[0001]
【産業上の利用分野】この発明は、優れた耐食性と伸び
フランジ性を有すると共にコイル内における特性の変動
が少ない、自動車足廻り材等の機械構造用として好適な
高強度熱延鋼板を生産性良く製造する方法に関するもの
である。BACKGROUND OF THE INVENTION The present invention relates to a high-strength hot-rolled steel sheet which has excellent corrosion resistance and stretch flangeability and has little variation in characteristics in a coil, and is suitable for use in mechanical structures such as undercarriage materials for automobiles. It concerns a good manufacturing method.
【０００２】[0002]
【従来の技術】連続熱間圧延によって製造されるいわゆ
る“熱延鋼板”は、比較的安価な構造材料として自動車
を始めとする各種の産業機器に広く使用されているが、
その用途にはプレス加工で成形される部材が多く、従っ
て高強度と加工性を両立している必要がある。特に加工
性に関しては、通常、穴拡げ試験等で評価される“伸び
フランジ性”が重要な指標の１つとして注目される。2. Description of the Related Art A so-called "hot-rolled steel sheet" manufactured by continuous hot rolling is widely used as a relatively inexpensive structural material in various industrial equipment such as automobiles.
For its use, many members are formed by press working, and therefore it is necessary to achieve both high strength and workability. In particular, regarding workability, “stretch flangeability” evaluated by a hole expanding test or the like is generally noted as one of important indexes.
【０００３】ところで、伸びフランジ性の良好な熱延鋼
板の製造にはSiの添加が有効であることが知られてい
る。例えば、特開平３−１８０４２６号公報，特開平３
−２１９０４９号公報，特開平４−８８１２５号公報に
は、Siのセメンタイト微細化効果を利用して熱延鋼板の
伸びフランジ性を改善する方法が開示されている。It is known that the addition of Si is effective for producing a hot-rolled steel sheet having good stretch flangeability. For example, JP-A-3-180426, JP-A-3-180426
JP-A-219049 and JP-A-4-88125 disclose a method for improving the stretch flangeability of a hot-rolled steel sheet by utilizing the effect of making cementite finer.
【０００４】しかしながら、上述のようにSiを添加する
と、熱延鋼板のデスケ−リング性が悪化して不均一な厚
みのスケ−ルが鋼板上に残存し、このスケ−ル厚みの不
均一性に起因して鋼板の冷却も不均一となり、そのため
コイル内の特性変動が大きくなって歩留悪化の原因とな
った。[0004] However, when Si is added as described above, the descaling property of the hot-rolled steel sheet deteriorates, and a scale having an uneven thickness remains on the steel sheet. As a result, the cooling of the steel sheet becomes non-uniform, and as a result, the characteristic fluctuation in the coil becomes large and the yield is deteriorated.
【０００５】もっとも、前記特開平３−２１９０４９号
公報や特開平４−８８１２５号公報には、熱間圧延に際
しての鋼片の加熱温度を１０００〜１２００℃と低目に
抑えてデスケ−リング性悪化の原因となるフェアライト
の生成を抑制することも開示されているが、この方策に
よる場合には低い温度で圧延がなされるために圧延荷重
（圧延負荷）が大きくなるという問題があった。[0005] However, the above JP-A-3-219049 and JP-A-4-88125 disclose that the heating temperature of the steel slab during hot rolling is kept at a low temperature of 1000 to 1200 ° C and the descaling property deteriorates. It is also disclosed that the generation of fairite which causes the above is suppressed, but in this method, there is a problem that the rolling load (rolling load) becomes large because the rolling is performed at a low temperature.
【０００６】一方、自動車部品用熱延鋼板には軽量化の
ために腐食代を可能な限り抑制したいという要求があ
り、そのため優れた耐食性も要求されている。なお、こ
のような耐食性の付与にはCu，Ｐの添加が有効であるこ
とは知られており、例えば特開平５−１７１２８９号公
報にもCu，Ｐを含有させた耐食性と加工性の良好な熱延
鋼板の製造方法が開示されている。しかしながら、Ｐの
含有量は熱延後の冷却条件や巻取温度に大きく影響し、
Ｐ含有量が多くなると巻取温度の高温化等といったＰの
粒界偏析を起こすような条件では粒界が脆くなって大幅
な伸びフランジ性の劣化を免れ得なかった。[0006] On the other hand, there is a demand for a hot-rolled steel sheet for an automobile part to reduce the corrosion allowance as much as possible in order to reduce the weight, and therefore, an excellent corrosion resistance is also required. It is known that the addition of Cu and P is effective for imparting such corrosion resistance. For example, Japanese Patent Application Laid-Open No. 5-171289 discloses that the addition of Cu and P provides good corrosion resistance and workability. A method for manufacturing a hot-rolled steel sheet is disclosed. However, the content of P greatly affects the cooling conditions after hot rolling and the winding temperature,
If the P content increases, the grain boundary becomes brittle under conditions that cause grain boundary segregation of P, such as an increase in the winding temperature, and the deterioration of stretch flangeability cannot be avoided.
【０００７】このようなことから、本発明が目的とした
のは、優れた耐食性と伸びフランジ性を有すると共にコ
イル内における特性の変動が少ない高強度熱延鋼板を歩
留良く製造することができる方法を確立することであ
る。Accordingly, an object of the present invention is to produce a high-strength hot-rolled steel sheet having excellent corrosion resistance and stretch flangeability and little change in characteristics in a coil with good yield. Is to establish a method.
【０００８】[0008]
【課題を解決するための手段】前述したように、素材鋼
にSiを添加するとデスケ−リング性が悪化して不均一な
厚みのスケ−ルが鋼板上に残存するようになり、熱間圧
延後の冷却過程でスケ−ル厚みの差に起因した不均一な
冷却が生じる結果、コイル内の特性変動が大きくなる。
この冷却不均一の原因は、スケ−ルの熱伝導性が悪いた
めにスケ−ルが厚く残存する部分では鋼板の保有熱がス
ケ−ル表面にまで速やかに伝わらず、そのため該部分の
表面のみが早く冷やされることとなり、その結果スケ−
ルが厚く残存する部分のみが膜沸騰冷却から核沸騰領域
に早く遷移し急激に冷却されることにある。As described above, when Si is added to the base steel, the descaling property is deteriorated, and a non-uniform thickness scale is left on the steel sheet. In the subsequent cooling process, non-uniform cooling due to the difference in scale thickness occurs, resulting in large fluctuations in characteristics in the coil.
The cause of this non-uniform cooling is that the heat conductivity of the steel sheet does not quickly reach the surface of the scale in the portion where the scale remains thick due to the poor thermal conductivity of the scale. Is cooled quickly, and as a result
Only the portion where the metal remains thick is rapidly transitioned from film boiling cooling to the nucleate boiling region and rapidly cooled.
【０００９】そこで、本発明者等は、これら不均一な冷
却を抑制する方法について検討を行ったところ、不均一
冷却の抑制には巻取温度を高温化して膜沸騰冷却から核
沸騰冷却への遷移温度以上とするのが有効であることを
見出した。しかしながら、耐食性向上のためにCuやＰを
添加した鋼、特にＰ添加鋼では、熱間圧延後の巻取温度
を高温化すると前述したようにＰの粒界偏析に起因して
伸びフランジ性の大幅な劣化を招く。そのため、Ｐを多
く含む鋼において熱間圧延後の不均一冷却を抑制し、か
つＰの粒界偏析に起因した伸びフランジ性の劣化を防止
する手立てについて鋭意研究を重ねた結果、熱間圧延後
に行う鋼板の冷却の殆どを冷却過程の前段で速やかに行
う“前段主体の冷却”とし、かつ巻取温度を４５０〜５
５０℃の範囲に調整することが重要であるとの知見を得
ることができた。The inventors of the present invention have studied methods for suppressing such non-uniform cooling. In order to suppress non-uniform cooling, the winding temperature is increased to change from film boiling cooling to nucleate boiling cooling. It has been found that it is effective to make the transition temperature or higher. However, in steels added with Cu or P to improve corrosion resistance, particularly in steels with P added, when the winding temperature after hot rolling is increased, the stretch flangeability due to the grain boundary segregation of P as described above. Causes significant deterioration. Therefore, as a result of intensive studies on measures to suppress uneven cooling after hot rolling in a steel containing a large amount of P and to prevent deterioration of stretch flangeability caused by grain boundary segregation of P, as a result, after hot rolling, Most of the cooling of the steel sheet to be performed is "cooling mainly in the former stage", which is performed immediately in the preceding stage of the cooling process, and the winding temperature is 450 to 5
It was found that it is important to adjust the temperature to the range of 50 ° C.
【００１０】即ち、本発明者等の研究により次のことが
明らかとなったのである。熱延後の冷却を“前段主体の
冷却”とした場合には、冷却過程の後段での水量や水圧
を減少することができるようになって膜沸騰冷却から核
沸騰冷却への遷移温度が４５０℃以下の低温側に移行す
る。そこで、この際、高温域を急冷すると共に巻取温度
が４５０〜５５０℃と比較的高温となるように制御すれ
ば、Ｐの添加量が多い場合でも伸びフランジ性の劣化を
顕在化させるほどのＰの粒界偏析が起きないように偏析
を抑制できる上、膜沸騰冷却主体の冷却が行われるので
冷却の不均一も抑制されることとなる。しかも、上記
“前段主体の冷却”を実施すると、セメンタイトの析出
が抑制されるため、それらの相乗効果により熱延鋼板に
良好な伸びフランジ性を確保することができる。That is, the following has been made clear by the study of the present inventors. When the cooling after hot rolling is defined as “cooling mainly in the former stage”, the amount of water and the water pressure in the latter stage of the cooling process can be reduced, and the transition temperature from film boiling cooling to nucleate boiling cooling becomes 450 ° C. Move to low temperature side below ℃. Therefore, in this case, if the high-temperature region is rapidly cooled and the winding temperature is controlled to be relatively high at 450 to 550 ° C., even if the amount of P added is large, the deterioration of the stretch flangeability is evident. The segregation can be suppressed so that the grain boundary segregation of P does not occur, and the non-uniformity of the cooling is also suppressed because the cooling mainly by the film boiling cooling is performed. In addition, when the above-mentioned "cooling mainly in the former stage" is performed, precipitation of cementite is suppressed, and therefore, a good stretch flangeability of the hot-rolled steel sheet can be secured by a synergistic effect thereof.
【００１１】本発明は、上記知見事項等を基にして完成
されたものであって「Ｃ：0.04〜0.15％（以降、 成分割
合を表す％は重量％とする),Si： 0.4〜 2.0％， Mn：
0.7〜 2.0％， Ｐ：0.01〜0.15％，Cu：0.15〜0.50
％， Ni：0.01〜0.30％， sol.Al： 0.004〜0.10％，
Ｓ： 0.015％以下を含むか、 あるいは更にCa：0.0002〜
0.01％， Ti： 0.005〜0.15％， Cr： 0.1〜 1.2
％の１種以上をも含むと共に残部がFe及び不可避不純物
から成る鋼片を、 １２００℃を超える温度に加熱して熱
間圧延を施し、 最終パス出側温度８３０〜９４０℃で熱
間圧延を終了した後、 ５０℃/s以上の冷却速度にて５４
０〜６４０℃まで冷却する第１段冷却と、 これに続く１
〜５秒間の空冷を行う第２段冷却とを施し、更に引続い
て５〜３０℃/sの冷却速度にて４５０〜５５０℃まで冷
却を行う第３段冷却を施してから巻取ることにより、 耐
食性並びに伸びフランジ性に優れると共にコイル内特性
変動の少ない高強度熱延鋼板を生産性良く安定製造し得
るようにした点」に大きな特徴を有している。The present invention has been completed on the basis of the above findings and the like. "C: 0.04 to 0.15% (hereinafter, the component ratio is represented by% by weight), Si: 0.4 to 2.0% , Mn:
0.7 to 2.0%, P: 0.01 to 0.15%, Cu: 0.15 to 0.50
%, Ni: 0.01 to 0.30%, sol.Al: 0.004 to 0.10%,
S: 0.015% or less, or Ca: 0.0002 ~
0.01%, Ti: 0.005 to 0.15%, Cr: 0.1 to 1.2
%, And the balance consisting of Fe and inevitable impurities is heated to a temperature exceeding 1200 ° C. and hot-rolled, and hot-rolled at a final pass exit side temperature of 830 to 940 ° C. After finishing, cool at a cooling rate of 50 ° C / s or more.
First stage cooling to 0-640 ° C, followed by 1
By performing the second stage cooling for performing air cooling for up to 5 seconds, and subsequently performing the third stage cooling for cooling to 450 to 550 ° C. at a cooling rate of 5 to 30 ° C./s, and then winding the film. A high-strength hot-rolled steel sheet which is excellent in corrosion resistance and stretch flangeability, and has little fluctuation in coil characteristics.
【００１２】[0012]
【作用】以下、本発明において鋼片の化学組成及び処理
条件を前記の如くに限定した理由を説明する。 (A) 鋼片の化学組成 a) Ｃ Ｃは高張力鋼板として必要な強度を確保するために必要
な成分であるが、その含有量が0.04％未満であると必要
強度の確保が困難となる。一方、Ｃは伸びフランジ成形
時の割れの起点である炭化物の析出量を増加させるの
で、優れた伸びフランジ性を確保するためにはＣ含有量
を0.15％以下に抑えなければならない。従って、Ｃ含有
量は0.04〜0.15％と定めた。The reasons for limiting the chemical composition of the steel slab and the processing conditions as described above in the present invention will now be described. (A) Chemical composition of billet a) C C is a component necessary to secure the necessary strength as a high-tensile steel sheet, but if the content is less than 0.04%, it becomes difficult to secure the required strength. . On the other hand, C increases the precipitation amount of carbides, which are the starting points of cracks at the time of forming the stretch flange, so that the C content must be suppressed to 0.15% or less in order to secure excellent stretch flangeability. Therefore, the C content was determined to be 0.04 to 0.15%.
【００１３】b) Si Siは、セメンタイトの析出を遅らせ、また変態強化を促
進する作用を通じて鋼板に高強度と伸びフランジ性を両
立させるのに重要な元素である。更に、Siは固溶強化元
素でもあり、フェライトを強化して伸びフランジを向上
させる効果をも有している。そして、十分な伸びフラン
ジ性を得るためには 0.4％以上のSi含有量を確保する必
要があるが、その含有量が 2.0％を超えると溶接性や靱
性の劣化を招くようになることから、Si含有量は 0.4〜
2.0％と定めた。B) Si Si is an important element for achieving both high strength and stretch flangeability of a steel sheet through the action of delaying the precipitation of cementite and promoting transformation strengthening. Further, Si is also a solid solution strengthening element and has an effect of strengthening ferrite and improving a stretch flange. In order to obtain sufficient stretch flangeability, it is necessary to secure a Si content of 0.4% or more. However, if the content exceeds 2.0%, deterioration of weldability and toughness will be caused. Si content is 0.4 ~
2.0%.
【００１４】c) Mn Mnは、高張力鋼板として必要な強度を確保すると共にセ
メンタイトの析出を抑制するのに不可欠な成分であり、
そのためには 0.7％以上を含有させる必要があるが、
2.0％を超えて含有させると溶接性の劣化を招くので好
ましくない。従って、Mn含有量は 0.7〜 2.0％と定めた
が、好ましくは 1.0〜 2.0％に調整するのが良い。C) Mn Mn is an essential component for securing the necessary strength as a high-tensile steel sheet and suppressing the precipitation of cementite.
For that purpose, it is necessary to contain 0.7% or more,
If the content exceeds 2.0%, the weldability deteriorates, which is not preferable. Therefore, the Mn content is determined to be 0.7 to 2.0%, but is preferably adjusted to 1.0 to 2.0%.
【００１５】d) Ｐ Ｐは鋼板に所望の耐食性を付与するのに必要な成分であ
り、この目的のためには0.01以上の含有量を確保しなけ
ればならないが、0.15％を超えて含有させると加工性や
靱性の劣化を招くことから、Ｐ含有量は0.01〜0.15％と
定めた。D) PP is a component necessary for imparting the desired corrosion resistance to the steel sheet. For this purpose, a content of 0.01 or more must be ensured, but the content is more than 0.15%. Therefore, the P content is determined to be 0.01 to 0.15% because it causes deterioration in workability and toughness.
【００１６】e) Cu Cuは、Ｐと同じく鋼板に所望の耐食性を付与するのに必
要な成分であり、そのためには0.15％以上の含有量を確
保しなければならない。しかし、0.50％を超えてCuを含
有させると、熱間圧延に際してのスラブ加熱時に表面濃
化したCuの液化に起因し熱延板の表面に微細な割れが発
生しやすくなる。従って、Cuの含有量は0.15〜0.50％と
定めた。E) Cu Cu, like P, is a component necessary for imparting a desired corrosion resistance to a steel sheet, and for that purpose, a content of 0.15% or more must be ensured. However, when Cu is contained in excess of 0.50%, fine cracks are likely to be generated on the surface of the hot-rolled sheet due to liquefaction of Cu concentrated at the surface during slab heating in hot rolling. Therefore, the content of Cu was determined to be 0.15 to 0.50%.
【００１７】f) Ni Niは、上述した“表面濃化したCuの液化現象”を抑えて
熱延板の表面に微細な割れが発生するのを防止する作用
を有している。しかし、その含有量が0.01％未満では前
記作用による所望の効果が得られず、一方、0.30％を超
えてNiを含有させてもその効果が飽和してしまうばかり
か、コストアップを招くようになる。従って、Ni含有量
は0.01〜0.30％と定めた。F) Ni Ni has an effect of suppressing the above-mentioned "liquefaction phenomenon of surface-enriched Cu" and preventing the occurrence of fine cracks on the surface of the hot-rolled sheet. However, if the content is less than 0.01%, the desired effect due to the above-described effect cannot be obtained. On the other hand, if the content exceeds 0.30%, the effect is not only saturated but also increases the cost. Become. Therefore, the Ni content was determined to be 0.01 to 0.30%.
【００１８】g) sol.Al Alは鋼の脱酸材として添加される元素であり、十分な脱
酸効果を得るためにはsol.Al量で 0.004％以上の含有量
を確保する必要があるが、0.10％を超える過度の添加は
非金属介在物の形成につながる。従って、Al含有量をso
l.Al量で 0.004〜0.10％と定めた。G) sol.Al Al is an element added as a steel deoxidizing material, and it is necessary to secure a content of 0.004% or more in sol.Al in order to obtain a sufficient deoxidizing effect. However, excessive addition above 0.10% leads to the formation of non-metallic inclusions. Therefore, the Al content is
l. The amount of Al was determined to be 0.004 to 0.10%.
【００１９】h) Ｓ Ｓは鋼中のMnと結合して非金属介在物を形成する不純物
元素であるので、その含有量は可能な限り低い方が良
い。ただ、Ｓ含有量が 0.015％以下であれば本発明が目
的とする所望特性の確保が可能となるため、Ｓ含有量の
上限を 0.015％と定めたが、より好ましい範囲は 0.005
％以下である。H) SS Since S is an impurity element that forms nonmetallic inclusions by combining with Mn in steel, the content of S is preferably as low as possible. However, if the S content is 0.015% or less, the desired characteristics aimed at by the present invention can be secured, so the upper limit of the S content is set to 0.015%, but a more preferable range is 0.005%.
% Or less.
【００２０】i) Ca，Ti及びCr Caは、介在物の形状を調整して冷間加工性を改善する作
用を有するので必要に応じて添加される成分であるが、
その含有量が0.0002％未満では前記作用による所望の効
果が得られず、一方、0.01％を超えて含有させると逆に
鋼中の介在物が多くなりすぎて冷間加工性が劣化するよ
うになることから、Ca含有量は0.0002〜0.01％と定め
た。また、Tiは析出強化により、そしてCrは変態強化に
より鋼板の強度を向上させる作用を有するので、何れも
やはり必要に応じて添加される成分であるが、該作用に
よる所望の効果を得るためには、Tiの場合には 0.005％
以上の含有量を、Crの場合には 0.1％以上の含有量を確
保する必要がある。しかしながら、Tiの場合には0.15％
を超えて含有させてもその効果は飽和し、一方、Crの場
合には 1.2％を超えて含有させると溶接性の劣化を招
く。従って、その含有量はTiでは 0.005〜0.15％、Crで
は 0.1〜 1.2％と定めた。I) Ca, Ti and Cr Ca is a component that is added as necessary because it has the effect of adjusting the shape of inclusions and improving cold workability.
If the content is less than 0.0002%, the desired effect due to the above-mentioned effect cannot be obtained. On the other hand, if the content is more than 0.01%, the inclusions in the steel become too large and the cold workability deteriorates. Therefore, the Ca content was determined to be 0.0002 to 0.01%. In addition, since Ti has the effect of improving the strength of the steel sheet by precipitation strengthening and Cr has the effect of improving the strength of the steel sheet, any of them is also a component added as needed, but in order to obtain a desired effect by the action. Is 0.005% for Ti
It is necessary to secure the above content, and in the case of Cr, a content of 0.1% or more. However, in the case of Ti, 0.15%
The effect is saturated even if the content exceeds 1.2%. On the other hand, if the content of Cr exceeds 1.2%, the weldability is deteriorated. Therefore, the content was determined to be 0.005 to 0.15% for Ti and 0.1 to 1.2% for Cr.
【００２１】(B) 処理条件 本発明では、熱間圧延に際しての鋼片の加熱温度は１２
００℃超とされる。これは、鋼中不純物を完全に固溶さ
せて偏析するのを防ぐと共に、鋼片の変形抵抗を下げて
圧延の負荷（特に粗圧延での荷重等の負荷）を軽減する
ために必要な処置である。(B) Processing Conditions In the present invention, the heating temperature of the slab during hot rolling is 12
It is assumed to be over 00 ° C. This is a necessary measure to completely dissolve the impurities in the steel to prevent segregation and to reduce the deformation resistance of the slab to reduce the rolling load (particularly the load such as the load in rough rolling). It is.
【００２２】また、熱間圧延の仕上温度は８３０〜９４
０℃に調整される。これは、仕上温度が８３０℃未満と
なって未再結晶域での圧下量が多くなると顕著なバンド
状組織が生成して伸びフランジ性（穴拡げ性）を劣化さ
せ、一方、仕上温度が９４０℃を超えた場合にはオ−ス
テナイト粒径が大きくなりすぎてフェライト生成量が減
少し、延性が低下するからである。The finishing temperature of the hot rolling is 830 to 94.
Adjusted to 0 ° C. This is because when the finishing temperature is lower than 830 ° C. and the amount of reduction in the non-recrystallized region increases, a remarkable band-like structure is generated to deteriorate stretch flangeability (hole expanding property), while the finishing temperature is 940 ° C. If the temperature exceeds ℃, the austenite particle size becomes too large, the amount of ferrite produced decreases, and the ductility decreases.
【００２３】そして、熱間圧延後、５０℃/s以上（好ま
しくは７０℃/s以上）の冷却速度で５４０〜６４０℃の
領域にまで第１段の急冷を施すのは、引続いて巻取温度
まで実施する後段の冷却の負荷を軽減して前述したよう
な膜沸騰−核沸騰遷移温度を低下させ、巻取温度の的中
率を向上させるためであり、加えてセメンタイトの粒界
への析出やＰの粒界偏析を抑制するためでもある。After the hot rolling, the first-stage quenching at a cooling rate of 50 ° C./s or more (preferably 70 ° C./s or more) to the region of 540 to 640 ° C. The purpose of this is to reduce the cooling load of the latter stage to be performed to the take-off temperature, to lower the film boiling-nucleate boiling transition temperature as described above, and to improve the hit ratio of the take-up temperature, and additionally to the cementite grain boundary. This is also for suppressing precipitation of P and grain boundary segregation of P.
【００２４】この場合、第１段冷却の冷却速度が５０℃
/c未満であったり、第１段冷却の終点温度が６４０℃超
であったりするとセメンタイトの粒界への析出やＰの粒
界偏析が抑えられずに伸びフランジ性が劣化する。ま
た、この第１段冷却の終点温度が６４０℃超であった場
合、良好な伸びフランジ性が確保できる巻取温度まで冷
却するには引続いて行われる空冷（第２段冷却）後の冷
却（第３段冷却）の冷却速度が速くなってしまい、膜沸
騰−核沸騰遷移温度が比較的高温側に移行するため島状
スケ−ルに起因した不均一な冷却が起こってコイル内特
性変動を免れることができない。一方、第１段冷却の終
点温度が５４０℃未満であるとフェライトの生成が不十
分で延性が低下する。In this case, the cooling rate of the first stage cooling is 50 ° C.
If it is less than / c, or if the end point temperature of the first stage cooling is more than 640 ° C., the precipitation flangeability deteriorates without suppressing precipitation of cementite at the grain boundaries and segregation of P at the grain boundaries. If the end point temperature of the first-stage cooling is higher than 640 ° C., cooling to the winding temperature at which good stretch flangeability can be ensured is followed by cooling after subsequent air cooling (second-stage cooling). The cooling rate of (third stage cooling) is increased, and the transition temperature between the film boiling and the nucleate boiling shifts to a relatively high temperature side, so that uneven cooling caused by the island scale occurs and the characteristic in the coil changes. Can not escape. On the other hand, when the end point temperature of the first-stage cooling is lower than 540 ° C., ferrite is insufficiently formed and ductility is reduced.
【００２５】本発明において、第１段冷却に続いて行わ
れる第２段冷却（空冷）は非常に重要な工程である。即
ち、本発明ではバンド組織生成を抑制するために熱間圧
延の仕上温度を高めた結果、オ−ステナイト粒が大きく
なってフェライトが生成しにくくなるので、この第２段
の空冷によってフェライトの生成を十分に行わせる必要
がある。空冷時間は１〜５秒が適当で、１秒未満では上
記効果が得られず、一方、５秒を超える時間空冷を行う
と、Ｐの粒界偏析が生じたり結晶粒界にセメンタイトが
析出してきて伸びフランジ性が劣化する。なお、好まし
くは空冷時間は１〜３秒とするのが良い。In the present invention, the second stage cooling (air cooling) performed after the first stage cooling is a very important step. That is, in the present invention, as a result of raising the finishing temperature of hot rolling in order to suppress the formation of band structure, austenite grains become large and ferrite is difficult to be formed. Needs to be performed sufficiently. The air cooling time is suitably from 1 to 5 seconds, and if the air cooling time is less than 1 second, the above effect cannot be obtained. On the other hand, if air cooling is performed for more than 5 seconds, segregation of P at the grain boundaries occurs or cementite precipitates at the crystal grain boundaries. As a result, the stretch flangeability deteriorates. Preferably, the air cooling time is 1 to 3 seconds.
【００２６】第２段冷却（空冷）の後は、引続き５〜３
０℃/s（好ましくは５〜２０℃/s）の冷却速度で４５０
〜５５０℃の巻取温度まで冷却する“第３段冷却”が実
施される。この第３段冷却において、冷却速度が３０℃
/sを超えたり、冷却終点温度（巻取温度）が４５０℃を
下回ったりすると、巻取までの冷却でスケ−ル厚みの厚
い部分から順に膜沸騰−核沸騰遷移温度を通過すること
になるため島状スケ−ルに起因したコイル内の不均一な
冷却が生じてコイル内特性変動を免れることができなく
なり、歩留が悪化する。一方、この場合に、冷却速度が
５℃/s未満であったり、冷却終点温度（巻取温度）が５
５０℃を上回っていると、Ｐの粒界偏析やセメンタイト
の粒界への析出が生じて伸びフランジ性が劣化する。な
お、第３段冷却終了後は速やかに巻取る必要がある。After the second stage cooling (air cooling), 5 to 3
450 ° C. at a cooling rate of 0 ° C./s (preferably 5-20 ° C./s)
"Third stage cooling" for cooling to a winding temperature of ~ 550 ° C is performed. In this third stage cooling, the cooling rate is 30 ° C.
If the temperature exceeds / s, or the cooling end point temperature (winding temperature) falls below 450 ° C, the film will pass through the film boiling-nucleate boiling transition temperature in order from the thicker part of the scale due to cooling until winding. As a result, uneven cooling in the coil due to the island scale occurs, making it impossible to avoid variations in the coil characteristics, and the yield is reduced. On the other hand, in this case, the cooling rate is less than 5 ° C / s, or the cooling end point temperature (winding temperature) is 5 ° C.
If the temperature exceeds 50 ° C., segregation of P at the grain boundaries and precipitation of cementite at the grain boundaries occur, and the stretch flangeability deteriorates. Note that it is necessary to wind up immediately after the third stage cooling.
【００２７】次に、本発明を実施例により説明する。Next, the present invention will be described with reference to examples.
【実施例】まず、表１に示す化学組成の鋼を転炉溶製
し、連続鋳造にてスラブとした。EXAMPLES First, steels having the chemical compositions shown in Table 1 were melted from a converter and continuously cast into slabs.
【００２８】[0028]
【表１】 [Table 1]
【００２９】次いで、表２及び表３に示す条件でスラブ
の再加熱，熱間圧延，冷却を順次実施した後、速やかに
巻取って 2.6mm厚の熱延鋼板を得た。更に、常法に従い
引続いてこの熱延鋼板に形状修正のためのスキンパスと
酸洗とを施した。Next, the slab was reheated, hot-rolled and cooled sequentially under the conditions shown in Tables 2 and 3, and then immediately rolled up to obtain a hot-rolled steel sheet having a thickness of 2.6 mm. Further, the hot-rolled steel sheet was successively subjected to a skin pass for shape correction and pickling according to a conventional method.
【００３０】[0030]
【表２】 [Table 2]
【００３１】[0031]
【表３】 [Table 3]
【００３２】そして、上述のように製造された各熱延鋼
板から圧延方向にＪＩＳ５号引張試験片を採取し、その
機械的性質を調べた。また、これとは別に、各熱延鋼板
から採取した試験片に１０％クリアランスで打ち抜いた
１２φ穴を６０°円錐ポンチで穴拡げするという“穴拡
げ試験”も実施し、伸びフランジ性を評価した。更に、
各熱延鋼板について耐食性の評価も行ったが、耐食性は
１週間に２回の割合で５％塩水噴霧を加える「９０日屋
外暴露試験」での“最大腐食深さ”で評価した。これら
の結果を前記表２及び表３に併せて示す。Then, JIS No. 5 tensile test pieces were sampled in the rolling direction from each of the hot-rolled steel sheets manufactured as described above, and the mechanical properties were examined. Separately from this, a "hole expanding test" in which a 12φ hole punched with a 10% clearance was expanded on a test piece sampled from each hot-rolled steel sheet with a 60 ° conical punch to evaluate the stretch flangeability. . Furthermore,
The corrosion resistance of each hot-rolled steel sheet was also evaluated. The corrosion resistance was evaluated by the “maximum corrosion depth” in a “90-day outdoor exposure test” in which 5% salt spray was applied twice a week. These results are shown in Tables 2 and 3 above.
【００３３】表２及び表３に示される結果からは、次の
ことを確認できる。即ち、本発明で規定する条件に従っ
て製造された試験番号１〜８及び試験番号16〜21に係る
熱延鋼板は、何れも優れた強度，伸び並びに耐食性を示
すと共に、“１００％を超える穴拡げ率”を有してお
り、また“巻取温度で±２５℃に入る高い冷却安定性
（これはコイル内特性変動の少ないことを意味する）”
が得られている。From the results shown in Tables 2 and 3, the following can be confirmed. That is, all of the hot-rolled steel sheets according to Test Nos. 1 to 8 and Test Nos. 16 to 21 manufactured according to the conditions specified in the present invention show excellent strength, elongation and corrosion resistance, and have a hole expansion exceeding 100%. Rate "and" high cooling stability within ± 25 ° C at the winding temperature (this means that there is little characteristic fluctuation in the coil) "
Has been obtained.
【００３４】これに対して、空冷開始温度の高い試験番
号10と、空冷時間の長い試験番号12と、巻取温度の高い
試験番号15に係る熱延鋼板は、粒界での炭化物の析出が
多く穴拡げ性が低い。また、空冷を実施しなかった試験
番号９と、空冷開始温度の低い試験番号11に係る熱延鋼
板は、何れも伸びが低い。更に、第３段冷却速度の速い
試験番号13と、巻取温度の低い試験番号14に係る熱延鋼
板は、スケ−ル厚みの差に起因した冷却の不均一が生
じ、コイル内特性バラツキの原因となる巻取温度のバラ
ツキが大きくなっている。そして、Si含有量の低い試験
番号22に係る熱延鋼板は、巻取温度の的中率は良いが穴
拡げ性が低い。On the other hand, in test No. 10 having a high air-cooling start temperature, test No. 12 having a long air-cooling time, and hot-rolled steel sheet according to test No. 15 having a high winding temperature, precipitation of carbides at grain boundaries was not observed. Many have low hole expansion properties. In addition, the elongation of each of Test No. 9 in which no air cooling was performed and Test No. 11 in which the air cooling start temperature is low has a low elongation. Further, in the hot-rolled steel sheet according to Test No. 13 having a high cooling rate in the third stage and Test No. 14 having a low winding temperature, uneven cooling occurs due to the difference in scale thickness, and the characteristic variation in the coil. The variation in the winding temperature that causes this is large. Then, the hot-rolled steel sheet according to Test No. 22 having a low Si content has a good hit ratio of the winding temperature, but has low hole expandability.
【００３５】一方、Ｐの添加を行わなかったＩ鋼を素材
とした試験番号23〜30に係る熱延鋼板は、成分系が近い
Ａ鋼を素材とした試験番号９〜15に係る熱延鋼板に比べ
て冷却条件の影響は小さいが、何れも最大腐食深さが深
く耐食性が低い。On the other hand, the hot-rolled steel sheets according to Test Nos. 23 to 30 using I-steel to which P was not added were the hot-rolled steel sheets according to Test Nos. 9 to 15 using A-steel having a similar component system as the material. Although the influence of the cooling conditions is smaller than that of, the maximum corrosion depth is deep and the corrosion resistance is low.
【００３６】[0036]
【効果の総括】以上に説明した如く、この発明によれ
ば、優れた耐食性を示し、しかも高強度と高伸びフラン
ジ性を両立していてア−ムやメンバ−等の自動車足廻り
部品用等として好適な熱延鋼板を提供することができる
上、その製造に際しては熱間圧延後の冷却過程での温度
制御が簡単なために製造歩留が非常に良好であるなど、
産業上極めて有用な効果がもたらされる。As described above, according to the present invention, excellent corrosion resistance is exhibited, high strength and high stretch flangeability are both achieved, and the present invention is used for parts around automobiles such as arms and members. In addition to being able to provide a hot rolled steel sheet suitable for the production, the production yield is very good because the temperature control in the cooling process after hot rolling is simple,
An extremely useful effect in industry is brought about.
───────────────────────────────────────────────────── フロントページの続き (58)調査した分野(Int.Cl.7，ＤＢ名) C21D 9/46 - 9/48 C21D 8/02 - 8/04 C22C 38/00 - 38/60 ──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. 7 , DB name) C21D 9/46-9/48 C21D 8/02-8/04 C22C 38/00-38/60
Claims (2)
0.4〜 2.0％， Mn： 0.7〜 2.0％，Ｐ：0.01〜0.15
％， Cu：0.15〜0.50％， Ni：0.01〜0.30％，sol.A
l： 0.004〜0.10％， Ｓ： 0.015％以下を含むと共に
残部がFe及び不可避不純物から成る鋼片を、１２００℃
を超える温度に加熱して熱間圧延を施し、最終パス出側
温度８３０〜９４０℃で熱間圧延を終了した後、５０℃
/s以上の冷却速度にて５４０〜６４０℃まで冷却する第
１段冷却と、これに続く１〜５秒間の空冷を行う第２段
冷却とを施し、更に引続いて５〜３０℃/sの冷却速度に
て４５０〜５５０℃まで冷却を行う第３段冷却を施して
から巻取ることを特徴とする、耐食性と伸びフランジ性
に優れ、コイル内特性変動の少ない高強度熱延鋼板の製
造方法。(1) C: 0.04 to 0.15% by weight, Si:
0.4 to 2.0%, Mn: 0.7 to 2.0%, P: 0.01 to 0.15
%, Cu: 0.15 to 0.50%, Ni: 0.01 to 0.30%, sol.A
l: A steel slab containing 0.004 to 0.10%, S: 0.015% or less, with the balance being Fe and unavoidable impurities.
After hot rolling at a temperature of 830 to 940 ° C. on the exit side of the final pass, heating to 50 ° C.
/ s at a cooling rate of 540-640 ° C. or higher, followed by a second-stage cooling for 1-5 seconds of air cooling, followed by 5-30 ° C./s Production of high-strength hot-rolled steel sheet with excellent corrosion resistance and stretch flangeability, with little fluctuation in coil characteristics, characterized by performing a third-stage cooling of cooling to 450 to 550 ° C. at a cooling rate of 300 ° C. Method.
0.4〜 2.0％， Mn： 0.7〜 2.0％，Ｐ：0.01〜0.15
％， Cu：0.15〜0.50％， Ni：0.01〜0.30％，sol.A
l： 0.004〜0.10％， Ｓ： 0.015％以下を含み、更にC
a：0.0002〜0.01％， Ti： 0.005〜0.15％， C
r： 0.1〜 1.2％の１種以上を含むと共に残部がFe及び
不可避不純物から成る鋼片を、１２００℃を超える温度
に加熱して熱間圧延を施し、最終パス出側温度８３０〜
９４０℃で熱間圧延を終了した後、５０℃/s以上の冷却
速度にて５４０〜６４０℃まで冷却する第１段冷却と、
これに続く１〜５秒間の空冷を行う第２段冷却とを施
し、更に引続いて５〜３０℃/sの冷却速度にて４５０〜
５５０℃まで冷却を行う第３段冷却を施してから巻取る
ことを特徴とする、耐食性と伸びフランジ性に優れ、コ
イル内特性変動の少ない高強度熱延鋼板の製造方法。2. C: 0.04 to 0.15% by weight, Si:
0.4 to 2.0%, Mn: 0.7 to 2.0%, P: 0.01 to 0.15
%, Cu: 0.15 to 0.50%, Ni: 0.01 to 0.30%, sol.A
l: 0.004 to 0.10%, S: 0.015% or less, and C
a: 0.0002 to 0.01%, Ti: 0.005 to 0.15%, C
r: A steel slab containing at least one of 0.1 to 1.2% and the balance consisting of Fe and unavoidable impurities is heated to a temperature exceeding 1200 ° C. and subjected to hot rolling.
After finishing the hot rolling at 940 ° C., a first stage cooling of cooling to 540 to 640 ° C. at a cooling rate of 50 ° C./s or more;
This is followed by a second stage cooling in which air cooling is performed for 1 to 5 seconds, and subsequently 450 to 450 ° C. at a cooling rate of 5 to 30 ° C./s.
A method for producing a high-strength hot-rolled steel sheet which is excellent in corrosion resistance and stretch flangeability, and has little fluctuation in characteristics in a coil, characterized in that it is subjected to third-stage cooling of cooling to 550 ° C. and then winding.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP07152669A JP3119122B2 (en) | 1995-05-26 | 1995-05-26 | Manufacturing method of high strength hot rolled steel sheet |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP07152669A JP3119122B2 (en) | 1995-05-26 | 1995-05-26 | Manufacturing method of high strength hot rolled steel sheet |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08325633A JPH08325633A (en) | 1996-12-10 |
| JP3119122B2 true JP3119122B2 (en) | 2000-12-18 |
Family
ID=15545515
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP07152669A Expired - Fee Related JP3119122B2 (en) | 1995-05-26 | 1995-05-26 | Manufacturing method of high strength hot rolled steel sheet |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3119122B2 (en) |
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| KR100430981B1 (en) * | 1999-08-10 | 2004-05-14 | 제이에프이 엔지니어링 가부시키가이샤 | Method for producing cold rolled steel sheet having excellent deep drawing property |
| KR100711476B1 (en) * | 2005-12-26 | 2007-04-24 | 주식회사 포스코 | Method for manufacturing high strength hot rolled steel sheet having excellent formability |
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-
1995
- 1995-05-26 JP JP07152669A patent/JP3119122B2/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20140044931A (en) | 2011-08-31 | 2014-04-15 | 제이에프이 스틸 가부시키가이샤 | Hot-rolled steel sheet for cold-rolled steel sheet, hot-rolled steel sheet for hot-dipped galvanized steel sheet, method for producing hot-rolled steel sheet for cold-rolled steel sheet, and method for producing hot-rolled steel sheet for hot-dipped galvanized steel sheet |
| US11098392B2 (en) | 2011-08-31 | 2021-08-24 | Jfe Steel Corporation | Hot rolled steel sheet for cold rolled steel sheet, hot rolled steel sheet for galvanized steel sheet, and method for producing the same |
| EP3561101A4 (en) * | 2016-12-20 | 2019-11-13 | Posco | High-strength hot-rolled steel plate having excellent weldability and ductility and method for manufacturing same |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08325633A (en) | 1996-12-10 |
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