JP2559272B2 - Method for producing high strength hot rolled steel sheet with excellent ductility - Google Patents
Method for producing high strength hot rolled steel sheet with excellent ductilityInfo
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- JP2559272B2 JP2559272B2 JP1127367A JP12736789A JP2559272B2 JP 2559272 B2 JP2559272 B2 JP 2559272B2 JP 1127367 A JP1127367 A JP 1127367A JP 12736789 A JP12736789 A JP 12736789A JP 2559272 B2 JP2559272 B2 JP 2559272B2
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- strength
- steel sheet
- rolled steel
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- ductility
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- Heat Treatment Of Sheet Steel (AREA)
Description
【発明の詳細な説明】 （産業上の利用分野） 本発明は、特にホイールディスク、各種メンバー類を
始めとする自動車用部材或いは建設用材等に使用され、
延性に優れた60kgf/mm2以上の強度を有する高強度熱延
鋼板及びその製造方法に関する。DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is used for wheel members, automobile members including various members, construction materials, and the like.
The present invention relates to a high-strength hot-rolled steel sheet having excellent ductility and a strength of 60 kgf / mm 2 or more, and a method for manufacturing the same.
（従来の技術及び解決しようとする課題） 近年、自動車用部材の軽量化のため、高強度で且つ高
延性の熱延鋼板の要求が強いが、従来は、二相（Dual P
hase）鋼（以下、「DP鋼」と称す）、すなわち、フェラ
イト＋マルテンサイト鋼が高強度と高延性を兼備した鋼
として使用されてきた。(Prior Art and Problems to be Solved) In recent years, there has been a strong demand for hot-rolled steel sheets having high strength and high ductility in order to reduce the weight of members for automobiles.
hase) steel (hereinafter referred to as “DP steel”), that is, ferrite + martensite steel has been used as a steel having both high strength and high ductility.
しかし、DP鋼といえども、強度−延性バランスがTS×
El≧2000を安定して得ることは困難であり、更なる高強
度化、又は複雑な成形を要する部材への適用が可能な鋼
材が求められている。However, even with DP steel, the strength-ductility balance is TS ×
It is difficult to stably obtain El ≧ 2000, and there is a demand for a steel material that can be applied to a member requiring higher strength or complicated forming.
さて、最近になってγＲのTRIP効果を利用した熱延鋼
板がTS×El＞2000を可能にする鋼として注目されるよう
になり、多くの提案がなされているが、Ｃ量が高いた
め、溶接性に問題があるものが多い。Recently, hot-rolled steel sheets that utilize the TRIP effect of γ R have come to the fore as steels that enable TS × El> 2000, and many proposals have been made, but since the amount of C is high. There are many problems with weldability.
すなわち、例えば、特開昭60−184664号ではγＲを残
留させる目的からＣが規制されており、Ｃ含有量は0.15
％越え、0.8％以下とされている。しかしながら、実際
にはＣ含有量は0.38％越えであり、多量のγＲが得られ
ので延性は良好なものの、溶接が困難であり、自動車用
としては問題がある。That is, for example, in JP-A-60-184664, C is regulated for the purpose of leaving γ R , and the C content is 0.15.
% And 0.8% or less. However, in reality, the C content exceeds 0.38% and a large amount of γ R is obtained, so that the ductility is good, but welding is difficult, and there is a problem for automobiles.
本発明は、かゝる事情に鑑みてなされたものであっ
て、強度−延性バランスに優れると共に溶接性の良好な
熱延鋼板を製造し得る方法を提供することを目的とする
ものである。The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method capable of producing a hot-rolled steel sheet having excellent strength-ductility balance and good weldability.
（課題を解決するための手段） 前記目的を達成するため、本発明者らは、強度−延性
バランスに優れ、且つ溶接性も良好な熱延鋼板が得られ
る方策について鋭意検討した。(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention diligently studied a method for obtaining a hot-rolled steel sheet having an excellent strength-ductility balance and a good weldability.
その結果、Ｃ量を低く抑え、溶接性に悪影響を及ぼさ
ぬ程度のSiとMnを添加して成分調整すると共に、熱延仕
上げ温度を規制し、更に熱延後の冷却過程において、α
＋γ２相域で緩冷却を行うことによりＣ濃度の低い軟質
なαを生成させ、且つ未変態オーステナイト中にＣの濃
化を図ることによってγＲを積極的に生成せしめること
により、可能であることを知見した。また、更にNbの添
加により組織を微細化し、安定したγＲを微細に分散さ
せることにより、強度−延性バランスに優れ、より高強
度の鋼板が得られることも知見し、ここに本発明を完成
するに至つたものである。As a result, the amount of C is kept low, the composition is adjusted by adding Si and Mn to the extent that they do not adversely affect the weldability, the hot rolling finishing temperature is regulated, and in the cooling process after hot rolling, α
What is possible by gently cooling in the + γ2 phase region to produce soft α with a low C concentration, and by actively producing γ R by concentrating C in untransformed austenite. I found out. Further, by further adding Nb to refine the structure and finely disperse the stable γ R , it was also found that a steel sheet having excellent strength-ductility balance and higher strength can be obtained, and the present invention is completed here. It is something that has led to.
すなわち、本発明は、C:0.15〜0.25％、Si:2.0〜4.0
％及びMn:1.0〜2.0％を含有し、必要に応じて更にNb:0.
01〜0.07％及びCa:0.005〜0.01％の１種又は２種を含有
し、残部が鉄及び不可避的不純物よりなる鋼につき、仕
上げ温度750〜950℃にて圧延を行った後、冷却速度20〜
200℃/secにてAr3〜600℃まで急冷し、続いて冷却速度2
0℃/sec未満にて３〜40secの間を緩冷却した後、300℃
〜450℃までを冷却速度20℃/sec以上で冷却して巻取る
ことにより、γＲ（残留オーステナイト）を面積率で５
〜20％有する組織を得ることを特徴とする延性の優れた
高強度熱延鋼板の製造方法を要旨とするものである。That is, the present invention, C: 0.15-0.25%, Si: 2.0-4.0
% And Mn: 1.0 to 2.0%, and Nb: 0.
A steel containing 01 to 0.07% and Ca: 0.005 to 0.01% of 1 or 2 and the balance of iron and unavoidable impurities is rolled at a finishing temperature of 750 to 950 ° C and then cooled at a cooling rate of 20. ~
Quench at Ar 3 to 600 ℃ at 200 ℃ / sec, and then cool at 2
After slow cooling for 3 to 40 seconds at less than 0 ° C / sec, 300 ° C
By cooling up to ~ 450 ° C at a cooling rate of 20 ° C / sec or more and winding it up, γ R (retained austenite) becomes 5 in area ratio.
The gist is a method for producing a high-strength hot-rolled steel sheet having excellent ductility, which is characterized in that a structure having a content of -20% is obtained.
以下、本発明について更に詳細に説明する。 Hereinafter, the present invention will be described in more detail.
（作用） まず、本発明における化学成分の限定理由について説
明する。(Operation) First, the reasons for limiting the chemical components in the present invention will be described.
C: Ｃは鋼の強化及びγＲの安定化に不可欠な元素であ
る。しかし、0.15％未満では充分なγＲが得られず、ま
た0.25％を越えると溶接性が劣化するので、Ｃ量は0.15
〜0.25％の範囲とする。C: C is an element essential for strengthening steel and stabilizing γ R. However, if it is less than 0.15%, sufficient γ R cannot be obtained, and if it exceeds 0.25%, the weldability deteriorates, so the C content is 0.15%.
The range is to 0.25%.
Si: Siは少ないＣ量で充分なγＲ量を得るために非常に重
要な元素である。すなわち、γ→α（フェライト）変態
を促進し、且つα中のＣ濃度を低下することによりαの
延性を向上させると共にγ中のＣ濃度を高めて安定化
し、γＲを得やすくする効果がある。所要の効果を得る
ためには2.0％以上が必要であるが、4.0％を越えて含有
させてもそれ以上効果が上がらないだけでなく、溶接性
を劣化させるので、Si量は2.0〜4.0％の範囲とする。Si: Si is a very important element for obtaining a sufficient amount of γ R with a small amount of C. That is, the effect of facilitating the γ → α (ferrite) transformation and improving the ductility of α by lowering the C concentration in α and increasing and stabilizing the C concentration in γ to easily obtain γ R is obtained. is there. 2.0% or more is required to obtain the required effect, but if the content exceeds 4.0%, not only the effect does not improve, but also the weldability deteriorates, so the Si content is 2.0 to 4.0%. The range is.
Mn: Mnは固溶強化元素として強度（TS）上昇に効果がある
だけでなく、γを安定化し、γＲを得るのに重要な元素
である。所要の効果を得るために1.0％以上が必要であ
るが、2.0％を越えて含有させるとバンド状組織を生成
し、加工性が劣化する。したがって、Mn量は1.0〜2.0％
の範囲とする。Mn: Mn is a solid solution strengthening element that is effective not only for increasing strength (TS) but also for stabilizing γ and obtaining γ R. 1.0% or more is necessary to obtain the desired effect, but if it exceeds 2.0%, a band-like structure is formed and the workability deteriorates. Therefore, the amount of Mn is 1.0-2.0%
Range.
本発明では上記の元素を必須成分とするが、必要に応
じて以下の元素Nb、Caの１種又は２種を適量で添加する
ことができる。In the present invention, the above elements are used as essential components, but if necessary, one or two of the following elements Nb and Ca can be added in appropriate amounts.
Nb: Nbは、変態前のγを細粒化するため、熱延板組織を微
細化すると共に、仕上げ圧延後の冷却時に残留するオー
ステナイト中へのＣの濃化を促進するので、γＲの生成
を助長する効果がある。また、γＲを微細に分散せしめ
ることにより、強度−延性バランスを向上させるのに重
要な元素である。このような所要の効果を得るには0.01
％以上が必要であるが、0.07％を越えて添加してもそれ
以上効果は上がらないだけでなく、延性（El）の劣化が
著しいので、Nb量は0.01〜0.07％の範囲とする。Nb: nb is to fine the gamma before transformation, with refining the hot rolled sheet structure, so to facilitate the concentration of C into the austenite remaining when cooling after finish rolling, the gamma R It has the effect of promoting generation. Further, by finely dispersing γ R , it is an important element for improving the strength-ductility balance. 0.01 to achieve the desired effect
% Or more is necessary, but if it is added in excess of 0.07%, the effect is not further improved, and the ductility (El) is significantly deteriorated, so the Nb content is set to 0.01 to 0.07%.
Ca: Caは加工性の改善、特に局部延性の改善に有効であ
る。しかし、0.0005％未満では所要の効果が得られず、
また0.01％を越えて加えてもそれ以上の効果がなく、逆
に介在物となり、加工性を劣化させるので、Ca量は0.00
05〜0.01％の範囲とする。Ca: Ca is effective in improving workability, especially in local ductility. However, if less than 0.0005%, the desired effect cannot be obtained,
Moreover, even if added in excess of 0.01%, there is no further effect, and on the contrary, it becomes an inclusion and deteriorates the workability, so the Ca content is 0.00
The range is from 05 to 0.01%.
次に、本発明により得られた熱延鋼板の組織について
述べる。Next, the structure of the hot rolled steel sheet obtained by the present invention will be described.
本発明で得られる鋼は、加工時のγＲの加工誘起マル
テンサイト変態を利用した高強度高延性型鋼板であり、
第１図にγＲ面積率と強度−延性バランス（TS×El）の
関係を示すように、所要の特性を得るには、５％以上の
γＲが必要である。しかし、本成分系においては、20％
以上のγＲを得るのは困難であり、20％以上のγＲを得
るべく更に合金を添加すると、伸びフランジ性及び溶接
性が劣化する。したがって、γＲの面積率を５〜20％と
する。The steel obtained by the present invention is a high-strength, high-ductility steel sheet that utilizes the work-induced martensitic transformation of γ R during working.
As shown in FIG. 1 showing the relationship between the γ R area ratio and the strength-ductility balance (TS × El), γ R of 5% or more is required to obtain the required characteristics. However, in this component system, 20%
It is to obtain the above gamma R is difficult, further to obtain the above 20% gamma R adding alloy deteriorates stretch flangeability and weldability. Therefore, the area ratio of γ R is set to 5 to 20%.
かゝる組織を有する熱延鋼板を得るための製造条件
（熱延、冷却条件）は以下のとおりである。The manufacturing conditions (hot rolling, cooling conditions) for obtaining a hot rolled steel sheet having such a structure are as follows.
仕上げ温度は、γを微細化することによりα変態の促
進及び微細化を図り、強度−延性バランスを向上すると
共に、未変態γを微細、分散させて安定化するために規
制する必要がある。そのためには、第２図に示すよう
に、950℃以下とする必要がある。しかし、仕上げ温度
が750℃未満では、加工αが混入するため、強度−延性
バランスが劣化する。したがって、仕上げ温度は750〜9
50℃の範囲とする。It is necessary to control the finishing temperature in order to promote and miniaturize the α transformation by refining γ, improve the strength-ductility balance, and finely disperse and stabilize the untransformed γ. For that purpose, as shown in FIG. 2, the temperature needs to be 950 ° C. or lower. However, when the finishing temperature is less than 750 ° C., the processing α is mixed, so that the strength-ductility balance deteriorates. Therefore, the finishing temperature is 750-9
It shall be in the range of 50 ℃.
なお、他の熱間圧延条件は特に制限する必要はない。 The other hot rolling conditions do not have to be particularly limited.
次に、熱延後の冷却条件の第１として、仕上げ後Ar3
〜600℃まで（望ましくはフェライト変態ノーズ近傍ま
で）を冷却速度20℃/sec以上にて急冷し、続いて冷却速
度20℃/sec未満にて３〜40secの間緩冷却を行うことに
より、α（フェライト）の生成を助長すると共に、未変
態γ中にＣを濃度させ、安定化を図る。Next, as the first cooling condition after hot rolling, after finishing Ar 3
~ 600 ℃ (preferably near the ferrite transformation nose) is rapidly cooled at a cooling rate of 20 ℃ / sec or more, and then slowly cooled at a cooling rate of less than 20 ℃ / sec for 3 to 40 seconds, The formation of (ferrite) is promoted and at the same time, C is concentrated in the untransformed γ for stabilization.
ここで、急冷速さが20℃/sec未満では粗大αの生成を
招くため、強度−延性バランスが劣化するので好ましく
ない。また、冷却速度の上限を200℃/secと定めたのは
設備上の制約によるものである。Here, if the quenching rate is less than 20 ° C./sec, coarse α is generated, so that the strength-ductility balance deteriorates, which is not preferable. Also, the upper limit of the cooling rate was set at 200 ° C / sec because of facility restrictions.
また、上記緩冷却域を30℃/secを越える冷却速度又は
3sec未満の冷却時間とすると、αの充分な生成並びにα
からのＣの拡散と未変態γ中へのＣの濃度が充分行われ
ないため、強度−延性バランスが劣化するので好ましく
ない。このため、十分良好な強度−延性バランスを確実
に得るため、緩冷却域を20℃/sec未満の冷却速度で、3s
ec以上冷却する。更に、緩冷却時間が40secを越える
と、パーライトの生成により未変態γ中の固溶Ｃ消費さ
れ、γＲ量が減少するので好ましくない。In addition, a cooling rate exceeding 30 ° C / sec in the slow cooling area or
If the cooling time is less than 3 seconds, sufficient α formation and α
C is not diffused sufficiently and the concentration of C in the untransformed γ is not sufficient, so that the strength-ductility balance is deteriorated, which is not preferable. For this reason, in order to ensure a sufficiently good strength-ductility balance, the slow cooling zone is cooled at a cooling rate of less than 20 ° C / sec for 3s.
Cool more than ec. Further, if the slow cooling time exceeds 40 sec, solid solution C in untransformed γ is consumed due to the formation of pearlite, and the amount of γ R decreases, which is not preferable.
緩冷却の後、300〜450℃までを冷却速度20℃/sec以上
で冷却して巻き取るのは、パーライトの生成を抑制し、
５％以上のγＲを得るためである。After gentle cooling, cooling from 300 to 450 ° C at a cooling rate of 20 ° C / sec or more and winding up suppresses the generation of pearlite,
This is to obtain γ R of 5% or more.
しかし、冷却速度が20℃/sec未満ではパーライトの生
成によりγＲ量が減少する。However, if the cooling rate is less than 20 ° C / sec, the amount of γ R decreases due to the generation of pearlite.
また、巻取り温度とγＲ量の関係は、第３図に示すよ
うに、300℃未満又は450℃より高温域ではγＲが所要の
５％を得ることができない。すなわち、300℃未満で
は、未変態γマルテンサイトに変態するため、所要のγ
Ｒ量が得られず、また、450℃より高温域では、パーラ
イト、ベイナイト変態が必要以上に進むため、所要のγ
Ｒ量が得られない。As for the relationship between the coiling temperature and the amount of γ R , as shown in FIG. 3, γ R cannot reach the required 5% in the region below 300 ° C. or higher than 450 ° C. That is, if the temperature is less than 300 ° C, the untransformed γ martensite is transformed, so that the required γ
R content cannot be obtained, and pearlite and bainite transformation progresses more than necessary in the temperature range higher than 450 ° C.
R amount cannot be obtained.
以下に本発明の実施例を示す。 Hereinafter, examples of the present invention will be described.
（実施例） 第１表に示す化学成分を有する供試鋼に対し、第２表
に示す条件で熱間圧延を行い、冷却して巻取った。な
お、第２表中の各条件記号T1〜T3、JI、C1〜C3は第４図
に示す温度ヒストグラムでの記号に対応している。(Example) A sample steel having the chemical composition shown in Table 1 was hot-rolled under the conditions shown in Table 2, cooled and wound. The condition symbols T 1 to T 3 , JI, and C 1 to C 3 in Table 2 correspond to the symbols in the temperature histogram shown in FIG.
得られた熱延鋼板の特性を第２表に併記する。 The properties of the obtained hot rolled steel sheet are also shown in Table 2.
第２表より明らかなように、本発明例のNo.1〜No.4
は、いずれも適正なγＲ量を有し、良好な強度−延性バ
ランス（TS×El）を示している。勿論、Ｃ量が少ないの
で溶接性（穴拡げ率）は良好である。As is clear from Table 2, No. 1 to No. 4 of the examples of the present invention
Have an appropriate amount of γ R and show a good strength-ductility balance (TS × El). Of course, since the amount of C is small, the weldability (hole expansion rate) is good.
一方、No.5〜No.11は比較例で、No.5〜No.7は化学成
分範囲が本発明範囲外の例、No.8〜No.11は冷却条件が
本発明範囲外の例であり、いずれも強度−延性バランス
がTS×El＜2000と劣っている。On the other hand, No. 5 ~ No. 11 is a comparative example, No. 5 ~ No. 7 is an example where the chemical composition range is outside the scope of the present invention, No. 8 ~ No. 11 is a cooling condition outside the scope of the present invention In each case, the strength-ductility balance is inferior at TS × El <2000.
（発明の効果） 以上詳述したように、本発明によれば、特に低いＣ含
有量により、γＲを多量に生成させることができるた
め、強度−延性バランス（TS×El）が優れていると共
に、溶接性も良好な熱延鋼板を容易に得ることができ
る。 (Effects of the Invention) As described in detail above, according to the present invention, a large amount of γ R can be generated with a particularly low C content, and therefore the strength-ductility balance (TS × El) is excellent. At the same time, it is possible to easily obtain a hot-rolled steel sheet having good weldability.
第１図はγＲ面積率と強度−延性バランス（TS×El）の
関係を示す図、 第２図は強度−延性バランス（TS×El）に及ぼす仕上げ
温度の影響を示す図、 第３図はγＲ面積率に及ぼす巻取り温度の影響を示す
図、 第４図は熱間圧延における温度ヒストグラムを示す図で
ある。FIG. 1 is a diagram showing the relationship between the γ R area ratio and strength-ductility balance (TS × El), and FIG. 2 is a diagram showing the effect of finishing temperature on the strength-ductility balance (TS × El). Is a diagram showing the influence of the winding temperature on the γ R area ratio, and FIG. 4 is a diagram showing a temperature histogram in hot rolling.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 難波 茂信 兵庫県神戸市灘区篠原伯母野山町２丁目 ３―１ (56)参考文献 特開 昭60−184634（ＪＰ，Ａ) ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigenobu Namba 2-3-1, Noyama-cho, Shinohara, Nada-ku, Kobe-shi, Hyogo Prefecture (56) References JP-A-60-184634 (JP, A)
Claims (3)
％、Si:2.0〜4.0％及びMn:1.0〜2.0％を含有し、残部が
鉄及び不可避的不純物よりなる鋼につき、仕上げ温度75
0〜950℃にて圧延を行った後、冷却速度20〜200℃/sec
にてAr3〜600℃まで冷却し、続いて冷却速度20℃/sec未
満にて３〜40secの間を緩冷却した後、300℃〜450℃ま
でを冷却速度20℃/sec以上で冷却して巻取ることによ
り、γＲ（残留オーステナイト）を面積率で５〜20％有
する組織を得ることを特徴とする延性の優れた高強度熱
延鋼板の製造方法。1. C: 0.15 to 0.25 in weight% (hereinafter the same)
%, Si: 2.0-4.0% and Mn: 1.0-2.0%, with the balance being iron and unavoidable impurities, and a finishing temperature of 75
After rolling at 0 ~ 950 ℃, cooling rate 20 ~ 200 ℃ / sec
After cooling to Ar 3 ~ 600 ℃ at 3 ℃ for less than 3 ℃ 40 seconds at a cooling rate of less than 20 ℃ / sec, then 300 ℃ ~ 450 ℃ at a cooling rate of 20 ℃ / sec or more A method for producing a high-strength hot-rolled steel sheet having excellent ductility, characterized by obtaining a structure having γ R (residual austenite) in an area ratio of 5 to 20% by winding.
ものである請求項１に記載の方法。2. The method according to claim 1, wherein the steel further contains Nb: 0.01 to 0.07%.
のである請求項１又は２に記載の方法。3. The method according to claim 1, wherein the steel further contains Ca: 0.005 to 0.01%.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1127367A JP2559272B2 (en) | 1989-05-20 | 1989-05-20 | Method for producing high strength hot rolled steel sheet with excellent ductility |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1127367A JP2559272B2 (en) | 1989-05-20 | 1989-05-20 | Method for producing high strength hot rolled steel sheet with excellent ductility |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02305925A JPH02305925A (en) | 1990-12-19 |
| JP2559272B2 true JP2559272B2 (en) | 1996-12-04 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP1127367A Expired - Fee Related JP2559272B2 (en) | 1989-05-20 | 1989-05-20 | Method for producing high strength hot rolled steel sheet with excellent ductility |
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| Country | Link |
|---|---|
| JP (1) | JP2559272B2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2805112B2 (en) * | 1991-05-17 | 1998-09-30 | 株式会社神戸製鋼所 | Method for manufacturing high-strength hot-rolled steel sheet with excellent ductility and workability |
| KR100450613B1 (en) * | 1999-12-28 | 2004-09-30 | 주식회사 포스코 | A method for manufacturing wire rod for thick plate welding with superior impact toughness |
| KR100711476B1 (en) * | 2005-12-26 | 2007-04-24 | 주식회사 포스코 | Method for manufacturing high strength hot rolled steel sheet having excellent formability |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6479345A (en) * | 1987-06-03 | 1989-03-24 | Nippon Steel Corp | High-strength hot rolled steel plate excellent in workability and its production |
-
1989
- 1989-05-20 JP JP1127367A patent/JP2559272B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02305925A (en) | 1990-12-19 |
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