JP3309893B2 - Method for producing steel plate excellent in bake hardenability after biaxial tensile deformation - Google Patents
Method for producing steel plate excellent in bake hardenability after biaxial tensile deformationInfo
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- JP3309893B2 JP3309893B2 JP32751395A JP32751395A JP3309893B2 JP 3309893 B2 JP3309893 B2 JP 3309893B2 JP 32751395 A JP32751395 A JP 32751395A JP 32751395 A JP32751395 A JP 32751395A JP 3309893 B2 JP3309893 B2 JP 3309893B2
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- tensile deformation
- steel
- biaxial tensile
- bake hardenability
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Description
【０００１】[0001]
【発明の属する技術分野】本発明は、自動車用外板パネ
ルなどの使用に適した、優れた塗装焼付硬化性を有する
鋼板の製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel sheet having excellent paint bake hardenability, which is suitable for use as an outer panel for automobiles.
【０００２】[0002]
【従来の技術】近年、地球環境保護の点から、自動車の
排気ガス低減が要求されている。このため、自動車業界
では、燃費の向上を目的として車体の軽量化を図ってい
る。軽量化には、鋼板の薄肉化が必要となり、これに伴
い、要求される特性の劣化が懸念される。外板に要求さ
れる特性の中で、耐デント性( 凹みにくさ) は、とくに
重要であり、これは、鋼板の降伏強度( 成形、塗装焼付
処理後) と板厚に依存する。板厚減少に伴う耐デント性
の劣化を抑制するため、塗装焼付処理後の降伏強度の一
層の向上、つまり、優れた焼付硬化性が望まれている。
鋼の焼付硬化性（ＢＨ性) は、固溶Ｃ、Ｎの転位への固
着現象によって決定されるので、ＢＨ性は固溶Ｃ、Ｎ
（特にＣ）量を制御して確保されている。2. Description of the Related Art In recent years, reduction of automobile exhaust gas has been demanded from the viewpoint of global environmental protection. For this reason, the automobile industry is trying to reduce the weight of a vehicle body for the purpose of improving fuel efficiency. In order to reduce the weight, it is necessary to reduce the thickness of the steel sheet, and with this, there is a concern that required characteristics may deteriorate. Among the properties required for the outer panel, dent resistance (resistance to dents) is particularly important, and depends on the yield strength (after forming and baking) and thickness of the steel sheet. In order to suppress the deterioration of the dent resistance due to the decrease in the sheet thickness, further improvement of the yield strength after the paint baking treatment, that is, excellent bake hardenability is desired.
The bake hardenability (BH property) of steel is determined by the phenomenon of solid solution C and N sticking to dislocations.
(Particularly C) is secured by controlling the amount.
【０００３】ＢＨ性の優れた鋼板を製造する方法として
は、例えば特公平３ー７２１３４号公報、特開平２ー２
３２３２１６号公報に、極低炭素鋼をベースとしてＮ
ｂ、Ｔｉ、Ｖ等の炭窒化物形成元素を添加した鋼板に連
続焼鈍を施し、焼鈍中に固溶Ｃ量を制御して、優れた焼
付硬化性を有する鋼板（ＢＨ鋼板）を製造する方法が開
示されている。As a method for producing a steel sheet having excellent BH properties, for example, Japanese Patent Publication No. 3-72134,
Japanese Patent No. 323216 discloses an N based on ultra low carbon steel.
A method for producing a steel sheet (BH steel sheet) having excellent bake hardenability by subjecting a steel sheet to which carbonitride forming elements such as b, Ti, and V are added to continuous annealing and controlling the amount of solid solution C during annealing. Is disclosed.
【０００４】[0004]
【発明が解決しようとする課題】ところで、従来、鋼板
の焼付硬化性（ＢＨ性）は、引張試験において、数％
（通常２％）の予ひずみを付与したのち、塗装焼き付け
相当熱処理( 通常１７０℃、２０分）を施し、熱処理前
後の降伏強度の上昇量で評価されている( 例えば、JIS
G 3135( 日本工業規格) に記載されている) 。しかし、
この評価法では、鋼板に付加される変形様式は単軸引張
り変形であり、張り出し成形(2軸引張り変形) などの実
プレス成形後の焼付硬化性は正確に表現されていない。By the way, conventionally, the bake hardenability (BH property) of a steel sheet is several% in a tensile test.
After applying a pre-strain of (usually 2%), it is subjected to heat treatment equivalent to paint baking (usually at 170 ° C. for 20 minutes), and evaluated by the amount of increase in yield strength before and after heat treatment (for example, JIS
G 3135 (described in Japanese Industrial Standards)). But,
In this evaluation method, the deformation mode added to the steel sheet is uniaxial tensile deformation, and the bake hardenability after actual press forming such as stretch forming (biaxial tensile deformation) is not accurately expressed.
【０００５】そこで、本発明者等は、実プレス成形後の
焼付硬化性をより正確に評価する目的から、ＢＨ性に及
ぼす変形様式の影響を調査した。その結果、図６に示す
ように、ＢＨ性は変形様式により大きく異なるという知
見を得た。つまり、極低炭素鋼において、単軸引張り変
形後のＢＨ性はひずみ量によらず高い値を示している
が、2 軸引張り変形後のそれは、１％程度以上のひずみ
（相当ひずみ（単軸引張り変形に換算したひずみ）で評
価）でほとんど零になっている。また、この現象は、従
来、低炭素鋼でみられたものとは大きく異なっている。
このことから、従来技術により製造した極低炭素鋼をベ
ースとしたＢＨ鋼板では、実成形品において所望のＢＨ
性が得られないことがわかる。Therefore, the present inventors investigated the influence of the deformation mode on the BH property in order to more accurately evaluate the bake hardenability after actual press molding. As a result, as shown in FIG. 6, it was found that the BH property greatly differs depending on the deformation mode. In other words, in ultra-low carbon steel, the BH property after uniaxial tensile deformation shows a high value regardless of the amount of strain, but that after biaxial tensile deformation shows a strain of about 1% or more (equivalent strain (uniaxial strain). It is almost zero in the evaluation of (strain) converted to tensile deformation). Also, this phenomenon is significantly different from that conventionally observed in low carbon steel.
From this, the BH steel sheet based on the ultra-low carbon steel manufactured by the prior art has a desired BH
It can be seen that the property cannot be obtained.
【０００６】本発明は、このような課題を解決するため
になされたもので、上記のような極低炭素系での２軸引
張り変形におけるＢＨ性の極端な低下を考慮し、実プレ
ス成形に近い変形（２軸引張り変形) を付与した場合に
おいても、優れた焼付硬化性（ＢＨ性）を得らしめる方
法を提供することを目的とする。The present invention has been made in order to solve such a problem, and in consideration of the extreme decrease in BH property in biaxial tensile deformation in an extremely low carbon system as described above, the present invention has been applied to actual press forming. It is an object of the present invention to provide a method for obtaining excellent bake hardenability (BH property) even when near deformation (biaxial tensile deformation) is applied.
【０００７】[0007]
【課題を解決するための手段】上記課題は、重量% で、
Ｃ：0.0005〜0.005 ％、Ｓｉ：≦1.0 ％、Ｍｎ：≦1.5
％、Ｐ：≦0.1 ％、Ｓ：≦0.02％、sol.Ａｌ： 0.01 〜
0.1 ％、Ｎ：≦0.005％、Ｎｂ：0.001 〜0.03％、Ｂ：
0.0002〜0.002 ％を含有し、さらに、式 Ｎｂ／Ｃ（原子当量比）＝ 0.4 〜0.8 ・・・・・(1) Ｂ／Ｎ（原子当量比）≦ 0.6 ・・・・・(2) を満足し、残部実質的にFeおよび不可避的不純物よりな
る組成の鋼を溶製した後、Ar3 点以上で熱間圧延を行な
い、600 ℃以上で巻取り、冷間圧延後、再結晶温度以上
のフェライト単相域で均熱した後、600 ℃までの冷却時
間ｔ（min ）を式 -0.6 ≦log(t)≦0.16(1-1050 ×B) ・・・・・(3) の範囲とし、続いて400 ℃まで0.5 〜200 ℃/sの平均速
度で冷却することを特徴とする2 軸引張り変形後の焼付
硬化性に優れた鋼板の製造方法により解決される。Means for Solving the Problems The above-mentioned problems are expressed in terms of% by weight,
C: 0.0005 to 0.005%, Si: ≤ 1.0%, Mn: ≤ 1.5
%, P: ≤0.1%, S: ≤0.02%, sol. Al: 0.01 to
0.1%, N: ≦ 0.005%, Nb: 0.001 to 0.03%, B:
0.0002-0.002%, and further, the formula Nb / C (atomic equivalent ratio) = 0.4-0.8 (1) B / N (atomic equivalent ratio) ≦ 0.6 (2) Satisfied, after melting steel with a composition consisting essentially of Fe and unavoidable impurities, hot rolling at Ar 3 points or higher, winding at 600 ° C or higher, cold rolling, and recrystallization temperature or higher After soaking in the single-phase region of ferrite, the cooling time t (min) to 600 ° C is in the range of -0.6 ≤ log (t) ≤ 0.16 (1-1050 × B). Then, it is cooled to 400 ° C. at an average speed of 0.5 to 200 ° C./s, which is solved by a method for producing a steel sheet having excellent bake hardenability after biaxial tensile deformation.
【０００８】極低炭素鋼は結晶粒界が極めて清浄である
ため、(a) 粒界強度が弱い、(b) 元素が粒界に析出しや
すいという特徴を有している。したがって、従来技術で
製造された極低炭素系のＢＨ鋼板では、Ｃは粒内以外
に、粒界にも存在している。さらに、単軸引張り変形と
違って、2 軸引張り変形は結晶粒界に対して厳しい変形
様式となるため、成形後、焼付処理中にＣが粒界に析出
するものと考えられる。こうした理由から、従来技術に
よる極低炭素鋼においては、固溶Ｃ量が極めて少ないた
め、2 軸引張り変形後ＢＨ性は得られないものと考えら
れる。一方、Ｂは、(a) 粒界偏析元素であり、Ｃとsite
competeする、(b) 粒界を強化するという特性を有して
いることが知られている。本発明者等は極低炭素鋼特有
の上記性質およびＢの上記特性に主眼を置き、鋭意検討
を重ねた結果、Ｎｂ、Ｂ添加の極低炭素鋼で、焼鈍時に
特定温度域での滞留時間を制御して、Ｂを効果的に粒界
に偏析させることで、2 軸引張り変形後の焼付硬化性に
優れた鋼板を製造できることを明確化して、本発明を完
成させた。[0008] Since ultra-low carbon steel has extremely clean grain boundaries, it has the characteristics that (a) the strength of the grain boundaries is weak, and (b) elements are easily precipitated at the grain boundaries. Therefore, in the ultra-low carbon type BH steel sheet manufactured by the conventional technique, C exists not only in the grain but also in the grain boundary. Furthermore, unlike uniaxial tensile deformation, biaxial tensile deformation has a severe deformation mode with respect to crystal grain boundaries, and it is considered that C precipitates at the grain boundaries during the baking treatment after molding. For these reasons, it is considered that the BH property after biaxial tensile deformation cannot be obtained in the ultra-low carbon steel according to the prior art because the amount of solid solution C is extremely small. On the other hand, B is (a) a grain boundary segregation element, and C and site
It is known to have the property of competing and (b) strengthening grain boundaries. The inventors of the present invention focused on the above-mentioned properties specific to ultra-low carbon steel and the above-mentioned properties of B, and as a result of diligent studies, as a result, the residence time in a specific temperature range at the time of annealing in Nb and B-added ultra-low carbon steel. The present invention was clarified that a steel sheet having excellent bake hardenability after biaxial tensile deformation can be manufactured by controlling B to effectively segregate B at the grain boundary, and completed the present invention.
【０００９】本発明の作用効果および請求範囲の限定理
由は下記のとおりである。 Ｃ：0.0005〜0.005 ％ Ｃは焼付硬化性を得るために必要な元素である。0.0005
％未満では、その効果は得られず、0.005 ％を超えると
常温時効性が劣化するため、下限を0.0005％、上限を0.
005 ％とする。The operational effects of the present invention and the reasons for limiting the claims are as follows. C: 0.0005 to 0.005% C is an element necessary for obtaining bake hardenability. 0.0005
If it is less than 0.005%, the effect will not be obtained, and if it exceeds 0.005%, the aging at room temperature will deteriorate, so the lower limit is 0.0005% and the upper limit is 0.005%.
005%.
【００１０】Ｓｉ：≦1.0 ％ Ｓｉは鋼を強化するために添加される。１％を超えると
延性劣化、表面性状の悪化をまねくため、１％以下とす
る。Si: ≦ 1.0% Si is added to strengthen the steel. If it exceeds 1%, ductility and surface properties may deteriorate, so the content is set to 1% or less.
【００１１】Ｍｎ：≦1.5 ％ Ｍｎは鋼の固溶強化、熱間脆性回避のために添加され
る。1.5 ％を超えると著しい延性の劣化をまねくため、
1.5 ％以下とする。Mn: ≦ 1.5% Mn is added for strengthening the solid solution of steel and avoiding hot brittleness. If it exceeds 1.5%, the ductility deteriorates significantly,
1.5% or less.
【００１２】Ｐ：≦0.1 ％ Ｐは鋼を強化するのに最も有効な元素であるため、添加
される。0.1 ％を超えると粒界に偏析して、延性の劣化
や後述するB の効果を阻害するため0.1 ％以下とする。P: ≦ 0.1% P is added because it is the most effective element for strengthening steel. If it exceeds 0.1%, it is segregated at the grain boundaries, impairing ductility and inhibiting the effect of B described later, so that the content is made 0.1% or less.
【００１３】Ｓ：≦0.02％ Ｓは鋼中で硫化物を形成し、熱間延性を劣化させるた
め、0.02％以下とする。S: ≦ 0.02% S forms sulfide in steel and deteriorates hot ductility, so S is set to 0.02% or less.
【００１４】sol.Ａｌ： 0.01 〜0.1 ％ sol.Ａｌは固溶ＮをＡｌＮとして固定し、固溶Ｎによる
ひずみ時効を抑制するために添加される。0.01％未満で
は固溶Ｎを完全に固定できず、0.1 ％を超えると、著し
い延性の劣化、表面性状の悪化を引き起こすため、 0.0
1 〜0.1 ％の範囲とする。Sol. Al: 0.01 to 0.1% sol. Al is added to fix solid solution N as AlN and to suppress strain aging due to solid solution N. If it is less than 0.01%, solid solution N cannot be completely fixed, and if it exceeds 0.1%, remarkable deterioration of ductility and surface properties is caused.
The range is 1 to 0.1%.
【００１５】Ｎ：≦0.005 ％ ＮはＡｌＮとして固定されるが、0.005 ％を超えると常
温時効性が懸念されるため、0.005 ％以下とする。N: ≦ 0.005% N is fixed as AlN, but if it exceeds 0.005%, aging at room temperature is concerned, so N is set to 0.005% or less.
【００１６】Ｎｂ：0.001 〜0.03％ Ｎｂは熱延、巻取りの段階でＣをＮｂＣとして部分的に
固定する。冷圧後、焼鈍中にＮｂＣは再溶解し、鋼中に
固溶Ｃを残留せしめる。また、ＮｂはＢとの複合添加に
おいて、Ｂの粒界への拡散を助長し、固溶Ｃの粒界偏析
を阻止することにより、焼付硬化性（ＢＨ性）に寄与す
る固溶Ｃ量を増加させる働きがあると考えられる。上記
効果は0.001 ％未満では得られず、0.03％を超えると飽
和するため、0.001〜0.03％の範囲とする。Nb: 0.001 to 0.03% Nb partially fixes C as NbC at the stage of hot rolling and winding. After the cold pressure, NbC is re-dissolved during annealing, leaving solid solution C in the steel. In addition, Nb promotes the diffusion of B to the grain boundary and prevents the segregation of the solid solution C at the grain boundary in the complex addition with B, thereby reducing the amount of solid solution C contributing to bake hardening (BH property). It is thought that it has a function to increase. The above effect is not obtained at less than 0.001%, and saturates at more than 0.03%, so that the content is in the range of 0.001 to 0.03%.
【００１７】Ｂ：0.0002〜0.002 ％ Ｂは焼鈍中に粒界に偏析し、Ｃの粒界への析出を抑制
し、焼付硬化性（ＢＨ性）に寄与する固溶Ｃ量を増加さ
せる効果がある。この効果は上述のようにＮｂとの複合
添加により一層発揮される。さらに、Ｂは粒界強化元素
であるため、2 軸引張り変形下での粒界の変形を抑制
し、焼付処理中の固溶Ｃの粒界偏析を抑止する効果があ
る。該効果は、0.0002％未満では得られず、0.002 ％を
超えると飽和するため、0.0002〜0.002 ％の範囲で添加
する。B: 0.0002% to 0.002% B segregates at the grain boundaries during annealing, suppresses the precipitation of C at the grain boundaries, and has the effect of increasing the amount of solute C that contributes to bake hardenability (BH property). is there. This effect is further exhibited by the combined addition with Nb as described above. Further, since B is a grain boundary strengthening element, it has an effect of suppressing the deformation of the grain boundary under biaxial tensile deformation and the grain boundary segregation of solid solution C during the baking treatment. The effect is not obtained at less than 0.0002%, and saturates at more than 0.002%, so that it is added in the range of 0.0002 to 0.002%.
【００１８】Ｎｂ／Ｃ（原子当量比）＝ 0.4 〜0.8 図１は、２軸引張変形後のＢＨ性に及ぼすＮｂとＣの影
響を、図２は、２軸引張変形後のＢＨ性に及ぼすＮｂ／
ＣとＢの影響を，それぞれ示したものである。図１にお
いて、横軸はＣ量、縦軸はＮｂ量を示す。図１から明ら
かなように、２軸引張変形後（歪み：１〜２０％）のＢ
Ｈ値が、５０ＭＰａ以上あり、かつＳＳ（ストレッチャ
ー・ストレイン）の発生が無いのは、Ｃが前述の範囲で
あると共に、Ｎｂ／Ｃの値が 0.4〜0.8 の範囲にある場
合である。また、図２においても、ＢＨ値が５０ＭＰａ
以上であるのは、Ｎｂ／Ｃの値が 0.4〜0.8 の範囲にあ
り、Ｂが添加されている場合である。よって、Ｎｂ／Ｃ
（原子当量比）を0.4 〜0.8 の範囲とする。Nb / C (atomic equivalent ratio) = 0.4-0.8 FIG. 1 shows the effect of Nb and C on BH properties after biaxial tensile deformation, and FIG. 2 shows the effects on BH properties after biaxial tensile deformation. Nb /
The effects of C and B are shown respectively. In FIG. 1, the horizontal axis indicates the C amount, and the vertical axis indicates the Nb amount. As is clear from FIG. 1, B after biaxial tensile deformation (strain: 1 to 20%)
The case where the H value is 50 MPa or more and no SS (stretcher strain) occurs is when C is in the above-mentioned range and the value of Nb / C is in the range of 0.4 to 0.8. Also, in FIG. 2, the BH value is 50 MPa.
The above is the case where the value of Nb / C is in the range of 0.4 to 0.8 and B is added. Therefore, Nb / C
(Atomic equivalent ratio) is in the range of 0.4 to 0.8.
【００１９】Ｂ／Ｎ（原子当量比）≦ 0.6 Ｂ／Ｎ（原子当量比）が0.6 超であると、ＢはＮを固定
してＢＮを形成するため、Ｂの上記効果は得られない。
従って、Ｂ／Ｎ（原子当量比）を0.6以下とする。B / N (atomic equivalent ratio) ≦ 0.6 If B / N (atomic equivalent ratio) is more than 0.6, B forms BN by fixing N, so that the above effect of B cannot be obtained.
Therefore, B / N (atomic equivalent ratio) is set to 0.6 or less.
【００２０】上記条件を満足し、残部Feおよび不可避的
不純物よりなる組成の鋼を溶製する方法は、通常の転炉
法、電気炉法のいずれでも良く、鋼の鋳造は造塊法、連
続鋳造法のいずれでも良い。The method of smelting steel satisfying the above conditions and having a composition comprising the balance of Fe and unavoidable impurities may be any of a normal converter method and an electric furnace method. Any of the casting methods may be used.
【００２１】鋳造後、スラブを直送圧延または再加熱
後、熱間圧延を行なう。Ar3 点以上で熱間仕上げ圧延を
終了し、600 ℃以上で巻取る。ここで、仕上げ圧延をAr
3 点以上とするのは、熱延組織を微細化することにより
焼鈍板の加工性を向上させるほかに、冷間圧延後、焼鈍
中にＢの析出サイトとなる粒界の面積を増加させるため
であり、巻取りを600 ℃以上とするのは、鋼中ＮをＡｌ
Ｎとして完全に固定し、固溶Ｎによる常温ひずみ時効を
回避するためである。After casting, the slab is subjected to direct rolling or reheating, followed by hot rolling. Finish hot finish rolling at 3 or more Ar points and wind at 600 ° C or more. Here, finish rolling is Ar
The reason for three or more points is to improve the workability of the annealed sheet by refining the hot-rolled structure, and also to increase the area of the grain boundary that becomes a precipitation site of B during annealing after cold rolling. The reason for winding at 600 ° C or higher is that N in steel is changed to Al.
The reason for this is to completely fix N as N and to avoid room temperature strain aging due to solid solution N.
【００２２】酸洗、冷間圧延後、再結晶温度以上のフェ
ライト単相域に均熱した後、600 ℃までの冷却時間ｔを
前記式(3)の範囲とし、続いて400℃まで 0.5 〜200℃／
ｓの平均速度で冷却する。冷間圧延は深絞り性を向上さ
せるために、60〜95% の圧下率で行なうことが望まし
い。焼鈍均熱温度は、2 相域であるとフェライト粒が粗
大化し、Ｂの析出サイトとなる粒界の面積が減少し、Ｂ
の偏析効果が得られないため、フェライト単相域とす
る。また、組織を完全フェライト再結晶組織とするた
め、15秒以下の均熱時間は望ましくない。After pickling, cold rolling, and soaking in a ferrite single phase region at a temperature equal to or higher than the recrystallization temperature, the cooling time t up to 600 ° C. is set in the range of the above formula (3), and then 0.5 to 400 ° C. 200 ℃ /
Cool at an average speed of s. Cold rolling is desirably performed at a rolling reduction of 60 to 95% in order to improve the deep drawability. When the annealing temperature is in the two-phase range, the ferrite grains are coarsened, the area of the grain boundaries serving as B precipitation sites is reduced, and the B
Since the effect of segregation cannot be obtained, the ferrite single phase region is used. Further, since the structure is a completely ferrite recrystallized structure, a soaking time of 15 seconds or less is not desirable.
【００２３】均熱後の冷却条件を、前記の範囲とするの
は、以下の理由による。図３、図４及び図５は、２軸引
張変形後のＢＨ性に及ぼす焼鈍均熱後の冷却条件の影響
を示す図である。図３、図４及び図５においては、それ
ぞれＢの含有量が１５ｐｐｍ、５ｐｐｍ、８ｐｐｍの３
水準の鋼について、横軸に600 ℃までの冷却時間ｔ（mi
n ）の常用対数をとり、縦軸に600 ℃〜400 ℃までの平
均冷却速度（対数目盛）をとって、これらの値と、２軸
引張変形（歪：１〜２０％）後のＢＨ値の関係が示され
ている。図中、●は50〜60ＭＰａ、半分黒の丸印が11〜
20ＭＰａ、○が１〜10ＭＰａのＢＨ値が得られたものを
示す。いずれの場合も、５０ＭＰａ以上のＢＨ値が得ら
れるのは、 -0.6 ≦log(t)≦0.16(1-1050 ×B)であっ
て、かつ、600 ℃〜400 ℃までの平均冷却速度が 0.5℃
／ｓ以上の場合である。log(t)の下限値(-0.6)未満で
は、Ｂの粒界偏析量は少なく、また、上限値(0.16(1-10
50×B)) を超えるとＣが粒界に偏析するため、ＢＨ性は
低下する。したがって上記範囲とすることで、ＢがＣに
対して優先的に結晶粒界に偏析し、Ｃの粒界偏析を抑制
する。この場合、ＢはＮｂと共存することで、ＮｂとＣ
の相互作用により、上記効果を相乗的に発揮する。その
あと、400 ℃まで0.5 ℃／ｓ以上の平均速度で冷却する
ことにより、ＮｂＣの再析出を抑制し、ＢＨ性に寄与す
る固溶Ｃ量を確保する。200℃/s超の冷却速度では、該
効果は飽和するため、0.5 〜200 ℃/sの範囲とする。望
ましくは5 〜200 ℃/sの範囲が良い。The reason for setting the cooling conditions after the soaking in the above range is as follows. FIGS. 3, 4 and 5 are diagrams showing the effect of cooling conditions after soaking on the BH properties after biaxial tensile deformation. 3, 4, and 5, the content of B was 15 ppm, 5 ppm, and 8 ppm, respectively.
For steel of the standard level, the horizontal axis shows the cooling time t (mi
n) The common logarithm is taken, and the vertical axis is the average cooling rate (logarithmic scale) from 600 ° C to 400 ° C. The relationship is shown. In the figure, ● is 50 to 60 MPa, half black circle is 11 to
20MPa and ○ show that a BH value of 1 to 10MPa was obtained. In any case, a BH value of 50 MPa or more is obtained when -0.6 ≦ log (t) ≦ 0.16 (1-1050 × B) and the average cooling rate from 600 ° C. to 400 ° C. is 0.5 ° C
/ S or more. If the log (t) is less than the lower limit (−0.6), the amount of B grain boundary segregation is small, and the upper limit (0.16 (1-10
If it exceeds 50 × B)), C segregates at the grain boundaries, so that the BH property decreases. Therefore, by setting the content within the above range, B segregates preferentially with respect to C at the crystal grain boundary, and suppresses C grain boundary segregation. In this case, B coexists with Nb, so that Nb and C
The above effects are synergistically exhibited by the interaction of Thereafter, by cooling to 400 ° C. at an average rate of 0.5 ° C./s or more, reprecipitation of NbC is suppressed, and the amount of solute C contributing to BH properties is secured. If the cooling rate is more than 200 ° C / s, the effect is saturated, so that the cooling rate is in the range of 0.5 to 200 ° C / s. Desirably, the range is 5 to 200 ° C / s.
【００２４】また、Ｎｉ，Ｃｕなど、炭窒化物形成傾向
の弱い元素を添加しても、本発明の効果は損なわれな
い。ただし、Ｔｉ、Ｚｒ、Ｍｏ等の炭窒化物形成元素を
添加した場合には、上記のようなＢの効果は得られな
い。The effect of the present invention is not impaired even if an element having a low tendency to form a carbonitride, such as Ni or Cu, is added. However, when a carbonitride forming element such as Ti, Zr, or Mo is added, the above-described effect of B cannot be obtained.
【００２５】以上の工程により、2 軸引張り変形後の焼
付硬化性に優れた鋼板が製造できる。また、本発明によ
り製造された鋼板に電気めっきなどの表面処理を施して
も、その特性を損なうことはない。Through the above steps, a steel sheet having excellent bake hardenability after biaxial tensile deformation can be manufactured. Further, even if the steel sheet manufactured according to the present invention is subjected to a surface treatment such as electroplating, its properties are not impaired.
【００２６】[0026]
【実施例】以下、本発明の具体的な実施例を説明する。DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.
( 実施例1)表１、表２に示す成分組成（重量％）の鋼を
溶製し、スラブとした。そのスラブを1200℃に加熱した
後、熱間圧延（仕上げ温度： 900℃、巻取温度： 650
℃）、冷間圧延（圧延率：75％）、連続焼鈍（均熱温
度： 850℃、均熱時間： 60sec、 600℃までの冷却時
間： 30sec、 400℃までの平均冷却速度:15 ℃／ｓ）を
施した。焼鈍後、0.5 ％の調質圧延を施し、ＢＨ測定に
供した。(Example 1) Steels having the component compositions (% by weight) shown in Tables 1 and 2 were melted to form slabs. After heating the slab to 1200 ° C, hot rolling (finish temperature: 900 ° C, winding temperature: 650
° C), cold rolling (rolling rate: 75%), continuous annealing (soaking temperature: 850 ° C, soaking time: 60sec, cooling time to 600 ° C: 30sec, average cooling rate to 400 ° C: 15 ° C / s). After annealing, the steel sheet was subjected to a temper rolling of 0.5% and subjected to BH measurement.
【００２７】まず、液圧バルジ試験機を用いて、供試鋼
板( ブランク:400×400)を張り出し成形（２軸引張り変
形）し、予ひずみを１〜20％（相当ひずみ）の範囲で与
えた。また、該試験では、曲率の異なったポンチ( ポン
チ径:300φ) を用いることにより、張り出し成形時の2
軸のひずみ比（εｘ／εｙ）を１〜５の範囲で変化させ
た。こうして成形されたサンプルから、JIS Z 2201 に
記載のＪＩＳ５号試験片を採取し、塗装焼付相当処理
（(170℃、20min 保持後、放冷) を施し、熱処理前後の
降伏強度の差を測定し、ＢＨ量とした。First, a test steel sheet (blank: 400 × 400) is stretch-formed (biaxial tensile deformation) using a hydraulic bulge tester, and a pre-strain is given in a range of 1 to 20% (equivalent strain). Was. Also, in this test, by using punches having different curvatures (punch diameter: 300φ), the
The axial strain ratio (εx / εy) was changed in the range of 1-5. From the sample thus formed, a JIS No. 5 test piece described in JIS Z 2201 was sampled, subjected to coating baking treatment (cooling after holding at 170 ° C. for 20 minutes, and measuring the difference in yield strength before and after heat treatment). , BH amount.
【００２８】鋼No.15〜18、22〜24、31〜33は、いずれ
もＮｂ／Ｃが本発明範囲外であるため、ＢＨは低い。Steel Nos. 15 to 18, 22 to 24, and 31 to 33 all have a low BH because Nb / C is outside the range of the present invention.
【００２９】表１、表２において、ＢＨの値は、予ひず
み１〜２０％における値であり、かっこ内の値は予ひず
みが５％における値を示す。また、ＳＳの欄で○印のも
のはＳＳの発生が無かったものを示し、×印のものはＳ
Ｓの発生があったものを示す。In Tables 1 and 2, the value of BH is a value at a prestrain of 1 to 20%, and the value in parentheses indicates a value at a prestrain of 5%. In the column of SS, those with a circle indicate those in which no SS occurred, and those with a cross indicate S
This indicates that S has occurred.
【００３０】鋼No.19 、20は、Ｂ／Ｎが本発明範囲外で
あるため、ＢＨが低い。鋼No.21 は、Ｃが低いため、Ｂ
Ｈが低い。鋼No.25 〜30はＣ過剰のため、成形中にＳＳ
（ストレッチャーストレイン）が発生する。Steel Nos. 19 and 20 have low BH because B / N is outside the range of the present invention. Steel No. 21 has low C, so B
H is low. Since steel No. 25 to 30 is excessive in C, SS
(Stretcher strain) occurs.
【００３１】鋼No.34 〜49は、成分が本発明範囲外であ
るため、ＢＨが低い。これらに対し、鋼No. 1 〜14の本
発明例は、ＢＨ性および耐ＳＳ性に優れている。Steel Nos. 34 to 49 have low BH because the components are outside the range of the present invention. On the other hand, the inventive examples of steel Nos. 1 to 14 are excellent in BH property and SS resistance.
( 実施例2)表１，表２の鋼No. ２、５、10、16、42、4
6、47、48を表３、表４の条件で製造し、ＢＨ性を調査
した。表３、表４において、例えば鋼No. ２-10 等とあ
るのは、鋼No. ２のもの第10番目の条件で製造したこと
を示す。(Example 2) Steel Nos. 2, 5, 10, 16, 42, 4 in Tables 1 and 2
6, 47 and 48 were produced under the conditions shown in Tables 3 and 4, and BH properties were investigated. In Tables 3 and 4, for example, steel No. 2-10 indicates that the steel No. 2 was manufactured under the tenth condition.
【００３２】表３、表４においてＢＨの欄の値、ＳＳの
欄の記号の意味は表１、表２におけるものと同じであ
り、仕上温度、巻取温度の単位は℃である。In Tables 3 and 4, the values in the column of BH and the meanings of the symbols in the column of SS are the same as those in Tables 1 and 2, and the units of the finishing temperature and the winding temperature are ° C.
【００３３】No.2-10 〜28、5-6 〜10、10-6〜10は、焼
鈍均熱後の冷却条件が本発明範囲外であるため、ＢＨは
低い。No.2-29 は、巻取温度が本発明範囲外であり、固
溶Ｎによる常温時効のため、成形中にＳＳが発生する。
No.2-30は、仕上温度が本発明範囲外であり、フェライ
ト粒の粗大化のため、Ｂの偏析効果が得られず、ＢＨは
低い。No.16-1 〜10，42-1〜5 、46-1〜5 、47-1〜5 、
48-1〜5 は成分が本発明範囲外であるため、ＢＨは低
い。本発明例である No.2-1 〜9 、5-1 〜5 、10-1〜5
は、ＢＨ性および耐ＳＳ性に優れている。Nos. 2-10 to 28, 5-6 to 10, and 10-6 to 10 have low BH since the cooling conditions after annealing and soaking are out of the range of the present invention. In No. 2-29, the winding temperature was out of the range of the present invention, and SS was generated during molding due to normal temperature aging by solid solution N.
In No. 2-30, the finishing temperature was outside the range of the present invention, and the segregation effect of B was not obtained due to coarse ferrite grains, and the BH was low. No. 16-1 to 10, 42-1 to 5, 46-1 to 5, 47-1 to 5,
48-1 to 5-5 have low BH because the components are outside the range of the present invention. Nos. 2-1 to 9, 5-1 to 5, 10-1 to 5
Are excellent in BH property and SS resistance.
【００３４】[0034]
【表１】 [Table 1]
【００３５】[0035]
【表２】 [Table 2]
【００３６】[0036]
【表３】 [Table 3]
【００３７】[0037]
【表４】 [Table 4]
【００３８】[0038]
【発明の効果】以上説明したように、本発明によれば、
自動車用外板パネルなどに使用される、焼付硬化性に優
れた鋼板を安定して製造することが可能である。As described above, according to the present invention,
It is possible to stably produce a steel sheet having excellent bake hardenability, which is used for an outer panel of an automobile.
【図１】 ２軸引張り変形後のＢＨ性におよぼすＮｂ、
Ｃの影響を示す図である。FIG. 1 shows the effect of Nb on BH properties after biaxial tensile deformation.
It is a figure which shows the influence of C.
【図２】 ２軸引張り変形後のＢＨ性におよぼすＮｂ／
Ｃ、Ｂの影響を示す図である。FIG. 2 shows the effect of Nb / on BH properties after biaxial tensile deformation.
It is a figure which shows the influence of C and B.
【図３】 ２軸引張り変形後のＢＨ性におよぼす焼鈍均
熱後の冷却条件の影響を示す図である。FIG. 3 is a graph showing the effect of cooling conditions after annealing and soaking on BH properties after biaxial tensile deformation.
【図４】 2 軸引張り変形後のＢＨ性におよぼす焼鈍均
熱後の冷却条件の影響を示す図である。FIG. 4 is a graph showing the effect of cooling conditions after annealing and soaking on BH properties after biaxial tensile deformation.
【図５】 2 軸引張り変形後のＢＨ性におよぼす焼鈍均
熱後の冷却条件の影響を示す図である。FIG. 5 is a view showing the effect of cooling conditions after annealing and soaking on BH properties after biaxial tensile deformation.
【図６】 ２軸引張り変形後のＢＨ性におよぼす予ひず
みの影響を示す図である。FIG. 6 is a diagram showing the effect of pre-strain on BH properties after biaxial tensile deformation.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭58−84928（ＪＰ，Ａ) 特開 平７−300623（ＪＰ，Ａ) 特公 平３−72134（ＪＰ，Ｂ２) (58)調査した分野(Int.Cl.7，ＤＢ名) C21D 9/46 - 9/48 C21D 8/00 - 8/02 C22C 38/00 - 38/60 ────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-58-84928 (JP, A) JP-A-7-300623 (JP, A) JP-B 3-72134 (JP, B2) (58) Field (Int.Cl. 7 , DB name) C21D 9/46-9/48 C21D 8/00-8/02 C22C 38/00-38/60
Claims (1)
ｉ：≦1.0 ％、Ｍｎ：≦1.5 ％、Ｐ：≦0.1 ％、Ｓ：≦
0.02％、sol.Ａｌ： 0.01 〜0.1 ％、Ｎ：≦0.005 ％、
Ｎｂ：0.001 〜0.03％、Ｂ：0.0002〜0.002 ％を含有
し、さらに、式(1),(2) を満足し、残部実質的にFeおよ
び不可避的不純物よりなる組成の鋼を溶製した後、Ar3
点以上で熱間圧延を行ない、600 ℃以上で巻取り、冷間
圧延後、再結晶温度以上のフェライト単相域で均熱した
後、600 ℃までの冷却時間ｔ（min ）を式(3) の範囲と
し、続いて400 ℃まで0.5 〜200 ℃/sの平均速度で冷却
することを特徴とする2 軸引張り変形後の焼付硬化性に
優れた鋼板の製造方法。 Ｎｂ／Ｃ（原子当量比）＝ 0.4 〜0.8 ・・・・・(1) Ｂ／Ｎ（原子当量比）≦ 0.6 ・・・・・(2) -0.6 ≦log(t)≦0.16(1-1050 ×B) ・・・・・(3)C. 0.0005 to 0.005% by weight, S
i: ≦ 1.0%, Mn: ≦ 1.5%, P: ≦ 0.1%, S: ≦
0.02%, sol. Al: 0.01 to 0.1%, N: ≦ 0.005%,
Nb: 0.001 to 0.03%, B: 0.0002 to 0.002%, and after melting a steel having a composition satisfying the formulas (1) and (2) and substantially consisting of Fe and unavoidable impurities. , Ar 3
Hot rolling at above the temperature, winding at 600 ° C. or higher, cold rolling, soaking in a ferrite single phase region at a temperature equal to or higher than the recrystallization temperature, and cooling time t (min) to 600 ° C. ), Followed by cooling to 400 ° C. at an average speed of 0.5 to 200 ° C./s, which is excellent in bake hardenability after biaxial tensile deformation. Nb / C (atomic equivalent ratio) = 0.4 to 0.8 (1) B / N (atomic equivalent ratio) ≤ 0.6 (2) -0.6 ≤ log (t) ≤ 0.16 (1- (1050 × B) ・ ・ ・ ・ ・ (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32751395A JP3309893B2 (en) | 1995-12-15 | 1995-12-15 | Method for producing steel plate excellent in bake hardenability after biaxial tensile deformation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32751395A JP3309893B2 (en) | 1995-12-15 | 1995-12-15 | Method for producing steel plate excellent in bake hardenability after biaxial tensile deformation |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09165625A JPH09165625A (en) | 1997-06-24 |
| JP3309893B2 true JP3309893B2 (en) | 2002-07-29 |
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ID=18199966
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|---|---|---|---|
| JP32751395A Expired - Fee Related JP3309893B2 (en) | 1995-12-15 | 1995-12-15 | Method for producing steel plate excellent in bake hardenability after biaxial tensile deformation |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102605250A (en) * | 2012-03-27 | 2012-07-25 | 首钢总公司 | Vehicle steel plate and production method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102304665A (en) * | 2011-09-21 | 2012-01-04 | 首钢总公司 | Steel plate for automobile and production method thereof |
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1995
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102605250A (en) * | 2012-03-27 | 2012-07-25 | 首钢总公司 | Vehicle steel plate and production method thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH09165625A (en) | 1997-06-24 |
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