JP4556362B2 - High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof - Google Patents

High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof Download PDF

Info

Publication number
JP4556362B2
JP4556362B2 JP2001251418A JP2001251418A JP4556362B2 JP 4556362 B2 JP4556362 B2 JP 4556362B2 JP 2001251418 A JP2001251418 A JP 2001251418A JP 2001251418 A JP2001251418 A JP 2001251418A JP 4556362 B2 JP4556362 B2 JP 4556362B2
Authority
JP
Japan
Prior art keywords
cold
rolled
less
steel sheet
strength
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
JP2001251418A
Other languages
Japanese (ja)
Other versions
JP2003064447A (en
Inventor
琢也 山崎
才二 松岡
坂田  敬
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
Original Assignee
JFE Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by JFE Steel Corp filed Critical JFE Steel Corp
Priority to JP2001251418A priority Critical patent/JP4556362B2/en
Publication of JP2003064447A publication Critical patent/JP2003064447A/en
Application granted granted Critical
Publication of JP4556362B2 publication Critical patent/JP4556362B2/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Images

Landscapes

  • Heat Treatment Of Sheet Steel (AREA)

Description

【0001】
【発明の属する技術分野】
本発明は、自動車用鋼板等の使途に好適な高張力冷延鋼板に係り、とくに深絞り性と成形後強度上昇熱処理能とがともに優れた高張力冷延鋼板に関する。
【0002】
【従来の技術】
近年、地球環境の保全問題からの排出ガス規制に関連して、自動車の車体重量の軽減が極めて重要な課題となっている。さらに、衝突事故における乗員保護などの安全性確保も重要な課題の一つである。このようなことから、最近、車体重量の軽減と衝突安全性確保のために、自動車車体用として鋼板板厚を薄くすると同時に高強度化した高張力薄鋼板を使用することが検討されている。
【0003】
鋼板を素材とする自動車の車体用部品の多くがプレス加工により成形されるため、使用される鋼板には、優れたプレス成形性を有することが要求される。プレス成形性向上のためには、鋼板の機械的特性として、高いランクフォード値(r値)と高い延性(伸びEl)を有することが必要となる。しかし、一般的には、鋼板を高強度化すると、r値および延性が低下し、プレス成形性が劣化する傾向となる。
【0004】
また、鋼板をプレス加工により自動車の車体用部品等のプレス成形体に成形するに際しては、プレス加工を容易にするため、鋼板は軟質であることが望まれる。一方、プレス成形体に塗装焼付け処理を施し、製品(部品)としたのちには、製品は高強度を有することが要求される。このようなプレス加工前の特性と加工後の特性を同時に満足できる鋼板として、BH鋼板が開発されている。このBH鋼板は、プレス成形前には軟質で、プレス成形後の塗装焼付け処理により硬化して強度が上昇する特性を有する鋼板である。
【0005】
プレス成形後の塗装焼付け処理により硬化する特性、いわゆる焼付け硬化性を向上させる方法として、たとえば、特開昭55−141526号公報には、鋼中の固溶C、N、Al含有量に応じてNbを添加し、at%でNb/(固溶C+固溶N)を特定範囲内に制限すると共に、焼鈍後の冷却速度を制御することによって、鋼中の固溶C量、固溶N量を調整する方法が記載されている。また、特公昭61−45689 号公報には、TiとNbの複合添加によって焼付け硬化性を向上させる方法が提案されている。
【0006】
しかしながら、上記した技術で製造された鋼板は、深絞り性に優れる材質とするために、素材鋼板の強度を低く設定しており、構造材料としては強度が必ずしも十分でないという問題があった。また、上記した技術で製造された鋼板では、鋼板中の微量な固溶C、固溶Nの働きにより成形ー塗装焼付け後の強度が上昇するが、良く知られているようにBH鋼板の場合は降伏強さのみが上昇し、引張強さを上昇させるものではない。したがって、上記した技術で製造された鋼板では、部品の変形開始応力を高める効果はあるが、変形開始から変形終了までの変形全域にわたる変形に要する応力(成形後引張強さ)を高める効果は十分とは言えなかった。
【0007】
一方、成形後に引張強さが上昇する冷延鋼板として、例えば特開平10-310847 号公報には、200 〜450 ℃の熱処理温度域で引張強さが60MPa 以上上昇する合金化溶融亜鉛めっき鋼板が開示されている。この鋼板は、重量百分率で、C:0.01〜0.08%、Mn:0.01〜3.0 %を含有し、かつW,Cr, Moの1種または2種以上を合計で0.05〜3.0 %含有し、また必要に応じてTi:0.005 〜0.1 %、Nb:0.005 〜0.1 %、V:0.005 〜0.1 %の1種または2種以上を含有する組成になり、かつフェライトまたはフェライト主体からなるミクロ組織を有する鋼板である。
【0008】
しかしながら、この技術は、成形後の熱処理により鋼板中で微細な炭化物を形成させ、プレス時に付与する歪に対し転位を効果的に増殖させて、歪量を増加させるものであるため、220 〜370 ℃の温度範囲で熱処理を行う必要があり、熱処理温度が一般的な塗装焼付け処理温度より高いという難点があった。
また、成形後に引張強さが上昇する熱延鋼板として、例えば特公平8−23048 号公報に、加工時には軟質で、加工後の焼付け塗装処理により疲労特性の改善に有効な引張強さを大幅に上昇させることができる、熱延鋼板の製造方法が開示されている。
【0009】
この技術では、C量を0.02%〜0.13mass%とし、Nを0.0080〜0.0250mass%と多量に添加した上で、仕上げ圧延温度および巻き取り温度を制御して多量の固溶Nを鋼中に残存させ、金属組織をフェライトとマルテンサイトを主体とする複合組織にすることで、成形後熱処理温度: 170℃にて、100MPa以上の引張強さの増加が達成されるとしている。
【0010】
また、特開平10−183301号公報には、鋼成分のうち、とくにCとNをC:0.01〜0.12mass%、N:0.0001〜0.01mass%に制限すると共に、平均結晶粒径を8μm以下に制御することにより80MPa 以上の高BH量を確保するとともに、AI値を 45MPa以下に制御することが可能な、焼付け硬化性および耐室温時効性に優れた熱延鋼板が開示されている。
【0011】
【発明が解決しようとする課題】
しかしながら、特公平8-23048号公報、特開平10−183301号公報に記載された鋼板はいずれも熱延鋼板であることから、仕上圧延後のオーステナイト/フェライト変態によりフェライトの集合組織がランダム化するため、r値はたかだか0.8 程度であり、自動車用鋼板として要求される、たとえば1.2 以上の高いr値を得ることは困難であり、十分な深絞り性を有しているとは言い難い。
【0012】
しかも、これらの技術で得られた熱延鋼板を出発材として冷間圧延および再結晶焼鈍を行ったとしても、必ずしも熱延鋼板と同等の成形−熱処理後の引張強さ上昇が得られるとは限らない。というのは、鋼組織が、冷間圧延および再結晶焼鈍により熱延時とは異なるミクロ組織となるからである。また冷延前に固溶N、固溶Cを析出固定(IF)化するという発想がないため、冷間圧延時に多量の固溶C、固溶Nが残存し、十分に高いr値を有する鋼板を得ることはできない。
【0013】
本発明は、上記した従来技術の問題を有利に解決し、優れた成形後強度上昇熱処理能と優れた深絞り性を有する高張力冷延鋼板および成形後強度上昇熱処理能と深絞り性がともに優れた冷延鋼板を安定して製造できる、高張力冷延鋼板の製造方法を提案することを目的とする。 なお、本発明でいう「成形後強度上昇熱処理能に優れる」とは、鋼板に引張歪10%の予変形後、170 ℃の温度に 20min保持する条件で熱処理(時効処理)したとき、この熱処理(時効処理)前後の引張強さ増加量(△TSと記す;△TS=(予変形熱処理後の引張強さ)−(予変形前の引張強さ))が 50MPa以上であることをいうものとする。また、本発明でいう「深絞り性に優れる」とは、r値が1.2 以上である場合をいうものとする。
【0014】
【課題を解決するための手段】
本発明者らは、上記した課題を達成するため、冷延鋼板のミクロ組織および再結晶集合組織におよぼす合金元素の影響について鋭意研究を重ねた。その結果、従来は炭窒化物形成元素としてTiおよびNbが主に使用されてきたが、本発明者らは窒化物がTi窒化物やNb窒化物より低い温度で溶解しやすいVに着目した。そして、C含有量を極低炭素域とし、適正範囲のNとVを含有することにより、再結晶焼鈍前には固溶C、固溶Nを極力低減させることができ、再結晶焼鈍により{1 1 1 }再結晶集合組織が強く発達して、1.2 以上の高いr値が得られること、また焼鈍を行うことによりV系窒化物が溶解し、焼鈍後には多量の固溶Nを鋼板中に含有させることができ、成形後強度上昇熱処理能が向上すること、を見いだし、優れた成形後強度上昇熱処理能と優れた深絞り性を同時に満足できる高張力冷延鋼板が製造可能であるという知見を得た。さらに本発明者らは、Vに加え、さらにNb、Bを複合して含有させることにより、組織のさらなる微細化が可能となることを知見した。
【0015】
まず、本発明者らが行った基礎的な実験結果について説明する。
質量%で、C:0.002 %、Si:0.02%、Mn:1.2 %、P:0.04%、S:0.004 %、Al:0.011 %、N:0.014 %、Nb:0.015 %、B:0.0014%を含み、V:0.03〜0.35%と変化した組成を有する各シートバーを、1250℃に加熱−均熱した後、仕上圧延終了温度が 910℃となるように3パスの熱間圧延により板厚 4.0mmの熱延板とした。なお、仕上圧延終了後、これら熱延板には、コイル巻取り相当処理として 700℃×1hの保温処理を施した。ついで、これら熱延板に、圧下率:70%の冷間圧延を施して板厚 1.2mmの冷延板とした。ついで、これらの冷延板に、840 ℃で40sの再結晶焼鈍を施した後、30℃/sの冷却速度で冷却し、冷延焼鈍板とした。
【0016】
得られた各冷延焼鈍板から、試験片を採取して、引張特性、成形後強度上昇熱処理能およびr値を求めた。
引張特性は、各冷延焼鈍板からJIS 5号引張試験片を採取し、引張試験を実施し求めた。また、各冷延焼鈍板から採取したJIS 5号引張試験片に、引張歪10%の予変形後、170 ℃で 20min保持する条件で熱処理を施したのち、引張試験を実施し、熱処理後の引張強さを求めた。この熱処理前後の引張強さ増加量(△TSと記す;△TS=(熱処理後の引張強さ)−(予変形前の引張強さ))を成形後強度上昇熱処理能とした。
【0017】
また、各冷延焼鈍板の、圧延方向(L方向)、圧延方向に45度方向(D方向)、圧延方向に垂直方向(C方向)からJIS 号試験片を採取し、これらの試験片に %の単軸引張予歪を付与したときの各試験片の幅歪と板厚歪を求め、幅歪と板厚歪の比
r=ln( w/w0 )/ln(t/t0
ここで、w0 、t0 は試験前の試験片の幅, 板厚であり、w、tは試験後の試験片の幅, 板厚である)
から各方向のr値(rL 、rC 、rD )をそれぞれ求め、次式
mean=(rL +rC +2×rD )/4
により平均r値rmeanを求めた。なお、本発明では、とくにことわらない限り、r値は平均r値を意味するものとする。
【0018】
図1に、r値と成形後強度上昇熱処理能(△TS)とにおよぼすV、C、Al、N含有量の影響を示す。なお、横軸は、パラメータ(V/51 +Nb/93 −C/12 + Al/27)/(N/14 )とした。ここで、V、C、Al、Nb、Nは各元素の含有量 (質量%)である。
図1から、(V/51 +Nb/93 −C/12 + Al/27)/(N/14 )が 0.5以上 3.0以下を満足する場合に、はじめて1.2 以上の高いr値とΔTSで50MPa 以上の高い成形後強度上昇熱処理能とが同時に満足されることがわかる。すなわち、(V/51 +Nb/93 −C/12 + Al/27)/(N/14 )が 0.5以上 3.0以下となるように成分調整することにより、優れた深絞り性と優れた成形後強度上昇熱処理能を有する高張力冷延鋼板が製造可能となるという知見を得た。
【0019】
本発明は、上記した知見に基づき、さらに検討して完成されたものである。
すなわち、本発明の要旨は下記のとおりである。
(1)質量%で、C:0.0050%未満、Si:0.005 〜 1.0%、Mn:0.01〜 1.5%、P: 0.1%以下、S:0.01%以下、Al:0.005 〜0.03%、N: 0.005〜 0.040%、Nb: 0.005〜 0.050%、B:0.0003〜0.0015%、V:0.01〜 0.5%を含み、かつC、Al、N、Nb、Vを次 (1) 式および次 (2) 式
0≦ {V/51 + Nb/93 ーC/12 } ……(1)
0.5 ≦{V/51 +Nb/93 −C/12 +Al/27 }/(N/14 )≦ 3.0……(2)
(ここで、C、Al、N、Nb、V:各元素の含有量 (質量%))
を満足する条件下で含有し、さらに固溶状態のNを0.0015%以上含み、残部Feおよび不可避的不純物からなる組成を有することを特徴とする、成形後強度上昇熱処理能と深絞り性に優れた高張力冷延鋼板。
(2)(1)において、前記組成に加えてさらに, 質量%で、Cu、Ni、Cr、Moのうちから選ばれた1種または2種以上を合計で 2.0%以下含有することを特徴とする高張力冷延鋼板。
(3)質量%で、C:0.0050%未満、Si:0.005 〜 1.0%、Mn:0.01〜 1.5%、P: 0.1%以下、S:0.01%以下、Al:0.005 〜0.03%、N: 0.005〜 0.040%、Nb: 0.005〜 0.050%、B:0.0003〜0.0015%、V:0.01〜 0.5%を含み、かつC、Al、N、Nb、Vを次 (1) 式および次 (2) 式
0≦ {V/51 + Nb/93 ーC/12 } ……(1)
0.5 ≦{V/51 +Nb/93 −C/12 +Al/27 }/(N/14 )≦ 3.0……(2)
(ここで、C、Al、N、Nb、V:各元素の含有量 (質量%))
を満足する条件下で含有し、残部Feおよび不可避的不純物からなる組成を有する鋼素材に、加熱温度: 900℃以上、仕上圧延終了温度: 800℃以上とする熱間圧延を施し熱延板とした後、該熱延板を巻取温度:400 〜800 ℃で巻取り、次いで該熱延板に圧下率:60〜95%の冷間圧延を施し冷延板としたのち、該冷延板に700 ℃以上の温度で再結晶焼鈍を施すことを特徴とする成形後強度上昇熱処理能と深絞り性に優れた高張力冷延鋼板の製造方法。
(4)(3)において、前記組成に加えてさらに, 質量%で、Cu、Ni、Cr、Moのうちから選ばれた1種または2種以上を合計で 2.0%以下含有することを特徴とする高張力冷延鋼板の製造方法。
【0020】
【発明の実施の形態】
本発明の冷延鋼板は、優れた成形後強度上昇熱処理能と優れた深絞り性を有する高張力冷延鋼板である。
まず、本発明冷延鋼板の組成限定理由について説明する。なお、質量%は単に%と記す。
【0021】
C:0.0050%未満
Cは、鋼の強度を増加させるが延性を低下させ、プレス成形性、深絞り性を劣化させる。このため、本発明ではできるだけ低減することが好ましいが、プレス成形性、深絞り性の向上という観点からCは極低炭素レベルとすることが好ましく、具体的には0.0050%未満とする。なお、好ましくは、0.0030%以下である。また、極端なコスト上昇を伴わずに達しうるC量の下限値は、現在の製造技術においては、0.0005%程度と考えられる。
【0022】
Si:0.005 〜 1.0%
Siは、伸びの低下を抑制し、また、強度を向上させる有用な元素であるが、このような効果は0.005 %以上の含有で認められるが、一方、 1.0%を超える含有は表面性状を悪化させ、延性の低下を招く。このため、Siは0.005 〜1.0 %の範囲に限定した。なお、好ましくは 0.005〜0.75%である。
【0023】
Mn:0.01〜 1.5%
Mnは、鋼の強化成分として有効であるとともに、 MnSを形成しSによる脆化を抑制する作用がある。このような効果は0.01%以上の含有で認められるが、1.5 %を超える含有は表面性状の悪化や延性の低下を招く。このため、Mnは0.01〜1.5 %の範囲に限定した。なお、好ましくは0.01〜0.75%である。
【0024】
P:0.1 %以下
Pは、固溶強化により鋼の強化に有効に寄与する元素であり、要求される強度レベルに応じ所定量含有できるが、0.1 %を超えて含有すると深絞り性が低下する。このため、Pは0.1 %以下に限定した。
S:0.01%以下
Sは、鋼中では主として介在物 (硫化物)として存在し、延性の低下を招くため、極力低減することが望ましいが、0.01%までは許容される。
【0025】
Al:0.005 〜 0.030%
Alは、脱酸剤として、また炭窒化物形成元素の歩留り向上のために含有させるが、含有量が 0.005%未満では十分な効果がなく、一方、0.030 %を超える含有は、鋼中に含有すべきN量の増大を招き、製鋼時のスラブ欠陥が発生しやすくなる。
【0026】
N:0.005 〜 0.040%
Nは、本発明では成形後強度上昇熱処理能を鋼板に付与する役割を果たす重要な元素である。しかし、0.005 %未満の含有では十分な固溶N量を確保することが困難であり、十分な成形後強度上昇熱処理能が得られない。一方、0.040 %を超える含有は、プレス成形性を低下させる。このため、Nは0.005 〜 0.040%の範囲に限定した。なお、好ましくは0.008 〜 0.015%である。
【0027】
Nb: 0.005〜 0.050%
Nbは、Bとともに含有され、熱延組織及び冷延再結晶焼鈍組織の微細化に寄与し、かつ固溶Cと結合し NbCとして析出、固溶Cを固定する作用を有する元素である。また、Nbは固溶Nと結合し NbNとして、固溶Nを固定する作用も有する。Nb含有量が 0.005%未満では、固溶Cを析出固定することが困難となるだけではなく、熱延組織及び冷延再結晶焼鈍組織の微細化が不十分となる。一方、0.050 %を超えて含有すると、延性の低下を招く。このため、Nbは0.005 〜 0.050%の範囲に限定する。なお、好ましくは、0.010 〜 0.030%である。
【0028】
B:0.0003〜0.0015%、
Bは、Nbと複合して含有することにより、熱延組織および冷延再結晶組織の微細化に寄与し、かつ耐二次加工脆性を改善する作用を有する元素である。B含有量が、0.0003%未満では十分な微細化効果が得られない。一方、0.0015%を超えて含有すると、BN析出量が増大し、かつスラブ加熱段階での溶体化に支障をきたす。このため、Bは0.0003〜0.0015%の範囲に限定した。なお、好ましくは0.0007〜0.0012%である。
【0029】
V:0.01〜 0.5%
Vは、本発明において最も重要な元素であり、再結晶焼鈍前にはV窒化物として析出しNを固定することにより固溶Nを低減させて、再結晶焼鈍時に{111}再結晶集合組織を強く発達させ高いr値を得る作用を有する。さらに、析出したV窒化物は再結晶焼鈍時には再溶解し、再び固溶Nを増加させ、成形後強度上昇熱処理能を向上させる作用を有する。このような効果は、0.01%以上の含有で認められるが、0.5 %を超えて含有すると、焼鈍時にV窒化物の再溶解が起こりにくくなり、優れた成形後強度上昇熱処理能が得られなくなる。このため、Vは0.01〜 0.5%の範囲に限定した。
【0030】
本発明の冷延鋼板では、上記した範囲内の組成としたうえで、さらにC,Al, N,V,Nb を、次 (1) 式および次 (2) 式を同時に満足する条件下で含有する。
0≦ {V/51 + Nb/93 ーC/12 } ……(1)
0.5 ≦{V/51 +Nb/93 −C/12 +Al/27 }/(N/14 )≦ 3.0……(2)
(ここで、C、Al、N、Nb、V:各元素の含有量 (質量%))
C含有量、Nb含有量とV含有量の関係が、 (1) 式を満足しない場合には、炭化物の生成量が少なく、固溶C量が増加し、再結晶時に所望の再結晶集合組織の発達が弱くなり、高r値が得られない。
【0031】
また、C,Al, N,V,Nb含有量の関係が (2) 式を満足しない、すなわち、(V/51 +Nb/93 −C/12 + Al/27)/(N/14 )が 0.5未満か、あるいは 3.0超えの場合には、固溶N量が多すぎるか, あるいは少なすぎて、図1に示すように、r値と成形後強度上昇熱処理能 (ΔTS)のうちいずれかが低下し、優れた深絞り性と優れた成形後強度上昇熱処理能を同時に満足できない。
【0032】
固溶状態のN:0.0015%以上
本発明の冷延鋼板では、十分な強度を確保し、さらに優れた成形後強度上昇熱処理能を得るためには、固溶状態のN(固溶Nともいう)を0.0015%以上の量(濃度)で存在させることが必要となる。
ここで、固溶N量は、鋼中の全N量から析出N量を差し引いて求めるものとする。なお、析出N量の分析方法としては、本発明者らが種々の分析法を比較検討した結果によれば、定電位電解法を用いた電解抽出分析法により求めるのが有効である。なお、抽出分析に用いる地鉄を溶解する方法として、酸分解法、ハロゲン法、および電解法などがある。この中で、電解法は炭火物、窒化物などの不安定な析出物を分解させることなく、安定して地鉄のみを溶解できる。電解液としてはアセチルアセトン系を用いて、定電位にて電解する。本発明では定電位電解法を用いて析出N量を測定した結果が、実際の部品強度ともっとも良い対応を示した。
【0033】
このようなことから、本発明では、定電位電解法により抽出した残渣を化学分析して残渣中のN量を求め、これを析出N量とする。なお、より高い△TSを得るためには、固溶N量は0.0030%以上、さらに高い値を得るためには0.0045%以上、さらにより高い値を得るためには0.0060%以上とするのが好ましい。
また、本発明では、上記した組成に加えてさらに、Cu、Ni、Cr、Moのうちの1種または2種以上を合計で 2.0%以下含有することが好ましい。
【0034】
Cu、Ni、Cr、Moは、いずれも鋼を強化する作用があり、必要に応じ選択して含有できる。これらの元素の含有量は、所望の強度に応じて適宜決定することができるが、上記した効果を得るためには、Cu:0.05%以上、Ni:0.05%以上、Cr:0.05%以上、Mo:0.05%以上含有することが望ましいが、過剰に含有すると深絞り性が劣化する。このため、Cu、Ni、Cr、Moは1種あるいは2種以上を合計で 2.0%以下とすることが好ましい。
【0035】
なお、上記した成分以外の成分として、Ca、Zr、REM 等を含有してもなんら問題はない。
上記した成分以外の残部は、Feおよび不可避的不純物である。不可避的不純物としては、Sb:0.01%以下、Sn:0.1 %以下、Zn:0.01%以下、Co:0.1 %以下が許容できる。
【0036】
つぎに、本発明の冷延鋼板の製造方法について説明する。
上記した組成を有する鋼を、転炉等の通常公知の溶製方法で溶製し、通常公知の連続鋳造法、薄スラブ鋳造法あるいは造塊法を用いて鋼素材(スラブ)とすることが好ましい。なお、成分のマクロ偏析を防止する観点からは、連続鋳造法で製造することがより好ましい。
【0037】
ついで、上記した組成の鋼素材(スラブ)を、加熱温度:900 ℃以上に加熱したのち、仕上圧延終了温度: 800℃以上とする熱間圧延を施して、熱延板とし、巻取温度:400 〜800 ℃として巻取る。
なお、本発明では、鋼素材(スラブ)は、従来と同様に、いったん室温まで冷却し、その後再度900 ℃以上に加熱しても、あるいは、室温まで冷却しないで、温片のままで加熱炉に挿入し、900 ℃以上に加熱する、あるいは鋼素材(スラブ)の温度が900 ℃以上であれば、わずかの保熱をおこなった後に直ちに圧延する、直送圧延・直接圧延などの省エネルギープロセスも問題なく適用できる。
【0038】
加熱温度:900 ℃以上
鋼素材(スラブ)の加熱温度は、深絞り性向上のためには、固溶C、固溶Nを固定し、析出物として粗大に析出させることが{111}再結晶集合組織の発達に有利であり、そのためにはできるだけ低温とすることが望ましい。しかし、加熱温度が 900℃未満では、熱間圧延時の圧延荷重が増大し、圧延トラブルが発生する危険性が増大する。このため、鋼素材の加熱温度は900 ℃以上とすることが好ましい。なお、酸化重量の増加にともなうスケールロスの増大などから、スラブ加熱温度は1300℃以下とすることが望ましい。
【0039】
なお、スラブ加熱温度を低くし、かつ熱間圧延時のトラブルを防止するといった観点から、シートバーを加熱する、いわゆるシートバーヒーターを活用することは、有効な方法であることは言うまでもない。
仕上圧延終了温度:800 ℃以上
本発明では、仕上げ圧延の終了温度FDTを 800℃以上とすることが好ましい。FDTを 800℃以上とすることにより、均一な熱延母板組織を得ることができ、冷延・再結晶焼鈍後に優れた深絞り性が得られる。一方、FDTが 800℃未満では、熱延母板組織が不均一となるとともに、熱間圧延時の圧延負荷が高くなり、熱間圧延時にトラブルが発生する危険性が増大する。このようなことから、熱間圧延のFDTは 800℃以上とするのが好ましい。
【0040】
巻取温度:400 ℃以上 800℃以下
巻取温度CTが 800℃を超えると、スケールが増加しスケールロスにより歩溜りが低下する傾向となるとともに、熱延板結晶粒が粗大化し深絞り性が低下する。CTが 400℃未満では、熱延板中でのVNの析出が不十分となり深絞り性が低下するとともに、鋼板形状の乱れが顕著となり、実際の使用にあたり不具合を生じる危険性が増大する。このため、CTは 400℃以上 800℃以下とすることが好ましい。
【0041】
なお、本発明では、熱間圧延時の圧延荷重を低減するために仕上圧延の一部または全部を潤滑圧延としてもよい。潤滑圧延を行うことは、鋼板形状の均一化、材質の均一化の観点からも有効である。なお、潤滑圧延の際の摩擦係数は0.25〜0.10の範囲とすることが好ましい。また、相前後するシートバー同士を接合し、連続的に仕上圧延する連続圧延プロセスとすることが、熱間圧延の操業安定性の観点から望ましい。
【0042】
ついで、熱延板は圧下率:60〜95%の冷間圧延を施され冷延板とされる。なお、熱延板は冷間圧延前に酸洗処理を施され、熱延スケールを除去されることが好ましい。
冷間圧下率:60〜95%
冷間圧延は、圧下率:60〜95%とすることが好ましい。圧下率が60%未満では{111}再結晶集合組織が発達せず、r値が低く深絞り性の顕著な向上が期待できない。また圧下率が95%を超えるとr値がかえって低下する。
【0043】
ついで、冷延板は、 700℃以上の温度で再結晶焼鈍を施され冷延焼鈍板とされる。
再結晶焼鈍の焼鈍温度:700 ℃以上
再結晶焼鈍の焼鈍温度は、V窒化物を再溶解させて固溶Nを確保するためには、 700℃以上とすることが好ましい。再結晶焼鈍の焼鈍温度が 700℃未満では再結晶が十分に完了せず、また、VNの再溶解も不十分となり、高いr値と高い成形後強度上昇熱処理能が得られない。なお好ましくは 800℃以上 900℃以下である。また、焼鈍温度での均熱時間(焼鈍時間)は5s以上とすることが好ましい。焼鈍時間が5s未満では再結晶が不十分であるか、あるいはVNの再溶解が不十分となる場合がある。このため, 焼鈍温度は5s以上とすることが好ましい。
また、再結晶焼鈍における均熱後の冷却速度はVNの再析出を抑制するため、焼鈍温度から 500℃以上の温度域を冷却速度:30℃/s以上とすることが好ましい。なお、より好ましくは50℃/s以上である。
【0044】
また、再結晶焼鈍工程後に、形状矯正、表面粗さ等の調整のために、伸び率10%以下の調質圧延を加えてもよいことはいうまでもない。
なお、本発明の冷延鋼板は、加工用冷延鋼板としてのみならず、加工用表面処理鋼板の原板としても適用できる。表面処理としては、亜鉛めっき(合金系を含む)、すずめっき、ほうろう等がある。
【0045】
また、本発明の冷延鋼板には、亜鉛めっき後、化学処理性、溶接性、プレス成形性および耐食性等の改善のために特殊な処理、例えば固形潤滑剤の塗布、Fe-P電気めっき等を施してもよい。
【0046】
【実施例】
表1に示す組成の溶鋼を転炉で溶製し、連続鋳造法でスラブ (鋼素材)とした。ついで、これら鋼素材(スラブ)を表2に示す種々の温度に加熱したのち、表2に示す条件で熱間圧延を施し、板厚 4.0mmの熱延鋼帯(熱延板)とした。引き続き、これら熱延鋼帯(冷延板)に酸洗処理を施し、表2に示す条件で冷間圧延を施し、板厚 1.2mmの冷延鋼帯(冷延板)とした。ついで、これら冷延鋼帯(冷延板)に、連続焼鈍ラインで、表2に示す焼鈍温度・時間で再結晶焼鈍を施し、冷延焼鈍鋼帯 (冷延焼鈍板)とした。なお、焼鈍後表2に示す条件で焼鈍温度から500 ℃まで冷却した。さらに、これら冷延焼鈍鋼帯 (冷延焼鈍板)に、さらに伸び率:0.8 %の調質圧延を施した。
【0047】
得られた冷延鋼帯から、試験片を採取し、下記に示す試験方法で、引張特性、r値、成形後強度上昇熱処理能を測定した。なお、得られた冷延鋼帯の固溶N量は前記した方法で測定した。
(1)引張特性
得られた各冷延鋼帯からJIS 5 号引張試験片を採取し、JIS Z 2241の規定に準拠して引張試験を行い、降伏応力YS、引張強さTS、伸びEIを求めた。
(2)r値
得られた各冷延鋼帯の圧延方向(L方向)、圧延方向に対し45゜方向(D方向)、および圧延方向に対し90゜方向(C方向)から採取した JIS 5号試験片に、15%の単軸引張予歪を付与した時の各試験片の幅歪と板厚歪を求め、幅歪と板厚歪の比、
r=1n(w/wo )/1n(t/to
(ここで、wo 、to は試験前の試験片の幅および板厚であり、w、tは試験後の試験片の幅および板厚である。)
から各方向のr値を求め、次式
mean=(rL +2rD +rC )/4
により平均r値rmeanを求め、これをr値とした。ここで、rD は圧延方向(L方向)のr値であり、rD は圧延方向(L方向)に対し45゜方向(D方向)のr値であり、rC は圧延方向(L方向)に対し90゜方向(C方向)のr値である。
(3)成形後強度上昇熱処理能
得られた各冷延鋼帯から、 JIS 5号試験片を圧延方向に採取し、10%の引張予歪を与えて、ついで 170℃× 20minの熱処理(時効処理)を施したのち、引張試験を実施し、予変形−熱処理(時効処理)後の引張強さTSHTを求め、△TS=TSHT−TSを算出した。なお、TSは予変形前の、すなわち得られた冷延鋼帯の引張強さである。
【0048】
これらの結果を表3に示す。
【0049】
【表1】

Figure 0004556362
【0050】
【表2】
Figure 0004556362
【0051】
【表3】
Figure 0004556362
【0052】
本発明例は、いずれも、El:35%以上の高い伸びElとΔTS:50MPa 以上の高い成形後強度上昇熱処理能を有し、さらにr値:1.2 以上の高いr値を有して、成形後強度上昇熱処理能と深絞り性に優れた冷延鋼板となっている。これに対し、本発明の範囲を外れる比較例では、△TSが低いか、あるいはr値が低下した鋼板となっている。
【0053】
【発明の効果】
本発明によれば、r値:1.2 以上という優れた深絞り性とΔTS:50MPa 以上という高い成形後強度上昇熱処理能を有する冷延鋼板を、安定して製造することが可能となり、産業上格段の効果を奏する。さらに、本発明の冷延鋼板を自動車部品に適用した場合、プレス成形が容易で自動車車体の軽量化に十分に寄与できるという効果もある。
【図面の簡単な説明】
【図1】r値と成形後強度上昇熱処理能(△TS)とにおよぼすV、Nb、C、Al、N含有量の影響を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-tensile cold-rolled steel sheet suitable for use in automobile steel sheets and the like, and more particularly to a high-tensile cold-rolled steel sheet excellent in both deep drawability and post-forming strength increasing heat treatment ability.
[0002]
[Prior art]
In recent years, in connection with exhaust gas regulations due to global environmental conservation issues, the reduction of vehicle body weight has become a very important issue. In addition, ensuring safety such as occupant protection in a collision accident is also an important issue. For these reasons, recently, in order to reduce the weight of the vehicle body and ensure collision safety, it has been studied to use a high-strength thin steel plate having a reduced strength while simultaneously reducing the thickness of the steel plate.
[0003]
Since many automotive body parts made of steel sheets are formed by press working, the steel sheets used are required to have excellent press formability. In order to improve press formability, it is necessary that the steel sheet has a high Rankford value (r value) and a high ductility (elongation El) as mechanical properties of the steel sheet. However, generally, when the strength of a steel plate is increased, the r value and ductility are lowered, and the press formability tends to deteriorate.
[0004]
Further, when forming a steel sheet into a press-molded body such as a car body part of an automobile by pressing, it is desired that the steel sheet is soft in order to facilitate the pressing. On the other hand, the product is required to have high strength after the press-molded body is subjected to a paint baking process to obtain a product (part). A BH steel sheet has been developed as a steel sheet that can simultaneously satisfy such characteristics before pressing and characteristics after processing. This BH steel sheet is a steel sheet that has a characteristic that it is soft before press molding and is hardened by a coating baking process after press molding to increase the strength.
[0005]
As a method for improving the so-called bake hardenability, which is a characteristic that is hardened by a coating baking process after press molding, for example, in Japanese Patent Application Laid-Open No. 55-141526, depending on the content of solid solution C, N, and Al in steel By adding Nb and limiting Nb / (Solution C + Solution N) to a specific range at at% and controlling the cooling rate after annealing, the amount of solute C and the amount of solute N in steel The method of adjusting is described. Japanese Patent Publication No. 61-45689 proposes a method for improving the bake hardenability by adding Ti and Nb in combination.
[0006]
However, the steel plate manufactured by the above-described technology has a problem that the strength of the material steel plate is set low in order to make the material excellent in deep drawability, and the strength is not necessarily sufficient as a structural material. Moreover, in the steel plate manufactured by the above-described technology, the strength after forming-paint baking is increased by the action of a small amount of solid solution C and solid solution N in the steel plate. Only increases the yield strength and does not increase the tensile strength. Therefore, the steel plate manufactured by the above-described technique has the effect of increasing the stress at the start of deformation of the part, but the effect of increasing the stress required for deformation over the entire deformation area from the start of deformation to the end of deformation (post-forming tensile strength) is sufficient. I couldn't say that.
[0007]
On the other hand, as a cold-rolled steel sheet whose tensile strength increases after forming, for example, JP-A-10-310847 discloses an alloyed hot-dip galvanized steel sheet whose tensile strength increases by 60 MPa or more in a heat treatment temperature range of 200 to 450 ° C. It is disclosed. This steel sheet contains C: 0.01 to 0.08%, Mn: 0.01 to 3.0% by weight percentage, and contains 0.05 to 3.0% of one or more of W, Cr and Mo in total, and is necessary. A steel sheet having a composition containing one or more of Ti: 0.005 to 0.1%, Nb: 0.005 to 0.1%, and V: 0.005 to 0.1%, and having a microstructure mainly composed of ferrite or ferrite. is there.
[0008]
However, this technique forms fine carbides in the steel sheet by heat treatment after forming, effectively increases the amount of strain by increasing the amount of strain by effectively increasing dislocations against the strain applied during pressing. Heat treatment needs to be performed in a temperature range of ° C., and there is a problem that the heat treatment temperature is higher than a general paint baking temperature.
Also, as a hot-rolled steel sheet whose tensile strength increases after forming, for example, in Japanese Patent Publication No. 8-23048, the tensile strength that is soft at the time of processing and effective in improving the fatigue characteristics by baking processing after processing is greatly increased. A method of manufacturing a hot-rolled steel sheet that can be raised is disclosed.
[0009]
In this technology, the amount of C is set to 0.02% to 0.13 mass%, N is added in a large amount of 0.0080 to 0.0250 mass%, and the finish rolling temperature and the winding temperature are controlled to add a large amount of solute N into the steel. It is said that an increase in tensile strength of 100 MPa or more is achieved at a post-molding heat treatment temperature of 170 ° C. by making the metal structure a composite structure mainly composed of ferrite and martensite.
[0010]
JP-A-10-183301 discloses that, among steel components, C and N are particularly limited to C: 0.01 to 0.12 mass% and N: 0.0001 to 0.01 mass%, and the average crystal grain size is 8 μm or less. A hot-rolled steel sheet having excellent bake hardenability and room temperature aging resistance capable of ensuring a high BH amount of 80 MPa or more and controlling the AI value to 45 MPa or less by controlling is disclosed.
[0011]
[Problems to be solved by the invention]
However, since the steel sheets described in Japanese Patent Publication No. 8-23048 and JP-A-10-183301 are both hot-rolled steel sheets, the ferrite texture is randomized by the austenite / ferrite transformation after finish rolling. Therefore, the r value is at most about 0.8, and it is difficult to obtain a high r value of 1.2 or more, which is required as a steel sheet for automobiles, and it is difficult to say that it has sufficient deep drawability.
[0012]
Moreover, even if cold rolling and recrystallization annealing are performed using the hot-rolled steel sheet obtained by these techniques as a starting material, an increase in the tensile strength after forming-heat treatment equivalent to that of the hot-rolled steel sheet is not necessarily obtained. Not exclusively. This is because the steel structure becomes a microstructure different from that during hot rolling due to cold rolling and recrystallization annealing. In addition, since there is no idea that the solid solution N and solid solution C are precipitated and fixed (IF) before cold rolling, a large amount of solid solution C and solid solution N remain at the time of cold rolling and have a sufficiently high r value. A steel plate cannot be obtained.
[0013]
The present invention advantageously solves the above-mentioned problems of the prior art, and has a high strength cold-rolled steel sheet having excellent post-forming strength increasing heat-treating ability and excellent deep drawing ability, and both post-forming strength increasing heat-treating ability and deep drawing ability. It aims at proposing the manufacturing method of the high tension cold-rolled steel plate which can manufacture the excellent cold-rolled steel plate stably. In the present invention, “excellent heat-strength heat treatment after forming” means that when a steel plate is pre-deformed with a tensile strain of 10% and then heat-treated (aging treatment) at a temperature of 170 ° C. for 20 minutes. (Aging treatment) Amount of increase in tensile strength before and after (denoted as △ TS; △ TS = (tensile strength after pre-deformation heat treatment)-(tensile strength before pre-deformation)) is 50 MPa or more And In the present invention, “excellent deep drawability” refers to a case where the r value is 1.2 or more.
[0014]
[Means for Solving the Problems]
In order to achieve the above-mentioned problems, the present inventors have conducted intensive studies on the influence of alloy elements on the microstructure and recrystallization texture of cold-rolled steel sheets. As a result, Ti and Nb have been mainly used as carbonitride-forming elements in the past, but the present inventors have focused on V in which nitride is easily dissolved at a lower temperature than Ti nitride and Nb nitride. And by making C content into an extremely low carbon region and containing N and V in an appropriate range, solid solution C and solid solution N can be reduced as much as possible before recrystallization annealing, and by recrystallization annealing, { 1 1 1} The recrystallized texture is strongly developed and a high r value of 1.2 or more can be obtained, and the V-based nitride is dissolved by annealing, and a large amount of solute N is dissolved in the steel sheet after annealing. It is possible to produce a high-tensile cold-rolled steel sheet that can simultaneously satisfy the excellent strength-increasing heat-treating ability after forming and the excellent deep drawability. Obtained knowledge. Furthermore, the present inventors have found that by adding Nb and B in addition to V, the structure can be further refined.
[0015]
First, basic experimental results performed by the present inventors will be described.
In mass%, C: 0.002%, Si: 0.02%, Mn: 1.2%, P: 0.04%, S: 0.004%, Al: 0.011%, N: 0.014%, Nb: 0.015%, B: including 0.0014% V: Each sheet bar having a composition changed from 0.03 to 0.35%, heated to 1250 ° C and soaked, and then hot rolled for 3 passes so that the finish rolling finish temperature is 910 ° C, and the sheet thickness is 4.0 mm. The hot rolled sheet was used. In addition, after finishing rolling, these hot-rolled sheets were subjected to a heat retention treatment of 700 ° C. × 1 h as a coil winding equivalent process. Subsequently, these hot-rolled sheets were cold-rolled at a reduction ratio of 70% to obtain cold-rolled sheets having a thickness of 1.2 mm. Then, these cold-rolled plates were subjected to recrystallization annealing at 840 ° C. for 40 s and then cooled at a cooling rate of 30 ° C./s to obtain cold-rolled annealed plates.
[0016]
Test pieces were sampled from the obtained cold-rolled annealed plates, and the tensile properties, post-molding strength increasing heat treatment ability and r value were determined.
Tensile properties were determined by collecting JIS No. 5 tensile test pieces from each cold-rolled annealed plate and conducting a tensile test. In addition, JIS No. 5 tensile test specimens collected from each cold-rolled annealed plate were heat-treated after pre-deformation with a tensile strain of 10% and maintained at 170 ° C for 20 minutes, and then a tensile test was conducted. Tensile strength was determined. The amount of increase in tensile strength before and after the heat treatment (denoted as ΔTS; ΔTS = (tensile strength after heat treatment) − (tensile strength before pre-deformation)) was defined as the post-molding strength increasing heat treatment ability.
[0017]
In addition, JIS test specimens were collected from each cold-rolled annealed sheet in the rolling direction (L direction), 45 degrees direction (D direction) in the rolling direction, and perpendicular direction (C direction) to the rolling direction. % Width and thickness strain of each specimen when% uniaxial tensile prestrain is applied, and the ratio of width strain to thickness strain
r = ln (w / w 0 ) / Ln (t / t 0 )
Where w 0 , T 0 Is the width and thickness of the specimen before the test, and w and t are the width and thickness of the specimen after the test)
R value in each direction (r L , R C , R D ) For each
r mean = (R L + R C + 2 × r D ) / 4
The average r value r mean Asked. In the present invention, the r value means an average r value unless otherwise specified.
[0018]
FIG. 1 shows the influence of the contents of V, C, Al, and N on the r value and the post-molding strength increasing heat treatment ability (ΔTS). The horizontal axis is parameter (V / 51 + Nb / 93-C / 12 + Al / 27) / (N / 14). Here, V, C, Al, Nb, and N are the contents (mass%) of each element.
From Fig. 1, when (V / 51 + Nb / 93-C / 12 + Al / 27) / (N / 14) satisfies 0.5 or more and 3.0 or less, it is the first time that a high r value of 1.2 or more and ΔTS of 50 MPa or more. It can be seen that a high post-molding strength-increasing heat treatment ability is simultaneously satisfied. That is, by adjusting the components so that (V / 51 + Nb / 93-C / 12 + Al / 27) / (N / 14) is 0.5 or more and 3.0 or less, excellent deep drawability and excellent strength after molding. It was found that a high-tensile cold-rolled steel sheet having ascending heat treatment ability can be produced.
[0019]
The present invention has been completed by further study based on the above findings.
That is, the gist of the present invention is as follows.
(1) By mass%, C: less than 0.0050%, Si: 0.005 to 1.0%, Mn: 0.01 to 1.5%, P: 0.1% or less, S: 0.01% or less, Al: 0.005 to 0.03%, N: 0.005 to 0.040%, Nb: 0.005 to 0.050%, B: 0.0003 to 0.0015%, V: 0.01 to 0.5%, and C, Al, N, Nb, and V in the following formulas (1) and (2)
0 ≦ {V / 51 + Nb / 93-C / 12} (1)
0.5 ≦ {V / 51 + Nb / 93 −C / 12 + Al / 27} / (N / 14) ≦ 3.0 (2)
(Here, C, Al, N, Nb, V: content of each element (mass%))
Excellent in heat-treating strength after forming and deep drawability, characterized by having a composition comprising 0.0015% or more of solid solution N and the balance Fe and inevitable impurities. High tensile cold-rolled steel sheet.
(2) In (1), in addition to the above composition, the composition further comprises one or two or more selected from Cu, Ni, Cr, and Mo in a mass% of 2.0% or less in total. High tensile cold-rolled steel sheet.
(3) By mass%, C: less than 0.0050%, Si: 0.005 to 1.0%, Mn: 0.01 to 1.5%, P: 0.1% or less, S: 0.01% or less, Al: 0.005 to 0.03%, N: 0.005 to 0.040%, Nb: 0.005 to 0.050%, B: 0.0003 to 0.0015%, V: 0.01 to 0.5%, and C, Al, N, Nb, and V in the following formulas (1) and (2)
0 ≦ {V / 51 + Nb / 93-C / 12} (1)
0.5 ≦ {V / 51 + Nb / 93 −C / 12 + Al / 27} / (N / 14) ≦ 3.0 (2)
(Here, C, Al, N, Nb, V: content of each element (mass%))
A steel material having a composition consisting of the remaining Fe and inevitable impurities, hot-rolled to a heating temperature of 900 ° C or higher and a finish rolling finish temperature of 800 ° C or higher. After that, the hot-rolled sheet is wound at a coiling temperature of 400 to 800 ° C., and then the hot-rolled sheet is subjected to cold rolling at a reduction ratio of 60 to 95% to obtain a cold-rolled sheet. A method for producing a high-tensile cold-rolled steel sheet excellent in post-forming strength-increasing heat treatment ability and deep drawability, characterized by subjecting to recrystallization annealing at a temperature of 700 ° C.
(4) In (3), in addition to the above composition, the composition further comprises one or two or more selected from Cu, Ni, Cr, and Mo in a mass% of 2.0% or less in total. A method for producing a high-tensile cold-rolled steel sheet.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
The cold-rolled steel sheet of the present invention is a high-tensile cold-rolled steel sheet having excellent post-forming strength increasing heat treatment ability and excellent deep drawability.
First, the reason for limiting the composition of the cold-rolled steel sheet of the present invention will be described. The mass% is simply written as%.
[0021]
C: Less than 0.0050%
C increases the strength of the steel but lowers the ductility and degrades press formability and deep drawability. For this reason, although it is preferable to reduce as much as possible in the present invention, C is preferably set to an extremely low carbon level from the viewpoint of improving press formability and deep drawability, specifically, less than 0.0050%. In addition, Preferably, it is 0.0030% or less. In addition, the lower limit value of the amount of C that can be reached without extreme cost increase is considered to be about 0.0005% in the current manufacturing technology.
[0022]
Si: 0.005 to 1.0%
Si is a useful element that suppresses the decrease in elongation and improves the strength, but such an effect is recognized with a content of 0.005% or more, while content exceeding 1.0% deteriorates the surface properties. Cause a drop in ductility. For this reason, Si was limited to the range of 0.005 to 1.0%. In addition, Preferably it is 0.005-0.75%.
[0023]
Mn: 0.01-1.5%
Mn is effective as a strengthening component of steel and has the effect of suppressing the embrittlement due to S by forming MnS. Such an effect is recognized when the content is 0.01% or more, but when the content exceeds 1.5%, surface properties are deteriorated and ductility is lowered. For this reason, Mn was limited to the range of 0.01 to 1.5%. In addition, Preferably it is 0.01 to 0.75%.
[0024]
P: 0.1% or less
P is an element that contributes effectively to strengthening steel by solid solution strengthening, and can be contained in a predetermined amount according to the required strength level, but if it exceeds 0.1%, deep drawability decreases. For this reason, P was limited to 0.1% or less.
S: 0.01% or less
S is present mainly as inclusions (sulfides) in steel and causes a reduction in ductility. Therefore, it is desirable to reduce S as much as possible, but it is allowed up to 0.01%.
[0025]
Al: 0.005 to 0.030%
Al is included as a deoxidizer and to improve the yield of carbonitride-forming elements, but if the content is less than 0.005%, there is no sufficient effect, while the content exceeding 0.030% is contained in the steel. The amount of N to be increased is increased, and slab defects are easily generated during steelmaking.
[0026]
N: 0.005 to 0.040%
In the present invention, N is an important element that plays a role of imparting post-forming strength increasing heat treatment ability to the steel sheet. However, if the content is less than 0.005%, it is difficult to secure a sufficient amount of solute N, and sufficient post-molding strength increasing heat treatment ability cannot be obtained. On the other hand, if it exceeds 0.040%, the press formability is lowered. For this reason, N was limited to the range of 0.005 to 0.040%. In addition, Preferably it is 0.008 to 0.015%.
[0027]
Nb: 0.005-0.050%
Nb is an element that is contained together with B, contributes to refinement of the hot-rolled structure and the cold-rolled recrystallization annealed structure, and has an action of binding to the solid solution C to precipitate and fix the solid solution C as NbC. Nb also has an action of fixing solute N as NbN by combining with solute N. When the Nb content is less than 0.005%, not only is it difficult to precipitate and fix the solid solution C, but the refinement of the hot-rolled structure and the cold-rolled recrystallization annealed structure becomes insufficient. On the other hand, if it exceeds 0.050%, ductility is lowered. For this reason, Nb is limited to the range of 0.005 to 0.050%. In addition, Preferably, it is 0.010 to 0.030%.
[0028]
B: 0.0003-0.0015%,
B is an element that contributes to refinement of the hot-rolled structure and the cold-rolled recrystallized structure and has the effect of improving the secondary work brittleness resistance by being contained in combination with Nb. If the B content is less than 0.0003%, a sufficient fine effect cannot be obtained. On the other hand, when it contains exceeding 0.0015%, the amount of BN precipitation will increase and it will interfere with the solution formation in the slab heating stage. For this reason, B was limited to the range of 0.0003 to 0.0015%. In addition, Preferably it is 0.0007 to 0.0012%.
[0029]
V: 0.01 to 0.5%
V is the most important element in the present invention. Before recrystallization annealing, V precipitates as V nitride and fixes N to reduce solute N, and {111} recrystallization texture during recrystallization annealing. Has the effect of obtaining a high r value. Further, the precipitated V nitride is re-dissolved during recrystallization annealing, and has the effect of increasing the solid solution N again and improving the strength-increasing heat treatment ability after forming. Such an effect is recognized when the content is 0.01% or more. However, when the content exceeds 0.5%, re-melting of the V nitride is difficult to occur during annealing, and excellent post-molding strength increasing heat treatment ability cannot be obtained. For this reason, V was limited to the range of 0.01 to 0.5%.
[0030]
The cold-rolled steel sheet of the present invention has a composition within the above range, and further contains C, Al, N, V, and Nb under the conditions that satisfy the following formulas (1) and (2) at the same time. To do.
0 ≦ {V / 51 + Nb / 93-C / 12} (1)
0.5 ≦ {V / 51 + Nb / 93 −C / 12 + Al / 27} / (N / 14) ≦ 3.0 (2)
(Here, C, Al, N, Nb, V: content of each element (mass%))
If the relationship between the C content, Nb content and V content does not satisfy the formula (1), the amount of carbide generated is small, the amount of solid solution C increases, and the desired recrystallization texture during recrystallization The development of this becomes weak, and a high r value cannot be obtained.
[0031]
Further, the relationship among the contents of C, Al, N, V, and Nb does not satisfy the formula (2), that is, (V / 51 + Nb / 93-C / 12 + Al / 27) / (N / 14) is 0.5. If it is less than or more than 3.0, the amount of dissolved N is too much or too little, and as shown in FIG. 1, either the r value or the heat treatment ability for increasing strength (ΔTS) decreases. However, excellent deep drawability and excellent post-molding strength increasing heat treatment ability cannot be satisfied at the same time.
[0032]
Solid solution N: 0.0015% or more
In the cold-rolled steel sheet of the present invention, in order to ensure sufficient strength and to obtain an excellent heat-treating ability for increasing strength after forming, the amount of N in solid solution (also referred to as solid solution N) is 0.0015% or more (concentration). ) Must be present.
Here, the solute N amount is obtained by subtracting the precipitated N amount from the total N amount in the steel. It should be noted that, as a method for analyzing the amount of precipitated N, it is effective to obtain by an electrolytic extraction analysis method using a constant potential electrolysis method according to the results of comparisons of various analysis methods by the present inventors. In addition, there are an acid decomposition method, a halogen method, an electrolysis method and the like as a method for dissolving the base iron used for the extraction analysis. Among these, the electrolytic method can stably dissolve only the ground iron without decomposing unstable precipitates such as charcoal and nitride. Electrolysis is performed at a constant potential using an acetylacetone system as the electrolytic solution. In the present invention, the result of measuring the amount of precipitated N using a constant potential electrolysis method showed the best correspondence with the actual component strength.
[0033]
For this reason, in the present invention, the residue extracted by the constant potential electrolysis method is chemically analyzed to determine the amount of N in the residue, which is used as the amount of precipitated N. In order to obtain a higher ΔTS, the amount of dissolved N is preferably 0.0030% or more, 0.0045% or more for obtaining a higher value, and 0.0060% or more for obtaining a higher value. .
Further, in the present invention, in addition to the above-described composition, it is preferable that one or more of Cu, Ni, Cr and Mo are further contained in a total of 2.0% or less.
[0034]
Cu, Ni, Cr, and Mo all have an action of strengthening steel, and can be selected and contained as necessary. The content of these elements can be appropriately determined according to the desired strength, but in order to obtain the above-described effects, Cu: 0.05% or more, Ni: 0.05% or more, Cr: 0.05% or more, Mo : 0.05% or more is desirable, but if it is excessively contained, deep drawability deteriorates. For this reason, Cu, Ni, Cr, and Mo are preferably one or two or more in total to 2.0% or less.
[0035]
It should be noted that there is no problem if Ca, Zr, REM or the like is contained as a component other than the components described above.
The balance other than the above components is Fe and inevitable impurities. As unavoidable impurities, Sb: 0.01% or less, Sn: 0.1% or less, Zn: 0.01% or less, Co: 0.1% or less are acceptable.
[0036]
Below, the manufacturing method of the cold-rolled steel plate of this invention is demonstrated.
The steel having the above composition is melted by a generally known melting method such as a converter, and a steel material (slab) is obtained by using a generally known continuous casting method, thin slab casting method or ingot forming method. preferable. In addition, it is more preferable to manufacture by a continuous casting method from a viewpoint of preventing the macrosegregation of a component.
[0037]
Next, the steel material (slab) having the above composition is heated to a heating temperature of 900 ° C. or higher, and then subjected to hot rolling at a finish rolling finish temperature of 800 ° C. or more to obtain a hot rolled sheet. Wind as 400-800 ° C.
In the present invention, the steel material (slab) is once cooled to room temperature and then heated again to 900 ° C. or higher, or it is not cooled to room temperature, and it remains in the heating furnace. If the steel material (slab) temperature is 900 ° C or higher, it will be rolled immediately after a little heat retention. Applicable without any problem.
[0038]
Heating temperature: 900 ℃ or more
The heating temperature of the steel material (slab) is advantageous for the development of {111} recrystallization texture by fixing solid solution C and solid solution N and precipitating coarsely as precipitates in order to improve deep drawability. Therefore, it is desirable to make the temperature as low as possible. However, if the heating temperature is less than 900 ° C, the rolling load during hot rolling increases and the risk of occurrence of rolling trouble increases. For this reason, it is preferable that the heating temperature of a steel material shall be 900 degreeC or more. Note that the slab heating temperature is desirably 1300 ° C. or less because of an increase in scale loss accompanying an increase in oxidized weight.
[0039]
Needless to say, using a so-called sheet bar heater that heats the sheet bar from the viewpoint of lowering the slab heating temperature and preventing troubles during hot rolling is of course effective.
Finishing rolling finish temperature: 800 ℃ or more
In the present invention, the finish rolling finish temperature FDT is preferably 800 ° C. or higher. By setting the FDT to 800 ° C. or more, a uniform hot-rolled mother board structure can be obtained, and excellent deep drawability can be obtained after cold rolling and recrystallization annealing. On the other hand, if the FDT is less than 800 ° C., the hot-rolled base metal structure becomes non-uniform, the rolling load during hot rolling increases, and the risk of trouble occurring during hot rolling increases. For this reason, the hot rolling FDT is preferably 800 ° C. or higher.
[0040]
Winding temperature: 400 ℃ or more and 800 ℃ or less
When the coiling temperature CT exceeds 800 ° C., the scale increases and the yield tends to decrease due to the scale loss, and the hot rolled plate crystal grains become coarse and the deep drawability decreases. If the CT is less than 400 ° C., the precipitation of VN in the hot-rolled sheet is insufficient and the deep drawability is deteriorated, and the shape of the steel sheet is significantly disturbed, which increases the risk of causing problems in actual use. For this reason, CT is preferably set to 400 ° C. or higher and 800 ° C. or lower.
[0041]
In the present invention, part or all of finish rolling may be lubricated rolling in order to reduce the rolling load during hot rolling. Performing lubrication rolling is also effective from the viewpoint of uniform steel plate shape and uniform material. In addition, it is preferable to make the friction coefficient in the case of lubrication rolling into the range of 0.25-0.10. Moreover, it is desirable from the viewpoint of the operational stability of hot rolling that a continuous rolling process is performed in which successive sheet bars are joined and finish-rolled continuously.
[0042]
Next, the hot-rolled sheet is subjected to cold rolling at a reduction ratio of 60 to 95% to obtain a cold-rolled sheet. In addition, it is preferable that a hot-rolled sheet is pickled before cold rolling, and a hot-rolled scale is removed.
Cold reduction rate: 60-95%
Cold rolling is preferably performed at a reduction ratio of 60 to 95%. If the rolling reduction is less than 60%, the {111} recrystallization texture does not develop, and the r value is low and a significant improvement in deep drawability cannot be expected. On the other hand, when the rolling reduction exceeds 95%, the r value decreases.
[0043]
Next, the cold-rolled sheet is subjected to recrystallization annealing at a temperature of 700 ° C. or higher to be a cold-rolled annealed sheet.
Recrystallization annealing temperature: 700 ℃ or more
The annealing temperature for recrystallization annealing is preferably set to 700 ° C. or higher in order to re-dissolve the V nitride and secure solid solution N. When the annealing temperature for recrystallization annealing is less than 700 ° C., recrystallization is not sufficiently completed, and remelting of VN is insufficient, and a high r value and high post-molding strength increasing heat treatment ability cannot be obtained. It is preferably 800 ° C. or higher and 900 ° C. or lower. The soaking time (annealing time) at the annealing temperature is preferably 5 s or more. If the annealing time is less than 5 s, recrystallization may be insufficient, or VN remelting may be insufficient. For this reason, it is preferable that an annealing temperature shall be 5 s or more.
Moreover, in order to suppress the reprecipitation of VN, the cooling rate after soaking in the recrystallization annealing is preferably set to a cooling rate of 30 ° C./s or more in the temperature range from the annealing temperature to 500 ° C. More preferably, it is 50 ° C./s or more.
[0044]
Needless to say, after the recrystallization annealing step, temper rolling with an elongation of 10% or less may be added to adjust the shape correction, surface roughness, and the like.
The cold-rolled steel sheet of the present invention can be applied not only as a cold-rolled steel sheet for processing but also as an original sheet of a surface-treated steel sheet for processing. Examples of the surface treatment include galvanization (including alloy system), tin plating, enamel and the like.
[0045]
Also, the cold-rolled steel sheet of the present invention is specially treated for improving chemical processability, weldability, press formability, corrosion resistance, etc. after galvanization, such as application of solid lubricant, Fe-P electroplating, etc. May be applied.
[0046]
【Example】
Molten steel having the composition shown in Table 1 was melted in a converter and made into a slab (steel material) by a continuous casting method. Subsequently, these steel materials (slabs) were heated to various temperatures shown in Table 2, and then hot-rolled under the conditions shown in Table 2 to obtain hot-rolled steel strips (hot-rolled plates) having a thickness of 4.0 mm. Subsequently, these hot-rolled steel strips (cold-rolled sheets) were pickled and cold-rolled under the conditions shown in Table 2 to obtain cold-rolled steel strips (cold-rolled sheets) having a thickness of 1.2 mm. Then, these cold-rolled steel strips (cold-rolled sheets) were subjected to recrystallization annealing at the annealing temperature and time shown in Table 2 in a continuous annealing line to obtain cold-rolled annealed steel bands (cold-rolled annealed plates). In addition, it cooled from annealing temperature to 500 degreeC on the conditions shown in Table 2 after annealing. Furthermore, these cold-rolled annealed steel strips (cold-rolled annealed sheets) were further subjected to temper rolling with an elongation of 0.8%.
[0047]
Test pieces were collected from the obtained cold-rolled steel strips and measured for tensile properties, r value, and post-strength strength increasing heat treatment ability by the following test methods. In addition, the amount of solute N of the obtained cold-rolled steel strip was measured by the method described above.
(1) Tensile properties
A JIS No. 5 tensile test piece was collected from each of the obtained cold-rolled steel strips, and subjected to a tensile test in accordance with the provisions of JIS Z 2241 to obtain yield stress YS, tensile strength TS, and elongation EI.
(2) r value
To each JIS 5 test piece taken from the rolling direction (L direction) of each cold-rolled steel strip, 45 ° direction (D direction) with respect to the rolling direction, and 90 ° direction (C direction) with respect to the rolling direction, Obtain the width strain and plate thickness strain of each specimen when 15% uniaxial tensile pre-strain was applied, and the ratio of the width strain to the plate thickness strain,
r = 1n (w / w o ) / 1n (t / t o )
(Where o , T o Is the width and thickness of the test piece before the test, and w and t are the width and thickness of the test piece after the test. )
The r value in each direction is obtained from
r mean = (R L + 2r D + R C ) / 4
The average r value r mean This was determined as the r value. Where r D Is the r value in the rolling direction (L direction), r D Is the r value in the 45 ° direction (D direction) with respect to the rolling direction (L direction). C Is the r value in the 90 ° direction (C direction) with respect to the rolling direction (L direction).
(3) Strength increasing heat treatment ability after molding
From each cold-rolled steel strip obtained, a JIS No. 5 specimen was taken in the rolling direction, given a pre-strain of 10%, and then subjected to heat treatment (aging treatment) at 170 ° C for 20 minutes, followed by a tensile test. And tensile strength TS after pre-deformation-heat treatment (aging treatment) HT △ TS = TS HT -TS was calculated. TS is the tensile strength of the cold-rolled steel strip before pre-deformation, that is, obtained.
[0048]
These results are shown in Table 3.
[0049]
[Table 1]
Figure 0004556362
[0050]
[Table 2]
Figure 0004556362
[0051]
[Table 3]
Figure 0004556362
[0052]
Each of the examples of the present invention has a high elongation El of 35% or higher and a high heat treatment ability for increasing strength after molding of ΔTS: 50 MPa or more, and further has a high r value of 1.2 or more. It is a cold-rolled steel sheet with excellent post-strength heat treatment ability and deep drawability. On the other hand, in the comparative example outside the scope of the present invention, the steel sheet has a low ΔTS or a low r value.
[0053]
【The invention's effect】
According to the present invention, it is possible to stably produce a cold-rolled steel sheet having excellent deep drawability of r value: 1.2 or more and high post-forming strength increasing heat treatment ability of ΔTS: 50 MPa or more. Has the effect of. Furthermore, when the cold-rolled steel sheet of the present invention is applied to automobile parts, there is an effect that press forming is easy and it can sufficiently contribute to weight reduction of the automobile body.
[Brief description of the drawings]
FIG. 1 is a graph showing the influence of the contents of V, Nb, C, Al, and N on r value and heat-treating ability to increase strength after forming (ΔTS).

Claims (4)

質量%で
C:0.0050%未満、 Si:0.005 〜 1.0%、
Mn:0.01〜 1.5%、 P: 0.1%以下、
S:0.01%以下、 Al:0.005 〜0.03%、
N: 0.005〜 0.040%、 Nb: 0.005〜 0.050%、
B:0.0003〜0.0015%、 V:0.01〜 0.5%
を含み、かつC、Al、N、Nb、Vを下記 (1) 式および下記 (2) 式を満足する条件下で含有し、さらに固溶状態のNを0.0015%以上含み、残部Feおよび不可避的不純物からなる組成を有することを特徴とする、成形後強度上昇熱処理能と深絞り性に優れた高張力冷延鋼板。

0≦ {V/51 + Nb/93 ーC/12 } ……(1)
0.5 ≦{V/51 +Nb/93 −C/12 +Al/27 }/(N/14 )≦ 3.0……(2)
ここで、C、Al、N、Nb、V:各元素の含有量 (質量%)
C: less than 0.0050% by mass%, Si: 0.005-1.0%,
Mn: 0.01 to 1.5%, P: 0.1% or less,
S: 0.01% or less, Al: 0.005 to 0.03%,
N: 0.005-0.040%, Nb: 0.005-0.050%,
B: 0.0003-0.0015%, V: 0.01-0.5%
And containing C, Al, N, Nb, and V under the conditions satisfying the following formula (1) and the following formula (2), further containing 0.0015% or more of N in a solid solution state, the balance Fe and inevitable A high-tensile cold-rolled steel sheet excellent in post-forming strength-increasing heat-treating ability and deep drawability, characterized by having a composition comprising mechanical impurities.
0 ≦ {V / 51 + Nb / 93-C / 12} (1)
0.5 ≦ {V / 51 + Nb / 93 −C / 12 + Al / 27} / (N / 14) ≦ 3.0 (2)
Here, C, Al, N, Nb, V: Content of each element (mass%)
前記組成に加えてさらに, 質量%で、Cu、Ni、Cr、Moのうちから選ばれた1種または2種以上を合計で 2.0%以下含有することを特徴とする請求項1に記載の高張力冷延鋼板。2. The high content according to claim 1, further comprising, in addition to the composition, 2.0% or less in total of one or more selected from Cu, Ni, Cr, and Mo by mass%. Tensile cold-rolled steel sheet. 質量%で
C:0.0050%未満、 Si:0.005 〜 1.0%、
Mn:0.01〜 1.5%、 P: 0.1%以下、
S:0.01%以下、 Al:0.005 〜0.03%、
N: 0.005〜 0.040%、 Nb: 0.005〜 0.050%、
B:0.0003〜0.0015%、 V:0.01〜 0.5%
を含み、かつC、Al、N、Nb、Vを下記 (1) 式および下記 (2) 式を満足する条件下で含有し、残部Feおよび不可避的不純物からなる組成を有する鋼素材に、加熱温度: 900℃以上、仕上圧延終了温度: 800℃以上とする熱間圧延を施し熱延板とした後、該熱延板を巻取温度:400 〜800 ℃で巻取り、次いで該熱延板に圧下率:60〜95%の冷間圧延を施し冷延板としたのち、該冷延板に700 ℃以上の温度で再結晶焼鈍を施すことを特徴とする成形後強度上昇熱処理能と深絞り性に優れた高張力冷延鋼板の製造方法。

0≦ {V/51 + Nb/93 ーC/12 } ……(1)
0.5 ≦{V/51 +Nb/93 −C/12 +Al/27 }/(N/14 )≦ 3.0……(2)
ここで、C、Al、N、Nb、V:各元素の含有量 (質量%)
C: less than 0.0050% by mass%, Si: 0.005-1.0%,
Mn: 0.01 to 1.5%, P: 0.1% or less,
S: 0.01% or less, Al: 0.005 to 0.03%,
N: 0.005-0.040%, Nb: 0.005-0.050%,
B: 0.0003-0.0015%, V: 0.01-0.5%
A steel material containing C, Al, N, Nb, and V under the conditions satisfying the following formula (1) and the following formula (2), and having a composition comprising the balance Fe and inevitable impurities: Temperature: 900 ° C. or higher, finish rolling finish temperature: 800 ° C. or higher, hot rolled into a hot rolled sheet, then rolled up at a coiling temperature of 400 to 800 ° C., then the hot rolled sheet After forming into a cold-rolled sheet by subjecting it to a cold rolling of 60 to 95%, the cold-rolled sheet is subjected to recrystallization annealing at a temperature of 700 ° C. or higher. A method for producing a high-tensile cold-rolled steel sheet with excellent drawability.
0 ≦ {V / 51 + Nb / 93-C / 12} (1)
0.5 ≦ {V / 51 + Nb / 93 −C / 12 + Al / 27} / (N / 14) ≦ 3.0 (2)
Here, C, Al, N, Nb, V: Content of each element (mass%)
前記組成に加えてさらに, 質量%で、Cu、Ni、Cr、Moのうちから選ばれた1種または2種以上を合計で 2.0%以下含有することを特徴とする請求項3に記載の高張力冷延鋼板の製造方法。4. The high content according to claim 3, further comprising, in addition to the composition, 2.0% or less in total of one or more selected from Cu, Ni, Cr, and Mo by mass%. A method for producing a tension cold-rolled steel sheet.
JP2001251418A 2001-08-22 2001-08-22 High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof Expired - Fee Related JP4556362B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2001251418A JP4556362B2 (en) 2001-08-22 2001-08-22 High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2001251418A JP4556362B2 (en) 2001-08-22 2001-08-22 High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof

Publications (2)

Publication Number Publication Date
JP2003064447A JP2003064447A (en) 2003-03-05
JP4556362B2 true JP4556362B2 (en) 2010-10-06

Family

ID=19080068

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2001251418A Expired - Fee Related JP4556362B2 (en) 2001-08-22 2001-08-22 High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof

Country Status (1)

Country Link
JP (1) JP4556362B2 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH1072640A (en) * 1996-08-30 1998-03-17 Kawasaki Steel Corp Steel sheet for can, increased in age hardenability and excellent in material stability, and its production
JP2000199033A (en) * 1998-12-28 2000-07-18 Kawasaki Steel Corp Cold rolled thin steel sheet for deep drawing excellent in fatigue resistance
JP2001335887A (en) * 2000-05-26 2001-12-04 Kawasaki Steel Corp Cold rolled steel sheet for deep drawing, excellent in strain aging hardenability, and manufacturing method

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH1072640A (en) * 1996-08-30 1998-03-17 Kawasaki Steel Corp Steel sheet for can, increased in age hardenability and excellent in material stability, and its production
JP2000199033A (en) * 1998-12-28 2000-07-18 Kawasaki Steel Corp Cold rolled thin steel sheet for deep drawing excellent in fatigue resistance
JP2001335887A (en) * 2000-05-26 2001-12-04 Kawasaki Steel Corp Cold rolled steel sheet for deep drawing, excellent in strain aging hardenability, and manufacturing method

Also Published As

Publication number Publication date
JP2003064447A (en) 2003-03-05

Similar Documents

Publication Publication Date Title
JP5884714B2 (en) Hot-dip galvanized steel sheet and manufacturing method thereof
JP5825481B2 (en) High-strength cold-rolled steel sheet excellent in deep drawability and bake hardenability and its manufacturing method
JP5310919B2 (en) Method for producing high-strength cold-rolled steel sheets with excellent aging resistance and seizure curability
US20090071574A1 (en) Cold rolled dual phase steel sheet having high formability and method of making the same
JP5408314B2 (en) High-strength cold-rolled steel sheet excellent in deep drawability and material uniformity in the coil and method for producing the same
CN111684091B (en) High-strength cold-rolled steel sheet, high-strength plated steel sheet, and methods for producing these
CN114207169B (en) Steel sheet and method for producing same
JP7095818B2 (en) Covered steel members, coated steel sheets and their manufacturing methods
CN113348259A (en) High-strength hot-dip galvanized steel sheet and method for producing same
JP6769576B1 (en) High-strength galvanized steel sheet and its manufacturing method
CN112955575B (en) High-strength member, method for producing high-strength member, and method for producing steel sheet for high-strength member
JP2004027249A (en) High tensile hot rolled steel sheet and method of producing the same
JP5034364B2 (en) Manufacturing method of high-strength cold-rolled steel sheet
CN115461482A (en) Steel sheet, component and method for producing same
JP6119655B2 (en) High strength alloyed hot dip galvanized steel strip excellent in formability with small material variations in steel strip and method for producing the same
JP5310920B2 (en) High strength cold-rolled steel sheet with excellent aging resistance and seizure hardening
JP4367205B2 (en) Strain aging treatment method for steel sheet and method for producing high-strength structural member
JP4826694B2 (en) Method for improving fatigue resistance of thin steel sheet
JP5034296B2 (en) Hot-rolled steel sheet with excellent strain age hardening characteristics and method for producing the same
JP4556363B2 (en) High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof
JP4556362B2 (en) High-tensile cold-rolled steel sheet excellent in heat-treating ability and strength of deep drawing after forming and manufacturing method thereof
JP3925064B2 (en) Hot-dip galvanized steel sheet excellent in press formability and strain age hardening characteristics and method for producing the same
JP5151227B2 (en) High strength steel plate and manufacturing method thereof
CN113544301B (en) Steel plate
JP4385777B2 (en) Cold-rolled steel sheet with excellent strain age hardening characteristics and method for producing the same

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20080423

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20100624

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20100629

A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20100712

R150 Certificate of patent or registration of utility model

Free format text: JAPANESE INTERMEDIATE CODE: R150

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20130730

Year of fee payment: 3

LAPS Cancellation because of no payment of annual fees