JPH03253543A - Cold rolled steel sheet or galvanized steel sheet for deep drawing having excellent secondary processing brittleness resistance or baking hardenability - Google Patents
Cold rolled steel sheet or galvanized steel sheet for deep drawing having excellent secondary processing brittleness resistance or baking hardenabilityInfo
- Publication number
- JPH03253543A JPH03253543A JP2051273A JP5127390A JPH03253543A JP H03253543 A JPH03253543 A JP H03253543A JP 2051273 A JP2051273 A JP 2051273A JP 5127390 A JP5127390 A JP 5127390A JP H03253543 A JPH03253543 A JP H03253543A
- Authority
- JP
- Japan
- Prior art keywords
- steel sheet
- steel
- amount
- less
- rolled steel
- 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.)
- Granted
Links
- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 29
- 229910001335 Galvanized steel Inorganic materials 0.000 title description 2
- 239000008397 galvanized steel Substances 0.000 title description 2
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 78
- 239000010959 steel Substances 0.000 claims abstract description 78
- 239000007787 solid Substances 0.000 claims abstract description 42
- 239000002344 surface layer Substances 0.000 claims abstract description 20
- 230000007423 decrease Effects 0.000 claims abstract description 12
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 12
- 238000005246 galvanizing Methods 0.000 claims abstract description 6
- 238000005255 carburizing Methods 0.000 claims description 21
- 229910052757 nitrogen Inorganic materials 0.000 claims description 18
- 239000000203 mixture Substances 0.000 claims description 11
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 239000000126 substance Substances 0.000 abstract description 19
- 238000009826 distribution Methods 0.000 abstract description 13
- 239000000463 material Substances 0.000 abstract description 6
- 229910001209 Low-carbon steel Inorganic materials 0.000 abstract description 5
- 230000001105 regulatory effect Effects 0.000 abstract description 2
- 239000006104 solid solution Substances 0.000 description 27
- 238000000034 method Methods 0.000 description 23
- 229910052799 carbon Inorganic materials 0.000 description 19
- 238000000137 annealing Methods 0.000 description 18
- 230000000694 effects Effects 0.000 description 11
- 230000003679 aging effect Effects 0.000 description 9
- 238000004519 manufacturing process Methods 0.000 description 9
- 239000007789 gas Substances 0.000 description 7
- 238000001953 recrystallisation Methods 0.000 description 7
- 238000005097 cold rolling Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 6
- 230000032683 aging Effects 0.000 description 5
- 239000011261 inert gas Substances 0.000 description 5
- 230000035882 stress Effects 0.000 description 5
- 239000011701 zinc Substances 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 4
- 238000005098 hot rolling Methods 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- 238000007747 plating Methods 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- 238000005204 segregation Methods 0.000 description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 229910052725 zinc Inorganic materials 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 238000004804 winding Methods 0.000 description 2
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910017108 Fe—Fe Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 238000009966 trimming Methods 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Landscapes
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Coating With Molten Metal (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
Abstract
Description
（産業上の利用分野）
本発明は耐２次加工脆性又は焼付は硬化性に優れた深絞
り用冷延鋼板又は溶融亜鉛メッキ冷延鋼板に関する。
（従来の技術及び解決しようとする課題）近年、自動車
部材や電気機器外板に使用される冷延鋼板には高いプレ
ス成形性及び耐蝕性が要求されている。
このような要求を満たすことを意図した冷延鋼板の製造
方法としては、極低炭素鋼にＴｉ、Ｎｂなとの炭窒化物
形成元素を単独又は複合添加して鋼中のＣ，Ｎを固定す
ることにより深絞り性に有利な（１１１）面方位集合組
織を発達させ、更に亜鉛メッキを施す方法が提案されて
いる。
しかし、一方では、Ｔｉ、Ｎｂなどの炭窒化物形成元素
により鋼中のＣ，Ｎを充分固定した極低炭素鋼では、プ
レス成形後の２次加工において脆性破断による割れが発
生する問題がある。更に、Ｐ添加鋼では粒界にＰが偏析
し、粒界の脆化を助長するという問題がある。これは、
鋼中の固溶Ｃが固定され、フェライト粒界へのＣの偏析
がなくなり、粒界が脆化するためである。特に溶融亜鉛
メッキ鋼板では、この脆弱化した粒界に溶融亜鉛が侵入
し易く、更に脆化を助長する。
この粒界脆化を解決する手段として、従来、予め鋼中の
Ｃ，Ｎが残存するようにＴｉやＮｂの添加量を制御して
溶製することが試みられていた。しかし、この方法では
、例え固溶Ｃ，Ｎが残存する成分鋼が溶製できたとして
も、この固溶Ｃ，Ｎは本質的に鋼のｒ値や延性を劣化さ
せるものであるので、プレス成形性の大幅な低下を来た
さざるを得なかった。すなわち、本質的にプレス成形性
と耐２次加工脆性は両立し得ないものであった。また一
方、このような微量Ｃ，Ｎを溶製段階で残存させること
は、技術上成り立つものでなかった。
この点、従来より、以下のような提案がなされているが
、プレス成形性と耐２次加工脆性を共に優れたものとす
ることは困難である。
例えば、深絞り用鋼板の耐２次加工脆性を改善する目的
で、Ｔｉ、Ｎｂを添加して鋼中のＣを固定し、冷延後オ
ープンコイル焼鈍時に浸炭を行い、鋼板表面に浸炭層を
形成する方法（特開昭６３−３８５５６号）が提案され
ている。しかし、この方法の場合、長時間に及ぶバッチ
焼鈍の際に浸炭を実施するため、鋼板の表層部に高濃度
の浸炭層（浸炭層の平均Ｃ量：０．０２〜０．１０％）
が形成され、また表層部と中心層でフェライト粒度に差
が生じている。更に、こうしたバッチ焼鈍タイプでは当
然ながら生産性が低いと共に圧延方向、板幅方向の材質
が不均一になり易い不利を生じる。
また、化成処理性を改善する目的で極く表面層にのみ極
めて微量の固溶Ｃ，Ｎを与える方法（特公平１−４２３
３１号）が提案されているが、耐２次加工脆性を考慮し
たものでなく、したがって。
この方法では耐２次加工脆性を改善するに必要な浸炭を
行なうことは不可能である。
また、同様に、Ｔｉ、Ｎｂを添加して深絞り用鋼板を製
造する方法として、冷延後再結晶焼鈍を行った後、更に
浸炭処理を施す方法（特開平１−９６３３０号）もある
が、主に多量の炭化物、窒化物の析出による強度の上昇
を狙ったものであって。
耐２次加工脆性に対する配慮がなく、また焼鈍後にバッ
チにて長時間浸炭、浸炭処理を行なうため、浸炭量、浸
窒量が過剰且つ不均一となり易く、しかも生産性が低く
、工程も煩雑になるという欠点がある。
また、上述の耐２次加工脆性の改善の問題のほか、最近
では、耐テント性を向上させるために、塗装焼付は後に
鋼板の降伏応力が上昇する特性、いわゆる焼付は硬化性
の要求が高まっている。
この要求に対して、Ｃに対するＴｉ添加量を少な目にし
て固溶Ｃを残存させる方法（特公昭６１−２７３２号）
が提案されている。しかし、この方法では、例え固溶Ｃ
，Ｎを残存する成分鋼が溶製できたとしても、この固溶
Ｃ，Ｎは本質的に鋼のｒ値を劣化させるものであるので
、プレス成形性の大幅な低下を来たさざるを得なかった
。すなわち、本質的にプレス成形性と焼付は硬化性は両
立し得ないものであった。
また、前述の焼鈍過程での浸炭処理を利用した方法（特
開昭６３−３８５５６号）や、化成処理性を改善する方
法（特公平１−４２３３１号）方法は。
いずれも焼付は硬化性を考慮したものではなく、焼付は
硬化性の向上は不可能である。
更にまた、前述の如く、Ｔｉ、Ｎｂなどの炭窒化物形成
元素により鋼中のＣ，Ｎを充分固定した極低炭素鋼では
、焼付は硬化性を得ることはできない。
また、固溶Ｃを残存させる方法は、目標値より多すぎる
と常温時効を劣化させ、少なすぎると焼付は硬化性を確
保できない。製鋼工程において最適量のＣの残存を制御
することは極めて困難である。
本発明は、上記従来技術の問題点を解決するためになさ
れたものであって、極低炭素Ｔ１又はＮｂ添加鋼を用い
て、深絞り性と耐２次加工脆性又は焼付は硬化性が共に
優れた冷延鋼板又は溶融亜鉛メッキ冷延鋼板を生産性よ
く製造する方法を提供することを目的とするものである
。
（課題を解決するための手段）
本発明者は、前記課題を解決するため、化学成分、並び
に固溶Ｃの量及び分布状況などについて鋭意研究を重ね
た結果、ここに本発明をなしたものである。
すなわち、本発明は、Ｃ：０．０１％以下、Ｓｉ：０．
２％以下、Ｍｎ：０．０５〜１．０％、Ｐ：０．１０％
以下、Ｓ：０．０２％以下、ｓｏｌ、Ａｌ１：０．０１
〜０．０８％及びＮ：Ｏ，００５％以下を含有し、更に
Ｔｉ及びＮｂの１種又は２種を、次式（１）で定義され
る有効Ｔｉ量（以下、Ｔｉ本という）及びＮｂ量とＣ量
との関係が次式（２）を満足する範囲で含有し、
Ｔｉ＊＝ｔｏｔ、ａ Ｑ Ｔｉ −（（４８／３２）
Ｘ Ｓ ＋ （４８／１４） Ｘ Ｎ）・・・（１）
１ ≦（Ｔｉ本／４８＋Ｎｂ／９３）／（Ｃ／１２）≦
４．５・・・（２）必要に応じて更にＢ：Ｏ，００３％
以下を含有し、残部がＦｅ及び不可避的不純物よりなる
組成を有する鋼であって、浸炭処理により表面から中心
部にかけて板厚方向に固溶Ｃ量が低下するような濃度勾
配を有し、表層１／１０の板厚比の部分の固溶Ｃ濃度の
最大量を１５ｐｐｍとし、鋼板全体の固溶Ｃ量を２〜１
０ｐｐ−とすることを特徴とする耐２次加工脆性に優れ
た深絞り用冷延鋼板又は溶融亜鉛メッキ冷延鋼板を要旨
とするものである。
また、他の本発明は、前記組成を有する鋼であって、浸
炭処理により表面から中心部にかけて板厚方向に固溶Ｃ
量が低下するような濃度勾配を有し、表層１／１０の板
厚比の部分の固溶Ｃ濃度の最大量を６０ｐｐｍとして、
鋼板全体の固溶Ｃ量を５〜３０ρρ−とすることを特徴
とする焼付は硬化性に優れた深絞り用冷延鋼板又は溶融
亜鉛メッキ冷延鋼板を要旨とするものである。
以下に本発明を更に詳細に説明する。
（作用）
まず、本発明における鋼の化学成分限定理由について説
明する。
Ｃ：
Ｃは、その含有量が増大するにつれてＣを固定するＴｉ
、Ｎｂの添加量が増加し、製造費用の増加につながり、
更にＴｉＣ及びＮｂＣ析出量が増大し、粒成長を阻害し
てｒ値を劣化させるので、０．０工％以下とする必要が
ある。なお、下限値は特に制限しないが、製鋼技術上の
観点から製鋼段階におけるＣ含有量の下限値０．０００
３％とするのが実際的である。したがって、Ｃ含有量は
０．０１％以下とし、０．０００３〜０．０１％が望ま
しい。
更には、後述するように、優れた耐２次加工脆性を得る
ためには、表面から中心部にかけて板厚方向に固溶Ｃ量
が低下するような濃度勾配を有し、表層ｌ／１０の板厚
比の部分の固溶Ｃ濃度の最大量を１５Ｐｐ■とし、鋼板
全体の固溶Ｃ量を２〜１０ ｐｐｍとする必要がある。
但し、優れた焼付は硬化性を得るためには、上記濃度勾
配を有すると共に、表層１／１０の板厚比の部分の固溶
Ｃ濃度の最大量は６０ｐｐ＋ｉまで許容でき、鋼板全体
の固溶Ｃ量を５〜３０ｐｐｍとする。なお、このような
固溶Ｃの存在状態を与えるための手段は問わないが、メ
ッキ処理前の焼鈍過程においてＣポテンシャルを有する
雰囲気から与えることが生産性の観点から好ましい。
Ｓｉ：
Ｓｉは溶鋼の脱酸を主目的に添加されるが、添加量方多
すぎると表面性状や亜鉛密着性、化成処理或いは塗装性
を劣化させるので、その含有量は０．２％以下とする。
Ｍｎ：
Ｍｎは熱間脆性の防止を主目的に添加されるが、０．０
５％より少ないとその効果が得られず、添加量が多すぎ
ると延性を劣化させるので、その含有量は０．０５〜１
．０％の範囲とする。
Ｐ：
Ｐはｒ値の低下を伴うことなく調速度を高める効果を有
するが１粒界に偏析し、２次加工脆性を起こし易くする
ので、その含有量は０．１０％以下に抑制する。
Ｓ：
ＳはＴ１と結合してＴｉＳを形成するので、その含有量
が増大するとＣ，Ｎを固定するのに必要なＴｉ量が増大
し、またＭｎＳ系伸長した介在物が増加して局部延性を
劣化させるので、その含有量は０．０２％以下に抑制す
る。
ｓｏｌ．Ａｌ：
ＡＱは溶鋼の脱酸を目的に添加されるが、その含有量が
ｓｏｌ、Ａｆｌで０．０１％より少ないと、その目的が
遠戚されず、一方、０．０８％を超えると脱酸効果は飽
和すると共にＡＱ２０３介在物が増加して加工成形性を
劣化させる。したがって、その含有量は、ｓｏｌ．Ａｌ
で０．０１〜０．０８％の範囲とする。
Ｎ：
ＮはＴｉと結合してＴｉＮを形成するので、その含有量
が増大するとＣを固定するのに必要なＴｉ量が増大する
。またＴｉＮ析出量が増加して粒成長が阻害され、ｒ値
が劣化する。したがって、その含有量は、少ないほど好
ましく、０．００５％以下に抑制する。
Ｔｉ、 Ｎｂ：
Ｔｉ、ＮｂはＣ，Ｎを固定することによってｒ値を高め
る作用がある。よって１本発明の目的に対してはＴｉ本
量、Ｎｂ量とＣ量との関係が次式（２）％式％（２）
を満足する範囲で含有させる必要がある。なお、Ｔｉは
前述の如＜Ｓ、Ｎと結合してＴｉＳ、ＴｉＮを形成する
ので、次式（１）に従い有効Ｔｉ量（Ｔｉ本量）に換算
する。
’ｒｉｍ＝ｔｏｔａＱ ’ｒｉ−（（４８／３２）Ｘ
Ｓ ＋（４８／１４）Ｘ Ｎ）・・・（１）
（２）式の値が１より小さいとＣ，Ｎを充分に固定する
ことができずにｒ値を劣化させる。また４゜５を超える
とｒ値を高める作用が飽和すると共に、固溶Ｔｉ、Ｎｂ
が後工程での雰囲気焼鈍時に侵入したＣをすぐに固定し
てしまい、Ｃの粒界偏析及び固溶Ｃとしての存在を阻止
するので好ましくない。
Ｂ：
Ｂは耐２次加工脆性に対して有効な元素であり、必要に
応じて添加することができる。焼付は硬化性の向上を意
図する場合にも耐２次加工脆性を補充するために添加し
てもよい。しかし、０．００３％を超えるとその効果は
飽和し、ｒ値を低下させるので、経済性をも考慮し、そ
の含有量は０゜００３％以下とする。なお、Ｏ，０ＯＯ
１％以下では上記効果が少ないので、０．０００１〜０
．０Ｏ３％の範囲が望ましい。
次に、本発明に係る鋼板の製造方法は、特に制限される
ものではないが、以下にその一例について説明する。
上記成分組成の鋼について、通常の製造工程、すなわち
、１０００〜１２５０℃に加熱した後、オーステナイト
域で熱間圧延を行う。熱間圧延後の巻取温度は鋼中の固
溶Ｃ，Ｎを炭窒化物として固定するために５００〜８０
０℃の範囲で行うことが好ましい。
冷間圧延においては、ｒ値に有利な（１１１）面方位集
合組織を発達させるために、６０〜９０％のトータル圧
延率で行うことが好ましい。この冷間圧延後、浸炭雰囲
気ガス中で再結晶温度以上の範囲で連続焼鈍を行い、ｒ
値に有利な（１１１）面方位集合組織を形成させる。
既に知られているように、ｒ値は主として鋼の（１１１
）面方位集合組織に依存しており、再結晶焼鈍前に巻取
処理によって固溶Ｃ及び固溶Ｎを完全に除くのは、上記
の集合組織を得るためである。
しかし、−旦、再結晶が完了し集合組織が形成されれば
、その後に侵入するＣやＮはｒ値には悪影響を与えない
。焼鈍雰囲気はカーボンポテンシャルを制御した浸炭ガ
スとする。これにより、浸炭雰囲気中より侵入したＣの
うち、ＴｉＣ，ＮｂＣとして固定されなかったＣが粒界
に偏析して耐２次加工脆性を改善し、所定量の固溶Ｃは
耐２次加工脆性や焼付は硬化性を改善する。
本発明では過時効処理を必要としないが、メッキ浴近傍
温度で過時効処理を行なってもよい。亜鉛メッキ冷延鋼
板を得る場合には、引き続いて溶融亜鉛メッキ浴に侵入
させ、メッキを行う。更に必要に応じて合金化処理を行
ってもよい。
勿論、焼鈍原板の製造方法として、フェライト域熱延、
ホットチャージローリング、薄スラブを用いての製造な
ど、如何なる手段を用いても良いことは云うまでもない
。
次に、固溶Ｃ量のコントロールと、耐２次加工脆性或い
は焼付は硬化性の関係について、以下に説明する。
２次加工脆性は、極低炭素Ｔｉ添加鋼等においては、粒
界の純度が向上し、粒界におけるＦｅ−Ｆｅ結合力が低
下することにより生ずる。更に溶融亜鉛メッキ処理にお
いてＺｎが粒界に拡散浸透し、更にＦｅ−Ｆｅ結合力を
低下する。したがって耐２次加工脆性を改善するために
は両者の要因を防止できれば達成される。前者の対策は
、Ｃを粒界に偏析させることであり、後者の対策は、同
様にＣを粒界に偏析させることで達成される。特に後者
についてＺｎの浸透深さが結晶粒数個分、すなわち５０
μ■程度であることから、その程度の板厚分だけ集中的
に浸炭させることが効果的である。よって、表面から中
心部にかけて板厚方向に固溶Ｃ量が低下するような濃度
勾配を有し、表層１／１０の板厚比の部分の固溶Ｃ濃度
の最大量を１５ｐｐ園とすることが最も優れた耐２次脆
性を発揮することとなる。また、深絞り成形後の脆性破
壊は表層部を起点することから１表層部の粒界強度が固
溶Ｃの粒界偏析により強化されておれば。
板厚中心部での粒界偏析Ｃが少なくとも、或いは０であ
っても、その顕著な効果が得られることも確認した。な
お、表層部の固溶Ｃ量が１５ｐｐｍを超えると、鋼板全
体の平均固溶Ｃ量が１０ｐｐｍを超えてしまい、その場
合には時効による材質劣化、強度の上昇、延性の低下等
の問題が生ずるため、好ましくない。鋼板全体の平均固
溶Ｃ量が２ ｐｐｍ未満では、固溶Ｃが不足し、耐２次
加工脆性を得ることができない。
一方、焼付は硬化性は、通常、極低炭素Ｔｉ添加鋼等に
おいては固溶Ｃが残存しないため、付与することは不可
能であるが、再結晶が完了し集合組織が形成された後で
固溶Ｃの導入が図れるならば、高いｒ値を維持しつつ焼
付は硬化性を付与させることができる。更に表面から中
心部にかけて板厚方向に固溶Ｃ量が低下するような濃度
勾配を有し、表層１／１０の板厚比の部分の固溶Ｃ濃度
の最大量を６０ｐｐｍとすることにより、表層部の硬化
が最も促進され、疲労強度の向上、石などの衝突による
表面損傷の防止、耐プントレジスタンス性の向上など、
自動車外板に求められる特性にとって優れた効果を発揮
することになる。表層部の固溶Ｃ量が６０ｐｐ−を超え
ると、鋼板全体の固溶Ｃ量を３０ｐｐｍ＋以下とするこ
とが不可能となり、その場合には時効による材質劣化の
問題が生ずるため好ましくない。鋼板全体の固溶Ｃ量が
５ ｐｐｍ未満では、固溶Ｃが不足し、焼付は硬化性を
付与することができない。
（実施例）
次に本発明の実施例を示す。
失嵐負上
第１表に示す化学成分を有する極低炭素鋼を１１５０℃
で３０分間加熱して溶体化処理を行った後、仕上温度８
９０℃で熱間圧延を終了し、その後６７０℃で巻取処理
を行い、酸洗後、圧下率７５％で冷間圧延を行い、浸炭
雰囲気又は不活性ガス中において連続焼鈍により７８０
℃で４０秒の再結晶焼鈍を行った。なお、浸炭ガスは０
．２〜０．８％ＣＯ＋４％Ｈ２＋Ｎ、を用い、不活性ガ
スは４％Ｈ，＋ Ｎ、を用いた。
その後、４５０℃で溶融亜鉛メッキ処理を行い、０ 、
８ ％のスキンパスを施した。
得られた溶融亜鉛メッキ冷延鋼板の機械的性質と固溶Ｃ
量（全板厚方向平均値）及び２次加工脆性限界温度を第
２表に示す。
なお、脆性試験は、総絞り比２．７でカップ成形して得
られたカップを３５■■高さにトリムした後、各試験温
度の冷媒中にカップを置いて、頂角４０″′の円錐ポン
チに押し込んで脆性破壌の発生しない限界温度を測定し
、これを２次加工脆性限界温度とした。
第２表より明らかなように、本発明鋼は、従来鋼に比べ
、探絞り用溶融亜鉛メッキ冷延鋼板としての要求を損ね
ることなく、耐２次加工脆性が改善されている。
因みに、本発明鋼恥３について、固溶Ｃ量の板厚方向の
分布を調べた結果、第１図に示すように浸炭処理した場
合に表面から中心部にかけて板厚方向に固溶Ｃ量が低下
する濃度分布を示していた。
しかも、ガスＢによる浸炭処理の場合１表層１／１０の
板厚比の部分の固溶Ｃ濃度が１５ｐｐ−以下であり、第
２図に示すように耐２次加工脆性及びｒ値が共に改善さ
れていることが確認された。
一方、第２表に示すように、本発明範囲の化学成分を有
していない比較鋼や、本発明範囲内の化学成分を有して
いても固溶Ｃ量に関する条件が本発明範囲外の比較鋼は
、ｒ値又は耐２次加工脆性のいずれかが劣っている。(Industrial Application Field) The present invention relates to a cold-rolled steel sheet for deep drawing or a hot-dip galvanized cold-rolled steel sheet that has excellent resistance to secondary processing brittleness or seizure hardening. (Prior Art and Problems to be Solved) In recent years, high press formability and corrosion resistance have been required of cold-rolled steel sheets used for automobile parts and outer panels of electrical equipment. A manufacturing method for cold-rolled steel sheets intended to meet these requirements involves adding carbonitride-forming elements such as Ti and Nb, either singly or in combination, to ultra-low carbon steel to fix C and N in the steel. A method has been proposed in which a (111) plane orientation texture, which is advantageous for deep drawability, is developed by applying zinc plating. However, on the other hand, ultra-low carbon steels in which C and N in the steel are sufficiently fixed by carbonitride-forming elements such as Ti and Nb have the problem of cracking due to brittle fracture during secondary processing after press forming. . Furthermore, P-added steel has the problem that P segregates at grain boundaries, promoting embrittlement of the grain boundaries. this is,
This is because the solid solution C in the steel is fixed, the segregation of C to the ferrite grain boundaries disappears, and the grain boundaries become brittle. Particularly in hot-dip galvanized steel sheets, molten zinc tends to penetrate into these weakened grain boundaries, further promoting embrittlement. As a means of solving this grain boundary embrittlement, conventional attempts have been made to control the amounts of Ti and Nb added so that C and N remain in the steel. However, with this method, even if a component steel in which solid solute C and N remain can be produced, since the solid solute C and N essentially deteriorate the r value and ductility of the steel, it is difficult to press the steel. This inevitably resulted in a significant decrease in moldability. In other words, press formability and resistance to secondary work brittleness were essentially incompatible. On the other hand, it has not been technically viable to allow such trace amounts of C and N to remain during the melting process. In this regard, the following proposals have been made in the past, but it is difficult to achieve both excellent press formability and resistance to secondary work brittleness. For example, in order to improve the secondary work brittleness resistance of a steel plate for deep drawing, Ti and Nb are added to fix C in the steel, and carburization is performed during open coil annealing after cold rolling to form a carburized layer on the surface of the steel plate. A method of forming such a material (Japanese Patent Laid-Open No. 63-38556) has been proposed. However, in the case of this method, since carburization is performed during batch annealing over a long period of time, a high concentration of carburized layer is formed on the surface layer of the steel sheet (average C content of carburized layer: 0.02 to 0.10%).
is formed, and there is a difference in ferrite grain size between the surface layer and the center layer. Furthermore, such a batch annealing type naturally has the disadvantage that productivity is low and the material quality tends to be non-uniform in the rolling direction and the sheet width direction. In addition, for the purpose of improving chemical conversion treatment properties, a method of applying extremely small amounts of solid solution C and N only to the surface layer (Japanese Patent Publication No. 1-423
No. 31) has been proposed, but it does not take into account secondary processing brittleness. With this method, it is impossible to perform the carburization necessary to improve the secondary work brittleness resistance. Similarly, as a method for manufacturing deep-drawing steel sheets by adding Ti and Nb, there is a method in which cold rolling is followed by recrystallization annealing, followed by further carburizing treatment (Japanese Unexamined Patent Publication No. 1-96330). , which mainly aims at increasing the strength by precipitating a large amount of carbides and nitrides. There is no consideration for secondary processing brittleness, and since carburizing and carburizing are performed in batches for a long time after annealing, the amount of carburizing and nitriding tends to be excessive and uneven, and productivity is low and the process is complicated. It has the disadvantage of becoming. In addition to the problem of improving secondary work brittleness mentioned above, recently, in order to improve tent resistance, there has been an increase in the demand for paint baking, which has the property of increasing the yield stress of the steel plate, and so-called baking hardenability. ing. In response to this requirement, a method of reducing the amount of Ti added to C to leave solid solution C (Japanese Patent Publication No. 61-2732)
is proposed. However, in this method, even solid solution C
Even if a steel containing residual C and N can be produced, the solid solution C and N essentially deteriorate the r-value of the steel, so there is no choice but to significantly reduce the press formability. I didn't get it. In other words, press formability, baking properties, and hardenability are essentially incompatible. Further, there is a method using carburizing treatment in the annealing process mentioned above (Japanese Patent Application Laid-Open No. 63-38556), and a method of improving chemical conversion properties (Japanese Patent Publication No. 1-42331). In either case, baking does not take hardenability into consideration, and it is impossible to improve hardenability with baking. Furthermore, as mentioned above, in ultra-low carbon steel in which C and N in the steel are sufficiently fixed by carbonitride-forming elements such as Ti and Nb, hardenability cannot be obtained by baking. In addition, in the method of leaving solid solution C, if the amount is too much than the target value, room temperature aging will be deteriorated, and if it is too little, hardenability cannot be ensured by baking. It is extremely difficult to control the optimum amount of C remaining in the steelmaking process. The present invention has been made to solve the problems of the prior art described above, and uses ultra-low carbon T1 or Nb-added steel to improve deep drawability, secondary work embrittlement resistance, and hardenability. The object of the present invention is to provide a method for manufacturing excellent cold-rolled steel sheets or hot-dip galvanized cold-rolled steel sheets with good productivity. (Means for Solving the Problems) In order to solve the above problems, the present inventor has hereby accomplished the present invention as a result of extensive research into chemical components, the amount and distribution of solid solution C, etc. It is. That is, in the present invention, C: 0.01% or less, Si: 0.
2% or less, Mn: 0.05-1.0%, P: 0.10%
Below, S: 0.02% or less, sol, Al1: 0.01
~0.08% and N:O, 0.05% or less, and further contains one or two of Ti and Nb, and an effective Ti amount (hereinafter referred to as Ti book) defined by the following formula (1) and Nb Ti*=tot, a Q Ti −((48/32)
X S + (48/14)
4.5...(2) Further B:O,003% if necessary
Steel containing the following, with the balance consisting of Fe and unavoidable impurities, and has a concentration gradient such that the amount of solid solute C decreases in the thickness direction from the surface to the center due to carburizing treatment, and the surface layer The maximum amount of solid solute C concentration in the part with a plate thickness ratio of 1/10 is 15 ppm, and the amount of solid solute C in the entire steel plate is 2 to 1.
The gist of the present invention is to provide a cold-rolled steel sheet for deep drawing or a hot-dip galvanized cold-rolled steel sheet with excellent resistance to secondary work brittleness, which is characterized by a 0 pp-. Another aspect of the present invention is a steel having the above-mentioned composition, wherein solid solution C is produced in the thickness direction from the surface to the center by carburizing treatment.
It has a concentration gradient such that the amount decreases, and the maximum amount of solid solution C concentration in the part with a plate thickness ratio of 1/10 of the surface layer is 60 ppm,
Baking, which is characterized by setting the amount of solid solute C in the entire steel sheet to 5 to 30 ρρ-, is aimed at producing cold-rolled steel sheets for deep drawing or hot-dip galvanized cold-rolled steel sheets with excellent hardenability. The present invention will be explained in more detail below. (Function) First, the reason for limiting the chemical composition of steel in the present invention will be explained. C: C is Ti that fixes C as its content increases
, the amount of Nb added increases, leading to an increase in manufacturing costs,
Furthermore, the amount of TiC and NbC precipitated increases, inhibiting grain growth and deteriorating the r value, so it is necessary to keep it at 0.0% or less. Note that the lower limit value is not particularly limited, but from the viewpoint of steel manufacturing technology, the lower limit value of C content at the steel manufacturing stage is 0.000.
It is practical to set it at 3%. Therefore, the C content should be 0.01% or less, preferably 0.0003 to 0.01%. Furthermore, as will be described later, in order to obtain excellent secondary work brittleness resistance, it is necessary to have a concentration gradient such that the amount of solid solute C decreases in the thickness direction from the surface to the center, and to It is necessary to set the maximum amount of solid solute C concentration in the plate thickness ratio portion to 15 Pp■, and to set the solid solute C amount in the entire steel plate to 2 to 10 ppm. However, in order to obtain good hardenability, it is necessary to have the above-mentioned concentration gradient, and the maximum solid solution C concentration in the surface layer with a plate thickness ratio of 1/10 is allowed to be up to 60 pp+i, and the solid solution C concentration in the entire steel plate must be maintained. The amount of C is set to 5 to 30 ppm. Although any means for providing such a state of solid solution C exists, it is preferable from the viewpoint of productivity to provide it from an atmosphere having C potential in the annealing process before plating. Si: Si is added mainly for the purpose of deoxidizing molten steel, but if it is added in too much, it will deteriorate the surface quality, zinc adhesion, chemical conversion treatment, or paintability, so its content should be 0.2% or less. do. Mn: Mn is added mainly to prevent hot embrittlement, but 0.0
If it is less than 5%, the effect cannot be obtained, and if it is added too much, the ductility deteriorates, so the content should be 0.05 to 1.
．． The range is 0%. P: Although P has the effect of increasing control speed without reducing the r value, it segregates at one grain boundary and tends to cause secondary work embrittlement, so its content is suppressed to 0.10% or less. S: S combines with T1 to form TiS, so when its content increases, the amount of Ti required to fix C and N increases, and the number of MnS-based elongated inclusions increases, resulting in local ductility. The content is suppressed to 0.02% or less. sol. Al: AQ is added for the purpose of deoxidizing molten steel, but if its content is less than 0.01% in sol and Afl, this purpose will not be achieved, whereas if it exceeds 0.08%, it will not be able to deoxidize. As the acid effect becomes saturated, AQ203 inclusions increase and the processability deteriorates. Therefore, its content is sol. Al
The range is 0.01 to 0.08%. N: Since N combines with Ti to form TiN, as its content increases, the amount of Ti required to fix C increases. Furthermore, the amount of TiN precipitated increases, grain growth is inhibited, and the r value deteriorates. Therefore, the content is preferably as low as possible, and is suppressed to 0.005% or less. Ti, Nb: Ti and Nb have the effect of increasing the r value by fixing C and N. Therefore, for the purpose of the present invention, it is necessary to contain Ti within a range where the relationship between the amount of Ti, the amount of Nb, and the amount of C satisfies the following formula (2). Incidentally, since Ti combines with S and N to form TiS and TiN as described above, it is converted into an effective Ti amount (Ti amount) according to the following equation (1). 'rim=totaQ'ri-((48/32)X
S + (48/14)X N) (1) If the value of equation (2) is smaller than 1, C and N cannot be fixed sufficiently, resulting in a deterioration of the r value. Moreover, when the temperature exceeds 4°5, the effect of increasing the r value is saturated, and the solid solution Ti, Nb
This is not preferable because it immediately fixes the C that has entered during the atmosphere annealing in the subsequent process, which prevents the segregation of C at grain boundaries and the presence of solid solute C. B: B is an element effective in improving resistance to secondary work brittleness, and can be added as necessary. Baking may be added to supplement secondary processing brittleness even when the intention is to improve hardenability. However, if it exceeds 0.003%, the effect will be saturated and the r value will decrease, so taking economic efficiency into consideration, the content should be 0°003% or less. In addition, O, 0OO
If it is less than 1%, the above effect will be small, so 0.0001 to 0.
．． A range of 0O3% is desirable. Next, although the method for manufacturing a steel plate according to the present invention is not particularly limited, an example thereof will be described below. Steel having the above-mentioned composition is subjected to a normal manufacturing process, that is, after being heated to 1000 to 1250°C, hot rolling is performed in the austenite region. The coiling temperature after hot rolling is 500-800℃ to fix solid solution C and N in the steel as carbonitrides.
Preferably, the temperature is 0°C. Cold rolling is preferably performed at a total rolling rate of 60 to 90% in order to develop a (111) plane orientation texture that is advantageous for the r value. After this cold rolling, continuous annealing is performed in a carburizing atmosphere gas at a temperature above the recrystallization temperature, and r
A (111) plane orientation texture with favorable values is formed. As is already known, the r value is mainly determined by the (111
) It depends on the surface orientation texture, and the purpose of completely removing solid solution C and solid solution N by winding treatment before recrystallization annealing is to obtain the above texture. However, once recrystallization is completed and a texture is formed, C and N that invade afterwards do not have an adverse effect on the r value. The annealing atmosphere is carburizing gas with controlled carbon potential. As a result, among the C that penetrated from the carburizing atmosphere, the C that was not fixed as TiC and NbC segregates at the grain boundaries and improves secondary work brittleness, and a predetermined amount of solid solution C improves secondary work brittleness. Baking improves hardenability. Although the present invention does not require overaging treatment, overaging treatment may be performed at a temperature near the plating bath. When obtaining a galvanized cold-rolled steel sheet, the steel sheet is subsequently introduced into a hot-dip galvanizing bath and plated. Furthermore, alloying treatment may be performed as necessary. Of course, the methods for producing annealed original sheets include ferrite region hot rolling,
Needless to say, any method such as hot charge rolling or production using a thin slab may be used. Next, the relationship between control of the amount of solid solute C and secondary processing brittleness or seizure hardenability will be explained below. Secondary work embrittlement occurs in ultra-low carbon Ti-added steel and the like because the purity of the grain boundaries improves and the Fe-Fe bonding strength at the grain boundaries decreases. Furthermore, during the hot-dip galvanizing process, Zn diffuses into the grain boundaries and further reduces the Fe--Fe bonding strength. Therefore, improvement in secondary work brittleness can be achieved if both factors can be prevented. The former measure is achieved by segregating C at the grain boundaries, and the latter measure is achieved by similarly segregating C at the grain boundaries. Especially for the latter, the penetration depth of Zn is several grains, that is, 50
Since the thickness is approximately μ■, it is effective to intensively carburize the plate thickness to that extent. Therefore, there should be a concentration gradient such that the amount of solid solute C decreases in the thickness direction from the surface to the center, and the maximum amount of solid solute C concentration in the part where the thickness ratio of the surface layer is 1/10 should be 15pp. exhibits the best secondary embrittlement resistance. Furthermore, since brittle fracture after deep drawing starts from the surface layer, the grain boundary strength of the first surface layer should be strengthened by grain boundary segregation of solid solution C. It was also confirmed that significant effects can be obtained even when the grain boundary segregation C at the center of the plate thickness is at least or zero. In addition, if the amount of solid solute C in the surface layer exceeds 15 ppm, the average amount of solid solute C in the entire steel sheet will exceed 10 ppm, and in this case, problems such as material deterioration due to aging, increase in strength, and decrease in ductility occur. This is not desirable because it occurs. If the average amount of solid solute C in the entire steel sheet is less than 2 ppm, there will be insufficient solid solute C, and secondary work brittleness resistance cannot be obtained. On the other hand, hardening by baking is usually impossible in ultra-low carbon Ti-added steel because no solid solution C remains, but after recrystallization is completed and a texture is formed, If solid solution C can be introduced, baking can impart hardenability while maintaining a high r value. Furthermore, by having a concentration gradient such that the amount of solid solute C decreases in the thickness direction from the surface to the center, and by setting the maximum amount of solute C concentration in the portion where the thickness ratio of the surface layer is 1/10 to 60 ppm, Hardening of the surface layer is accelerated the most, improving fatigue strength, preventing surface damage caused by collisions with stones, etc., and improving punto resistance.
This results in excellent effects on the properties required for automobile exterior panels. If the amount of solid solute C in the surface layer portion exceeds 60 pp-, it becomes impossible to reduce the amount of solid solute C in the entire steel sheet to 30 ppm+ or less, and in this case, the problem of material deterioration due to aging occurs, which is not preferable. If the amount of solid solute C in the entire steel sheet is less than 5 ppm, the solid solute C is insufficient and baking cannot impart hardenability. (Example) Next, an example of the present invention will be shown. Ultra-low carbon steel having the chemical composition shown in Table 1 was heated to 1150℃.
After solution treatment by heating for 30 minutes at a finishing temperature of 8.
Hot rolling was completed at 90°C, followed by winding at 670°C, pickling, cold rolling at a rolling reduction of 75%, and continuous annealing in a carburizing atmosphere or inert gas to 780°C.
Recrystallization annealing was performed at ℃ for 40 seconds. In addition, carburizing gas is 0
．． 2 to 0.8% CO + 4% H + N was used, and 4% H, + N was used as the inert gas. After that, hot-dip galvanizing treatment was performed at 450℃, and
A skin pass of 8% was applied. Mechanical properties and solid solution C of the obtained hot-dip galvanized cold-rolled steel sheet
Table 2 shows the amount (average value in the entire plate thickness direction) and secondary processing brittleness limit temperature. In addition, the brittleness test was performed by trimming the cup obtained by molding the cup at a total drawing ratio of 2.7 to a height of 35mm, and then placing the cup in a refrigerant at each test temperature. The limit temperature at which brittle fracture does not occur was measured by pressing the steel into a conical punch, and this was taken as the brittle limit temperature for secondary processing. The resistance to secondary work brittleness is improved without compromising the requirements for a hot-dip galvanized cold-rolled steel sheet.Incidentally, as a result of investigating the distribution of the amount of solid solute C in the thickness direction of the steel of the present invention 3, it was found that As shown in Figure 1, when carburized, the concentration distribution showed that the amount of solid solute C decreased in the thickness direction from the surface to the center.Moreover, in the case of carburizing with gas B, 1/10 of the surface layer of the plate It was confirmed that the solid solution C concentration in the thickness ratio part was 15 pp- or less, and as shown in Figure 2, the secondary work brittleness resistance and r value were both improved.On the other hand, as shown in Table 2 As such, comparative steels that do not have chemical components within the scope of the present invention, and comparative steels that have chemical components within the scope of the present invention but whose conditions regarding the amount of solid solute C are outside the scope of the present invention, have an r value or Poor secondary processing brittleness.
矢１０生え
第１表に示す化学成分を有する供試鋼について。
実施例１において、浸炭雰囲気又は不活性ガス中での連
続焼鈍による再結晶焼鈍を行った後、０゜８％のスキン
パスを施して冷延鋼板を得た。他の条件は実施例１と同
じである。
得られた冷延鋼板の機械的性質と固溶Ｃ量（全板厚方向
平均値）及び２次加工脆性限界温度を第３表に示す。
第３表より明らかなように、本発明鋼は、従来鋼に比べ
、深絞り用冷延鋼板としての要求を損ねることなく、耐
２次加工脆性が改善されている。
因みに、第３表中の本発明鋼血３について、固溶Ｃ量の
板厚方向の分布を調べた結果、第３図に示すように浸炭
処理した場合に表面から中心部にかけて板厚方向に固溶
Ｃ量が低下する濃度分布を示していた。しかも、ガスＢ
による浸炭処理の場合１表層１／１０の板厚比の部分の
固溶Ｃ濃度が１５ｐρ■以下であり、第４図に示すよう
に耐２次加工脆性及びｒ値が共に改善されていることが
確認された。
一方、第３表に示すように、本発明範囲の化学成分を有
していない比較鋼や、本発明範囲内の化学成分を有して
いても固溶Ｃ量に関する条件が本発明範囲外の比較鋼は
、ｒ値又は耐２次加工脆性のいずれかが劣っている。Regarding the test steel having the chemical composition shown in Table 1. In Example 1, after performing recrystallization annealing by continuous annealing in a carburizing atmosphere or inert gas, a 0°8% skin pass was applied to obtain a cold rolled steel sheet. Other conditions are the same as in Example 1. Table 3 shows the mechanical properties, solute C content (average value in the entire sheet thickness direction), and secondary processing brittleness limit temperature of the obtained cold rolled steel sheet. As is clear from Table 3, the steel of the present invention has improved resistance to secondary work brittleness compared to the conventional steel without impairing the requirements as a cold-rolled steel plate for deep drawing. Incidentally, as a result of investigating the distribution of the amount of solid solute C in the thickness direction of the steel plate 3 of the present invention shown in Table 3, it was found that when carburized, as shown in Figure 3, the distribution in the thickness direction from the surface to the center It showed a concentration distribution in which the amount of solid solute C decreased. Moreover, gas B
In the case of carburizing treatment, the solid solution C concentration in the surface layer with a plate thickness ratio of 1/10 is 15 pρ or less, and as shown in Figure 4, both the secondary work brittleness resistance and the r value are improved. was confirmed. On the other hand, as shown in Table 3, there are comparison steels that do not have chemical components within the scope of the present invention, and conditions regarding the amount of solid solute C that are outside the scope of the present invention even though they have chemical components within the scope of the present invention. Comparative steels are inferior in either r value or secondary work brittleness resistance.
去１１４工
第１表に示す化学成分を有する供試鋼について、実施例
１において、冷間圧延後、浸炭雰囲気又は不活性ガス中
においてメッキ処理前の焼鈍工程で８００℃で１分間の
再結晶焼鈍を行い、その後、４５０℃で溶融亜鉛メッキ
処理を行い、０．８％のスキンパスを施した。
得られた溶融亜鉛メッキ冷延鋼板の機械的性質と固溶Ｃ
量（全板厚方向平均値）、並びに常温時効性（ＡＩ）及
び焼付は硬化性（Ｂ Ｈ）を第４表に示す。
なお、常温時効性はＡＩで評価した。ＡＩは。
１０％引張時の応力（σ、）と１００℃Ｘ１ｈｒの時効
処理後の再引張時の下降状応力（σ２）から、Ａ４＝σ
２−σ□で求めた。
焼付は硬化性はＢＨで評価した。ＢＨは、２％引張時の
応力（σ３）と１７ ｏ’ｃｘ ２０ｍ１ｎの時効処理
後の再、引張時の下降状応力（σ４）から、ＢＨ＝σ、
−σ３で求めた。
第４表より明らかなように、本発明鋼は、従来鋼に比べ
、深絞り用溶融亜鉛メッキ冷延鋼板としての要求を損ね
ることなく、優れた焼付は硬化性が付与されている。ま
た常温時効性も良好である。
因みに、第４表中の本発明鋼Ｎａ７について、固溶Ｃ量
の板厚方向の分布を調べた結果、第５図に示すように浸
炭処理した場合に表面から中心部にかけて板厚方向に固
溶Ｃ量が低下する濃度分布を示していた。しかも、ガス
Ｂによる浸炭処理の場合、表層１／１０の板厚比の部分
の固溶Ｃ濃度が６０ｐｐｍ以下であり、第６図に示すよ
うに焼付は硬化性及びｒ値が共に改善されていることが
確認された。
一方、第４表に示すように１本発明範囲の化学成分を有
していない比較鋼や、本発明範囲内の化学成分を有して
いても固溶Ｃ量に関する条件が本発明範囲外の比較鋼は
、ｒ値又は焼付は硬化性のいずれかが劣っている。In Example 1, the test steel having the chemical composition shown in Table 1 was recrystallized for 1 minute at 800°C in an annealing process before plating in a carburizing atmosphere or inert gas after cold rolling. Annealing was performed, followed by hot-dip galvanizing at 450° C. and a 0.8% skin pass. Mechanical properties and solid solution C of the obtained hot-dip galvanized cold-rolled steel sheet
Table 4 shows the amount (average value in the entire plate thickness direction), room temperature aging property (AI), and baking hardenability (BH). In addition, room temperature aging property was evaluated by AI. AI is. From the stress at 10% tension (σ,) and the descending stress (σ2) at re-tension after aging treatment at 100°C for 1 hr, A4=σ
It was determined by 2-σ□. Baking and hardenability were evaluated using BH. BH is calculated from the stress at 2% tension (σ3) and the descending stress at re-tension after aging treatment of 17 o'cx 20m1n (σ4), BH=σ,
-σ3. As is clear from Table 4, the steel of the present invention has excellent baking and hardenability compared to the conventional steel without impairing the requirements as a hot-dip galvanized cold-rolled steel sheet for deep drawing. It also has good aging properties at room temperature. Incidentally, as a result of investigating the distribution of solid solution C content in the thickness direction of the invention steel Na7 shown in Table 4, it was found that when carburized, as shown in Figure 5, hardening occurs in the thickness direction from the surface to the center. The concentration distribution showed a decreasing amount of dissolved C. Furthermore, in the case of carburizing treatment with gas B, the solid solution C concentration in the surface layer with a plate thickness ratio of 1/10 is 60 ppm or less, and as shown in Fig. 6, both the hardenability and the r value are improved in the case of baking. It was confirmed that there is. On the other hand, as shown in Table 4, there are comparative steels that do not have chemical components within the scope of the present invention, and conditions regarding the amount of solid solute C that are outside the scope of the present invention even if the steels have chemical components within the scope of the present invention. Comparative steels are inferior in either r-value or seizure hardenability.
矢１ｕ生渠
第１表に示す化学成分を有する供試鋼について、実施例
３において、浸炭雰囲気又は不活性ガス中での連続焼鈍
による再結晶焼鈍を行った後、約８０℃／Ｓの冷却速度
で４００℃まで冷却した後、その温度で３分間の過時効
処理を行ない、工％のスキンパスを施して冷延鋼板を得
た。他の条件は実施例３と同じである。
得られた冷延鋼板の機械的性質と固溶Ｃ量（全板厚方向
平均値）、並びに常温時効性（ＡＩ）及び焼付は硬化性
（Ｂ Ｈ）を第５表に示す。
第５表より明らかなように１本発明鋼は、従来鋼に比べ
、深絞り用冷延鋼板としての要求を損ねることなく、優
れた焼付は硬化性が付与されている。また常温時効性も
良好である。
因みに、第５表中の本発明鋼ＮＱ７について、固溶Ｃ量
の板厚方向の分布を調べた結果、第７図に示すように浸
炭処理した場合に表面から中心部にかけて板厚方向に固
溶Ｃ量が低下する濃度分布を示していた。しかも、ガス
Ｂによる浸炭処理の場合、表層１／１０の板厚比の部分
の固溶Ｃ濃度が６Ｑｐｐ＋ｍ以下であり、第８図に示す
ように焼付は硬化性及びｒ値が共に改善されていること
が確認された。
一方、第５表に示すように、本発明範囲の化学成分を有
していない比較鋼や、本発明範囲内の化学成分を有して
いても固溶Ｃ量に関する条件が本発明範囲外の比較鋼は
、ｒ値又は焼付は硬化性のいずれかが劣っている。In Example 3, the test steel having the chemical composition shown in Table 1 was recrystallized by continuous annealing in a carburizing atmosphere or inert gas, and then cooled at about 80°C/S. After cooling at a speed of 400° C., an overaging treatment was performed at that temperature for 3 minutes, and a skin pass of 10% was performed to obtain a cold rolled steel sheet. Other conditions are the same as in Example 3. Table 5 shows the mechanical properties and solute C content (average value in the entire plate thickness direction) of the obtained cold rolled steel sheet, as well as room temperature aging property (AI) and baking hardenability (BH). As is clear from Table 5, the steel of the present invention has excellent baking and hardenability compared to the conventional steel without impairing the requirements for cold-rolled steel sheets for deep drawing. It also has good aging properties at room temperature. Incidentally, as a result of investigating the distribution of the amount of solute C in the thickness direction of the steel of the present invention, NQ7 in Table 5, it was found that when carburized, as shown in Figure 7, hardening occurs in the thickness direction from the surface to the center. The concentration distribution showed a decreasing amount of dissolved C. Moreover, in the case of carburizing treatment with gas B, the solid solution C concentration in the surface layer with a plate thickness ratio of 1/10 is 6Qpp+m or less, and as shown in Figure 8, both the hardenability and the r value are improved. It was confirmed that there is. On the other hand, as shown in Table 5, there are comparison steels that do not have chemical components within the scope of the present invention, and conditions regarding the amount of solid solute C that are outside the scope of the present invention even though they have chemical components within the scope of the present invention. Comparative steels are inferior in either r-value or seizure hardenability.
（発明の効果）
以上詳述したように、本発明によれば、極低炭素鋼の化
学成分を調整すると共に固溶Ｃ量及びその板厚方向分布
を規制したので、深絞り用冷延鋼板又は溶融亜鉛メッキ
冷延鋼板としての要求を損なうことなく、優れた耐２次
加工脆性又は焼付は硬化性を有する材料を生産性よく提
供することができる。(Effects of the Invention) As detailed above, according to the present invention, the chemical composition of ultra-low carbon steel is adjusted, and the amount of solid solute C and its distribution in the thickness direction are regulated, so cold-rolled steel sheets for deep drawing are Alternatively, it is possible to provide a material with excellent secondary processing brittleness or seizure resistance and hardenability with good productivity without impairing the requirements for a hot-dip galvanized cold-rolled steel sheet.
第１図、第３図、第５図及び第７図は実施例における鋼
板について板厚方向に研削によって１／↓Ｏの厚さに削
り出した試料の内部摩擦値から換算した板厚方向の固溶
Ｃ量分布を示す図で、第１図は実施例１の鋼尚３、第３
図は実施例２の鋼尚３、第５図は実施例３の鋼面７、第
７図は実施例４の鋼ＮＱ７の場合であり、
第２図、第４図、第６図及び第８図は実施例におけるＰ
添加量０．０２％以下の鋼板についての（Ｔｉｅ／４８
＋ Ｎｂ／９３）／ （Ｃ／１２）と機械的性質の関係
を示す図で、各実施例の鋼Ｎｃｌ、Ｎ１１２、Ｎα３．
ＮＱ＆５、
正７、
Ｎα８の場合である。Figures 1, 3, 5, and 7 show the values of the steel plates in the thickness direction calculated from the internal friction values of samples that were ground to a thickness of 1/↓O in the thickness direction. This is a diagram showing the solid solute C content distribution, and FIG.
The figure shows the steel surface 3 of Example 2, the figure 5 shows the case of steel surface 7 of Example 3, and the figure 7 shows the case of steel NQ7 of Example 4. Figure 8 shows P in the example.
(Tie/48
+ Nb/93)/(C/12) and the mechanical properties of the steels Ncl, N112, Nα3.
This is the case of NQ&5, positive 7, and Nα8.
Claims (3)
Ｓｉ：０．２％以下、Ｍｎ：０．０５〜１．０％、Ｐ：
０．１０％以下、Ｓ：０．０２％以下、ｓｏｌ．Ａｌ：
０．０１〜０．０８％及びＮ：０．００５％以下を含有
し、更にＴｉ及びＮｂの１種又は２種を、次式（１）で
定義される有効Ｔｉ量（以下、Ｔｉ＊という）及びＮｂ
量とＣ量との関係が次式（２）を満足する範囲で含有し
、 Ｔｉ＊＝ｔｏｔａｌＴｉ−｛（４８／３２）×Ｓ＋（４
８／１４）×Ｎ｝・・・（１） １≦（Ｔｉ＊／４８＋Ｎｂ／９３）／（Ｃ／１２）≦４
．５・・・（２）残部がＦｅ及び不可避的不純物よりな
る組成を有する鋼であって、浸炭処理により表面から中
心部にかけて板厚方向に固溶Ｃ量が低下するような濃度
勾配を有し、表層１／１０の板厚比の部分の固溶Ｃ濃度
の最大量を１５ｐｐｍとし、鋼板全体の固溶Ｃ量を２〜
１０ｐｐｍとすることを特徴とする耐２次加工脆性に優
れた深絞り用冷延鋼板又は溶融亜鉛メッキ冷延鋼板。(1) In weight% (the same applies hereinafter), C: 0.01% or less,
Si: 0.2% or less, Mn: 0.05-1.0%, P:
0.10% or less, S: 0.02% or less, sol. Al:
0.01 to 0.08% and N: 0.005% or less, and further contains one or two of Ti and Nb to reduce the effective Ti amount defined by the following formula (1) (hereinafter referred to as Ti*). ) and Nb
Ti*=totalTi−{(48/32)×S+(4
8/14)×N}...(1) 1≦(Ti*/48+Nb/93)/(C/12)≦4
．． 5...(2) A steel having a composition in which the remainder consists of Fe and unavoidable impurities, and has a concentration gradient such that the amount of solid solute C decreases in the thickness direction from the surface to the center due to carburizing treatment. , the maximum amount of solid solute C concentration in the surface layer with a plate thickness ratio of 1/10 is 15 ppm, and the amount of solid solute C in the entire steel plate is 2 to 2.
A cold-rolled steel sheet for deep drawing or a hot-dip galvanized cold-rolled steel sheet with excellent resistance to secondary work brittleness, characterized by a concentration of 10 ppm.
処理により表面から中心部にかけて板厚方向に固溶Ｃ量
が低下するような濃度勾配を有し、表層１／１０の板厚
比の部分の固溶Ｃ濃度の最大量を６０ｐｐｍとして、鋼
板全体の固溶Ｃ量を５〜３０ｐｐｍとすることを特徴と
する焼付け硬化性に優れた深絞り用冷延鋼板又は溶融亜
鉛メッキ冷延鋼板。(2) A steel having the composition according to claim 1, which has a concentration gradient such that the amount of solid solute C decreases in the thickness direction from the surface to the center by carburizing, and the steel has a concentration gradient of 1/10 of the surface layer. Cold-rolled steel sheet for deep drawing or hot-dip galvanizing with excellent bake hardenability, characterized in that the maximum amount of solid solute C concentration in the thickness ratio part is 60 ppm, and the amount of solid solute C in the entire steel sheet is 5 to 30 ppm. Cold rolled steel plate.
を含有するものである請求項１又は２に記載の鋼板。(3) The steel plate according to claim 1 or 2, wherein the steel having the composition further contains B: 0.003% or less.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2051273A JPH03253543A (en) | 1990-03-02 | 1990-03-02 | Cold rolled steel sheet or galvanized steel sheet for deep drawing having excellent secondary processing brittleness resistance or baking hardenability |
| CA002037316A CA2037316C (en) | 1990-03-02 | 1991-02-28 | Cold-rolled steel sheets or hot-dip galvanized cold-rolled steel sheets for deep drawing |
| US07/663,310 US5133815A (en) | 1990-03-02 | 1991-03-01 | Cold-rolled steel sheets or hot-dip galvanized cold-rolled steel sheets for deep drawing |
| DE69104747T DE69104747T2 (en) | 1990-03-02 | 1991-03-04 | Cold-rolled steel sheets or cold-rolled and hot-dip galvanized steel sheets for deep drawing. |
| EP91301767A EP0444967B1 (en) | 1990-03-02 | 1991-03-04 | Cold-rolled steel sheets or hot-dip galvanized cold rolled steel sheets for deep drawing |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2051273A JPH03253543A (en) | 1990-03-02 | 1990-03-02 | Cold rolled steel sheet or galvanized steel sheet for deep drawing having excellent secondary processing brittleness resistance or baking hardenability |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH03253543A true JPH03253543A (en) | 1991-11-12 |
| JPH0530900B2 JPH0530900B2 (en) | 1993-05-11 |
Family
ID=12882341
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2051273A Granted JPH03253543A (en) | 1990-03-02 | 1990-03-02 | Cold rolled steel sheet or galvanized steel sheet for deep drawing having excellent secondary processing brittleness resistance or baking hardenability |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH03253543A (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0466647A (en) * | 1990-07-07 | 1992-03-03 | Kobe Steel Ltd | Hot-dip galvanized cold rolled steel sheet for deep drawing having galvanized film excellent in adhesion and its manufacture |
| JPH05195148A (en) * | 1992-01-20 | 1993-08-03 | Nippon Steel Corp | Cold-rolled steel sheet excellent in curing performance for baking paint and secondary workability, galvanized cold-rolled steel sheet and production thereof |
| JPH05302125A (en) * | 1992-04-06 | 1993-11-16 | Kobe Steel Ltd | Production of baking hardened high strength steel sheet for hot dip galvannealing excellent in plating adhesion and production of the plated steel sheet |
| JPH05331612A (en) * | 1992-06-01 | 1993-12-14 | Kobe Steel Ltd | Production of galvannealed steel sheet excellent in deep drawability and plating adhesion |
| US5372654A (en) * | 1992-09-21 | 1994-12-13 | Kawasaki Steel Corporation | Steel sheet for press working that exhibits excellent stiffness and satisfactory press workability |
| EP1347070A1 (en) * | 2000-12-21 | 2003-09-24 | Toyo Kohan Co., Ltd. | Steel sheet for porcelain enameling and method for production thereof, and enameled product and method for production thereof |
| CN116164616A (en) * | 2022-12-13 | 2023-05-26 | 揭阳市汇宝昌电器有限公司 | Product quality key index system detection method for mirror surface deep drawing motor shell |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6442331A (en) * | 1987-08-10 | 1989-02-14 | Hisankabutsu Glass Kenkyu | Production of chalcogenide glass containing aluminum |
| JPH0196330A (en) * | 1987-10-05 | 1989-04-14 | Kobe Steel Ltd | Manufacture of cold rolled steel sheet combining high gamma-value with high tensile strength |
-
1990
- 1990-03-02 JP JP2051273A patent/JPH03253543A/en active Granted
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6442331A (en) * | 1987-08-10 | 1989-02-14 | Hisankabutsu Glass Kenkyu | Production of chalcogenide glass containing aluminum |
| JPH0196330A (en) * | 1987-10-05 | 1989-04-14 | Kobe Steel Ltd | Manufacture of cold rolled steel sheet combining high gamma-value with high tensile strength |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0466647A (en) * | 1990-07-07 | 1992-03-03 | Kobe Steel Ltd | Hot-dip galvanized cold rolled steel sheet for deep drawing having galvanized film excellent in adhesion and its manufacture |
| JPH05195148A (en) * | 1992-01-20 | 1993-08-03 | Nippon Steel Corp | Cold-rolled steel sheet excellent in curing performance for baking paint and secondary workability, galvanized cold-rolled steel sheet and production thereof |
| JPH05302125A (en) * | 1992-04-06 | 1993-11-16 | Kobe Steel Ltd | Production of baking hardened high strength steel sheet for hot dip galvannealing excellent in plating adhesion and production of the plated steel sheet |
| JPH05331612A (en) * | 1992-06-01 | 1993-12-14 | Kobe Steel Ltd | Production of galvannealed steel sheet excellent in deep drawability and plating adhesion |
| US5372654A (en) * | 1992-09-21 | 1994-12-13 | Kawasaki Steel Corporation | Steel sheet for press working that exhibits excellent stiffness and satisfactory press workability |
| EP1347070A1 (en) * | 2000-12-21 | 2003-09-24 | Toyo Kohan Co., Ltd. | Steel sheet for porcelain enameling and method for production thereof, and enameled product and method for production thereof |
| EP1347070A4 (en) * | 2000-12-21 | 2004-08-04 | Toyo Kohan Co Ltd | Steel sheet for porcelain enameling and method for production thereof, and enameled product and method for production thereof |
| CN116164616A (en) * | 2022-12-13 | 2023-05-26 | 揭阳市汇宝昌电器有限公司 | Product quality key index system detection method for mirror surface deep drawing motor shell |
| CN116164616B (en) * | 2022-12-13 | 2024-05-14 | 揭阳市汇宝昌电器有限公司 | Product quality key index system detection method for mirror surface deep drawing motor shell |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0530900B2 (en) | 1993-05-11 |
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