JPH04173946A - Manufacture of high-ductility and high strength galvannealed steel sheet - Google Patents
Manufacture of high-ductility and high strength galvannealed steel sheetInfo
- Publication number
- JPH04173946A JPH04173946A JP29915990A JP29915990A JPH04173946A JP H04173946 A JPH04173946 A JP H04173946A JP 29915990 A JP29915990 A JP 29915990A JP 29915990 A JP29915990 A JP 29915990A JP H04173946 A JPH04173946 A JP H04173946A
- Authority
- JP
- Japan
- Prior art keywords
- steel sheet
- cooling
- cooling rate
- hot
- temperature
- 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
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 11
- 229910000831 Steel Inorganic materials 0.000 title abstract description 26
- 239000010959 steel Substances 0.000 title abstract description 26
- 238000001816 cooling Methods 0.000 claims abstract description 61
- 238000005246 galvanizing Methods 0.000 claims abstract description 18
- 238000010438 heat treatment Methods 0.000 claims abstract description 12
- 238000000137 annealing Methods 0.000 claims abstract description 8
- 238000001953 recrystallisation Methods 0.000 claims abstract description 8
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 3
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 3
- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 17
- 239000008397 galvanized steel Substances 0.000 claims description 17
- 238000007747 plating Methods 0.000 claims description 16
- 238000005275 alloying Methods 0.000 claims description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 2
- 238000005097 cold rolling Methods 0.000 claims 1
- 239000010960 cold rolled steel Substances 0.000 abstract description 6
- 229910045601 alloy Inorganic materials 0.000 abstract description 2
- 239000000956 alloy Substances 0.000 abstract description 2
- 229910052748 manganese Inorganic materials 0.000 abstract description 2
- 238000000034 method Methods 0.000 description 16
- 229910000859 α-Fe Inorganic materials 0.000 description 16
- 229910000734 martensite Inorganic materials 0.000 description 13
- 229910001566 austenite Inorganic materials 0.000 description 12
- 239000000463 material Substances 0.000 description 10
- 229910001563 bainite Inorganic materials 0.000 description 9
- 239000002131 composite material Substances 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- 230000015572 biosynthetic process Effects 0.000 description 8
- 238000005728 strengthening Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 229910001562 pearlite Inorganic materials 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000000203 mixture Substances 0.000 description 4
- 238000005098 hot rolling Methods 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 238000005452 bending Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- 230000000670 limiting effect Effects 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000009422 growth inhibiting effect Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Landscapes
- Coating With Molten Metal (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
（産業上の利用分野）
本発明は、加工性に優れた高強度合金化溶融亜鉛めっき
鋼板の製造方法に関し、より詳しくは。
引張強さ６０〜１２０ｋｇｆ／ｍｍ”級の複合組織合金
化溶融亜鉛めっき鋼板の製造方法に関する。
（従来の技術）
近年、自動車の安全性及び軽量化対策として加工性の優
れた高強度冷延鋼板が使用されるに至っている。また、
自動車の寿命向上のために冷延鋼板に防錆力の向上が強
く望まれており、このような溶融亜鉛めっき鋼板、及び
スポット溶接性と塗装性に優れる合金化溶融亜鉛めっき
鋼板の開発が必要とされている。特に、最近においては
、自動車バンパー、ドアインパクトバー等の補強部材に
ライても、引張強さ６０〜１００ｋｇｆ／ｍｍ”級の合
金化溶融亜鉛めっき鋼板が要望されている。
（発明が解決しようとする課題）
従来、引張強さが６０ ｋｇｆ ／ ａｍ２級のものは
、固溶強化及び析出強化により製造されているため、添
加元素が多くなって、コストアップになるという問題が
あった。また、８０ ｋｇｆ ／ ｍ＋ｎ”以上のもの
を得るには、これらの強化方法では、延性の劣化が大き
いばかりでなく圧延も困難となる。したがって、このよ
うな高強度薄鋼板で高延性を得るためには、ベイナイト
或いはマルテンサイトのような硬質相を含む変態組織強
化が有利なことが知られている・
か＼る問題を解決するために１例えば、特開昭５５−５
０４５５号公報では、Ｍｎ等を添加した鋼板をＡｃｉ〜
Ａｃ、の２相域加熱し、この加熱温度からめっき浴温度
までの冷却速度及びめっき処理後の冷却速度を限定する
ことによりフェライト・マルテンサイトの複合組織にし
、加工性に優れた高強度亜鉛めっき鋼板を得る方法が提
案されている。しかし、この方法では、合金化処理する
とパーライト或いは粗いベイナイトを生じ、加工性に優
れた高強度合金化溶融亜鉛めっき鋼板を得ることができ
ない。
また、特開昭５５−１２２８２０号公報では、合金化温
度をＡｃ工〜Ａｃ３の２相域にし、その後の冷却速度を
制御することにより複合組織鋼板とすることが提案され
ている。しかし、この方法においては１合金化温度が高
いために、合金層の鉄濃度が高くなり、パウダリング性
不良等が生じて材質劣化させるという問題点がある。
一方、特開昭５６−１４２８２１号公報では、Ａｃ０〜
９００℃の加熱を行い、冷却速度を制御することにより
パーライト及びベイナイトの生成を抑制し、組織をフェ
ライト・マルテンサイト（一部残留オーステナイトを含
む）の複合組織にすることにより、加工性の優れた溶融
亜鉛めっき鋼板を製造する方法が提案されている。しか
し、この方法では、フェライトとマルテンサイトの硬さ
の差が大きく、局部伸びや曲げ加工性が低い。特に、引
張強さが７ Ｑ ｋｇｆ ／ ｍ＋＊２以上ではマルテ
ンサイト体積率が大きくなり、穴広げ率が著しく低下す
るため、バンパー等のチャンネル型成形で行なわれる厳
しい曲げ加工では、加工性が不十分である。
以上のように、高延性高強度合金化溶融亜鉛めっき鋼板
を製造するに際しては、高強度を得る点で有利な複合組
織強化が必要となるが、単に、化学成分や冷却速度に着
目した方法では、高延性高強度合金化溶融亜鉛めっき鋼
板を製造することは困難である。
本発明は、上記従来技術の問題点を解決して、複合組織
化により優れた高延性と高強度を有する合金化溶融亜鉛
めっき鋼板を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）
本発明者らは、前記課題を解決するために鋭意研究を重
ねた結果、鋼の化学成分及び連続溶融亜鉛めっきライン
の加熱温度、加熱温度からめっき浴温度までの冷却を徐
冷と急冷の２段階の冷却にすること、更には合金化温度
及び合金化温度からＭｓ点までの冷却速度を制御するこ
とにより、組織を微細かつ均一なフェライト・ベイナイ
ト・マルテンサイト（一部残留オーステナイトを含む）
の複合組織にし、高延性高強度合金化溶融亜鉛めっき鋼
板が得られることを見い出して、本発明に至ったもので
ある。
すなわち、本発明は、Ｃ：０．０６〜０．３０％、Ｓｉ
：０．６％以下、Ｐ：０．１％以下、Ｎｂ：０．０１〜
０．２０％及びｓｏｌ．Ａｌ：０．０１〜０．１０％を
含有し、更にＭｎ：Ｑ、６〜３．０％、Ｃｒ−０，１〜
１．５％及びＭｏ：０．１〜１．０％の１種又は２種以
上を含有し、残部が鉄及び不可避的不純物よりなる鋼を
、通常の方法で熱間圧延、酸洗、冷間圧延した後、連続
溶融亜鉛めっきラインにて再結晶焼鈍する際に、その加
熱温度をＡｃ、点−５０℃〜９００”Ｃにし、めっき浴
までの冷却を、２０℃／Ｓ以下の冷却速度にて５００〜
６５０℃の温度域に冷却し、次いで、めっき浴温度まで
ｌｎＣＲ＝−１，１８Ｍｅｑ＋３．３７二こで、Ｍｅｑ
（％）＝Ｍｎ＋１．５２Ｍｏ＋１．１ＯＣｒ＋０．１０
Ｓｉ＋２．１Ｐ
で示される臨界冷却速度ＣＲ（℃／Ｓ）以上にて冷却し
た後、溶融亜鉛めっきし、次いで５００℃〜Ａｃ工点の
温度にて合金化処理を施した後、ＣＲ以上の冷却速度に
てＭｓ点点上下冷却することを特徴とする高延性高強度
合金化溶融亜鉛めっき鋼板の製造方法を要旨とするもの
である。
以下に本発明を更に詳細に説明する。
（作用）
第１図は本発明における連続亜鉛めっきラインの熱履歴
を示している。ここで、均熱温度から５００〜６５０℃
までの冷却を１次冷却、次のめっき浴温度までの冷却を
２次冷却、合金化処理後の冷却を３次冷却とし、それぞ
れの冷却速度を１次冷却速度、２次冷却速度、３次冷却
速度と呼ぶ。
なお、１次冷却から２次冷却に変わる時の温度を急冷開
始温度と呼ぶ。
まず、本発明における化学成分の限定理由について説明
する６
Ｃ：
Ｃは鋼板の強化に不可欠な元素であって、目的とする強
度を有する鋼板を得るには、少なくともｏ、０６％を添
加する必要があるが、０．３０％を超えると硬質なマル
テンサイトの体積率が高くなり、加工性が劣化するばか
りでなく、スポット溶接性も低下する。したがって、Ｃ
量は０．０６〜０．３０％の範囲とする。
Ｓｊ：
Ｓｉはフェライト中の固溶Ｃをオーステナイト中へ排出
する効果を有するため、フェライト延性を向上させるこ
とができる。しかし、過多に添加するとめっき不良を生
じるので、Ｓｉ量は０．６％以下とする。
Ｐ：
Ｐは、０．０２％以上の添加によってＳｉと同様の作用
を有し、強度と伸びとのバランスを確保するために有効
であるが、０．１％を超えて添加するとめっき不良等が
発生するので、Ｐ量は０．１％以下とする。
Ｎｂ：
Ｎｂは鋼板の強度を高めるための有効な元素であり、単
に析出強化として寄与するだけでなく、焼入性を向上さ
せる。また、組織を超微細均一ニする効果があり、均−
伸びを低下することなく局部伸びを高める効果がある。
このような効果を発揮するためには、０．０１％以上が
必要である６しかし０．２０％よりも過多に添加すると
延性を劣化させるので好ましくない。したがって、Ｎｂ
量はｏ、０１〜０．２０％の範囲とする。
ｓｏｌ、Ａ Ｑ ：
ＡＱは鋼の脱酸のために添加され、少なくとも０．０１
％が必要である。しかし、過多に添加してもこの効果が
飽和するのみならず、めっき不良を招くので好ましくな
い。したがって、添加量はｓｏｌ．Ａｌで０．０１〜０
．１％の範囲とする。
また、本発明において用いる鋼は、上記元素に加えて、
Ｍｎ、Ｃｒ及びＭＯの１種又は２種以上を適量で含有さ
せなければならない。
Ｍｎ：
Ｍｎはオーステナイト相を安定化し、冷却過程において
硬質相の生成を容易にし、高強度を得るために添加され
る。しかし、添加量が少ないと高強度を達成するための
十分な硬質相を得ることができないので、その下限を０
．６％とする。一方、過多に添加するとバンド組織が発
達し、加工性が劣化するばかりでなく、コスト高になる
ので、上限を３．０％とする。
Ｃｒ：
ＣｒはＭｎと同様な効果を有し、オーステナイト相を安
定化し、硬質相の生成を容易にして高強度を得るために
、必要に応じて添加される。しかし、その効果を得るに
は少なくとも０．１％が必要であるが、過多に添加する
と均−伸び及び局部伸びを低下させるので、添加量の上
限を１．５％とする。
ｏ ａ
ＭＯはオーステナイト相を著しく安定化し、冷却過程に
おいて硬質相の生成を容易にし、高強度化するために添
加される。しかし、添加量が少なぃと高強度を達成する
ための硬質相を得ることができないので、その下限を０
．１％とする。一方、１．０％を超えて添加すると、マ
ルテンサイトがバンド状で多量に生成するため、加工性
が劣化するので、１．０％を上限とする。
次に、本発明の方法における製造条件について説明する
。
上記の化学成分を有する鋼は、通常の工程により、製鋼
１分塊又は連続鋳造を経てスラブとした後、熱間圧延を
経て、ホットコイルにする。熱間圧延については、その
条件は特に限定する必要はないが、均一微細なフェライ
トとマルテンサイト等の複合組織の溶融亜鉛めっき高強
度鋼板を得るには、熱間圧延の巻取温度を低くし、均一
なフェライトとベイナイトの組織にした方が好ましい。
熱間圧延後、常法に従って、酸洗し、冷間圧延を施して
薄鋼板を得る。冷間加工率は３０％以上が望ましい。
次いで、この薄鋼板を連続溶融亜鉛めっきラインに導い
て、以下の条件で再結晶焼鈍、溶融亜鉛めっき及び合金
化処理を施す。
再結晶焼鈍は、その加熱温度をＡ ｃ ３点−５０℃〜
９００℃にする必要がある。加熱温度がＡｃ、点−５０
℃よりも低いと、未変態の再結晶フェライトが多く、均
一微細な組織にすることができなし）ので、高い局部伸
びを得ることが困難となる。他方、加熱温度が９００℃
よりも高いと、オーステナイト粒が粗大化し、１次、２
次冷却過程でのフェライトの核が少なくなり、フェライ
ト粒が粗大化し、組織が不均一となるため、局部伸びが
劣化する。
この再結晶焼鈍からめつき浴までの冷却は、まず、５０
０〜６５０℃の温度域に２０℃／Ｓ以下の冷却速度で冷
却する。この１次冷却過程は、伸び及び局部伸びを高め
るのに重要な工程である。
すなわち、Ｎｂ添加による変態抑止効果及び粒成長抑止
効果により、低温でフェライトを微細かつ均一に析出さ
せ、残りのオーステナイトのＣ濃度を高める。このため
、オーステナイトは安定化し、めっき浴温度以上でベイ
ナイトの生成を抑制する。
しかし、冷却速度が２０℃／Ｓを超えると、十分にフェ
ライトが析出できず、オーステナイトのＣ濃度が低いた
めに、冷却過程でベイナイトの生成量が多くなり、均−
伸び及び局部伸びは劣化するので好ましくない。
次いで、急冷開始温度から、めっき槽の温度まで、
Ｑ ｎＣＲ＝ −１，１８Ｍｅｑ＋３．３７ここで、Ｍ
ｅｑ（％）＝Ｍｎ＋１．５２Ｍｏ＋１．１０Ｃｒ＋０．
１０Ｓｉ＋２．１Ｐ
で示される臨界冷却速度ＣＲ（℃／ｓ）以上にて冷却す
る。次いで、溶融亜鉛めっきを施した後、５００℃〜Ａ
ｃｔ点の温度にて合金化処理した後、臨界冷却速度ＣＲ
以上の冷却速度にてＭｓ点以下に冷却することにより、
微細均一な複合組織鋼板を得ることができる。この２次
冷却と３次冷却のいずれの冷却速度ともＣＲよりも小さ
いと、パーライトの生成或いはベイナイト体積率が多く
なり、高延性高強度を得るのが困難である。
以下に本発明の一実施例を示す。
（実施例）
第１表に示す化学成分を有する鋼を４０ｋｇ真空溶製し
、２０ｍｍ厚のスラブにした。このスラブを１２００℃
に加熱し、仕上温度８５０℃、巻取温度５６０℃で熱間
圧延し、３．２ｍｍ厚の熱延鋼板とした。得られた鋼板
を酸洗、冷間圧延して、１．２ｍｍ厚（圧下率６２．５
％）の冷延鋼板を得た。
これらの冷延鋼板について第２表に示す条件で連続亜鉛
めっき処理して合金化溶融亜鉛めっき鋼板を得た。
得られた合金化溶融亜鉛めっき鋼板について引張特性及
び１０φｍｍ打抜き穴広げ率を調べた。その結果を第２
表に併記する。
第２表より以下の如く考察される。
本発明材のＮｕ １〜＆ ２はいずれも８５ｋｇｆ／ａ
ｍ”以上の高強度で、２２％以上の高い伸びと４０％以
上の高い穴広げ率（λ）を示している。
一方、Ｎｃｌ及びＮα２と同じ化学成分を有する比較材
翫３は、急冷開始温度が８００℃と高いため、フェライ
トの析出が不十分であり、伸びが劣っている。
比較材Ｎα４、ＮＨ３、＆９はいずれも、Ｎｂが添加さ
れていないので、本発明材よりも組織が粗く、強度及び
穴広げ率が劣っている。
比較材ｈ６は、冷却速度がＣＲよりも遅いため、パーラ
イトが生成し、本発明材Ｎα５よりも強度及び穴広げ率
が劣っている。
比較材＆１０は、Ｍｎ量が３．５１％と多いため、多量
のマルテンサイトが生成し、伸び及び穴広げ率が低い。
比較材嵐１１は、Ｃ量が低く、また冷却速度がＣＲより
も遅いため、マルテンサイトが得られず、目的とする強
度が得られていない。
また、本発明材Ｎα８は８０ ｋｇｆ ／ ｍａｄ”の
高強度で、伸び及び穴拡げ率が優れている。(Industrial Application Field) The present invention relates to a method for manufacturing a high-strength alloyed galvanized steel sheet with excellent workability, and more specifically, to a method for manufacturing a high-strength alloyed hot-dip galvanized steel sheet with excellent workability. This invention relates to a method for producing a composite structure alloyed hot-dip galvanized steel sheet with a tensile strength of 60 to 120 kgf/mm. has come to be used.Also,
In order to extend the lifespan of automobiles, there is a strong desire for cold-rolled steel sheets to have improved anti-rust properties, and it is necessary to develop such hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets with excellent spot weldability and paintability. It is said that In particular, recently there has been a demand for alloyed hot-dip galvanized steel sheets with a tensile strength of 60 to 100 kgf/mm" class, which can be used as reinforcing members for automobile bumpers, door impact bars, etc. Conventionally, products with a tensile strength of 60 kgf/am2 class have been manufactured by solid solution strengthening and precipitation strengthening, so there was a problem that the number of added elements increased, resulting in increased costs.Also, In order to obtain 80 kgf/m+n'' or more, these strengthening methods not only cause a large deterioration in ductility but also make rolling difficult. Therefore, in order to obtain high ductility in such high-strength thin steel sheets, it is known that strengthening the transformation structure containing a hard phase such as bainite or martensite is advantageous. For example, JP-A-55-5
In Publication No. 0455, a steel plate added with Mn etc. is
By heating in the two-phase region of Ac, and limiting the cooling rate from this heating temperature to the plating bath temperature and the cooling rate after plating processing, a composite structure of ferrite and martensite is created, resulting in high-strength zinc plating with excellent workability. A method for obtaining steel plates has been proposed. However, this method produces pearlite or coarse bainite during alloying treatment, making it impossible to obtain a high-strength alloyed hot-dip galvanized steel sheet with excellent workability. Furthermore, Japanese Patent Application Laid-Open No. 55-122820 proposes that the alloying temperature be set in the two-phase range of Ac to Ac3, and the subsequent cooling rate be controlled to produce a composite structure steel sheet. However, in this method, since the alloying temperature is high, the iron concentration in the alloy layer becomes high, resulting in poor powdering properties and the like, leading to material deterioration. On the other hand, in JP-A-56-142821, Ac0~
By heating to 900℃ and controlling the cooling rate, the formation of pearlite and bainite is suppressed, and the structure becomes a composite structure of ferrite and martensite (including some retained austenite), resulting in excellent workability. A method of manufacturing hot-dip galvanized steel sheet has been proposed. However, with this method, there is a large difference in hardness between ferrite and martensite, and local elongation and bending workability are low. In particular, when the tensile strength is 7 Q kgf/m+*2 or more, the martensite volume fraction increases and the hole expansion rate decreases significantly, resulting in poor workability in severe bending performed in channel molding of bumpers etc. It is enough. As described above, when producing high-ductility, high-strength alloyed galvanized steel sheets, it is necessary to strengthen the composite structure, which is advantageous in terms of obtaining high strength. , it is difficult to produce high ductility high strength alloyed galvanized steel sheet. An object of the present invention is to solve the above-mentioned problems of the prior art and provide a method for manufacturing an alloyed hot-dip galvanized steel sheet having excellent high ductility and high strength through composite texture. (Means for Solving the Problems) As a result of intensive research to solve the above problems, the present inventors have found that the chemical composition of steel, the heating temperature of a continuous hot-dip galvanizing line, and the temperature range from heating temperature to plating bath temperature. By using two stages of cooling, slow cooling and rapid cooling, and by controlling the alloying temperature and the cooling rate from the alloying temperature to the Ms point, the structure can be made into a fine and uniform ferrite, bainite, and martensite. (Including some retained austenite)
The inventors have discovered that a highly ductile, high-strength alloyed hot-dip galvanized steel sheet can be obtained by forming a composite structure of That is, in the present invention, C: 0.06 to 0.30%, Si
: 0.6% or less, P: 0.1% or less, Nb: 0.01~
0.20% and sol. Contains Al: 0.01 to 0.10%, further Mn: Q, 6 to 3.0%, Cr-0.1 to
1.5% and Mo: 0.1 to 1.0% of one or more types, with the balance consisting of iron and unavoidable impurities. After rolling, during recrystallization annealing in a continuous hot-dip galvanizing line, the heating temperature is set to Ac, a point of -50°C to 900''C, and the cooling rate to the plating bath is set to a cooling rate of 20°C/S or less. 500~
Cool to a temperature range of 650°C, then reduce Meq to the plating bath temperature at lnCR=-1,18Meq+3.37
(%)=Mn+1.52Mo+1.1OCr+0.10
After cooling at a critical cooling rate CR (°C/S) indicated by Si+2.1P, hot-dip galvanizing, then alloying treatment at a temperature of 500°C to Ac work point, then cooling at a CR or higher. The gist of the present invention is a method for producing a high ductility, high strength alloyed hot-dip galvanized steel sheet, which is characterized by cooling above and below the Ms point at a speed of 1. The present invention will be explained in more detail below. (Function) FIG. 1 shows the thermal history of the continuous galvanizing line in the present invention. Here, 500 to 650℃ from the soaking temperature
Cooling up to the temperature of the plating bath is called primary cooling, cooling to the next plating bath temperature is called secondary cooling, cooling after alloying is called tertiary cooling, and the respective cooling rates are called primary cooling rate, secondary cooling rate, and tertiary cooling. It is called cooling rate. Note that the temperature at which the primary cooling changes to the secondary cooling is called the rapid cooling start temperature. First, we will explain the reasons for limiting the chemical components in the present invention. 6 C: C is an element essential for strengthening steel sheets, and in order to obtain steel sheets with the desired strength, it is necessary to add at least 0.6%. However, if it exceeds 0.30%, the volume fraction of hard martensite increases, which not only deteriorates workability but also reduces spot weldability. Therefore, C
The amount should be in the range of 0.06-0.30%. Sj: Since Si has the effect of discharging solid solution C in ferrite into austenite, it can improve ferrite ductility. However, since adding too much Si causes plating defects, the amount of Si is set to 0.6% or less. P: P has the same effect as Si when added in an amount of 0.02% or more, and is effective in ensuring a balance between strength and elongation, but when added in an amount exceeding 0.1%, it may cause poor plating, etc. is generated, so the amount of P is set to 0.1% or less. Nb: Nb is an effective element for increasing the strength of steel sheets, and not only contributes to precipitation strengthening but also improves hardenability. In addition, it has the effect of making the structure ultra-fine and uniform.
It has the effect of increasing local elongation without reducing elongation. In order to exhibit such an effect, 0.01% or more is required6. However, adding more than 0.20% is not preferable because it deteriorates ductility. Therefore, Nb
The amount is o, in the range of 0.01 to 0.20%. sol, AQ: AQ is added to deoxidize steel, and has a content of at least 0.01
%is necessary. However, adding too much of it not only saturates this effect but also causes poor plating, which is not preferable. Therefore, the amount added is sol. 0.01~0 for Al
．． The range is 1%. In addition to the above elements, the steel used in the present invention also contains:
One or more of Mn, Cr and MO must be contained in appropriate amounts. Mn: Mn is added to stabilize the austenite phase, facilitate the formation of a hard phase during the cooling process, and obtain high strength. However, if the amount added is small, it is not possible to obtain sufficient hard phase to achieve high strength, so the lower limit is set to 0.
．． 6%. On the other hand, if added in excess, a band structure develops, which not only deteriorates workability but also increases costs, so the upper limit is set at 3.0%. Cr: Cr has the same effect as Mn, and is added as necessary to stabilize the austenite phase, facilitate the formation of a hard phase, and obtain high strength. However, in order to obtain this effect, at least 0.1% is required, but since adding too much will reduce the uniform elongation and local elongation, the upper limit of the amount added is set at 1.5%. o a MO is added to significantly stabilize the austenite phase, facilitate the formation of a hard phase during the cooling process, and increase the strength. However, if the amount added is small, it is not possible to obtain the hard phase needed to achieve high strength, so the lower limit is set to 0.
．． 1%. On the other hand, if it is added in an amount exceeding 1.0%, a large amount of martensite is produced in band form, which deteriorates workability, so the upper limit is set at 1.0%. Next, manufacturing conditions in the method of the present invention will be explained. Steel having the above-mentioned chemical composition is made into a slab through normal steps such as steel manufacturing ingot or continuous casting, and then hot rolled into a hot coil. There is no need to particularly limit the conditions for hot rolling, but in order to obtain a hot-dip galvanized high-strength steel sheet with a uniform fine composite structure of ferrite and martensite, it is necessary to lower the coiling temperature during hot rolling. , it is preferable to have a uniform structure of ferrite and bainite. After hot rolling, the steel sheet is pickled and cold rolled according to a conventional method to obtain a thin steel sheet. It is desirable that the cold working rate is 30% or more. Next, this thin steel sheet is led to a continuous hot-dip galvanizing line, and subjected to recrystallization annealing, hot-dip galvanizing, and alloying treatment under the following conditions. For recrystallization annealing, the heating temperature is A c 3 points -50°C ~
It is necessary to raise the temperature to 900°C. Heating temperature is Ac, point -50
If it is lower than °C, there is a large amount of untransformed recrystallized ferrite, making it impossible to form a uniform fine structure), making it difficult to obtain high local elongation. On the other hand, the heating temperature is 900℃
If it is higher than , the austenite grains will become coarser and the
During the next cooling process, the number of ferrite nuclei decreases, the ferrite grains become coarser, and the structure becomes non-uniform, resulting in poor local elongation. The cooling from this recrystallization annealing to the plating bath is
Cool to a temperature range of 0 to 650°C at a cooling rate of 20°C/S or less. This primary cooling process is an important process for increasing elongation and local elongation. That is, due to the transformation inhibiting effect and grain growth inhibiting effect of Nb addition, ferrite is finely and uniformly precipitated at low temperature, and the C concentration of the remaining austenite is increased. Therefore, austenite is stabilized and the formation of bainite is suppressed at temperatures above the plating bath temperature. However, if the cooling rate exceeds 20°C/S, ferrite cannot be sufficiently precipitated, and since the C concentration of austenite is low, a large amount of bainite is generated during the cooling process, resulting in an even
Elongation and local elongation are undesirable because they deteriorate. Next, from the quenching start temperature to the temperature of the plating tank, Q nCR = -1,18Meq + 3.37, where M
eq (%)=Mn+1.52Mo+1.10Cr+0.
Cooling is performed at a critical cooling rate CR (° C./s) or higher expressed by 10Si+2.1P. Then, after hot-dip galvanizing, 500℃~A
After alloying at the temperature of the ct point, the critical cooling rate CR
By cooling below the Ms point at the above cooling rate,
A finely uniform composite structure steel sheet can be obtained. If the cooling rate of both the secondary cooling and the tertiary cooling is lower than the CR, pearlite formation or bainite volume fraction increases, making it difficult to obtain high ductility and high strength. An example of the present invention is shown below. (Example) 40 kg of steel having the chemical composition shown in Table 1 was vacuum melted and made into a 20 mm thick slab. Heat this slab to 1200℃
and hot rolled at a finishing temperature of 850°C and a coiling temperature of 560°C to obtain a 3.2 mm thick hot rolled steel plate. The obtained steel plate was pickled and cold rolled to a thickness of 1.2 mm (reduction rate of 62.5
%) cold rolled steel plate was obtained. These cold-rolled steel sheets were subjected to continuous galvanizing treatment under the conditions shown in Table 2 to obtain alloyed hot-dip galvanized steel sheets. The obtained alloyed hot-dip galvanized steel sheet was examined for tensile properties and 10φmm punched hole expansion rate. The second result is
Also listed in the table. The following considerations can be made from Table 2. Nu 1 to & 2 of the present invention materials are all 85 kgf/a
It has a high strength of more than m", a high elongation of more than 22%, and a high hole expansion rate (λ) of more than 40%. On the other hand, comparative material 3, which has the same chemical composition as Ncl and Nα2, has a high strength of more than 22% and a high hole expansion rate (λ) of more than 40%. Because the temperature is as high as 800°C, ferrite precipitation is insufficient, resulting in poor elongation. Comparative materials Nα4, NH3, and &9 all have coarser structures than the present invention materials because no Nb is added. , the strength and hole expansion rate are inferior. Comparative material h6 has a slower cooling rate than CR, so pearlite is generated, and the strength and hole expansion rate are inferior to the invention material Nα5. Comparative material &10 , Since the Mn content is as high as 3.51%, a large amount of martensite is generated, and the elongation and hole expansion rate are low. Comparative material Arashi 11 has a low C content and a cooling rate slower than CR, so martensite is produced. No site was obtained, and the desired strength was not obtained. In addition, the material of the present invention, Nα8, has a high strength of 80 kgf/mad'' and is excellent in elongation and hole expansion rate.
（発明の効果）
以上詳述したように、本発明によれば、再結晶焼鈍の加
熱温度から亜鉛めっき温度までの冷却速度を徐冷と急冷
の２段階に制御することにより、均−伸び、局部伸びの
向上に寄与するフェライトを微細均一に十分析出させ、
また、この過程で残部オーステナイトのＣ濃度を高め、
安定化することにより、亜鉛めっきから合金化処理まで
の間でパーライトの生成を抑制し、ベイナイトの多量の
生成を防ぎ、合金化処理後の冷却により、オーステナイ
トをマルテンサイトに変態させることにより、フェライ
ト、マルテンサイトを主体とした微細均一な組織にする
ことができる。
したがって、６０〜１２０ ｋｇｆ／ ｍｍ２級で高延
性高強度合金化溶融亜鉛めっき鋼板を得ることができる
ので、めっきむら、パウダリング等１表面性状の向上に
加えて、エネルギー費用の低減も可能である。(Effects of the Invention) As detailed above, according to the present invention, by controlling the cooling rate from the heating temperature for recrystallization annealing to the galvanizing temperature in two stages: gradual cooling and rapid cooling, uniform elongation, The ferrite that contributes to the improvement of local elongation is produced finely and uniformly,
In addition, in this process, the C concentration of the residual austenite is increased,
By stabilizing, the formation of pearlite is suppressed during the period from galvanizing to alloying treatment, preventing the formation of a large amount of bainite, and cooling after alloying treatment transforms austenite into martensite, thereby producing ferrite. , it is possible to form a fine and uniform structure mainly composed of martensite. Therefore, it is possible to obtain highly ductile and high strength alloyed galvanized steel sheets in the 60 to 120 kgf/mm2 class, which not only improves surface properties such as coating unevenness and powdering, but also reduces energy costs. .
第１図は本発明における連続亜鉛めっきラインの熱履歴
を示す図である。
特許出願人 株式会社神戸製鋼所
代理人弁理士 中 村 尚FIG. 1 is a diagram showing the thermal history of a continuous galvanizing line in the present invention. Patent applicant Hisashi Nakamura, patent attorney representing Kobe Steel, Ltd.
Claims (1)
、Ｓｉ：０．６％以下、Ｐ：０．１％以下、Ｎｂ：０．
０１〜０．２０％及びｓｏｌ．Ａｌ：０．０１〜０．１
０％を含有し、更にＭｎ：０．６〜３．０％、Ｃｒ：０
．１〜１．５％及びＭｏ：０．１〜１．０％の１種又は
２種以上を含有し、残部が鉄及び不可避的不純物よりな
る鋼を、通常の方法で熱間圧延、酸洗、冷間圧延した後
、連続溶融亜鉛めっきラインにて再結晶焼鈍する際に、
その加熱温度をＡｃ＿３点−５０℃〜９００℃にし、め
っき浴までの冷却を、２０℃／ｓ以下の冷却速度にて５
００〜６５０℃の温度域に冷却し、次いで、めっき浴温
度まで ｌｎＣＲ＝−１．１８ Ｍｅｑ＋３．３７ ここで、Ｍｅｑ（％）＝Ｍｎ＋１．５２Ｍｏ＋１．１０
Ｃｒ＋０．１０Ｓｉ＋２．１Ｐ で示される臨界冷却速度ＣＲ（℃／ｓ）以上にて冷却し
た後、溶融亜鉛めっきし、次いで５００℃〜Ａｃ＿１点
の温度にて合金化処理を施した後、ＣＲ以上の冷却速度
にてＭｓ点以下に冷却することを特徴とする高延性高強
度合金化溶融亜鉛めっき鋼板の製造方法。[Claims] In weight% (the same applies hereinafter), C: 0.06 to 0.30%
, Si: 0.6% or less, P: 0.1% or less, Nb: 0.
01-0.20% and sol. Al: 0.01-0.1
0%, further Mn: 0.6 to 3.0%, Cr: 0
．． 1 to 1.5% and Mo: 0.1 to 1.0%, and the remainder is iron and unavoidable impurities. , After cold rolling, when recrystallization annealing is performed on a continuous hot-dip galvanizing line,
The heating temperature was set to Ac_3 points -50°C to 900°C, and cooling to the plating bath was performed at a cooling rate of 20°C/s or less for 5
Cooled to a temperature range of 00 to 650°C, then heated to the plating bath temperature lnCR = -1.18 Meq + 3.37 where Meq (%) = Mn + 1.52 Mo + 1.10
After cooling at a critical cooling rate CR (°C/s) shown by Cr+0.10Si+2.1P, hot-dip galvanizing, and then alloying treatment at a temperature of 500°C to Ac_1 point, A method for producing a highly ductile, high-strength alloyed hot-dip galvanized steel sheet, characterized by cooling to a cooling rate below the Ms point.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29915990A JP2761096B2 (en) | 1990-11-05 | 1990-11-05 | Manufacturing method of high ductility and high strength alloyed hot-dip galvanized steel sheet |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29915990A JP2761096B2 (en) | 1990-11-05 | 1990-11-05 | Manufacturing method of high ductility and high strength alloyed hot-dip galvanized steel sheet |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04173946A true JPH04173946A (en) | 1992-06-22 |
| JP2761096B2 JP2761096B2 (en) | 1998-06-04 |
Family
ID=17868897
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP29915990A Expired - Fee Related JP2761096B2 (en) | 1990-11-05 | 1990-11-05 | Manufacturing method of high ductility and high strength alloyed hot-dip galvanized steel sheet |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2761096B2 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05179402A (en) * | 1992-01-08 | 1993-07-20 | Nkk Corp | High strength hot-dip galvanized steel material excellent in stability of material as well as in workability and its production |
| US6709535B2 (en) | 2002-05-30 | 2004-03-23 | Kobe Steel, Ltd. | Superhigh-strength dual-phase steel sheet of excellent fatigue characteristic in a spot welded joint |
| JP2005538248A (en) * | 2002-09-06 | 2005-12-15 | ユジノール | Ultra high mechanical strength steel material and method for producing the sheet coated with zinc or zinc alloy |
| JP2018508653A (en) * | 2015-01-14 | 2018-03-29 | エーケー スティール プロパティ−ズ、インク． | Duplex steel sheet with improved properties |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1443124B1 (en) * | 2000-01-24 | 2008-04-02 | JFE Steel Corporation | Hot-dip galvanized steel sheet and method for producing the same |
| JP5194811B2 (en) | 2007-03-30 | 2013-05-08 | Ｊｆｅスチール株式会社 | High strength hot dip galvanized steel sheet |
| JP5119903B2 (en) | 2007-12-20 | 2013-01-16 | Ｊｆｅスチール株式会社 | Method for producing high-strength hot-dip galvanized steel sheet and high-strength galvannealed steel sheet |
-
1990
- 1990-11-05 JP JP29915990A patent/JP2761096B2/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH05179402A (en) * | 1992-01-08 | 1993-07-20 | Nkk Corp | High strength hot-dip galvanized steel material excellent in stability of material as well as in workability and its production |
| US6709535B2 (en) | 2002-05-30 | 2004-03-23 | Kobe Steel, Ltd. | Superhigh-strength dual-phase steel sheet of excellent fatigue characteristic in a spot welded joint |
| JP2005538248A (en) * | 2002-09-06 | 2005-12-15 | ユジノール | Ultra high mechanical strength steel material and method for producing the sheet coated with zinc or zinc alloy |
| JP2018508653A (en) * | 2015-01-14 | 2018-03-29 | エーケー スティール プロパティ−ズ、インク． | Duplex steel sheet with improved properties |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2761096B2 (en) | 1998-06-04 |
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