JP2004211158A - Galvanized steel for welding, and electric resistance welded tube thereof - Google Patents

Galvanized steel for welding, and electric resistance welded tube thereof Download PDF

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JP2004211158A
JP2004211158A JP2002382256A JP2002382256A JP2004211158A JP 2004211158 A JP2004211158 A JP 2004211158A JP 2002382256 A JP2002382256 A JP 2002382256A JP 2002382256 A JP2002382256 A JP 2002382256A JP 2004211158 A JP2004211158 A JP 2004211158A
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steel
alloy
zinc
welding
plated
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JP4173990B2 (en
Inventor
Shinji Kodama
真二 児玉
Hideki Hamaya
秀樹 濱谷
Nobuo Mizuhashi
伸雄 水橋
Akihiro Miyasaka
明博 宮坂
Kazumi Nishimura
一実 西村
Takuya Hara
卓也 原
Akira Tanaka
暁 田中
Junichi Kobayashi
順一 小林
Kenichi Asai
謙一 浅井
Manabu Takahashi
学 高橋
Yasuhide Morimoto
康秀 森本
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Nippon Steel Corp
新日本製鐵株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a galvanized steel for welding excellent in the quality of the welded part and capable of suppressing the occurrence of liquid metal brittle crack in the welded heat affected part when the galvanized steel to be used for welded structural member such as building, automobile is welded in various kinds of method, further when an electric resistance welding is applied after tube-making by using the galvanized steel, and to provide an electronic resistance welded tube thereof. <P>SOLUTION: In this galvanized steel, a galvanized layer is formed on the surface of steel consisting of, by mass%, 0.01-0.3% C, 0.01-2.0% Si, 0.1-3.0% Mn, ≤ 0.015% S, 0.001-0.5% Al, 3-40 ppm B, 0.0005-0.006% N and the balance Fe with inevitable impurities. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【0001】
【発明の属する技術分野】
本発明は、主に、建築、自動車などの溶接構造部材に使用される亜鉛系合金めっき鋼材およびその電縫鋼管に関し、特に、このような亜鉛系合金めっき鋼材を種々の方法で溶接する際、さらには、亜鉛系合金めっき鋼材を用いて造管後、電縫溶接する際に、溶接熱影響部における液体金属脆化割れ(以下、亜鉛めっき割れということもある)の発生を抑制できる溶接用亜鉛系合金めっき鋼材およびその電縫鋼管に関する。
【0002】
【従来の技術】
Znめっき鋼材は、建築や自動車の構造部材の耐食性向上の観点から幅広く用いられ、最近ではZnめっき中にAl、MgまたはSiを添加したZn−Al−Mg系合金めっき、Zn−Al−Mg−Si系合金めっきなどの亜鉛系合金めっきを鋼材表面に施した耐食性に優れた亜鉛系合金めっき鋼材が特許文献1および特許文献2で知られている。これら亜鉛系合金めっき鋼材は、種々の溶接法により溶接して溶接鋼構造物として使用される場合が多い。
【0003】
また、これら亜鉛系合金めっき鋼材を用いて管状に成形後、突合せ端部を高周波誘導溶接および高周波抵抗溶接(以下、電縫溶接という。)等により溶接した鋼管や角管も多く使用されている。
【0004】
しかし、これら亜鉛系合金めっき鋼材を溶接する際に、鋼材の溶接熱影響部(以下、溶接HAZ部という。)では、溶接入熱により溶融された亜鉛系合金めっきが鋼材表面に溶融状態のまま残留しやすく、かつ、鋼材組織は結晶粒が成長、粗大化した組織となりやすい。このような状態で鋼材に引用応力が働いた場合には、鋼材の溶接HAZ部組織によっては、溶融めっきが鋼材表面の結晶粒界に侵入して粒界が脆化した領域、つまり脆化域が形成され、割れが発生する場合がある。特に被溶接部材が著しく拘束された状態での溶接時に溶接HAZ部の脆化域で割れが発生することがある。
【0005】
一方、従来から、鋼材を溶接して得られた溶接構造物を高温溶融亜鉛合金めっき浴中でめっき処理する際にも、溶接構造物の溶接部、特に溶接止端部(溶接ビード(溶接金属)と鋼材との境界)近傍に残留した引張応力(以下、残留引張応力という)やめっき浴中で発生する熱歪みなどが作用し同様な割れが発生することが知られていた。
【0006】
これらのように、高温で或る種の液体金属が或る種の固体金属表面に接触し、かつ固体金属表面にある大きさの引張応力が作用する場合に、固体金属表面に脆化域が形成され、割れが発生する現象を液体金属脆化割れ:LME(Liquid Metal Embrittlement)と称され、例えば、非特許文献1で知られている。
【0007】
従来、溶接継ぎ手を高温溶融めっき浴中でめっきする際に発生する液体金属脆化割れ(LME)を抑制するための手法としては、鋼材の成分規定による組織制御が試みられており、LME炭素当量式がJIS(例えば、鋼材用はJIS G3219−1995、また、鋼管用はJIS G 3474−1995)で規格化されている。
【0008】
また、特許文献3では、Zn−Al合金めっきが施される鋼材に対して鋼材の各成分を限定するとともに、特にBに対しては0.0002%以下の厳しい制約を設けている。
【0009】
しかし、上記LME炭素当量式は、溶接継ぎ手を高温溶融めっき浴でめっき処理する際の液体金属脆化割れ(LME)を対象とし、その割れが発生する温度域はめっき浴の温度:450℃(めっき金属の融点)程度であり、亜鉛系合金めっき鋼材を溶接する際のビーク温度:1500℃に比べて非常に低い温度条件で発生する液体金属脆化割れ(LME)を対象とする。これに対して、亜鉛系合金めっき鋼材を溶接する際に発生する液体金属脆化割れ(LME)は、1500℃程度の鋼材が溶融する高温域から450℃程度のめっき金属の融点までの広い温度域で発生するため、従来のLME炭素当量式を溶接用の亜鉛系合金めっき鋼材に適用しても、溶接時の液体金属脆化割れ(LME)を充分に抑制することは困難であった。
【0010】
また、従来、プレス成形性が要求される極低炭素のIF(Interstitial Free)鋼材のろう付けにおいて、はんだ脆性による上記液体金属脆化割れの発生が知られており、その対策として、例えば、特許文献4では、Cが0.0005〜0.03%と低くいIF鋼に対して、Tiを0.01〜0.2%添加してNを固定するとともに、Bを0.0002〜0.003%添加することにより溶融金属の粒界への進入を防ぎ、割れ発生を抑制している。
【0011】
この方法は、成形性が要求される低強度で極低炭素のIF鋼を対象とし、また、その割れが発生する温度域がはんだ付けのビーク温度:900〜1000℃(はんだの融点に相当)程度である場合を前提とするものである。一方、IF鋼より強度が高く(引張強度:350MPa以上程度)、高炭素(C:0.01〜0.3%程度)である高張力鋼を母材とした亜鉛系合金めっき鋼材を、ビーク温度が1500℃(鋼材の融点に相当)程度の条件で溶接する場合には、900℃より低い温度域でも液体金属脆化割れは発生するため、上記の方法を高張力鋼の溶接に適用しても液体金属脆化割れを充分に抑制することは困難である。
【0012】
近年、特に、自動車分野などでは、亜鉛系合金めっき鋼板として、自動車の軽量化及び燃費向上、ひいては地球環境を配慮して、従来の成形性を重視した低炭IF鋼板に替えて、より引っ張り強度が高く、Cや合金元素などの含有量が高い高強度鋼を母材とし、かつその母材表面に従来のZnめっきよりも耐食性が高いZn−Al系、Zn−Al−Mg系、Zn−Al−Mg−Si系などの亜鉛系合金めっきを施した鋼板が適用されるようになり、それに伴って従来は問題にならなかった鋼材溶接時の液体金属脆化割れの発生が顕在化するようになってきた。
【0013】
また、従来の自動車、建築分野においては、普通鋼材を溶接後、その溶接構造物を高温亜鉛めっき浴中でめっき処理する、後付けめっき処理が主流であったが、近年、工程省略、製造コスト削減の観点からめっき鋼材またはその成形部材を溶接する、プレめっき鋼材の溶接施工が適用されるようになり、溶接時に発生するめっき割れを抑制するための技術に対する産業上の意義が大きくなってきた。
【0014】
また、耐食性に優れた鋼管を製造する方法として、生産性向上および製造コスト低減の観点から、従来の電縫鋼管製品を後付けめっき処理する方法に替えて、近年、亜鉛系合金めっき鋼板を用いて管状に成形後、突合せ端部を電縫溶接する方法も実用化されている。
【0015】
しかし、造管後の電縫溶接時には、大きなスプリングバック力(加工反力)、成形歪または熱収縮力が作用するため、Zn−Al−Mg系合金めっき、Zn−Al−Mg−Si系合金めっきなどの亜鉛系合金めっきの成分系の種類によっては、900℃より低い温度域で溶接熱影響部表面に残留した溶融亜鉛系合金めっきが鋼材表面から粒界に浸入して液体金属脆化割れが発生する。
【0016】
従来、このような亜鉛系合金めっき鋼板の電縫溶接時の割れ抑制技術として、例えば、特許文献5では、Zn−Al−Mg系合金めっき鋼板を造管してその突合せ端部を溶接する際にアップセット量を制御することで、溶接止端部の形状をなだらかにして引っ張り応力の集中を低減し、割れを解消する技術が開示されている。しかし、このアップセット量制御による引っ張り応力集中の低減が可能となる条件は一部の鋼管サイズや特定鋼種に限定され、幅広い条件で安定した効果を発揮することは困難である。
【0017】
【特許文献1】
特開平10−226865号公報
【特許文献2】
特開2000−64061号公報
【特許文献3】
特開平05−156406号公報
【特許文献4】
特開昭60−92453号公報
【特許文献5】
特開2002−115793号公報
【非特許文献1】
Journal of Institute of Metals (1914) p.108. (A.K.Huntington)
【0018】
【発明が解決しようとする課題】
本発明は、上述したような従来技術の問題点を踏まえ、例えば、めっき鋼材、特に、Zn−Al系合金めっき、Zn−Al−Mg系合金めっき、Zn−Al−Mg−Si系合金めっきなどを施した亜鉛合金系めっき鋼材を種々の方法で溶接する際、さらには、亜鉛系合金めっき鋼材を用いて造管後、電縫溶接する際に、溶接熱影響部における液体金属脆化割れの発生を抑制でき、溶接部品質に優れた溶接用亜鉛系合金めっき鋼材およびその電縫鋼管を提供することを目的とする。
【0019】
【課題を解決するための手段】
本発明は、上記課題を解決するためになされたもので、その要旨は次の通りである。
(1)亜鉛系合金めっき層を鋼材表面に設けた亜鉛系合金めっき鋼材において、前記鋼材が、質量%で、
C:0.01〜0.3%
Si:0.01〜2.0%
Mn:0.1〜3.0%
S:0.015%以下
Al:0.001〜0.5%
B:3〜40ppm
N:0.0005〜0.006%
を含有し、残部がFeおよび不可避的不純物からなることを特徴とする溶接用亜鉛系合金めっき鋼材。
(2)前記鋼材が、さらに、質量%で、Ti:0.001〜0.5%を含有し、かつ下記(1)式で与えられる条件を満足することを特徴とする上記(1)に記載の溶接用亜鉛系合金めっき鋼材。
【0020】
0.5≧[%Ti]+[%Al]≧0.001 … (1)
但し、[%X]は、合金元素Xの質量%で表した含有量を示す。
(3)前記鋼材におけるS含有量が、質量%で、0.003%以下であることを特徴とする上記(1)または(2)記載の溶接用亜鉛系合金めっき鋼材。
(4)前記鋼材が、さらに、質量%で、P:0.02〜0.05%を含有することを特徴とする上記(1)から(3)のうちの何れかに記載の溶接用亜鉛系合金めっき鋼材。
(5)前記亜鉛系合金めっきが、Zn−Al系合金めっき、Zn−Al−Mg系合金めっき、および、Zn−Al−Mg−Si系合金めっきのうちの何れか1種であることを特徴とする上記(1)から(4)のうちの何れかに記載の溶接用亜鉛系合金めっき鋼材。
(6)前記Zn−Al系合金めっきが、質量%で、Al:0.18〜5%を含有し、さらに、Mg:0.01〜0.5%、La:0.001〜0.5%、および、Ce:0.001〜0.5%のうちのいずれか1種または2種以上を含有し、残部がZnおよび不可避的不純物であることを特徴とする上記(5)に記載の溶接用亜鉛系合金めっき鋼材。
(7)前記Zn−Al−Mg系合金めっきが、質量%で、Al:2〜19%、Mg:0.5〜10%を含有し、残部がZnおよび不可避的不純物であることを特徴とする上記(5)に記載の溶接用亜鉛系合金めっき鋼材。
(8)前記Zn−Al−Mg−Si系合金めっきが、質量%で、Al:2〜19%、Mg:1〜10%、Si:0.01〜2%を含有し、残部がZnおよび不可避的不純物であることを特徴とする上記(5)に記載の溶接用亜鉛系合金めっき鋼材。
(9)質量%で、
C:0.01〜0.15%
Si:0.01〜2.0%
Mn:0.1〜3.0%
S:0.015%以下
Al:0.001〜0.5%
B:6〜15ppm
N:0.0005〜0.006%
を含有し、残部がFeおよび不可避的不純物からなる鋼板の表面に亜鉛系合金めっき層を設けた亜鉛系合金めっき鋼板を管状に成形後、その突合せ端部を電縫溶接したことを特徴とする亜鉛系合金めっき電縫鋼管。
(10)前記鋼板が、さらに、質量%で、Ti:0.001〜0.5%を含有し、かつ下記(1)式で与えられる条件を満足することを特徴とする上記(9)に記載の亜鉛系合金めっき電縫鋼管。
【0021】
0.5≧[%Ti]+[%Al]≧0.001 … (1)
但し、[%X]は、合金元素Xの質量%で表した含有量を示す。
(11)前記鋼板におけるS含有量が、質量%で、0.003%以下であることを特徴とする上記(9)または(10)記載の亜鉛系合金めっき電縫鋼管。
(12)前記鋼板が、さらに、質量%で、P:0.02〜0.05%を含有することを特徴とする上記(9)から(11)のうちの何れかに記載の亜鉛系合金めっき電縫鋼管。
(13)前記亜鉛系合金めっきが、Zn−Al系合金めっき、Zn−Al−Mg系合金めっき、および、Zn−Al−Mg−Si系合金めっきのうちの何れか1種であることを特徴とする上記(9)から(12)のうちの何れかに記載の亜鉛系合金めっき電縫鋼管。
(14)前記Zn−Al系合金めっきが、質量%で、Al:0.18〜5%を含有し、さらに、Mg:0.01〜0.5%、La:0.001〜0.5%、および、Ce:0.001〜0.5%のうちのいずれか1種または2種以上を含有し、残部がZnおよび不可避的不純物であることを特徴とする上記(13)に記載の亜鉛系合金めっき電縫鋼管。
(15)前記Zn−Al−Mg系合金めっきが、質量%で、Al:2〜19%、Mg:0.5〜10%を含有し、残部がZnおよび不可避的不純物であることを特徴とする上記(13)記載の亜鉛系合金めっき電縫鋼管。
(16)前記Zn−Al−Mg−Si系合金めっきが、質量%で、Al:2〜19%、Mg:1〜10%、Si:0.01〜2%を含有し、残部がZnおよび不可避的不純物であることを特徴とする上記(13)に記載の亜鉛系合金めっき電縫鋼管。
【0022】
【発明の実施の形態】
一般に、鋼材を溶接した後の溶接部は、溶融した溶接金属が凝固した後、室温までの冷却過程で熱収縮するため、溶接部に外力が加わっていない状態でも溶接部の溶接金属および母材熱影響部には熱収縮に伴う引っ張り応力が発生する。Zn−Al系、Zn−Al−Mg系、Zn−Al−Mg−Si系などの特定成分系の亜鉛系合金めっきを施した鋼材を溶接する場合に発生する液体金属脆化割れは、溶接後に蒸発せずに溶接熱影響部表面に残存した溶融亜鉛系合金めっきが、溶接熱影響部の熱収縮に伴って発生した引っ張り応力を引き金として、結晶粒界に浸入して起きるものと考えられる。
【0023】
溶接後の熱収縮に伴って発生する引っ張り応力は、温度に応じて変化する溶接部周囲の鋼材の高温強度により変化し、例えば、溶接部が900℃程度の高温状態で生じる引張応力は比較的小さいのに対し、亜鉛系合金めっきの融点に相当する400〜500℃程度の低温域では溶接部周囲の高温強度の回復並びに熱収縮量の増加により大きな引っ張り応力が働く。また、鋼材の高温強度は通常その冷間強度に依存するため、被溶接鋼材の引っ張り強度が高くなるほど熱収縮に伴う引っ張り応力は大きくなる。また、その熱収縮に伴う引っ張り応力の大きさは、溶接時の溶接部の拘束状態によっても変化し、溶接変形抑制のために治具などで溶接部近傍を機械的に拘束して溶接する場合や、電縫鋼管製造プロセスにおける管状成形後の端部突合せ溶接などの加工反力が大きい継ぎ手形状で溶接する場合などでは、熱収縮に伴う引っ張り応力は増大する。
【0024】
従来の極低炭素のIF鋼材のろう付けの場合の割れ発生は、はんだの融点である約900℃以上の高温域でのみで発生じていたのに対して、亜鉛系合金めっき鋼材の溶接では、900℃より低い温度からめっき融点に相当する400℃程度の低温域までの広い温度範囲で割れが発生し、その割れは溶接部の熱収縮に伴う大きな引っ張り応力が作用して発生する点で従来のIF鋼材のろう付けの脆化割れと異なる。
【0025】
本発明は、亜鉛系合金めっき鋼材の溶接施工において、900℃以上の高温域だけでなく、それより低い温度から400℃程度の低温域までの範囲で多く発生するめっき割れを抑制するために、溶接時に溶接熱影響部(以下、これを溶接HAZ部と称する)の引っ張り応力に対する耐力、つまり粒界強度を向上させることを技術思想とするものである。
【0026】
本発明は、この技術思想を基に、母材の引っ張り強度が350MPa程度以上、800MPa程度以下程度と、IF鋼よりも高い強度の鋼材で、その表面に亜鉛系合金めっきが施された亜鉛系合金めっき鋼材を対象とし、その溶接時の液体金属脆化割れ防止策を詳細に検討した結果、母材成分としてCを質量%で0.01〜0.3%含有する鋼材にBを0.0003〜0.004%添加することにより溶接部の靭性を確保しつつ、溶接時の液体金属脆化割れを防止できるという新たな知見を得てこれをもとに発明がなされたものである。
【0027】
以下に本発明を詳細に説明する。
【0028】
先ず、溶接過程において大きな引張応力の発生する比較的低温域での割れの防止を検証した結果、Cによる焼き入れ性の向上が有効であるという知見を得た。理由は明確ではないが、おそらく溶融状態の亜鉛系合金めっきが残存する鋼材の溶接HAZ部の強度の増化により引張応力に伴う塑性歪が低減されたことが有効に作用したと考えられる。
【0029】
しかしながら、溶接変形を防止する等の目的で、予め治具により拘束して溶接する場合には、熱収縮による引っ張り応力がより大きくなるため、このような拘束状態での極めて厳しい溶接条件での溶接では、依然として割れが発生するという問題が残っている。特に、耐食性に優れた鋼管を製造するプロセスにおいて、亜鉛系合金めっき鋼板を管状に成形加工後、突合せ端部を電縫溶接する場合には、溶接部に熱収縮力と合わせて、成形加工に起因して大きなスプリングバック力(加工反力)が作用するため、溶融亜鉛系合金めっき割れが生じやすくなる。
【0030】
このような厳しい溶接条件では、溶接HAZ部の引張応力が比較的穏やかと考えられる高温域においても所定の引っ張り応力が発生し液体金属脆化割れにつながると思われるため、C含有量の制御だけでは不十分である。
【0031】
そこで、所定C量を含有する鋼材におけるBの影響を検討した。
【0032】
従来から、はんだ脆化割れ防止技術として、極低炭素のIF鋼材のろう付けの際にB添加により約900℃以上のオーステナイト温度域でBの粒界偏析・濃化により低融点溶融金属の粒界侵入の抑制効果があることが知られている。本発明は、はんだ付けに比べて溶接ピーク温度が1500℃(鋼材融点に相当)以上と非常に高い溶接条件での溶接割れを対象とするので、高温域での脆化割れの抑制に対してはこのようなBの粒界偏析・濃化による溶融状態の亜鉛系合金めっきの粒界への侵入抑制効果が同様に得られるものと考えられる。このBの粒界偏析は、オーステナイト−フェライト二相域以上の温度で起こり、粒界の空孔・欠陥にBが浸入することにより界面エネルギーが低下し、溶融しためっき成分の粒界侵入・拡散の抵抗となるが、温度低下に応じてBの粒界偏析は起き難くなる。
【0033】
本発明者らの検討の結果、上記Bの作用効果に加えて、新たな知見として、Bはオーステナイト−フェライト二相域より低い温度域においても、溶接HAZ部のように冷却速度が比較的速い領域では、Bは旧オーステナイト粒界の強化元素として働くため、熱収縮によって溶接HAZ部に発生する引っ張り応力に対する粒界強度の向上、ひいては低温度域での溶融めっき割れ防止に有効であることがわかった。
【0034】
C量およびB量を変化させた鋼材の表面に亜鉛系合金めっきが施された亜鉛系合金めっき鋼材をアーク溶接したときの実験結果として、図1に溶接部の割れ深さ状況、図2に溶接部の靭性の劣化率を示す。図1における割れ深さは、母材板厚に対する割れ深さの比で表現し、図2における靭性の劣化率は、B無添加鋼材(B量0%)のHAZ靭性値に対する各々のB量添加鋼材のHAZ靭性値の比で表現した。また、亜鉛系合金めっき鋼材には板厚6mmで11%Al+3%Mg+0.2%Si+Znめっき層が施されたものを用いた。
【0035】
溶接部の割れの評価方法としては、図4(a)、(b)に示すように厚手鋼材1の内側に評価対象となるめっき鋼材2を嵌め込み溶接3し、さらにめっき鋼材2上に丸鋼4を円周溶接5することによって円周溶接5の溶接ビードのクレータ部(終端部)に発生する割れの深さを測定し、評価した。厚手鋼材1にめっき鋼材2を溶接することにより、めっき鋼材2を円周溶接5する際の拘束条件を厳しくした。
【0036】
なお、溶接部の割れ深さは溶接部断面を観察し、鋼材表面から割れの伸展している板厚方向の長さを測定することによって求めた。
【0037】
図1から、鋼材中のC量に係わらずB量の増加により溶接部の割れは低下する傾向にあるものの、低C材(C:0.005%)に比べて、中C材(C:0.01%)、高C材(C:0.15%)では、B量が3ppmと比較的少ない量でも溶接部の割れが急激に低下され、B量が5ppm 以上で溶接部の割れ発生はほぼなくなることがわかる。一方、低C材(C:0.005%)または中C材(C:0.01%)の場合でも、B量を20ppm以上または40ppm以上と多量に添加すると溶接部の割れは比較的小さくなるが、図2に示すように溶接部の靭性値が低下し、目標とする靱性(80%以上)が得られないことがわかる。これは、高C材に比べて低C材、中C材では、結晶粒が粗大化しやすいためB量の増加に伴ってBの粒界偏析による靭性値の低下が大きくなったと考えられる。図1及び図2からC:0.01%以上の中C材、高C材を母材とする亜鉛系合金めっき鋼材をアーク溶接する際に、溶接部の目標とする靭性を確保しつつ溶融亜鉛系合金めっき割れを防止するための鋼材中のB含有量は3〜40ppmとする必要がある。
【0038】
さらに、C量およびB量を変化させた鋼材の表面に亜鉛系合金めっきが施された亜鉛系合金めっき鋼板を用いて、これを管状に成形加工後、突合せ端部を電縫溶接して鋼管を製造したときの実験結果として、図3に溶接部の割れ深さおよび靭性の劣化率を示す。なお、溶接部の割れ深さは溶接部断面を観察し、鋼材表面から割れの伸展している板厚方向の長さを測定することによって求めた。溶接部の割れ深さおよび靭性の劣化率は、上述の図1および2と同じ方法で求めた。また、亜鉛系合金めっき鋼板は板厚6mmで11%Al+3%Mg+0.3%Si+Znめっき層が施されたものを用いた。
【0039】
図3から、鋼管の電縫溶接時の溶融亜鉛系合金めっき割れについては、C量が0.15%以下の中C材、高C材においてB添加量の増加によりその割れは効果的に低下しB添加量が6ppm 以上で溶接部の割れ発生はほぼなくなるが、C量が0.35%程度の高C材では、B添加による割れ低減効果はほとんど得られない。一方、C量が0.15%以下の中C材、高C材においてB添加量を増加するとともに溶接部の靭性値は低下する。目標とする靱性(80%以上)を確保しつつ鋼管の電縫溶接時の溶融亜鉛系合金めっき割れを防止するための鋼材中のB含有量は6〜15ppmとする必要がある。
【0040】
以上の知見と踏まえて、本発明の溶接用亜鉛系合金めっき鋼材の母材成分およびその含有量の範囲を以下の通りとする。なお、以下の%は、特に説明がない限り質量%を示すものとする。
【0041】
C:本発明では、Cは350MPa以上の引っ張り強さを確保するために必要であると共に、上述のように溶接時の熱収縮により生じる引っ張り応力に対して、溶接HAZ部の焼入れ向上すなわち応力集中部の塑性歪の低減による割れ防止のために必須な元素である。上記図1及び図2からB添加との組み合わせにより溶接部の割れ発生を充分防止でき、かつ良好な靱性を確保できるC含有量として、その下限を0.01%とした。なお、Cの過剰の添加は溶接HAZ部を硬化させ曲げ性能低下や遅れ割れの発生につながるのみならず、Fe−C−B析出物を形成しやすくなりBのめっき脆化抑制効果を低減してしまうためC含有量の上限を0.3%とした。
【0042】
また、図3に示すように鋼管の電縫溶接時、または溶接部周囲を高い拘束力で拘束した状態で溶接する時には、溶接HAZ部の割れが発生しやすくなるためにC含有量の上限を0.15%とするのが好ましい。
【0043】
Si:Siは母材の脱酸のために必要であり、その含有量の下限値を0.01%とした。また、Siは固溶強化作用の作用があり下記のMnとともに母材強度の調整に用いる。なお、過剰のSi添加は熱間圧延時の酸化スケールの増加、延性低下につながるためその含有量の上限は2.0%とした。
【0044】
また、熱延鋼板にめっきする場合には問題ないが、冷延鋼板にめっきする場合にはめっき付着性が劣化するためSi量は0.1%以下にすることがより好ましい。
【0045】
Mn:Mnは鋼材の熱間脆性の原因となる鋼中の不可避的不純物のSをMnSとして固定して無害化するためその含有量の下限値を0.1%とした。一方、Mnの過剰の添加は溶接HAZ部を硬化させ曲げ性能低下や遅れ割れの発生につながるためその含有量の上限を3.0%とした。
【0046】
S:Sは鋼材の熱間加工性を低下させる元素であるから少ないほど好ましく、上限値を0.015%とした。
【0047】
また、Sは、溶接時のめっき脆化割れ抑制の観点からは、低S化することにより脆化抑制効果が認められるため、その含有量の上限を0.003%とするのが好ましい。
【0048】
Al:Alは鋼の脱酸元素であるとともに、鋼中のNを固定する作用を有するために、Bが窒化物として析出するのを防ぎ溶融亜鉛系合金めっきの液体金属脆化割れを抑制する効果もある。これらの効果を得るために0.001%以上添加する必要がある。一方、過剰にAlを添加すると粗大な非金属介在物を生成して鋼材の靭性等の性能を低下させるので上限値は0.5%とした。
【0049】
B:Bは上述のように溶接時のオーステナイト域またはオーステナイト−フェライト二相域以上の温度で、粒界に偏析・濃化または粒界の空孔・欠陥に浸入して界面エネルギーを低下して溶融状態の亜鉛系合金めっきの粒界への浸入・拡散を抑制する作用効果がある。また、溶接部の冷却過程では、Bは焼入れ性向上元素であり、ベーナイトあるはマルテンサイト組織の形成を促進し、組織の微細化および、熱収縮による引っ張り応力に対して特に溶接HAZ部の粒界強化により応力、塑性歪の低減効果も得られる。図1から所定C量の下で溶接部の割れ発生を充分防止できるB含有量として、その下限を3ppmとし、一方、上記図2から溶接部の靭性劣化抑制のためB含有量の上限を40ppmとする。
【0050】
また、図3に示すように鋼管の電縫溶接時、または溶接部周囲を高い拘束力で拘束した状態で溶接する時には、溶接HAZ部の割れが発生しやすくなるためにB含有量の下限を6ppmとし、溶接部の靭性劣化抑制のためB含有量の上限を15ppmとするのが好ましい。
【0051】
N:Nは鋼材の強度を上昇させる一方で、多大なNの添加は鋼材の靭性を低下させるとともに、BをBNなどの窒化物として析出させ、Bのめっき脆化抑制効果も損ねてしまう。そこで、上限値を0.006%とした。Nは少ないほど好ましいが0.0005%以下にすることはコストの増加を招くため下限値を0.0005%とした。
【0052】
本発明では、上記成分に加えて以下の理由でさらに以下の成分添加量を規定する。
【0053】
Ti:Tiは、鋼中のNを窒化物として固定し、BがBNなどの窒化物として析出するのを防ぐ作用があるため、溶融亜鉛系合金めっきの液体金属脆化割れをさらに抑制するためには、0.001%以上添加することが好ましい。一方、Tiは0.5%を超えて添加しても割れ抑制効果が飽和し、いたずらに合金添加コストが上昇するだけであるのでその含有量の上限値を0.5%とした。
【0054】
また、Tiの含有量は、Tiと同様にNを固定する作用を有するAlの含有量のとの合計量が0.001%以上、0.5%以下となるように調整することが好ましい。
【0055】
P:Pは、高温割れ等の一般に溶接性向上の観点からは低減化することが望ましいが、溶接時のめっき脆化割れに対してはPの粒界偏析による割れ低減効果が認められるため、0.02%以上添加することが好ましい。一方、過度の添加は、高温割れを発生させる、その含有量の上限値を0.05%とするのが好ましい。
【0056】
また、本発明において、上記成分を含有する鋼材の表面に施される亜鉛系合金めっきとしては、特許文献1に記載されているようなZn−Al−Mg系、特許文献2に記載されているようなZn−Al−Mg−Si系、或いはZn−Al系の亜鉛系合金めっきをいう。因みに、Zn−Al系合金めっきでは、Al:0.18〜5%を含有し、さらに、Mg:0.01〜0.5%、La:0.001〜0.5%、および、Ce:0.001〜0.5%のうちのいずれか1種または2種以上を含有し、残部がZnからなり、Zn−Al−Mg系合金めっきでは、Al:2〜19%、Mg:0.5〜10%、残部Znからなるめっきからなり、Zn−Al−Mg−Si系合金めっきでは、Al:2〜19%、Mg:0.5〜10%、Si:0.01〜2%、残部Znからなるめっきからなる。本発明は、これらの亜鉛系合金めっきのうちの何れか1種のめっきが施された亜鉛系合金めっき鋼材を溶接して溶接構造物とする際に上述した顕著な効果を発揮する。
【0057】
また、本発明における亜鉛系合金めっき電縫鋼管は、これらの亜鉛系合金めっき鋼板を用い、この鋼板を管状に成形加工後、その突合せ端部を高周波誘導溶接または高周波抵抗溶接などの電縫溶接を行うことにより製造した電縫鋼管である。
【0058】
本発明の亜鉛系合金めっき電縫鋼管は、亜鉛系合金めっき鋼板を電縫溶接して製造した溶接部割れのない品質に優れた鋼管であり、従来の電縫鋼管製品を後付けめっき処理する方法によって製造した亜鉛系合金めっき電縫鋼管に比べて、溶接部の品質を良好に維持しつつ、生産性の向上および製造コストの低減が可能となる。
【0059】
なお、上記の本発明の実施形態の説明では、溶接方法をアーク溶接、または、鋼管の電縫溶接に限って説明したが、これらの溶接方法に限定するものではない。例えば、レーザ溶接、スポット溶接、プロジェクション溶接でもアーク溶接と同様の熱サイクルを受け、溶接部近傍には引っ張り応力が働くため、溶接部の液体金属脆化割れが生じる可能性があり、本願発明の適用により同様に溶接時のめっき割れ防止効果が得られる。
【0060】
【実施例】
[実施例1]
表1に示す成分を含有する母材鋼材に、目付量片面90g/m のMg:3%、Al:11%、Si:0.3%、残部Znからなる亜鉛系合金めっきを施した引っ張り強度:400MPa 級の6mm厚の亜鉛系合金めっき鋼材をアーク溶接し前記評価方法と同様に溶接部の割れおよび靱性の評価を行った。なお、上記Zn−Al−Mg−Si合金めっきは従来の単なるZnめっきに比較して極めて優れた耐食性を示すことが知られている。
【0061】
溶接はパルスMAGアーク溶接で溶接電流200A、溶接電圧23V、溶接速度30cm/min とし、溶接ワイヤにはYGW−12を使用した。なお、溶接部の割れの検査は、図4(a)、(b)に示すように円周溶接5の溶接ビードで発生しやすい溶接終端部において断面観察し割れ深さ(表1は母材板厚に対する割れ深さの比で示した)を求めた。また、靭性の劣化率はB無添加(B量0%)の場合の溶接HAZ部の靭性値に対する各B量を添加した場合の溶接HAZ部の靭性値の比で評価した。なお、割れ深さ率および靭性定価率は、各々5%以下、80%以上を良好と判断した。
【0062】
表1に母材鋼材中の主要な成分と割れおよび靱性の低下率の結果を示す。記号1〜10は本発明例である。記号1〜10の発明例においてC量が0.03と比較的少ない場合(記号1)は僅かに割れが生じたが、実用上無視できる程度であり、その他は割れが皆無であった。また、いずれの発明例も溶接HAZ靭性の大幅な低下は見られなかった。
【0063】
一方、記号11〜14は本発明の鋼材成分範囲から外れた比較例である。
【0064】
記号11および12はB量が本発明で規定する範囲より少ないため液体金属脆化割れが生じた。
【0065】
記号13はC量が本発明で規定する範囲より少ないために溶接HAZ靭性の低下が激しかった。
【0066】
記号14は本発明で規定する範囲に比べBが多いため、発生した割れは極めて小さかったが、溶接HAZ部の靭性値の低下が激しかった。
【0067】
以上の実施例では溶接方法としてアーク溶接を用いたが、同様にレーザ溶接、スポット溶接、プロジェクション溶接を用いた試験においても、溶接部の液体金属脆化割れは抑制でき、かつ溶接HAZ部の靭性は良好であった。
【0068】
【表1】
【0069】
[実施例2]
表2に示す成分を含有する母材鋼板に、目付量片面90g/m のMg:3%、Al:11%、Si:0.3%、残部Znからなる亜鉛系合金めっきを施した引っ張り強度:400MPa級の6mm厚の亜鉛系合金めっき鋼板を用いて、これを管状に成形後、その突合せ端部を溶接速度:30m/min、高周波パワー:450kW、アプセット量:3mmの条件で電縫溶接し、外径355mmの電縫鋼管を製造した。電縫鋼管の溶接HAZ部の割れ長さ(板厚方向の割れの深さ)は断面観察により計測し、母材板厚に対する割れ深さの比で評価した。また、室温でのシャルピー試験によって鋼板の溶接HAZ部の靭性を計り、靭性の劣化率はB無添加(B量0%)の場合の溶接HAZ部の靭性値に対する各B量を添加した場合の溶接HAZ部の靭性値の比で評価した。なお、割れ深さ率および靭性定価率は、各々5%以下、80%以上を良好と判断した。
【0070】
表2に母材鋼材中の主要な成分と割れおよび靱性の低下率の結果を示す。記号1〜11は本発明例である。記号1〜11の発明例において溶接部の割れは実用上無視できる程度か、または皆無であった。また、いずれの発明例も溶接HAZ靭性の大幅な低下は見られなかった。
【0071】
一方、記号12〜24は本発明の鋼材成分範囲から外れた比較例である。
【0072】
記号12から20はB量が本発明で規定する範囲より少ないため液体金属脆化割れが生じた。
【0073】
記号21および22は本発明で規定する範囲に比べBが多いため、割れは皆無であったが、溶接HAZ部の靭性値の低下が激しかった。
【0074】
記号23および24はC量およびB量が本発明で規定する範囲より多いために割れの程度大きくかつ溶接HAZ靭性の低下が激しかった。
【0075】
【表2】
【0076】
【発明の効果】
以上述べたように、本発明は、建築、自動車などの溶接構造部材として使用される亜鉛系合金めっき鋼材を種々の方法で溶接する際、さらには、亜鉛系合金めっき鋼材を用いて造管後、電縫溶接する際に、溶接熱影響部における液体金属脆化割れを抑制でき、溶接部品質に優れた亜鉛系合金めっき鋼材およびその電縫鋼管を提供することが可能となる。
【図面の簡単な説明】
【図1】CおよびB添加量とアーク溶接による溶接部の割れ深さの度合いを示す図。
【図2】CおよびB添加量とアーク溶接による溶接HAZ部の靱性劣化の度合いを示す図。
【図3】鋼管の電縫溶接における溶接部の割れ深さおよび溶接HAZ部の靭性劣化の度合いを示す図。
【図4】アーク溶接における液体金属脆化割れの評価方法を示す図。
【符号の説明】
1…厚手鋼板
2…めっき鋼板
3…嵌め込み溶接
4…丸鋼
5…円周溶接
[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention mainly relates to a zinc-based alloy-plated steel material and an electric resistance welded steel pipe used for a welding structure member of a building, an automobile, etc., and particularly, when welding such a zinc-based alloy-plated steel material by various methods, In addition, it is possible to suppress the occurrence of liquid metal embrittlement cracking (hereinafter, sometimes referred to as galvanizing cracking) in the heat affected zone when performing ERW after forming pipes using galvanized steel. The present invention relates to a zinc-based alloy-plated steel material and its electric resistance welded steel pipe.
[0002]
[Prior art]
Zn-plated steel is widely used from the viewpoint of improving the corrosion resistance of structural members of buildings and automobiles. Recently, Zn-Al-Mg-based alloy plating in which Al, Mg or Si is added during Zn plating, Zn-Al-Mg- Patent Literature 1 and Patent Literature 2 disclose zinc-based alloy-plated steel materials having excellent corrosion resistance in which zinc-based alloy plating such as Si-based alloy plating is applied to a steel material surface. These zinc-based alloy-plated steel materials are often used as welded steel structures by welding by various welding methods.
[0003]
Further, a steel pipe or a square pipe in which a butt end is welded by high-frequency induction welding or high-frequency resistance welding (hereinafter referred to as ERW) or the like after being formed into a tubular shape using these zinc-based alloy-plated steel materials is also used in many cases. .
[0004]
However, when welding these zinc-based alloy-plated steel materials, in the weld heat-affected zone of the steel material (hereinafter referred to as the welded HAZ portion), the zinc-based alloy plating melted by the welding heat input remains in a molten state on the steel material surface. It is likely to remain, and the steel structure tends to be a structure in which crystal grains grow and become coarse. When quoted stress acts on the steel material in such a state, depending on the weld HAZ structure of the steel material, a region in which hot-dip coating enters crystal grain boundaries on the surface of the steel material and the grain boundaries are embrittled, that is, an embrittlement region May be formed and cracks may occur. In particular, cracks may occur in the embrittled region of the weld HAZ during welding in a state where the member to be welded is significantly restrained.
[0005]
On the other hand, conventionally, when a welded structure obtained by welding steel materials is subjected to plating treatment in a hot-dip galvanized alloy plating bath, a welded portion of the welded structure, particularly, a weld toe (a weld bead (weld metal)) is formed. It has been known that similar cracks occur due to tensile stress (hereinafter referred to as residual tensile stress) remaining in the vicinity of the boundary between the steel sheet and the steel material) and thermal strain generated in the plating bath.
[0006]
As described above, when a certain liquid metal contacts a certain solid metal surface at a high temperature and a certain amount of tensile stress acts on the solid metal surface, a brittle zone is formed on the solid metal surface. The phenomenon of formation and cracking is called liquid metal embrittlement cracking: LME (Liquid Metal Embrittlement), which is known, for example, from Non-Patent Document 1.
[0007]
Conventionally, as a technique for suppressing liquid metal embrittlement cracking (LME) that occurs when plating a welding joint in a high-temperature hot-dip plating bath, microstructure control by specifying the composition of a steel material has been attempted. The formula is standardized by JIS (for example, JIS G3219-1995 for steel materials and JIS G 3474-1995 for steel pipes).
[0008]
Further, in Patent Document 3, each component of the steel material is limited with respect to the steel material on which the Zn-Al alloy plating is performed, and in particular, B is strictly restricted to 0.0002% or less.
[0009]
However, the above LME carbon equivalent equation is intended for liquid metal embrittlement cracking (LME) when plating a welding joint in a high-temperature hot-dip plating bath, and the temperature range in which the crack occurs is 450 ° C. (Melting point of plated metal), and a liquid metal embrittlement crack (LME) which is generated under a very low temperature condition as compared with a beak temperature of 1500 ° C. when welding a zinc-based alloy plated steel material. In contrast, liquid metal embrittlement cracking (LME), which occurs when welding a zinc-based alloy-plated steel material, is a wide temperature range from a high temperature range where the steel material melts at about 1500 ° C. to a melting point of the plated metal at about 450 ° C. Therefore, it is difficult to sufficiently suppress liquid metal embrittlement cracking (LME) during welding even when the conventional LME carbon equivalent equation is applied to a zinc-based alloy-plated steel material for welding.
[0010]
In addition, conventionally, in the brazing of extremely low carbon IF (Interstitial Free) steel materials requiring press formability, the occurrence of the above-described liquid metal embrittlement cracking due to solder embrittlement has been known. In Reference 4, 0.01 to 0.2% of Ti is added to IF steel having a low C of 0.0005 to 0.03% to fix N, and B is set to 0.0002 to 0.03%. The addition of 003% prevents the molten metal from entering the grain boundaries and suppresses the occurrence of cracks.
[0011]
This method is intended for low-strength, ultra-low carbon IF steel requiring formability, and the temperature range in which cracks occur is a soldering beak temperature: 900 to 1000 ° C (corresponding to the melting point of solder). It is assumed that this is the case. On the other hand, a zinc-based alloy-plated steel material having a base material of high-strength steel having higher strength (tensile strength: about 350 MPa or more) and high carbon (C: about 0.01 to 0.3%) than IF steel is used as a beak. When welding at a temperature of about 1500 ° C. (corresponding to the melting point of steel), liquid metal embrittlement cracking occurs even in a temperature range lower than 900 ° C. Therefore, the above method is applied to welding of high-tensile steel. However, it is difficult to sufficiently suppress liquid metal embrittlement cracking.
[0012]
In recent years, especially in the field of automobiles, zinc-based alloy plated steel sheets have been replaced with low-carbon IF steel sheets, which emphasized formability, in consideration of the reduction in weight and fuel consumption of automobiles, and in consideration of the global environment, have a higher tensile strength. High-strength steel with a high content of C and alloying elements is used as a base material, and the base material surface has a higher corrosion resistance than conventional Zn plating. Zn-Al, Zn-Al-Mg, Zn- A steel sheet plated with a zinc-based alloy such as an Al-Mg-Si system has been applied, and as a result, the occurrence of liquid metal embrittlement cracking during welding of steel, which has not been a problem in the past, has become apparent. It has become.
[0013]
In the past, in the field of automobiles and construction, post-plating treatment, in which ordinary steel is welded and then the welded structure is plated in a high-temperature galvanizing bath, has been the mainstream. In view of the above, welding of a pre-plated steel material, in which a plated steel material or a molded member thereof is welded, has been applied, and the technology for suppressing plating cracks generated during welding has become more industrially significant.
[0014]
In addition, as a method of manufacturing steel pipes with excellent corrosion resistance, from the viewpoint of improving productivity and reducing manufacturing costs, in recent years, zinc-alloy plated steel sheets have been used instead of the conventional method of post-plating ERW steel pipe products. A method of forming a tubular shape and then welding the butt end portions by electric resistance welding has also been put to practical use.
[0015]
However, at the time of ERW after pipe forming, a large springback force (processing reaction force), molding distortion or heat shrinkage acts, so that Zn-Al-Mg-based alloy plating and Zn-Al-Mg-Si-based alloy are applied. Depending on the type of zinc-based alloy plating, such as galvanizing, molten zinc-based alloy plating remaining on the surface of the heat affected zone at temperatures lower than 900 ° C penetrates into the grain boundary from the steel surface and causes liquid metal embrittlement cracking. Occurs.
[0016]
Conventionally, as a technique for suppressing such a crack at the time of electric resistance welding of a zinc-based alloy-plated steel sheet, for example, in Patent Document 5, a Zn-Al-Mg-based alloy-plated steel sheet is formed and its butt end is welded. A technique has been disclosed in which the upset amount is controlled to make the shape of the weld toe portion smooth, thereby reducing the concentration of tensile stress and eliminating cracks. However, the conditions under which the tensile stress concentration can be reduced by this upset amount control are limited to some steel pipe sizes and specific steel types, and it is difficult to exhibit a stable effect under a wide range of conditions.
[0017]
[Patent Document 1]
JP-A-10-226865
[Patent Document 2]
JP 2000-64061 A
[Patent Document 3]
JP 05-156406 A
[Patent Document 4]
JP-A-60-92453
[Patent Document 5]
JP-A-2002-115793
[Non-patent document 1]
Journal of Institute of Metals (1914) p. 108. (AK Huntington)
[0018]
[Problems to be solved by the invention]
The present invention is based on the above-mentioned problems of the prior art, for example, plated steel materials, particularly, Zn-Al-based alloy plating, Zn-Al-Mg-based alloy plating, Zn-Al-Mg-Si-based alloy plating, etc. Metal alloy-plated steel material subjected to anodization by various methods, furthermore, after pipe-forming using zinc-based alloy-plated steel material, when performing ERW welding, liquid metal embrittlement cracking in the weld heat affected zone An object of the present invention is to provide a zinc-based alloy-plated steel material for welding which can suppress occurrence thereof and has excellent weld quality and an electric resistance welded steel pipe thereof.
[0019]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and the gist thereof is as follows.
(1) In a zinc-based alloy-plated steel material in which a zinc-based alloy plating layer is provided on a steel material surface,
C: 0.01-0.3%
Si: 0.01 to 2.0%
Mn: 0.1-3.0%
S: 0.015% or less
Al: 0.001 to 0.5%
B: 3 to 40 ppm
N: 0.0005 to 0.006%
A zinc-based alloy-plated steel material for welding, characterized by containing Fe and the balance consisting of Fe and inevitable impurities.
(2) The above (1), wherein the steel material further contains, by mass%, 0.001 to 0.5% of Ti and satisfies a condition given by the following formula (1). The described zinc-based alloy-plated steel material for welding.
[0020]
0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
Here, [% X] indicates the content represented by mass% of the alloying element X.
(3) The zinc-based alloy-plated steel material for welding according to the above (1) or (2), wherein the S content in the steel material is 0.003% or less by mass%.
(4) The welding zinc according to any one of (1) to (3), wherein the steel material further contains P: 0.02 to 0.05% by mass%. Alloy plated steel.
(5) The zinc-based alloy plating is one of Zn-Al-based alloy plating, Zn-Al-Mg-based alloy plating, and Zn-Al-Mg-Si-based alloy plating. The zinc-based alloy-plated steel material for welding according to any one of the above (1) to (4).
(6) The Zn-Al-based alloy plating contains, by mass%, Al: 0.18 to 5%, Mg: 0.01 to 0.5%, and La: 0.001 to 0.5. % And Ce: any one or more of 0.001 to 0.5%, with the balance being Zn and inevitable impurities. Zinc alloy plated steel for welding.
(7) The Zn—Al—Mg based alloy plating contains 2 to 19% of Al and 0.5 to 10% of Mg by mass%, with the balance being Zn and unavoidable impurities. The zinc-based alloy-plated steel material for welding according to the above (5).
(8) The Zn-Al-Mg-Si-based alloy plating contains, by mass%, Al: 2 to 19%, Mg: 1 to 10%, and Si: 0.01 to 2%, with the balance being Zn and The zinc-based alloy-plated steel material for welding according to the above (5), which is an unavoidable impurity.
(9) In mass%,
C: 0.01-0.15%
Si: 0.01 to 2.0%
Mn: 0.1-3.0%
S: 0.015% or less
Al: 0.001 to 0.5%
B: 6 to 15 ppm
N: 0.0005 to 0.006%
After forming a zinc-based alloy plated steel sheet having a zinc-based alloy plating layer on the surface of a steel sheet composed of Fe and unavoidable impurities, the balance end portion of the steel sheet is welded by electric resistance welding. ERW steel pipe plated with zinc alloy.
(10) The above-mentioned (9), wherein the steel sheet further contains 0.001 to 0.5% by mass of Ti, and satisfies a condition given by the following formula (1). The described zinc-based alloy-plated electric resistance welded steel pipe.
[0021]
0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
Here, [% X] indicates the content represented by mass% of the alloying element X.
(11) The zinc-based alloy-plated electric resistance welded steel pipe according to the above (9) or (10), wherein the S content in the steel sheet is 0.003% or less by mass%.
(12) The zinc alloy according to any one of (9) to (11), wherein the steel sheet further contains, by mass%, P: 0.02 to 0.05%. Plating ERW steel pipe.
(13) The zinc-based alloy plating is one of Zn-Al-based alloy plating, Zn-Al-Mg-based alloy plating, and Zn-Al-Mg-Si-based alloy plating. The zinc-based alloy-plated electric resistance welded steel pipe according to any one of the above (9) to (12).
(14) The Zn-Al-based alloy plating contains 0.18 to 5% of Al by mass%, and further contains 0.01 to 0.5% of Mg and 0.001 to 0.5 of La. % And Ce: 0.001 to 0.5%, any one or more of which are contained, with the balance being Zn and unavoidable impurities. ERW steel pipe plated with zinc alloy.
(15) The Zn-Al-Mg alloy plating contains, by mass%, Al: 2 to 19% and Mg: 0.5 to 10%, with the balance being Zn and unavoidable impurities. The zinc-based alloy-plated electric resistance welded steel pipe according to the above (13).
(16) The Zn-Al-Mg-Si based alloy plating contains Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2% by mass%, with the balance being Zn and The zinc-based alloy-plated electric resistance welded steel pipe according to the above (13), which is an unavoidable impurity.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
In general, the welded portion after welding the steel material heat-shrinks during the cooling process to room temperature after the molten weld metal solidifies, so even when no external force is applied to the welded portion, the weld metal and the base metal of the welded portion are welded. A tensile stress is generated in the heat-affected zone due to heat shrinkage. Liquid metal embrittlement cracking that occurs when welding a steel material that has been subjected to zinc-based alloy plating of a specific component such as Zn-Al-based, Zn-Al-Mg-based, Zn-Al-Mg-Si-based, It is considered that the hot-dip zinc-based alloy plating remaining on the surface of the weld heat-affected zone without evaporating is caused by infiltration into crystal grain boundaries, triggered by the tensile stress generated due to the heat shrinkage of the weld heat-affected zone.
[0023]
The tensile stress generated due to heat shrinkage after welding changes depending on the high temperature strength of the steel material around the weld that changes according to the temperature. For example, the tensile stress generated when the weld is at a high temperature of about 900 ° C. is relatively small. On the other hand, in the low temperature range of about 400 to 500 ° C. corresponding to the melting point of the zinc-based alloy plating, a large tensile stress acts due to the recovery of the high-temperature strength around the weld and an increase in the heat shrinkage. Also, since the high-temperature strength of a steel material usually depends on its cold strength, the higher the tensile strength of the steel material to be welded, the greater the tensile stress accompanying thermal shrinkage. In addition, the magnitude of the tensile stress due to the heat shrinkage also varies depending on the restrained state of the welded part during welding, and when welding is performed by mechanically restraining the vicinity of the welded part with a jig etc. to suppress welding deformation When welding is performed in a joint shape having a large processing reaction force such as end butt welding after tubular forming in the electric resistance welded steel pipe manufacturing process, the tensile stress accompanying thermal shrinkage increases.
[0024]
In the case of conventional brazing of ultra-low carbon IF steel, cracking occurred only in the high temperature region of about 900 ° C or higher, which is the melting point of solder, whereas welding of zinc-based alloy plated steel material Cracks occur in a wide temperature range from a temperature lower than 900 ° C. to a low temperature range of about 400 ° C. corresponding to a plating melting point, and the cracks are generated by a large tensile stress caused by heat shrinkage of a weld. This is different from the embrittlement crack of brazing of conventional IF steel.
[0025]
The present invention, in welding construction of zinc-based alloy-plated steel material, in order to suppress not only high-temperature region of 900 ℃ or more, to suppress plating cracks that often occur in a range from a lower temperature to a low temperature region of about 400 ℃, The technical idea is to improve the resistance to tensile stress of a welding heat affected zone (hereinafter referred to as a welding HAZ zone) during welding, that is, to improve the grain boundary strength.
[0026]
The present invention is based on this technical idea, a base material having a tensile strength of about 350 MPa or more and about 800 MPa or less, a steel material having a strength higher than that of IF steel, and a zinc-based alloy plated on the surface thereof. As a result of a detailed study of measures to prevent liquid metal embrittlement cracking during welding of alloy-plated steel materials, B was added to steel materials containing 0.01 to 0.3% by mass of C as a base metal component. The present invention has been made based on a new finding that liquid metal embrittlement cracking during welding can be prevented while securing the toughness of the welded portion by adding 0003 to 0.004%.
[0027]
Hereinafter, the present invention will be described in detail.
[0028]
First, as a result of verifying the prevention of cracking in a relatively low temperature range where a large tensile stress occurs in the welding process, it was found that the improvement of hardenability by C was effective. Although the reason is not clear, it is considered that the plastic strain accompanying the tensile stress was effectively reduced by increasing the strength of the welded HAZ of the steel material in which the zinc-based alloy plating in the molten state remains.
[0029]
However, when welding is performed with a jig restrained in advance for the purpose of preventing welding deformation, etc., the tensile stress due to heat shrinkage becomes larger, so welding under extremely severe welding conditions in such a restrained state Then, the problem that cracks still occur remains. In particular, in the process of manufacturing steel pipes with excellent corrosion resistance, after forming a zinc-based alloy-plated steel sheet into a tube and then welding the butt end parts with ERW, the welding process is combined with the heat shrinkage force to form the work. As a result, a large springback force (working reaction force) acts, so that a zinc-based alloy plating crack is likely to occur.
[0030]
Under such severe welding conditions, it is considered that a predetermined tensile stress is generated even in a high temperature region where the tensile stress of the welded HAZ is considered to be relatively mild, leading to liquid metal embrittlement cracking. Is not enough.
[0031]
Therefore, the effect of B on steel containing a predetermined amount of C was examined.
[0032]
Conventionally, as a technique for preventing solder embrittlement cracking, the addition of B during the brazing of ultra-low carbon IF steels has resulted in grain boundary segregation and enrichment of B in the austenite temperature range of about 900 ° C or higher by the addition of B. It is known that there is an effect of suppressing intrusion into the world. The present invention is intended for welding cracking under welding conditions having a very high welding peak temperature of 1500 ° C. (corresponding to the melting point of steel material) or higher as compared with soldering. It is considered that the effect of suppressing the penetration of the zinc-based alloy plating in the molten state into the grain boundaries by the segregation and concentration of B at the grain boundaries is similarly obtained. The grain boundary segregation of B occurs at a temperature equal to or higher than the austenite-ferrite two-phase region, and B penetrates into vacancies / defects at the grain boundary to lower the interfacial energy. However, the segregation of B at the grain boundary hardly occurs as the temperature decreases.
[0033]
As a result of the study by the present inventors, in addition to the effect of B, as a new finding, B has a relatively high cooling rate like a welded HAZ even in a temperature range lower than the austenite-ferrite two-phase range. In the region, B acts as a strengthening element for the former austenite grain boundary, so that it is effective in improving the grain boundary strength against the tensile stress generated in the weld HAZ due to heat shrinkage, and thereby preventing hot-dip cracking in a low temperature range. all right.
[0034]
FIG. 1 shows the results of arc welding of a zinc-based alloy-plated steel material in which a zinc-based alloy plating was applied to the surface of a steel material in which the amounts of C and B were changed. It shows the rate of deterioration of the toughness of the weld. The crack depth in FIG. 1 is represented by the ratio of the crack depth to the base material plate thickness, and the toughness deterioration rate in FIG. 2 is the B content for each HAZ toughness value of the B-free steel (B content 0%). It was expressed by the ratio of the HAZ toughness value of the added steel material. Further, a zinc-based alloy-plated steel material having a thickness of 6 mm and provided with an 11% Al + 3% Mg + 0.2% Si + Zn plating layer was used.
[0035]
As shown in FIGS. 4 (a) and 4 (b), a method for evaluating cracks in a welded portion is to fit a plated steel material 2 to be evaluated into a thick steel material 1 and weld it to the inside. 4 was circumferentially welded 5 to measure and evaluate the depth of cracks generated in the crater portion (end portion) of the weld bead of circumferential weld 5. By welding the plated steel material 2 to the thick steel material 1, the restraint conditions when the plated steel material 2 is circumferentially welded 5 are strict.
[0036]
The crack depth of the weld was determined by observing the cross section of the weld and measuring the length of the crack extending from the steel surface in the thickness direction.
[0037]
From FIG. 1, although the crack in the welded portion tends to decrease due to the increase in the B content regardless of the C content in the steel material, the medium C material (C: In the case of high C material (C: 0.15%), cracks in the welded portion are sharply reduced even with a relatively small B content of 3 ppm. Is almost eliminated. On the other hand, even in the case of a low C material (C: 0.005%) or a medium C material (C: 0.01%), when the B content is as large as 20 ppm or more or 40 ppm or more, cracks in the welded portion are relatively small. However, as shown in FIG. 2, it can be seen that the toughness value of the weld decreases and the target toughness (80% or more) cannot be obtained. This is presumably because the crystal grain is more likely to be coarser in the low C material and the medium C material than in the high C material, and the decrease in toughness due to B grain boundary segregation increases as the B content increases. FIGS. 1 and 2 show that, when arc-welding a zinc-based alloy-plated steel material having a medium C material and a high C material of 0.01% or more as a base material, melting while securing the target toughness of the welded portion. The B content in the steel material for preventing the zinc-based alloy plating cracks needs to be 3 to 40 ppm.
[0038]
Further, using a zinc-based alloy-plated steel sheet in which a zinc-based alloy plating is applied to the surface of a steel material in which the amount of C and the amount of B are changed, this is formed into a tube, and the butt ends are welded by electric resistance welding to form a steel pipe. FIG. 3 shows the crack depth and the toughness deterioration rate of the welded portion as an experimental result when the aluminum alloy was manufactured. The crack depth of the weld was determined by observing the cross section of the weld and measuring the length of the crack extending from the steel surface in the thickness direction. The crack depth and toughness deterioration rate of the welded portion were determined by the same method as in FIGS. 1 and 2 described above. The zinc-based alloy-plated steel sheet used had a thickness of 6 mm and was provided with an 11% Al + 3% Mg + 0.3% Si + Zn plating layer.
[0039]
From FIG. 3, it can be seen that the cracking of hot-dip zinc-based alloy plating during electric resistance welding of steel pipes is effectively reduced by increasing the amount of B added in medium C materials and high C materials with a C content of 0.15% or less. When the amount of B added is 6 ppm or more, the occurrence of cracks in the welded portion is almost eliminated. However, in the case of a high C material having a C amount of about 0.35%, the effect of reducing B is hardly obtained by the addition of B. On the other hand, in a medium C material and a high C material having a C content of 0.15% or less, the toughness value of the welded portion decreases as the amount of B added increases. The B content in the steel material for preventing the galvanized alloy plating crack during the electric resistance welding of the steel pipe while securing the target toughness (80% or more) needs to be 6 to 15 ppm.
[0040]
Based on the above findings, the base metal components and the range of the content of the zinc-based alloy-plated steel material for welding of the present invention are as follows. In addition, the following% indicates mass% unless otherwise specified.
[0041]
C: In the present invention, C is necessary for ensuring a tensile strength of 350 MPa or more, and also improves quenching of the welded HAZ, that is, stress concentration, against the tensile stress generated by heat shrinkage during welding as described above. It is an essential element for preventing cracking by reducing the plastic strain of the part. 1 and 2, the lower limit of the C content is set to 0.01% as the C content that can sufficiently prevent the occurrence of cracks in the welded portion and secure good toughness by combining with the addition of B. In addition, excessive addition of C not only leads to hardening of the welded HAZ to lower bending performance and delayed cracking, but also facilitates the formation of Fe-CB precipitates, thereby reducing the effect of suppressing plating embrittlement of B. Therefore, the upper limit of the C content is set to 0.3%.
[0042]
Further, as shown in FIG. 3, when performing ERW welding of a steel pipe or when welding is performed in a state in which the periphery of the weld is restrained with a high restraining force, the upper limit of the C content is set because cracks in the weld HAZ are likely to occur. It is preferably 0.15%.
[0043]
Si: Si is necessary for deoxidizing the base material, and the lower limit of the content is set to 0.01%. Further, Si has a solid solution strengthening action and is used together with Mn described below for adjusting the strength of the base material. In addition, since excessive Si addition leads to an increase in oxide scale and a decrease in ductility during hot rolling, the upper limit of the content is set to 2.0%.
[0044]
Although there is no problem when plating on a hot-rolled steel sheet, when plating on a cold-rolled steel sheet, the plating adhesion deteriorates, so the Si content is more preferably 0.1% or less.
[0045]
Mn: The lower limit of the content of Mn is set to 0.1% in order to fix S, which is an unavoidable impurity in steel that causes hot brittleness of the steel material, as MnS and render it harmless. On the other hand, excessive addition of Mn hardens the welded HAZ and leads to a decrease in bending performance and delayed cracking. Therefore, the upper limit of the content is set to 3.0%.
[0046]
S: Since S is an element that lowers the hot workability of the steel material, it is preferable that S is small, and the upper limit is set to 0.015%.
[0047]
Further, from the viewpoint of suppressing plating embrittlement cracking during welding, the effect of embrittlement suppression is recognized by reducing S, so the upper limit of the content of S is preferably set to 0.003%.
[0048]
Al: Since Al is a deoxidizing element of steel and has an action of fixing N in steel, it prevents B from being precipitated as a nitride and suppresses liquid metal embrittlement cracking of galvanized alloy plating. There is also an effect. To obtain these effects, it is necessary to add 0.001% or more. On the other hand, if Al is excessively added, coarse nonmetallic inclusions are formed and the performance such as toughness of the steel material is deteriorated. Therefore, the upper limit is set to 0.5%.
[0049]
B: As described above, at a temperature equal to or higher than the austenite region or the austenite-ferrite two-phase region during welding, B segregates and concentrates at the grain boundary or penetrates into vacancies and defects at the grain boundary to lower the interface energy. This has the effect of suppressing the penetration and diffusion of the zinc-based alloy plating in the molten state into the grain boundaries. In the process of cooling the weld, B is an element that improves the quenchability, promotes the formation of bainite or martensite structure, and refines the structure and reduces the tensile stress due to thermal shrinkage. The effect of reducing stress and plastic strain can also be obtained by strengthening the boundary. From FIG. 1, the lower limit is set to 3 ppm as the B content that can sufficiently prevent the occurrence of cracks in the welded portion under the predetermined C amount, while from FIG. 2 the upper limit of the B content is 40 ppm for suppressing the toughness deterioration of the welded portion. And
[0050]
Further, as shown in FIG. 3, at the time of electric resistance welding of a steel pipe or when welding is performed in a state in which the periphery of a weld is restrained with a high restraining force, the lower limit of the B content is set because cracks in the weld HAZ are likely to occur. It is preferably 6 ppm, and the upper limit of the B content is preferably 15 ppm for suppressing the toughness deterioration of the welded portion.
[0051]
N: While N increases the strength of the steel material, the addition of a large amount of N lowers the toughness of the steel material, precipitates B as a nitride such as BN, and impairs the effect of suppressing the embrittlement of plating of B. Therefore, the upper limit is made 0.006%. The smaller the N, the better, but if it is made 0.0005% or less, the cost increases, so the lower limit was made 0.0005%.
[0052]
In the present invention, in addition to the above components, the following component addition amounts are further defined for the following reasons.
[0053]
Ti: Ti has an effect of fixing N in steel as a nitride and preventing B from being precipitated as a nitride such as BN, so that liquid metal embrittlement cracking of hot-dip zinc alloy plating is further suppressed. Is preferably added at 0.001% or more. On the other hand, even if Ti is added in excess of 0.5%, the effect of suppressing cracking saturates and the cost of alloy addition simply increases unnecessarily, so the upper limit of the content is set to 0.5%.
[0054]
Further, the content of Ti is preferably adjusted so that the total amount of the content of Al having the function of fixing N similarly to Ti is 0.001% or more and 0.5% or less.
[0055]
P: P is generally desired to be reduced from the viewpoint of improving weldability, such as high temperature cracking, but the effect of reducing the brittleness of plating during welding due to the segregation of P at the grain boundary is recognized. It is preferable to add 0.02% or more. On the other hand, excessive addition causes hot cracking, and the upper limit of the content is preferably set to 0.05%.
[0056]
Further, in the present invention, as a zinc-based alloy plating applied to the surface of a steel material containing the above components, a Zn-Al-Mg based as described in Patent Document 1, and described in Patent Document 2 Such Zn-Al-Mg-Si-based or Zn-Al-based zinc-based alloy plating is referred to. Incidentally, Zn-Al-based alloy plating contains 0.18 to 5% of Al, and further contains 0.01 to 0.5% of Mg, 0.001 to 0.5% of La, and Ce: One or more of 0.001 to 0.5% is contained, and the balance is made of Zn. In the case of Zn-Al-Mg based alloy plating, Al: 2 to 19%, Mg: 0. 5 to 10%, with the balance being Zn. In the case of Zn-Al-Mg-Si alloy plating, Al: 2 to 19%, Mg: 0.5 to 10%, Si: 0.01 to 2%, It consists of plating of the remainder Zn. The present invention exerts the above-described remarkable effects when welding a zinc-based alloy-plated steel material coated with any one of these zinc-based alloy platings into a welded structure.
[0057]
The zinc-based alloy-plated electric resistance welded steel pipe of the present invention uses these zinc-based alloy-plated steel sheets. After forming the steel sheet into a tube, the butt ends thereof are subjected to electric resistance welding such as high-frequency induction welding or high-frequency resistance welding. This is an electric resistance welded steel pipe manufactured by performing
[0058]
The zinc-based alloy-plated ERW steel pipe of the present invention is a steel pipe having excellent quality without cracks at a welded portion manufactured by ERW welding of a zinc-based alloy-plated steel sheet, and is a method of post-plating a conventional ERW steel pipe product. As compared with the zinc-based alloy-plated electric resistance welded steel pipe manufactured by the method described above, it is possible to improve the productivity and reduce the manufacturing cost while maintaining the quality of the welded portion satisfactorily.
[0059]
In the above description of the embodiment of the present invention, the welding method is described as being limited to arc welding or electric resistance welding of a steel pipe, but is not limited to these welding methods. For example, laser welding, spot welding, projection welding also undergoes the same thermal cycle as arc welding, and a tensile stress acts near the weld, so that liquid metal embrittlement cracking of the weld may occur. By applying the same, an effect of preventing plating cracks at the time of welding can be obtained.
[0060]
【Example】
[Example 1]
A base steel material containing the components shown in Table 1 had a basis weight of 90 g / m on one side. 2 The above evaluation method was carried out by arc welding a zinc-based alloy-plated steel material of 400 MPa class having a thickness of 6 mm and having a zinc-based alloy plating consisting of 3% of Mg, 11% of Al, 0.3% of Si and the balance of Zn. In the same manner as above, the crack and toughness of the welded part were evaluated. It is known that the Zn-Al-Mg-Si alloy plating exhibits extremely excellent corrosion resistance as compared with conventional simple Zn plating.
[0061]
The welding was performed by pulse MAG arc welding with a welding current of 200 A, a welding voltage of 23 V, a welding speed of 30 cm / min, and YGW-12 as a welding wire. In addition, as shown in FIGS. 4 (a) and 4 (b), the inspection of the cracks in the welded portion is performed by observing a cross section at a weld end portion that is likely to be generated in the weld bead of the circumferential weld 5, and the crack depth (Table 1 shows the base metal). (Indicated by the ratio of the crack depth to the plate thickness). The toughness deterioration rate was evaluated by the ratio of the toughness value of the welded HAZ portion when each B amount was added to the toughness value of the welded HAZ portion when B was not added (B amount 0%). The crack depth rate and toughness fixed rate were determined to be 5% or less and 80% or more, respectively, as good.
[0062]
Table 1 shows the main components in the base steel material and the results of the cracking and toughness reduction rates. Symbols 1 to 10 are examples of the present invention. In the invention examples of symbols 1 to 10, when the C content was relatively small as 0.03 (symbol 1), cracks occurred slightly, but were practically negligible, and there were no cracks in other cases. Also, none of the invention examples showed a significant decrease in the weld HAZ toughness.
[0063]
On the other hand, symbols 11 to 14 are comparative examples out of the steel material component range of the present invention.
[0064]
Symbols 11 and 12 had liquid metal embrittlement cracking because the B content was less than the range specified in the present invention.
[0065]
In the case of symbol 13, since the C content was smaller than the range specified in the present invention, the decrease in the weld HAZ toughness was severe.
[0066]
In the symbol 14, since the amount of B was larger than the range specified in the present invention, the generated cracks were extremely small, but the toughness value of the welded HAZ was significantly reduced.
[0067]
In the above embodiments, arc welding was used as the welding method. Similarly, in tests using laser welding, spot welding, and projection welding, liquid metal embrittlement cracking in the welded portion can be suppressed, and the toughness of the welded HAZ portion can be suppressed. Was good.
[0068]
[Table 1]
[0069]
[Example 2]
A base steel sheet containing the components shown in Table 2 had a basis weight of 90 g / m on one side. 2 Using a 6 mm thick zinc-based alloy-plated steel plate of 400 MPa class with a zinc-based alloy plating consisting of Mg: 3%, Al: 11%, Si: 0.3%, and the balance being Zn Then, the butt end was subjected to ERW under the conditions of a welding speed of 30 m / min, a high-frequency power of 450 kW, and an upset amount of 3 mm to produce an ERW steel pipe having an outer diameter of 355 mm. The crack length (depth of crack in the thickness direction) of the welded HAZ portion of the ERW steel pipe was measured by cross-sectional observation, and evaluated by the ratio of the crack depth to the base metal sheet thickness. Further, the toughness of the welded HAZ portion of the steel sheet was measured by a Charpy test at room temperature, and the toughness degradation rate was determined by adding each B amount to the toughness value of the welded HAZ portion when B was not added (B amount 0%). It was evaluated by the ratio of the toughness value of the welded HAZ. The crack depth rate and toughness fixed rate were determined to be 5% or less and 80% or more, respectively, as good.
[0070]
Table 2 shows the main components in the base steel material and the results of the cracking and toughness reduction rates. Symbols 1 to 11 are examples of the present invention. In the invention examples of symbols 1 to 11, cracks in the welded portion were practically negligible or were not present at all. Also, none of the invention examples showed a significant decrease in the weld HAZ toughness.
[0071]
On the other hand, symbols 12 to 24 are comparative examples out of the steel material component range of the present invention.
[0072]
In symbols 12 to 20, liquid metal embrittlement cracking occurred because the B content was less than the range specified in the present invention.
[0073]
Symbols 21 and 22 had more B than the range specified in the present invention, so there was no cracking, but the toughness value of the welded HAZ was drastically reduced.
[0074]
In the symbols 23 and 24, since the C content and the B content were larger than the ranges specified in the present invention, the degree of cracking was large and the reduction in weld HAZ toughness was severe.
[0075]
[Table 2]
[0076]
【The invention's effect】
As described above, the present invention is applicable to welding a zinc-based alloy-plated steel material used as a welding structural member of a building, an automobile, or the like by various methods. In addition, when performing ERW, it is possible to provide a zinc-based alloy-plated steel material having excellent weld quality and an ERW steel pipe that can suppress liquid metal embrittlement cracking in the heat affected zone.
[Brief description of the drawings]
FIG. 1 is a view showing the amounts of C and B added and the degree of crack depth of a welded portion by arc welding.
FIG. 2 is a diagram showing the amounts of C and B added and the degree of toughness deterioration of a welded HAZ part by arc welding.
FIG. 3 is a view showing a crack depth of a welded portion and a degree of toughness deterioration of a welded HAZ portion in the electric resistance welding of a steel pipe.
FIG. 4 is a diagram showing a method for evaluating liquid metal embrittlement cracking in arc welding.
[Explanation of symbols]
1: thick steel plate
2 ... Plated steel sheet
3 ... Inset welding
4: Round steel
5 ... circumferential welding

Claims (16)

  1. 亜鉛系合金めっき層を鋼材表面に設けた亜鉛系合金めっき鋼材において、前記鋼材が、質量%で、
    C:0.01〜0.3%
    Si:0.01〜2.0%
    Mn:0.1〜3.0%
    S:0.015%以下
    Al:0.001〜0.5%
    B:3〜40ppm
    N:0.0005〜0.006%
    を含有し、残部がFeおよび不可避的不純物からなることを特徴とする溶接用亜鉛系合金めっき鋼材。
    In a zinc-based alloy-plated steel material in which a zinc-based alloy plating layer is provided on a steel material surface,
    C: 0.01-0.3%
    Si: 0.01 to 2.0%
    Mn: 0.1-3.0%
    S: 0.015% or less Al: 0.001 to 0.5%
    B: 3 to 40 ppm
    N: 0.0005 to 0.006%
    A zinc-based alloy-plated steel material for welding, characterized by containing Fe and the balance consisting of Fe and inevitable impurities.
  2. 前記鋼材が、さらに、質量%で、Ti:0.001〜0.5%を含有し、かつ下記(1)式で与えられる条件を満足することを特徴とする請求項1に記載の溶接用亜鉛系合金めっき鋼材。
    0.5≧[%Ti]+[%Al]≧0.001 … (1)
    但し、[%X]は、合金元素Xの質量%で表した含有量を示す。
    2. The welding material according to claim 1, wherein the steel material further contains 0.001 to 0.5% by mass of Ti and satisfies a condition given by the following formula (1). 3. Zinc alloy plated steel.
    0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
    Here, [% X] indicates the content represented by mass% of the alloying element X.
  3. 前記鋼材におけるS含有量が、質量%で、0.003%以下であることを特徴とする請求項1または2記載の溶接用亜鉛系合金めっき鋼材。3. The zinc-based alloy-plated steel material for welding according to claim 1, wherein the S content in the steel material is 0.003% or less in mass%. 4.
  4. 前記鋼材が、さらに、質量%で、P:0.02〜0.05%を含有することを特徴とする請求項1から3のうちの何れかに記載の溶接用亜鉛系合金めっき鋼材。The zinc-based alloy-plated steel material for welding according to any one of claims 1 to 3, wherein the steel material further contains, by mass%, P: 0.02 to 0.05%.
  5. 前記亜鉛系合金めっきが、Zn−Al系合金めっき、Zn−Al−Mg系合金めっき、および、Zn−Al−Mg−Si系合金めっきのうちの何れか1種であることを特徴とする請求項1から4のうちの何れかに記載の溶接用亜鉛系合金めっき鋼材。The zinc-based alloy plating is one of Zn-Al-based alloy plating, Zn-Al-Mg-based alloy plating, and Zn-Al-Mg-Si-based alloy plating. Item 5. A zinc-based alloy-plated steel material for welding according to any one of Items 1 to 4.
  6. 前記Zn−Al系合金めっきが、質量%で、Al:0.18〜5%を含有し、さらに、Mg:0.01〜0.5%、La:0.001〜0.5%、および、Ce:0.001〜0.5%のうちのいずれか1種または2種以上を含有し、残部がZnおよび不可避的不純物であることを特徴とする請求項5に記載の溶接用亜鉛系合金めっき鋼材。The Zn—Al-based alloy plating contains, by mass%, Al: 0.18 to 5%, and further, Mg: 0.01 to 0.5%, La: 0.001 to 0.5%, and , Ce: 0.001 to 0.5%, and the balance is Zn and inevitable impurities, with the balance being Zn. Alloy plated steel.
  7. 前記Zn−Al−Mg系合金めっきが、質量%で、Al:2〜19%、Mg:0.5〜10%を含有し、残部がZnおよび不可避的不純物であることを特徴とする請求項5記載の溶接用亜鉛系合金めっき鋼材。The Zn-Al-Mg-based alloy plating contains, by mass%, Al: 2 to 19% and Mg: 0.5 to 10%, with the balance being Zn and unavoidable impurities. 5. A zinc-based alloy-plated steel material for welding according to 5.
  8. 前記Zn−Al−Mg−Si系合金めっきが、質量%で、Al:2〜19%、Mg:1〜10%、Si:0.01〜2%を含有し、残部がZnおよび不可避的不純物であることを特徴とする請求項5に記載の溶接用亜鉛系合金めっき鋼材。The Zn—Al—Mg—Si alloy plating contains, by mass%, Al: 2 to 19%, Mg: 1 to 10%, and Si: 0.01 to 2%, with the balance being Zn and inevitable impurities. The zinc-based alloy-plated steel material for welding according to claim 5, wherein:
  9. 質量%で、
    C:0.01〜0.15%
    Si:0.01〜2.0%
    Mn:0.1〜3.0%
    S:0.015%以下
    Al:0.001〜0.5%
    B:6〜15ppm
    N:0.0005〜0.006%
    を含有し、残部がFeおよび不可避的不純物からなる鋼板の表面に亜鉛系合金めっき層を設けた亜鉛系合金めっき鋼板を管状に成形後、その突合せ端部を電縫溶接したことを特徴とする亜鉛系合金めっき電縫鋼管。
    In mass%,
    C: 0.01-0.15%
    Si: 0.01 to 2.0%
    Mn: 0.1-3.0%
    S: 0.015% or less Al: 0.001 to 0.5%
    B: 6 to 15 ppm
    N: 0.0005 to 0.006%
    After forming a zinc-based alloy plated steel sheet having a zinc-based alloy plating layer on the surface of a steel sheet composed of Fe and unavoidable impurities, the balance end portion of the steel sheet is welded by electric resistance welding. ERW steel pipe plated with zinc alloy.
  10. 前記鋼板が、さらに、質量%で、Ti:0.001〜0.5%を含有し、かつ下記(1)式で与えられる条件を満足することを特徴とする請求項9に記載の亜鉛系合金めっき電縫鋼管。
    0.5≧[%Ti]+[%Al]≧0.001 … (1)
    但し、[%X]は、合金元素Xの質量%で表した含有量を示す。
    The zinc-based steel according to claim 9, wherein the steel sheet further contains 0.001 to 0.5% of Ti in mass%, and satisfies a condition given by the following expression (1). Alloy plated ERW steel pipe.
    0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
    Here, [% X] indicates the content represented by mass% of the alloying element X.
  11. 前記鋼板におけるS含有量が、質量%で、0.003%以下であることを特徴とする請求項9または10記載の亜鉛系合金めっき電縫鋼管。The zinc-based alloy plated electric resistance welded steel pipe according to claim 9 or 10, wherein the S content in the steel sheet is 0.003% or less by mass%.
  12. 前記鋼板が、さらに、質量%で、P:0.02〜0.05%を含有することを特徴とする請求項9から11のうちの何れかに記載の亜鉛系合金めっき電縫鋼管。The zinc-based alloy-plated electric resistance welded steel pipe according to any one of claims 9 to 11, wherein the steel sheet further contains P: 0.02 to 0.05% by mass%.
  13. 前記亜鉛系合金めっきが、Zn−Al系合金めっき、Zn−Al−Mg系合金めっき、および、Zn−Al−Mg−Si系合金めっきのうちの何れか1種であることを特徴とする請求項9から12のうちの何れかに記載の亜鉛系合金めっき電縫鋼管。The zinc-based alloy plating is one of Zn-Al-based alloy plating, Zn-Al-Mg-based alloy plating, and Zn-Al-Mg-Si-based alloy plating. Item 13. A zinc-based alloy-plated electric resistance welded steel tube according to any one of Items 9 to 12.
  14. 前記Zn−Al系合金めっきが、質量%で、Al:0.18〜5%を含有し、さらに、Mg:0.01〜0.5%、La:0.001〜0.5%、および、Ce:0.001〜0.5%のうちのいずれか1種または2種以上を含有し、残部がZnおよび不可避的不純物であることを特徴とする請求項13に記載の亜鉛系合金めっき電縫鋼管。The Zn—Al-based alloy plating contains, by mass%, Al: 0.18 to 5%, and further, Mg: 0.01 to 0.5%, La: 0.001 to 0.5%, and , Ce: 0.001 to 0.5% of any one or more of the following, with the balance being Zn and unavoidable impurities, the zinc-based alloy plating according to claim 13, characterized in that: ERW steel pipe.
  15. 前記Zn−Al−Mg系合金めっきが、質量%で、Al:2〜19%、Mg:0.5〜10%を含有し、残部がZnおよび不可避的不純物であることを特徴とする請求項13記載の亜鉛系合金めっき電縫鋼管。The Zn-Al-Mg-based alloy plating contains, by mass%, Al: 2 to 19% and Mg: 0.5 to 10%, with the balance being Zn and unavoidable impurities. 14. A zinc-based alloy-plated electric resistance welded steel pipe according to item 13.
  16. 前記Zn−Al−Mg−Si系合金めっきが、質量%で、Al:2〜19%、Mg:1〜10%、Si:0.01〜2%を含有し、残部がZnおよび不可避的不純物であることを特徴とする請求項13に記載の亜鉛系合金めっき電縫鋼管。The Zn—Al—Mg—Si alloy plating contains, by mass%, Al: 2 to 19%, Mg: 1 to 10%, and Si: 0.01 to 2%, with the balance being Zn and inevitable impurities. The zinc-based alloy-plated electric resistance welded steel pipe according to claim 13, characterized in that:
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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009228079A (en) * 2008-03-24 2009-10-08 Nisshin Steel Co Ltd Zn-Al-Mg BASED STEEL SHEET HAVING EXCELLENT HOT DIP METAL EMBRITTLEMENT CRACK RESISTANCE AND METHOD FOR PRODUCING THE SAME
JP2009228080A (en) * 2008-03-24 2009-10-08 Nisshin Steel Co Ltd HIGH-YIELD RATIO TYPE Zn-Al-Mg BASED STEEL SHEET HAVING EXCELLENT HOT DIP METAL EMBRITTLEMENT CRACK RESISTANCE AND METHOD FOR PRODUCING THE SAME
JP2013091094A (en) * 2011-10-27 2013-05-16 Ihi Corp Weld crack testing method for laser arc hybrid welding
KR20160077397A (en) 2014-12-22 2016-07-04 주식회사 포스코 METHOD FOR MANUFACTURING Zn ALLOY PLATED STEEL TUBE HAVING EXCELLNT CORROSION RESISTANCE
JP2016160476A (en) * 2015-02-27 2016-09-05 新日鐵住金株式会社 Zinc-based alloy plating welded h-section steel and manufacturing method thereof
WO2018162937A1 (en) 2017-03-07 2018-09-13 Arcelormittal Resistance spot welding method for joining zinc coated steel sheets
WO2018234938A1 (en) 2017-06-20 2018-12-27 Arcelormittal Zinc-coated steel sheet with high resistance spot weldability
CN110923600A (en) * 2019-12-09 2020-03-27 晋江安能建材制造有限公司 Steel plate with zinc-manganese-magnesium-silicon alloy hot-dip coating and production method thereof
JP6750759B1 (en) * 2019-05-09 2020-09-02 日本製鉄株式会社 Steel plate and manufacturing method thereof
WO2020225936A1 (en) * 2019-05-09 2020-11-12 日本製鉄株式会社 Steel sheet and method for manufacturing same
CN112281079A (en) * 2020-09-25 2021-01-29 河钢股份有限公司承德分公司 Hot-base galvanized steel coil and preparation method thereof

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Publication number Priority date Publication date Assignee Title
JP2009228080A (en) * 2008-03-24 2009-10-08 Nisshin Steel Co Ltd HIGH-YIELD RATIO TYPE Zn-Al-Mg BASED STEEL SHEET HAVING EXCELLENT HOT DIP METAL EMBRITTLEMENT CRACK RESISTANCE AND METHOD FOR PRODUCING THE SAME
JP2009228079A (en) * 2008-03-24 2009-10-08 Nisshin Steel Co Ltd Zn-Al-Mg BASED STEEL SHEET HAVING EXCELLENT HOT DIP METAL EMBRITTLEMENT CRACK RESISTANCE AND METHOD FOR PRODUCING THE SAME
JP2013091094A (en) * 2011-10-27 2013-05-16 Ihi Corp Weld crack testing method for laser arc hybrid welding
KR20160077397A (en) 2014-12-22 2016-07-04 주식회사 포스코 METHOD FOR MANUFACTURING Zn ALLOY PLATED STEEL TUBE HAVING EXCELLNT CORROSION RESISTANCE
JP2016160476A (en) * 2015-02-27 2016-09-05 新日鐵住金株式会社 Zinc-based alloy plating welded h-section steel and manufacturing method thereof
WO2018163017A1 (en) 2017-03-07 2018-09-13 Arcelormittal Resistance spot welding method for joining zinc coated steel sheets
WO2018162937A1 (en) 2017-03-07 2018-09-13 Arcelormittal Resistance spot welding method for joining zinc coated steel sheets
WO2018234839A1 (en) 2017-06-20 2018-12-27 Arcelormittal Zinc coated steel sheet with high resistance spot weldability
WO2018234938A1 (en) 2017-06-20 2018-12-27 Arcelormittal Zinc-coated steel sheet with high resistance spot weldability
EP3892748A1 (en) 2017-06-20 2021-10-13 ArcelorMittal A method for the fabrication of a resistance spot weld
JP6750759B1 (en) * 2019-05-09 2020-09-02 日本製鉄株式会社 Steel plate and manufacturing method thereof
WO2020225936A1 (en) * 2019-05-09 2020-11-12 日本製鉄株式会社 Steel sheet and method for manufacturing same
CN110923600A (en) * 2019-12-09 2020-03-27 晋江安能建材制造有限公司 Steel plate with zinc-manganese-magnesium-silicon alloy hot-dip coating and production method thereof
CN112281079A (en) * 2020-09-25 2021-01-29 河钢股份有限公司承德分公司 Hot-base galvanized steel coil and preparation method thereof

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