JPH0563548B2

JPH0563548B2 -

Info

Publication number: JPH0563548B2
Application number: JP30755388A
Authority: JP
Inventors: Yukinobu Higuchi; Kenichi Asakawa; Toshinori Mizuguchi; Takashi Ichikawa; Kunio Nishimura
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1988-12-05
Filing date: 1988-12-05
Publication date: 1993-09-10
Also published as: JPH02153059A

Description

【発明の詳細な説明】[Detailed description of the invention]

（産業上の利用分野）本発明はめつき層の均一被覆性及び密着性にす
ぐれた高耐食性溶融Al及びAl合金めつきCr含有
鋼板の製造法に関するものである。（従来の技術） Cr含有鋼板に耐食性のすぐれたAl及びAl合金
めつきを施す方法としては、例えば特公昭52−
33579号公報、特開昭60−245727号公報、特開昭
61−6261号公報等記載のものがある。特公昭52−33579号公報には、Cr含有鋼板にAl
或いはAl合金めつき層を施す方法として、めつ
き前処理法でめつき原板を酸化させずに焼鈍、還
元の加熱処理を行うか或いは鋼表面が酸化された
場合には研削等の手段で酸化膜を除去してAlめ
つき処理を行う方法が開示されている。一方、特
開昭60−245727号公報及び特開昭61−6261号公報
には、Cr含有鋼板表面にNi、Co等の下地めつき
層を施して加熱処理炉の酸化を防止し、まためつ
き浴との濡れ性を向上させることによつてすぐれ
たAlめつき鋼板を製造する方法が開示されてい
る。しかしながら、これらの方法について詳細に検
討してみると、安定した製造技術とはいえず、工
業的には製造面及び性能面に次のような問題点が
あつた。すなわち、Alめつき前の加熱処理工程
において、加熱炉中に不可避的に混入してくる微
量のO₂或いはH₂OによつてCr含有鋼板表面に強
固な酸化膜が形成される。Cr含有鋼表面に酸化
膜が一旦形成されると容易に還元されず、或いは
加熱炉中での研削等の機械的手段では除去し難か
つた。このため、めつき浴の濡れ性を阻害し、ま
た研削により原板にミクロ的な凹凸を形成してめ
つき浴表面に浮遊する酸化膜を付着し、めつき層
の均一被覆性を阻害し、ピンホール、不めつきを
多く発生して耐食性を著しく劣化させる問題があ
つた。また、通常の酸洗方法による活性化処理で
はCr含有量鋼板表面に形成された酸化膜は除去
され難いため、Ni、Co等の下地めつき層の被覆
性と密着性とを劣化して加熱処理工程のロール擦
等により剥離する現象があつた。このためAlめ
つき層も不めつきやピンホールを多く発生し、ま
たAlめつき鋼板に高度な加工を行う場合には鋼
表面と下地めつき層の界面あるいは下地めつき層
から剥離する問題があつた。（発明が解決しようとする課題） Al或いはAl合金溶融めつきを行う場合、一般
にめつき原板は材質調整のための焼鈍と原板表面
のガス還元による活性化処理が前処理として同時
に行われる。しかし、この工程において、Cr含
有鋼板はその表面が微量の酸素或いは水蒸気等の
存在で酸化され易く、また一旦酸化膜が形成され
ると容易に還元され難い。このため、めつき前の
これらの焼鈍、還元工程において、Cr含有鋼板
表面の活性化処理が均一かつ十分に行われ難く、
Al或いはAl合金めつき層はピンホール、不めつ
き等も発生して均一被覆性、密着性が劣化する。
このような焼鈍、還元工程における酸化を防止
し、かつAl系めつき浴との濡れ性を増加させる
ため、予め冷間圧延材にNi、Co等の下地めつき
被覆を施した場合でも、既にめつき原板の表面に
安定で強固な酸化膜が形成されているため、従来
の酸洗等の手段では表面が十分に活性化されず、
ピンホールを多く発生した下地被覆層が形成され
る。従つて、焼鈍、還元工程において、加熱炉内の
搬送ロールによる擦過によつて下地被覆層が剥離
し、その剥離部分或いはピンホール部分が酸化さ
れ、酸化膜を形成する。その結果、Al或いはAl
合金めつき層の密着性と耐食性が劣化する。本発明は、Crを必須成分として含有する鋼板
の溶融Al及びAl合金めつき鋼板の製造において、
鋼中のCrが鋼表面に濃化して強固な酸化膜を形
成して生じる前記のような問題点を解決して、被
覆層の均一被覆性、めつき層の密着性、耐食性に
すぐれたAl及びAl合金めつきCr含有鋼板の製造
法を提供することを目的とする。（課題を解決するための手段）本発明は、25％以下のCrを含有する鋼板を、
金属イオンのNi²⁺、Co²⁺の１種又は２種が全
SO₄ ^2-イオン濃度に対する重量比率で１／50≦
（金属イオン濃度）／（全SO₄ ^2-イオン濃度）≦
１／５、遊離硫酸75〜350ｇ／を含有する水溶
液中で7.5A／ｄm²以上の電流密度で１〜15秒間
陰極電解処理し、次いでNi²⁺、Co²⁺、Fe²⁺の１
種又は２種以上の金属イオンをSO₄ ^2-イオンと
Cl^-イオンの総和に対する重量比率で50％以上含
有しかつPH3.0以下のめつき浴で0.01〜1μ厚さの
Ni、Co、Fe被覆層或いはこれらの２種以上から
なる合金被覆層を施した後、該被覆層に溶融Al
及びAl合金めつき層を施すことを特徴とする均
一被覆性及び被覆層の密着性にすぐれた高耐食性
Al及びAl合金めつきCr含有鋼板の製造法である。（作用）本発明では、冷間圧延後の表面に生成した強固
な酸化膜を効率的に除去して活性化し、次いで該
表面にピンホールが少なく、均一被覆性、密着性
にすぐれたNi、Co、Fe下地めつき層或いはこれ
らの２種以上で構成される合金下地めつき層を施
す。この下地めつき層は、めつき原板に焼鈍及び
表面活性化処理が行われる酸化炉方式或いは無酸
化炉方式など加熱炉内でのCr含有鋼表面の酸化
及び酸化膜の生成を防止する。また、たとえ酸化
されても容易に還元性ガスで還元、活性化され
る。そして、ピンホールが少なく、均一被覆性と
密着性にすぐれた高耐食性Al及びAl合金めつき
Cr含有鋼板の製造が可能になる。このCr含有鋼・冷間圧延材表面の酸化膜を効
率的に除去し、活性化するため、遊離H₂SO₄を
主成分にしてこれに硫酸塩の形態でNi²⁺、Co²⁺
の１種又は２種の金属イオンを含有する処理浴を
用いて陰極電解処理をする。この処理浴の金属イ
オン量を適正に選択すると共に、適正な電解処理
条件を設定することによつて効率的な鋼板表面の
酸化膜除去と活性化、微量の金属イオンの析出を
同時に行なう。鋼表面に生成されている酸化膜の厚さ、クラツ
クの生成度合等は鋼板の表面性状によつて相違す
る。酸化膜は除去され易い部分から剥離して活性
化し、金属イオンが析出し、次いで他の活性化さ
れにくい部分に電流が集中して酸化膜を除去し、
活性化し、金属イオンが析出する。このような作
用が順次繰り返されて、鋼板表面にめつきが施さ
れる。この電解液中に遊離HCl或いは遊離Cl^-イオン
が存在する場合、鋼表面の活性化が容易に行なえ
る部分では穿孔腐食の危険性があるので、遊離
HCl、Cl^-イオンが不可避的不純物として含有さ
れる以外は使用しない。すなわち、本発明では遊
離H₂SO₄、SO₄ ^2-イオンを主成分とする処理浴を
使用する。また、浴中のSO₄ ^2-イオン濃度に比して金属イ
オン量を少なく含有し、処理時間を短縮化し、電
解電流密度を適正化することによつて、鋼表面の
酸化膜を除去し、活性化し、同時に微量の金属を
析出する。また、この微量の金属析出物は、本発
明ではNi、Co、Ni−Co合金等の耐酸化性にすぐ
れた金属を選定しているため、次の金属めつき処
理までの間の酸化膜の再生成を極力防止する。次いで、本発明では、Ni、Co、Fe等の金属イ
オンの含有量が多く、電解効率にすぐれためつき
浴を用いて下地被覆層を施し、その結果としてそ
の後のAl或いはAl合金めつき層の均一被覆性と
めつき層の密着性を改善し、耐食性にすぐれた
Al及びAl合金めつきCr含有鋼板の製造が可能と
なる。以下、本発明について詳細に説明する。転炉、電気炉等の溶解炉で溶製された溶鋼を連
続鋳造法又は造塊、分塊法でスラブとし、熱間圧
延、酸洗、冷間圧延されたCr含有量25％以下の
鋼板材を使用する。本発明において、めつき原板
のCr含有量を規制する理由は、Cr含有量が25％
を越えて含有される場合、その鋼表面の酸化膜を
SO₄ ^2-イオンと金属イオン（Ni²⁺、Co²⁺の１種又
は２種）からなる処理浴を用い１〜15秒間の陰極
電解処理で除去し、活性化することは困難であ
り、従つて、密着性と均一被覆性、耐食性にすぐ
れた金属めつき層を得ることは困難だからであ
る。また、めつき原板中のCr含有量の下限は特
に規制されないが、2.5％以上のCrを含有する鋼
板の使用が好ましい。すなわち、めつき原板の
Cr含有量が2.5％未満の場合、本発明のような処
理によらなくても表面の活性化処理が容易に行わ
れ、またNi等の金属めつき層を均一被覆性或い
は密着性にすぐれためつき層として設けることが
可能である。しかしながら、活性化処理後に下地
めつき及びAl及びAl合金めつき作業をいかに細
心の注意を払つて行つても微量のピンホールが生
成される。或いは、成形加工時、地鉄に達する疵
の発生部から赤錆や穿孔腐食を発生し、めつき鋼
板の耐食性が劣化する。従つて、めつき層の電位
が原板より貴になる自動車排ガス凝結水に曝され
る腐食環境や亜硫酸ガスが含有される高温湿潤雰
囲気等では、めつき原板欠陥部や加工時の疵部等
から腐食を生じる。このような理由から、本発明
においてはめつき原板のCr含有量は2.5〜25％、
好ましくは５〜20とする。本発明では原板として例えば以下の様な鋼板を
使用するのがよい。 (1) 重量％で、Ｃ；0.20％以下、酸可溶Al；
0.005〜0.10％、Cr；2.5〜25％、残部Fe及び不可
避的不純物（Si、Ｐ、Ｓ、Mn等）からなる鋼板 (2) 上記(1)の組成の鋼板に添加元素としてNi；
0.05〜10％、Cu；0.05〜１％、Mo；0.05〜１％、
Si；0.2〜１％、Ｐ；0.02〜0.05％、Al；0.1〜５
％、Ｂ；0.0001〜0.005％の１種又は２種以上を
含有する鋼板 (3) 重量％で、Ｃ；0.02％以下、酸可溶Al；
0.005〜0.10％、Cr；2.5〜25％を含有し、さらに
Ti；0.01〜0.8％、Nb；0.01〜0.8％、Ｖ；0.01〜
0.8％、Zr；0.01〜0.8％の１種又は２種以上を含
有し、残部Fe及び不可避的不純物からなる鋼板 (4) 上記(3)の組成の鋼板に添加元素としてNi；
0.05〜10％、Cu；0.05〜１％、Mo；0.05〜１％、
Si；0.2〜１％、Ｐ；0.02〜0.05％、Al0.1〜５％、
Ｂ；0.0001〜0.005％の１種又は２種以上を含有
する鋼板これらのCrを含有するめつき原板の冷間圧延
材は通常の製造工程を経て製造され、脱脂処理
（オルケイ酸ソーダーあるいはリン酸ソーダー等
に界面活性剤を添加した溶液中での電解処理等）
された後、本発明に使用される。まず、これらの鋼板に対して、金属イオンとし
てNi²⁺、CO²⁺の１種又は２種をSO₄ ^2-イオンと
の重量比率が１／50≦（金属イオン濃度）／
（SO₄ ^2-イオン濃度）≦１／５、遊離硫酸75〜350
ｇ／からなる水溶液中で、7.5A／ｄm²以上の
電流密度で１〜15秒間の陰極電解処理を施す。す
なわち、この処理はCr含有鋼板の表面に生成さ
れている強固な酸化膜を除去する表面活性化と、
Ni、Co、Ni−Co合金の析出処理とを同時に行な
う。この処理浴には、上記の条件を満足する（硫酸
−硫酸ニツケル）、（硫酸−硫酸コバルト）、（硫酸
−硫酸ニツケル−硫酸コバルト）浴、或いはこれ
らに電導性を増すために硫酸ナトリウム等を加え
た処理浴が使用される。処理浴の遊離硫酸濃度が75ｇ／未満では原板
表面の酸化膜を均一に除去し、表面を活性化する
のが困難であり、またNi等の同時析出を充分に
行なうこともできない。一方、遊離硫酸濃度が
350ｇ／を越える場合はその効果を飽和すると
共に、処理浴の持ち出しによる経済的な損失が大
きくなり、また処理浴のミスト発生が多く、作業
環境の劣化、処理装置の損耗が著しい等工業的に
不利になる。従つて、本発明においては遊離硫酸
濃度は75〜350ｇ／、好ましくは100〜300ｇ／
である。この遊離硫酸に対して、本発明の処理浴では、
硫酸ニツケル等の硫酸塩の形態で、金属イオンす
なわちNi²⁺、Co²⁺あるいは（Ni²⁺＋Co²⁺）を
１／50≦（金属イオン濃度）／（SO₄ ^2-イオン濃
度）≦１／５の範囲で添加する。この金属イオン
が含有された処理浴を用いることにより、原板表
面の酸化膜が効率的に除去され、密着性の良好な
Ni、Co等の金属が微量同時析出する。すなわち、
Cr含有鋼表面の酸化膜は均一でなく、本処理浴
中での陰極電解処理によつて酸化膜の除去され易
い部分から除去され、活性化され、この部分に浴
中の金属イオンがまず析出する。次いで、他の酸
化膜の剥離していない部分に電流集中されて酸化
膜が除去され、金属イオンが析出する。このよう
な反応が順次繰り返され、強固な酸化膜が生成さ
れたCr含有鋼表面が活性化され、密着性のすぐ
れたNi等の金属が同時析出する。また、この析出金属の効果によつて処理後電気
めつきまでの間に酸化膜が再生成されるのが防止
され、次工程のめつき密着性を向上する。 Ni²⁺、Co²⁺（Ni²⁺＋Co²⁺）の金属イオン濃度が
処理浴中の全SO₄ ^2-イオン濃度に対して１／50未
満では、金属イオン含有量が少なすぎて酸化膜の
除去と金属イオンの同時析出が行なわれにくく、
また、金属イオン濃度が全SO₄ ^2-イオン濃度に対
して１／５を越える場合には、処理浴中の金属イ
オン含有量が多すぎるため、めつき原板の活性化
されない表面に密着性の劣るめつき層或いは含有
金属の水酸化物、酸化物等を析出して密着性を劣
化し、いずれにしても本発明の目的が達成されな
い。従つて、本発明では金属イオン濃度と全
SO₄ ^2-イオン濃度の比率を１／50〜１／５、好ま
しくは１／25〜１／10とする。陰極電解処理は電流密度7.5A／ｄm²以上、処
理時間１〜15秒で行なう。電流密度が鋼板1dm²
当り7.5A未満の場合には、短時間の処理で酸化
膜除去と金属の同時析出を行なうことが困難であ
り、本発明では7.5A／ｄm²以上、好ましくは
10A／ｄm²以上の陰極電流密度で処理する。ま
た、電流密度の上限は特に規制されるものではな
いが、電流密度が高くなりすぎると、Cr含有鋼
板は比抵抗が高く、通板時の鋼板抵抗も高く、コ
ンダクターロールと処理浴との間で板厚によつて
は鋼板が発熱し、鋼の酸化が助長される。従つ
て、本発明では35A／ｄm²以下の電流密度が好ま
しい。その場合の処理時間については、１秒未満
では酸化膜除去による表面活性化と金属イオンの
同時析出を行なうのに充分でなく、また15秒を越
える長時間の陰極処理を行なう場合は、効果が飽
和すると共に、Ni等の金属イオンの析出部に更
に重畳して金属イオンが析出し、部分的に厚さの
異なる金属めつき層が生成され、次いで行われる
金属めつきの厚さも不均一になる。従つて、本発
明の処理時間は１〜15秒間、好ましくは1.5〜7.5
秒間とする。尚、処理浴温度については特に規制されず、常
温〜90℃の範囲で処理する。この処理に使用する電極としては、Pb−Sn電
極、ステンレス電極、チタンに白金めつきした電
極等の不溶性電極、或いはニツケル、コバルト等
の可溶性電極のいずれも使用しうる。しかし、工
業的に安定して処理作業を実施するためには、可
溶性電極は電極からの電解金属イオンが蓄積さ
れ、浴中の金属イオンの前記比率を維持するのが
困難であるため、不溶性電極を使用し、処理によ
る金属イオンの減少割合に対応して炭酸ニツケル
等の炭酸塩の形態で金属イオンを補給し、その含
有比率を維持するのが有利である。遊離塩酸或いはCl^-イオンは処理装置の構成材
料或いは原板組成によつてはめつき原板の穿孔腐
食を発生する原因となるので好ましいものではな
いが、本発明で使用する処理浴中に不可避的不純
物として含有する程度の量では特に影響はない。
また、不純物元素として処理浴中にFe²⁺イオン
が含有される場合、他のNi²⁺、Co²⁺イオンの析
出を妨げるので、その含有量は５ｇ／以下が好
ましく、2.5ｇ／以下がより好ましい。次いで、前記の処理で余剰の処理浴を払拭した
後或いは水洗した後、Ni、Co、Fe、Ni−Co、
Ni−Fe、Co−Fe、Ni−Co−Fe系の下地被覆処
理を施す。下地被覆めつき層は、Al及びAl合金
めつき前の加熱処理工程の酸化剥離を防止するも
ので、均一被覆性にすぐれ、ピンホールの生成量
が少なく、密着性にすぐれていることが重要であ
る。そのため、陰極電解処理後に電解効率にすぐ
れ、均一被覆性の良好なめつき層を得るため、金
属イオンNi²⁺、Co²⁺、Fe²⁺の１種又は２種以上
をめつき浴中の電解効率に関与する全SO₄ ^2-＋全
Cl^-イオンに対して50％以上、好ましくは60％以
上含有するめつき浴を用いて下地めつき層を施
す。下地被覆めつき層厚は0.01〜1μとする。この
下地被覆層の厚さが0.01μ未満では加熱工程にお
けるCr含有鋼板表面の酸化を防止することが困
難であり、またAl、Al合金めつき浴との濡れ性
の改善効果も小さく、本発明の目的とするAl及
びAl合金めつき鋼板が得られにくい。また、下
地被覆層の厚さが1μを越える場合は、その効果
が飽和し経済的でなくなるとともに、場合によつ
ては700〜1000℃程度の加熱処理工程において、
ロール等による擦過或いは急速加熱による熱衝撃
によつて剥離する原因になる。従つて、本発明で
はこの下地被覆層の厚さは0.01〜1μ、好ましくは
0.03〜0.5μである。また、本発明においては、この下地めつき浴に
PHが3.0以下の低PH浴を使用する。すなわち、め
つき浴のPHが3.0以下では、下地被覆処理後めつ
き工程までの間のNi等の析出物表面の酸化或い
はこれら析出物のピンホール部での原板の再酸化
による酸化膜を除去する効果が得られる。その結
果、より一層の均一被覆性にすぐれ、ピンホール
の生成量が少なく、密着性にすぐれたNi、Co等
の下地被覆が得られる。特にPH2.5以下が好まし
い。さらに、下地被覆層の均一被覆性をすぐれたも
のとするため、これら下地被覆層のめつき浴とし
て金属イオンを浴中の全SO₄ ^2-イオンと全Cl^-イ
オンに対して50％以上、好ましくは60％含有する
電解効率にすぐれためつき浴を使用する。例え
ば、硫酸ニツケル240ｇ／、塩化ニツケル45
ｇ／、ホウ酸30ｇ／（Ni²⁺／（SO₄ ^2-＋Cl^-）
＝65％）組成で、H₂SO₄を添加してPHを3.0以下
に調整しためつき浴を使用する。次に、この下地めつき層を施した後、水洗、乾
燥し、材質の調整のための焼鈍及び表面のガスク
リーニングを行うための加熱処理炉に導入する。
この加熱処理方法、条件等は本発明では特に規制
しない。Al或いはAl合金めつきの場合、この加
熱処理炉としては一般的にはめつき原板表面の圧
延油等の表面残存油脂類の酸化雰囲気での燃焼除
去と予備加熱を行つて、還元炉で焼鈍、還元を行
う酸化炉方式と、表面残存油脂類の弱酸化性或い
は無酸化雰囲気での気化除去と予備加熱を行つ
て、還元炉で焼鈍、還元を行う無酸化炉方式が用
いられる。本発明においては両方式とも用いられ
るが、前記のように下地めつき層表面には残存油
脂類が付着していないので、無酸化炉方式での加
熱処理が好ましい。この加熱処理工程において、
本発明の前記の性能特性にすぐれた下地めつき層
が施されているため、Cr含有鋼表面の酸化は殆
ど生じることがない。また、下地めつき層表面は
酸化されても、還元ガスによつて容易に還元、活
性化され、Al及びAl合金めつきが容易に行われ
る。この還元性雰囲気炉としては、一般にH₂含
有量10％以上、好ましくは15％以上のH₂とN₂と
の混合ガス、アンモニア分解ガス等を使用すると
よい。使用されるめつき原板の鋼成分によつて、また
必要とする材質特性によつて各々異なるが、600
〜1050℃程度の加熱温度で10〜180秒間程度、焼
鈍、ガスクリーニングされた後炉内でめつき浴温
度或いはめつき浴温より30℃程度高い温度まで冷
却し、空気に曝すことなくAl及びAl合金めつき
浴に導入し、浸漬めつきを行つた後、高圧流体等
の払拭手段でめつき量を調整する。本発明においてAl及びAl合金めつき浴は特に
規制されないが、以下のようなめつき浴が使用さ
れる。例えば、Al及びAl−Si、Al−Cr、Al−
Mg、Al−Si−Cr、Al−Si−Mg合金等及びこれ
らにめつき機器、めつき原板等から不可避的に含
有される不純物、例えばFe等が含まれているAl
及びAl合金めつき浴を使用する。本発明の方法では、前記したように、これらの
Al及びAl合金めつき浴に対して濡れ性にすぐれ、
かつ表面が活性化されている下地めつき層表面に
溶融Al及びAl合金めつきが施される。従つて、
Al及びAl合金めつき層の均一被覆性にすぐれ、
ピンホールの生成量も少なく、めつき密着性にす
ぐれ、かつ耐食性にすぐれたAl及びAl合金めつ
き鋼板が得られる。尚、以上は主として冷間圧延
材に本発明を適用する場合について説明してきた
が、冷間圧延、焼鈍後のフルフイニツシユ材に適
用しても同様の効果が得られる。すなわち、フル
フイニツシユ材に本発明の方法を適用して前記の
加熱処理を行つて無酸化方式の溶融めつきを行つ
てもよいし、またフラツクス方式によるめつき方
式に適用しても同様の効果がある。実施例Ａ第１表に示す鋼成分の冷間圧延材をめつき原板
として、以下に示す処理法を適用してAl及びAl
合金めつき鋼板を製造した。実施例 A1 …鋼A1を使用〈陰極電解処理〉 80ｇ／H₂SO₄−10ｇ／CoSO₄・7H₂O系水
溶液（金属イオン濃度／SO₄ ^2-イオン濃度（Ｍ／
Ｓ）＝1.3／50）中で8A／ｄm²の電流密度で1.2秒
間の陰極処理（浴温25℃、ステンレス製電極使
用）〈下地被覆層処理〉 340ｇ／CoSO₄・7H₂O−45ｇ／CoCl₂・
6H₂O−ホウ酸45ｇ／（金属イオンのSO₄ ^2-イ
オンとCl^-イオンの総和に対する重量比率（Ｍ／
Ｉ）＝63.7％）系浴にH₂SO₄を添加してPH2.8に調
整した全Cl^-イオン濃度13.4ｇ／のめつき浴中
で、電流密度10A／ｄm²で0.1μのCoめつき比較例 A1 …鋼A1を使用〈陰極電解処理〉 80ｇ／H₂SO₄浴中で8A／ｄm²の電流密度で
1.2秒間の陰極処理（浴温25℃、ステンレス製電
極使用）〈下地被覆層処理〉実施例A1と同一処理実施例 A2 …鋼A2を使用〈陰極電解処理〉 120ｇ／H₂SO₄−60ｇ／NiSO₄・7H₂O系水
溶液（Ｍ／Ｓ＝4.55／50）中で15A／ｄm²の電流
密度で８秒間の陰極処理（浴温35℃、Ti＋Ptめ
つき電極使用）〈下地被覆層処理〉 240ｇ／NiSO₄・7H₂O−30ｇ／NiCl₂・
6H₂O−ホウ酸30ｇ／（Ｍ／Ｉ）＝70％）系浴
にH₂SO₄を添加してPH2.4に調整した全Cl^-イオン
濃度8.91ｇ／のめつき浴を用いて、電流密度
7.5A／ｄm²で0.06μのNiめつき比較例 A2 …鋼A2を使用〈陰極電解処理〉 100ｇ／H₂SO₄−250ｇ／NiSO₄・7H₂O系
水溶液（Ｍ／Ｓ＝1.425／５）中で30A／ｄm²の
電流密度で８秒間の陰極処理（浴温35℃、Ti＋
Ptめつき電極使用）〈下地被覆層処理〉実施例A2と同一処理実施例 A3(1) …鋼A3を使用〈陰極電解処理〉 150ｇ／H₂SO₄−30ｇ／NiSO₄・7H₂O系水
溶液（Ｍ／Ｓ＝２／50）中で20A／ｄm²の電流密
度で４秒間の陰極処理（浴温40℃、Pb−Sn電極
使用）〈下地被覆層処理〉 240ｇ／NiSO₄・7H₂O−45ｇ／NiCl₂・
6H₂O−ホウ酸40ｇ／（Ｍ／Ｉ＝64.2％）系浴
にH₂SO₄を添加してPH1.8に調整した全Cl^-イオン
濃度13.4ｇ／のめつき浴中で、電流密度15A／
ｄm²で0.12μのNiめつき実施例 A3(2) …鋼A3を使用〈陰極電解処理〉実施例A3(1)と同一処理〈下地被覆層処理〉 125ｇ／NiSO₄・7H₂O−125ｇ／FeSO₄・
7H₂O−20ｇ／NiCl₂・6H₂O−20ｇ／
FeCl₂・6H₂O−ホウ酸30ｇ／（Ｍ／Ｉ＝62.2
％）系浴にH₂SO₄を添加してPHを1.5に調整した
全Cl^-イオン濃度12.0ｇ／のめつき浴を用いて、
電流密度12.5A／ｄm²で0.03μのNi−85％合金め
つき比較例 A3(1) …鋼A3を使用〈陰極電解処理〉 150ｇ／H₂SO₄−５ｇ／NiSO₄・7H₂O系水
溶液（Ｍ／Ｓ＝0.35／50）中で20A／ｄm²の電流
密度で４秒間の陰極処理（浴温40℃、Pb−Sn電
極使用）〈下地被覆層処理〉実施例A1と同一処理比較例 A3(3) …鋼A3を使用〈陰極電解処理〉実施例A3(1)と同一浴を用いて電流密度4A／ｄ
m²で４秒間の陰極処理（浴温40℃、Pb−Sn電極
使用）〈下地被覆層処理〉実施例A3(2)と同一処理実施例 A4 …鋼A4を使用〈陰極電解処理〉 200ｇ／H₂SO₄−210ｇ／NiSO₄・7H₂O系
水溶液（Ｍ／Ｓ＝8.2／50）中で30A／ｄm²の電
流密度で８秒間の陰極処理（浴温55℃、Pb−
SnAg電極使用）〈下地被覆層処理〉 120ｇ／NiSO₄・7H₂O−180ｇ／CoSO₄・
7H₂O−12ｇ／NiCl₂・6H₂O−18ｇ／
CoCl₂・6H₂O−ホウ酸20ｇ／（Ｍ／Ｉ＝63％）
系浴に硫酸を添加してPH1.6に調整した全Cl^-イオ
ン濃度8.9ｇ／のめつき浴中で、電流密度
30A／ｄm²で0.5μのNi−60％Co合金めつき比較例 A4 …鋼A4を使用〈陰極電解処理〉実施例A4と同一処理〈下地被覆層処理〉 120ｇ／NiSO₄・7H₂O−30ｇ／NiCl₂・
6H₂O−ホウ酸30ｇ／−250ｇ／H₂SO₄（Ｍ／
Ｉ＝11％）からなるPH＜O.5のめつき浴を用い、
30A／ｄm²の電流密度で0.1μのNiめつき実施実施例 A5 …鋼A5を使用〈陰極電解処理〉 300ｇ／H₂SO₄−150ｇ／NiSO₄・7H₂O系
水溶液（Ｍ／Ｓ＝4.55／50）中で12.5A／ｄm²の
電流密度で2.5秒間の陰極処理（浴温65℃、Pb−
Sn−Ir電極使用）〈下地被覆層処理〉 280ｇ／NiSO₄・7H₂O−35ｇ／NiCl₂・
6H₂O−35ｇ／ホウ酸（Ｍ／Ｉ＝63.3％）系浴
にH₂SO₄を添加してPH1.75に調整した全Cl^-イオ
ン濃度10.4ｇ／のめつき浴中で、電流密度
5A／ｄm²で0.08μのNiめつき実施比較例 A5 …鋼A5を使用〈陰極電解処理〉実施例A5と同一処理〈下地被覆層処理〉実施例A5と同一浴成分系で、PHのみ3.5のめつ
き浴を用い、同条件で0.08μのNiめつき実施以上により製造した鋼板について、各々下記に
示す評価法によりめつき層の均一被覆性、めつき
層の密着性、及び自動車排気系用途を想定した耐
食性について、その性能評価を行ない、結果を第
２表に示す。尚、評価試験方法及び評価基準は以
下の通りである。〔評価試験方法及び評価基準〕１めつき被覆層の均一被覆性ラインスピード100ｍ／minで片面当りのめつ
き量が60ｇ／m²のAl−10.5％Si系合金めつき鋼板
を製造し、その外観を調査し、以下の評価基準で
評価して、その均一被覆性を検討した。 ◎…めつき浴の濡れ性極めて良好で、めつき外観
極めて良好〇…めつき浴の濡れ性比較的良好で、10dm²の評
価面に対して流れ模様（めつき厚さの部分的
に厚い部分）が２点以下発生 △…めつき浴の濡れ性若干劣るため、10dm²の評
価面にざらつき状の点状欠陥部（微小不めつ
きが10数点群発）が発生 ×…めつき浴の濡れ性著しく劣るため、10dm²の
評価面にざらつき状の点状欠陥部が多量に発
生２めつき層の密着性 0.6mmの板厚にAl−８％Si系合金めつき層を片
面当りの付着量で40ｇ／m²施してから、板厚と同
一の曲率半径で衝撃曲げ加工後、セロテープ（登
録商標）を貼付、剥離して、めつき層の剥離状況
を調査した。尚、評価基準は以下の通りである。 ◎…めつき層の剥離なく、セロテープ（登録商
標）への剥離物の付着なし〇…めつき層の表面部が若干剥離、セロテープ
（登録商標）に極軽微な剥離物が付着 △…めつき層の鋼板界面からの部分的剥離が発
生、セロテープ（登録商標）への剥離物の付
着が明瞭に認められる ×…めつき層全面剥離 (1) 評価法Ａ 100×100mmサイズの鋼板について、高温排ガス
雰囲気を対象にして排ガス雰囲気中で700℃で
1000時間の連続加熱試験を実施し、その赤錆発生
状況調査した。すなわち、高温排ガス雰囲気に曝
された場合に、めつき欠陥部（不めつき部）が発
生源となる赤錆発生状況を調査することによつ
て、めつき層の均一被覆性と高温耐食性を評価し
た。尚、評価基準は以下の通りである。はAl
−６％Si40ｇ／m²、はAl−10％Si60ｇ／m²で
ある。 ◎…赤錆発生なし〇…点状の赤錆発生個数１〜10個 △…点状の赤錆発生個数11個以上或いは面積状の
赤錆発生部分が３個所以下 ×…面積状の赤錆発生部分が４個所以上 (2) 評価法Ｂ 50×100mmの評価材を（NH₄）₂SO₄1000mg／
−NH₄NO₃500mg／−NH₄Cl1000mg／系水溶
液をSO₄ ^2-でPH３に調整した腐食試験液を用い、
80℃で500時間浸漬し、その赤錆の発生状況を調
査した。すなわち、排ガス凝結水を対象とした湿
食雰囲気におけるめつき層の均一被覆性と耐食性
について評価を行つた。尚、評価基準は以下の通
りである。はAl80ｇ／m²、はAl−８％Si−
0.5％Co50ｇ／m²である。 ◎…点状赤錆発生個数５個以下〇…点状赤錆発生個数６〜10個以下 △…点状赤錆発生個数11個以上30個以下 ×…点状赤錆発生個数31個以上或いは面積状の赤
錆発生 (3) 評価法Ｃ自動車・マフラー内部の腐食環境を想定して腐
食促進溶液としてSO₄ ^2-（1000ppm）−NO₃ ^-
（150ppm）−Cl^-（300ppm）−CO₃ ^2-（4000ppm）−
NH₄ ⁺（3000ppm）−HCOOH（1000ppm）−
CH₃COOH（1000ppm）系水溶液をPH８に調整し
たものを用い、以下の条件でサイクルテストを行
つた。すなわち、評価材（30×50mm）を、＜350℃
で60分加熱→腐食試験液・半没テスト（密閉容器
を用い、評価材の1/2部を腐食溶液中に浸漬、80
℃、５時間）→乾燥（100℃、24時間）→腐食試
験液・半没テスト（80℃、24時間）→乾燥（100
℃、24時間）→腐食試験液・半没テスト（180℃、
24時間）→室内曝露（30℃、56時間）＞を１サイ
クルとして、３サイクルテスト後の外観腐食状況
を調査し、このマフラー内の腐食を想定した湿
食、乾燥繰り返し腐食雰囲気下でのめつき層の均
一被覆性が耐食性に及ぼす影響についての評価を
行つた。尚、評価基準は以下の通りである。は
Al−７％Si45ｇ／m²、はAl−10％Si70ｇ／m²
である。 ◎…腐食溶液浸漬部の気−液界面部における赤錆
の発生が微小点錆10点以下〇…腐食溶液浸漬部の気−液界面部を中心に微小
赤錆11点以上20点以下或いは赤錆発生率で
0.1％以下 △…上記の気−液界面部或いは他の部分にかなり
の赤錆発生 ×…赤錆の発生状況は上記△の状況でかつ錆下に
穿孔状の腐食著しく発生 (Industrial Application Field) The present invention relates to a method for manufacturing a highly corrosion-resistant molten Al and Al alloy plated Cr-containing steel sheet with excellent uniform coverage and adhesion of the plated layer. (Prior art) As a method of applying Al or Al alloy plating with excellent corrosion resistance to a Cr-containing steel plate, for example,
Publication No. 33579, Japanese Patent Publication No. 60-245727, Japanese Patent Publication No. Sho
There are those described in Publication No. 61-6261, etc. In Japanese Patent Publication No. 52-33579, Al
Alternatively, as a method of applying an Al alloy plating layer, heat treatment such as annealing and reduction is performed without oxidizing the plated original plate using a plating pretreatment method, or if the steel surface is oxidized, oxidation is performed by means such as grinding. A method of removing the film and performing Al plating treatment is disclosed. On the other hand, in JP-A-60-245727 and JP-A-61-6261, an underplating layer such as Ni or Co is applied to the surface of a Cr-containing steel sheet to prevent oxidation in a heat treatment furnace. A method for producing an excellent Al-plated steel sheet by improving wettability with a soaking bath is disclosed. However, when these methods were examined in detail, it was found that they were not stable manufacturing techniques and had the following problems in terms of manufacturing and performance from an industrial perspective. That is, in the heat treatment step before Al plating, a strong oxide film is formed on the surface of the Cr-containing steel sheet due to trace amounts of O ₂ or H ₂ O that inevitably enter the heating furnace. Once an oxide film is formed on the surface of Cr-containing steel, it is not easily reduced or removed by mechanical means such as grinding in a heating furnace. For this reason, the wettability of the plating bath is inhibited, and the grinding forms microscopic irregularities on the original plate, resulting in an oxide film floating on the surface of the plating bath, which inhibits the uniform coverage of the plating layer. There was a problem in that many pinholes and defects occurred, resulting in a significant deterioration in corrosion resistance. In addition, since the oxidized film formed on the surface of the Cr-containing steel sheet is difficult to remove with the activation treatment using the normal pickling method, heating may deteriorate the coverage and adhesion of the underlying plating layer such as Ni and Co. There was a phenomenon of peeling due to roll rubbing during the processing process. For this reason, the Al-plated layer also generates many imperfections and pinholes, and when advanced processing is performed on Al-plated steel sheets, there is a problem of peeling from the interface between the steel surface and the base plating layer, or from the base plating layer. It was hot. (Problems to be Solved by the Invention) When hot-melting Al or Al alloy, generally the plating original plate is subjected to annealing for material adjustment and activation treatment by gas reduction on the surface of the original plate at the same time as pretreatment. However, in this process, the surface of the Cr-containing steel sheet is easily oxidized in the presence of trace amounts of oxygen or water vapor, and once an oxide film is formed, it is difficult to be reduced easily. For this reason, in these annealing and reduction steps before plating, it is difficult to uniformly and sufficiently activate the surface of the Cr-containing steel sheet.
In the Al or Al alloy plating layer, pinholes, imperfections, etc. occur, resulting in deterioration of uniform coverage and adhesion.
In order to prevent oxidation during such annealing and reduction processes and increase wettability with the Al-based plating bath, even if the cold-rolled material is coated with a base plating coating such as Ni or Co in advance, the Because a stable and strong oxide film is formed on the surface of the plated plate, the surface cannot be activated sufficiently by conventional methods such as pickling.
A base coating layer with many pinholes is formed. Therefore, in the annealing and reduction steps, the base coating layer is peeled off due to abrasion by the conveyor roll in the heating furnace, and the peeled portion or pinhole portion is oxidized to form an oxide film. As a result, Al or Al
The adhesion and corrosion resistance of the alloy plating layer deteriorates. The present invention relates to the production of molten Al and Al alloy plated steel sheets containing Cr as an essential component.
By solving the above-mentioned problems caused by Cr in steel concentrating on the steel surface and forming a strong oxide film, we have developed Al that has excellent uniformity of coating layer, adhesion of plating layer, and corrosion resistance. The purpose of the present invention is to provide a method for producing a Cr-containing steel plate plated with an Al alloy. (Means for solving the problem) The present invention provides a steel plate containing 25% or less of Cr.
One or both of the metal ions Ni ²⁺ and Co ²⁺ are present in all
SO ₄ ^2- Weight ratio to ion concentration 1/50≦
(Metal ion concentration)/(Total SO ₄ ^2- ion concentration) ≦
1/5, cathodic electrolysis treatment for 1 to 15 seconds at a current density of 7.5 A/dm ² or more in an aqueous solution containing 75 to 350 g of free sulfuric acid, and then 1 to 1 of Ni ²⁺ , Co ²⁺ , Fe ²⁺
species or two or more metal ions with SO ₄ ^2- ion
0.01 to 1μ thick in a plating bath containing 50% or more of Cl ^- ions in terms of weight ratio to the total and pH 3.0 or less.
After applying a Ni, Co, Fe coating layer or an alloy coating layer consisting of two or more of these, molten Al is applied to the coating layer.
High corrosion resistance with excellent uniform coverage and adhesion of the coating layer, characterized by applying an Al alloy plating layer.
This is a method for producing Al and Al alloy-plated Cr-containing steel sheets. (Function) In the present invention, the strong oxide film formed on the surface after cold rolling is efficiently removed and activated, and then Ni, which has few pinholes and has excellent uniform coverage and adhesion, is activated. A Co, Fe underplating layer, or an alloy underplating layer composed of two or more of these is applied. This base plating layer prevents oxidation of the Cr-containing steel surface and the formation of an oxide film in a heating furnace such as an oxidation furnace method or a non-oxidation furnace method in which annealing and surface activation treatment are performed on the plated original plate. Moreover, even if it is oxidized, it is easily reduced and activated with a reducing gas. Highly corrosion resistant Al and Al alloy plating with few pinholes and excellent uniform coverage and adhesion.
It becomes possible to manufacture Cr-containing steel sheets. In order to efficiently remove and activate the oxide film on the surface of this Cr-containing steel/cold rolled material, free H ₂ SO ₄ is the main component, and Ni ²⁺ and Co ²⁺ are added to it in the form of sulfate.
Cathodic electrolytic treatment is performed using a treatment bath containing one or two types of metal ions. By appropriately selecting the amount of metal ions in this treatment bath and setting appropriate electrolytic treatment conditions, efficient removal and activation of the oxide film on the surface of the steel sheet and precipitation of a trace amount of metal ions can be performed simultaneously. The thickness of the oxide film formed on the steel surface, the degree of crack formation, etc. differ depending on the surface properties of the steel sheet. The oxide film is peeled off and activated from the parts that are easy to remove, metal ions are precipitated, and then current is concentrated on other parts that are difficult to activate and remove the oxide film.
It is activated and metal ions are precipitated. These actions are repeated one after another, and the surface of the steel plate is plated. If free HCl or free Cl ^- ions are present in this electrolyte, there is a risk of pitting corrosion in areas where the steel surface can be easily activated.
Do not use unless HCl or Cl ^- ions are contained as unavoidable impurities. That is, in the present invention, a treatment bath containing free H ₂ SO ₄ and SO ₄ ^2- ions as main components is used. In addition, by containing a small amount of metal ions compared to the SO ₄ ^2- ion concentration in the bath, shortening the treatment time, and optimizing the electrolytic current density, the oxide film on the steel surface can be removed. Activates and simultaneously deposits trace amounts of metal. In addition, in the present invention, metals with excellent oxidation resistance such as Ni, Co, and Ni-Co alloys are selected to remove this small amount of metal precipitates, so that the oxide film is removed until the next metal plating process. Prevent regeneration as much as possible. Next, in the present invention, a base coating layer is applied using a matting bath that has a high content of metal ions such as Ni, Co, and Fe and has excellent electrolytic efficiency, and as a result, the subsequent Al or Al alloy plated layer is coated. Improved uniform coverage and adhesion of the plating layer, offering excellent corrosion resistance.
It becomes possible to manufacture Al and Al alloy-plated Cr-containing steel sheets. The present invention will be explained in detail below. A steel plate with a Cr content of 25% or less that is made from molten steel produced in a melting furnace such as a converter or electric furnace and made into a slab by continuous casting, ingot making, or blooming, and then hot rolled, pickled, and cold rolled. Use materials. In the present invention, the reason for regulating the Cr content of the plated original plate is that the Cr content is 25%.
If it is contained in excess of
It is difficult to remove and activate by cathodic electrolytic treatment for 1 to 15 seconds using a treatment bath consisting of SO ₄ ^2- ions and metal ions (one or two of Ni ²⁺ and Co ²⁺ ). Therefore, it is difficult to obtain a metal plating layer with excellent adhesion, uniform coverage, and corrosion resistance. Further, although the lower limit of the Cr content in the plated original plate is not particularly regulated, it is preferable to use a steel plate containing 2.5% or more of Cr. In other words, the plating original plate
When the Cr content is less than 2.5%, the surface can be easily activated without the treatment of the present invention, and the coating with a metal plating layer such as Ni can be coated uniformly or has excellent adhesion. It can be provided as a layer. However, no matter how carefully the undercoat plating and Al and Al alloy plating operations are performed after the activation treatment, a small amount of pinholes are generated. Alternatively, during the forming process, red rust or perforation corrosion occurs from the occurrence of flaws that reach the base steel, and the corrosion resistance of the plated steel sheet deteriorates. Therefore, in corrosive environments where the plating layer is exposed to condensed water from automobile exhaust gases, where the potential of the plating layer is more noble than that of the original plate, or in high-temperature, humid atmospheres containing sulfur dioxide gas, the potential of the plating layer is more noble than that of the original plate. Causes corrosion. For these reasons, in the present invention, the Cr content of the plating original plate is 2.5 to 25%,
Preferably it is 5-20. In the present invention, it is preferable to use, for example, the following steel plates as the original plate. (1) In weight%, C; 0.20% or less, acid-soluble Al;
Steel plate (2) consisting of 0.005 to 0.10%, Cr; 2.5 to 25%, balance Fe and unavoidable impurities (Si, P, S, Mn, etc.) Ni as an added element to the steel plate with the composition of (1) above;
0.05-10%, Cu; 0.05-1%, Mo; 0.05-1%,
Si; 0.2-1%, P; 0.02-0.05%, Al; 0.1-5
%, B: Steel plate containing one or more of 0.0001 to 0.005% (3) Weight %, C: 0.02% or less, acid-soluble Al;
Contains 0.005-0.10%, Cr; 2.5-25%, and
Ti; 0.01~0.8%, Nb; 0.01~0.8%, V; 0.01~
Steel plate containing 0.8%, Zr; 0.01 to 0.8% of one or more types, and the balance consisting of Fe and inevitable impurities (4) Ni as an added element to the steel plate with the composition of (3) above;
0.05-10%, Cu; 0.05-1%, Mo; 0.05-1%,
Si: 0.2~1%, P: 0.02~0.05%, Al0.1~5%,
B: Steel plate containing one or more of 0.0001 to 0.005% These cold-rolled plated original sheets containing Cr are manufactured through the normal manufacturing process, and are degreased (sodium orsilicate or sodium phosphate). electrolytic treatment in a solution containing a surfactant, etc.)
After that, it is used in the present invention. First, for these steel sheets, the weight ratio of one or two of Ni ²⁺ and CO ²⁺ as metal ions to SO ₄ ^2- ions is 1/50≦(metal ion concentration)/
(SO ₄ ^2- ion concentration) ≦1/5, free sulfuric acid 75-350
A cathodic electrolytic treatment is carried out for 1 to 15 seconds at a current density of 7.5 A/dm ² or more in an aqueous solution consisting of 1.5 A/dm 2 or more. In other words, this treatment involves surface activation to remove the strong oxide film formed on the surface of the Cr-containing steel sheet,
Ni, Co, and Ni-Co alloy precipitation treatments are performed simultaneously. This treatment bath may be a (sulfuric acid-nickel sulfate), (sulfuric acid-cobalt sulfate), (sulfuric acid-nickel sulfate-cobalt sulfate) bath that satisfies the above conditions, or may contain sodium sulfate or the like to increase conductivity. An additional treatment bath is used. If the concentration of free sulfuric acid in the treatment bath is less than 75 g/l, it is difficult to uniformly remove the oxide film on the surface of the original plate and activate the surface, and it is also impossible to sufficiently perform simultaneous precipitation of Ni, etc. On the other hand, the free sulfuric acid concentration
If it exceeds 350g/, the effect will be saturated, and the economic loss due to taking out the processing bath will be large, and there will be a lot of mist generated from the processing bath, resulting in deterioration of the working environment, significant wear and tear on the processing equipment, etc., resulting in industrial problems. be at a disadvantage. Therefore, in the present invention, the free sulfuric acid concentration is 75 to 350 g/, preferably 100 to 300 g/
It is. In the treatment bath of the present invention, for this free sulfuric acid,
In the form of sulfates such as nickel sulfate, metal ions, i.e., Ni ²⁺ , Co ²⁺ or (Ni ²⁺ +Co ²⁺ ), are added at a ratio of 1/50≦(metal ion concentration)/(SO ₄ ^2- ion concentration)≦1. Add in the range of /5. By using a treatment bath containing these metal ions, the oxide film on the surface of the original plate is efficiently removed and good adhesion is achieved.
Trace amounts of metals such as Ni and Co precipitate simultaneously. That is,
The oxide film on the surface of Cr-containing steel is not uniform, and the cathodic electrolytic treatment in this treatment bath removes and activates the oxide film from the easily removed parts, and the metal ions in the bath first precipitate in these parts. do. Next, current is concentrated on the other oxide film that has not been peeled off, the oxide film is removed, and metal ions are precipitated. These reactions are repeated in sequence, and the surface of the Cr-containing steel on which a strong oxide film has been formed is activated, and metals such as Ni, which have excellent adhesion, are precipitated simultaneously. Further, the effect of the deposited metal prevents the oxide film from being regenerated after the treatment and before electroplating, improving the plating adhesion in the next step. If the metal ion concentration of Ni ²⁺ and Co ²⁺ (Ni ²⁺ +Co ²⁺ ) is less than 1/50 of the total SO ₄ ^2- ion concentration in the treatment bath, the metal ion content is too small and the oxide film removal of metal ions and simultaneous precipitation of metal ions is difficult,
In addition, if the metal ion concentration exceeds 1/5 of the total SO ₄ ^2- ion concentration, the metal ion content in the treatment bath is too high, and the adhesion to the unactivated surface of the plated original plate is reduced. An inferior plating layer or hydroxides, oxides, etc. of the contained metals are deposited, resulting in deterioration of adhesion, and in any case, the object of the present invention is not achieved. Therefore, in the present invention, the metal ion concentration and the total
The ratio of SO ₄ ^2- ion concentration is 1/50 to 1/5, preferably 1/25 to 1/10. The cathodic electrolytic treatment is carried out at a current density of 7.5 A/dm ² or more and a treatment time of 1 to 15 seconds. Current density is steel plate ^1dm2
If the current is less than 7.5 A/dm ² , it is difficult to remove the oxide film and simultaneously deposit the metal in a short period of time.
Treat with a cathode current density of 10 A/dm ² or more. Furthermore, although the upper limit of the current density is not particularly regulated, if the current density becomes too high, the resistivity of the Cr-containing steel sheet will be high, the resistance of the steel sheet during threading will also be high, and the gap between the conductor roll and the treatment bath will increase. Depending on the thickness of the plate, the steel plate may generate heat, promoting oxidation of the steel. Therefore, in the present invention, a current density of 35 A/dm ² or less is preferred. In this case, if the treatment time is less than 1 second, it is not sufficient to activate the surface by removing the oxide film and simultaneously deposit metal ions, and if the cathode treatment is performed for a long time exceeding 15 seconds, the effect will not be sufficient. As it becomes saturated, metal ions further precipitate over the precipitated areas of metal ions such as Ni, forming a metal plating layer with partially different thicknesses, and the thickness of the subsequent metal plating also becomes non-uniform. . Therefore, the processing time of the present invention is 1 to 15 seconds, preferably 1.5 to 7.5 seconds.
Seconds. Note that the temperature of the treatment bath is not particularly regulated, and the treatment is carried out within the range of room temperature to 90°C. As the electrode used in this treatment, any of insoluble electrodes such as Pb-Sn electrodes, stainless steel electrodes, and platinum-plated titanium electrodes, or soluble electrodes such as nickel and cobalt electrodes can be used. However, in order to perform industrially stable processing operations, soluble electrodes must be used because electrolytic metal ions from the electrodes accumulate and it is difficult to maintain the aforementioned ratio of metal ions in the bath. It is advantageous to maintain the content ratio by replenishing metal ions in the form of carbonates such as nickel carbonate in response to the reduction rate of metal ions due to treatment. Free hydrochloric acid or Cl ^- ions are not preferable because they can cause perforation corrosion of the plated original plate depending on the constituent materials of the processing equipment or the composition of the original plate, but they may be present as unavoidable impurities in the processing bath used in the present invention. There is no particular effect if the amount is contained.
In addition, when Fe ²⁺ ions are contained in the treatment bath as impurity elements, the content is preferably 5 g/or less, and 2.5 g/or less, since it prevents the precipitation of other Ni ²⁺ and Co ²⁺ ions. More preferred. Next, after wiping off the excess treatment bath in the above treatment or washing with water, Ni, Co, Fe, Ni-Co,
Apply Ni-Fe, Co-Fe, Ni-Co-Fe base coating treatment. The base coating plating layer prevents oxidation peeling during the heat treatment process before Al and Al alloy plating, and it is important that it has excellent uniform coverage, few pinholes, and excellent adhesion. It is. Therefore, in order to obtain a plating layer with excellent electrolytic efficiency and good uniform coverage after cathodic electrolytic treatment, one or more metal ions Ni ²⁺ , Co ²⁺ , and Fe ²⁺ are added to the electrolytic solution in the plating bath. Total SO ₄ ^2- + total involved in efficiency
A base plating layer is applied using a plating bath containing 50% or more, preferably 60% or more of Cl ^- ions. The thickness of the base coating plating layer is 0.01 to 1μ. If the thickness of this base coating layer is less than 0.01μ, it is difficult to prevent the surface of the Cr-containing steel sheet from oxidizing during the heating process, and the effect of improving wettability with Al and Al alloy plating baths is also small. It is difficult to obtain the desired Al and Al alloy plated steel sheets. In addition, if the thickness of the base coating layer exceeds 1μ, the effect will be saturated and it will become uneconomical, and in some cases, during the heat treatment process at about 700 to 1000℃,
Scraping by a roll or the like or thermal shock caused by rapid heating may cause peeling. Therefore, in the present invention, the thickness of this base coating layer is 0.01 to 1μ, preferably
It is 0.03-0.5μ. In addition, in the present invention, this base plating bath
Use a low PH bath with a PH of 3.0 or less. In other words, if the pH of the plating bath is 3.0 or less, the oxide film due to oxidation of the surface of precipitates such as Ni between the base coating treatment and the plating process, or the reoxidation of the original plate at the pinholes of these precipitates, is removed. The effect of As a result, a base coating of Ni, Co, etc. can be obtained which has more uniform coverage, fewer pinholes, and excellent adhesion. In particular, pH of 2.5 or less is preferred. Furthermore, in order to achieve excellent uniform coverage of the base coating layer, metal ions are used in the plating bath for these base coating layers in an amount of at least 50% of the total SO ₄ ^2- ions and total Cl ^- ions in the bath. Preferably, a fermentation bath containing 60% and excellent electrolytic efficiency is used. For example, nickel sulfate 240g/, nickel chloride 45
g/, boric acid 30g/(Ni ²⁺ /(SO ₄ ^2- +Cl ^- )
= 65%) composition, and use a tightening bath in which the pH is adjusted to 3.0 or less by adding H ₂ SO ₄ . Next, after applying this base plating layer, it is washed with water, dried, and introduced into a heat treatment furnace for annealing to adjust the material quality and gas cleaning of the surface.
This heat treatment method, conditions, etc. are not particularly restricted in the present invention. In the case of Al or Al alloy plating, this heat treatment furnace generally burns and removes residual oils and fats on the surface of the plated plate in an oxidizing atmosphere, such as rolling oil, and performs preheating, followed by annealing and reduction in a reducing furnace. An oxidation furnace method is used in which the oils and fats remaining on the surface are removed by vaporization in a weakly oxidizing or non-oxidizing atmosphere, preliminary heating is performed, and annealing and reduction are performed in a reduction furnace. Although both methods are used in the present invention, heat treatment in a non-oxidizing furnace method is preferable because residual oils and fats are not attached to the surface of the base plating layer as described above. In this heat treatment step,
Since the base plating layer of the present invention has excellent performance characteristics as described above, oxidation of the Cr-containing steel surface hardly occurs. Further, even if the surface of the base plating layer is oxidized, it is easily reduced and activated by reducing gas, and Al and Al alloy plating can be easily performed. As this reducing atmosphere furnace, it is generally preferable to use a mixed gas of H ₂ and N ₂ having an H ₂ content of 10% or more, preferably 15% or more, ammonia decomposition gas, or the like. Although it varies depending on the steel composition of the plated base plate used and the required material properties,
After annealing and gas cleaning at a heating temperature of ~1050℃ for 10 to 180 seconds, the aluminum and After introducing it into an Al alloy plating bath and performing immersion plating, the amount of plating is adjusted by wiping means such as high-pressure fluid. In the present invention, Al and Al alloy plating baths are not particularly limited, but the following plating baths are used. For example, Al and Al-Si, Al-Cr, Al-
Mg, Al-Si-Cr, Al-Si-Mg alloys, etc. and Al containing impurities such as Fe etc. that are unavoidably contained in these from plating equipment, plating original plates, etc.
and use an Al alloy plating bath. In the method of the present invention, as described above, these
Excellent wettability for Al and Al alloy plating baths,
Then, molten Al and Al alloy plating is applied to the surface of the activated base plating layer. Therefore,
Excellent uniform coverage of Al and Al alloy plating layers,
Al and Al alloy plated steel sheets with less pinhole formation, excellent plating adhesion, and excellent corrosion resistance can be obtained. In addition, although the case where the present invention is mainly applied to cold-rolled materials has been described above, the same effect can be obtained even if the present invention is applied to full-finish materials after cold rolling and annealing. That is, the method of the present invention may be applied to a full finish material and subjected to the heat treatment described above to perform non-oxidation melt plating, or the same effect can be obtained by applying the method to a flux plating method. be. Example A A cold-rolled material with the steel composition shown in Table 1 was used as a plated original plate, and the treatment method shown below was applied to coat Al and Al.
An alloy plated steel plate was manufactured. Example A1...Using steel A1 (cathode electrolytic treatment) 80g/ _H2SO4-10g / _CoSO4・_7H2O -based aqueous solution (metal ion _{concentration} / _SO42 ^- ion concentration (M/
Cathode treatment for 1.2 seconds at a current density of 8A/ ^dm2 in S) = 1.3/50) (bath temperature 25℃, stainless steel electrodes used) <Undercoat layer treatment> 340g/CoSO ₄ 7H ₂ O-45g/ _CoCl2・
6H ₂ O-boric acid 45 g/(weight ratio of metal ions to the sum of SO ₄ ^2- ions and Cl ^- ions (M/
I) = 63.7%) In a plating bath with a total Cl ^- ion concentration of 13.4 g/adjusted to pH 2.8 by adding H ₂ SO ₄ to the system bath, 0.1 μ Co metal was applied at a current density of 10 A/dm ^2. Comparative example A1...Using steel A1 (cathodic electrolytic treatment) at a current density of 8A/ ^dm2 in _a 80g/ _H2SO4 bath.
Cathode treatment for 1.2 seconds (bath temperature 25°C, stainless steel electrode used) <Base coating layer treatment> Same treatment example A2... using steel A2 <Cathode electrolysis treatment> 120g/H ₂ SO ₄ -60g/ Cathode treatment for 8 seconds at a current density of 15 A/dm ² in a NiSO ₄ 7H ₂ O aqueous solution (M/S = 4.55/50) (bath temperature 35°C, using Ti + Pt plated electrodes) <Undercoat layer treatment> 240g/ _NiSO4・_7H2O −30g/ _NiCl2・
Using a plating bath with a total Cl ^- ion concentration of 8.91 g/6H ₂ O-boric acid 30 g/(M/I) = 70%), which was adjusted to pH 2.4 by adding H ₂ SO ₄ to the bath, Current density
Comparative example of Ni plating of 0.06μ at 7.5A/ ^dm2 A2...Using steel A2 <Cathodic electrolytic treatment> 100g/H ₂ SO ₄ -250g/NiSO ₄ 7H ₂ O aqueous solution (M/S = 1.425/5 ) for 8 seconds at a current density of 30 A/dm ² (bath temperature 35°C, Ti +
(Using Pt plated electrode) <Undercoating layer treatment> Same treatment example as Example A2 A3(1) ...Using steel A3 <Cathode electrolytic treatment> 150g/H ₂ SO ₄ -30g/NiSO ₄ 7H ₂ O system Cathode treatment for 4 seconds at a current density of 20 A/dm ² in an aqueous solution (M/S = 2/50) (bath temperature 40°C, Pb-Sn electrode used) <Undercoat layer treatment> 240 g/NiSO ₄ 7H ₂ O−45g/ _NiCl2・
6H ₂ O-boric acid 40 g/(M/I = 64.2%) in a plating bath with a total Cl ^- ion concentration of 13.4 g/(M/I = 64.2%), which was adjusted to pH 1.8 by adding H ₂ SO ₄ to the current density. 15A/
Example A3(2) with Ni plating of 0.12μ at dm ² ...Using steel A3 (cathodic electrolytic treatment) Same treatment as Example A3(1) (base coating layer treatment) 125g/NiSO ₄・7H ₂ O−125g / _FeSO4・
7H ₂ O−20g/NiCl ₂・6H ₂ O−20g/
_FeCl2・_6H2O -boric acid 30g/(M/I=62.2
%) using a plating bath with a total Cl ^- ion concentration of 12.0 g / 1.5 by adding H ₂ SO ₄ to the system bath,
Comparative example of Ni-85% alloy plating of 0.03μ at current density 12.5A/ ^dm2 A3(1)...Using steel A3 (cathode electrolytic treatment) 150g/H ₂ SO ₄ -5g/NiSO ₄・7H ₂ O system Cathode treatment for 4 seconds at a current density of 20 A/dm ² in an aqueous solution (M/S = 0.35/50) (bath temperature 40°C, Pb-Sn electrode used) <Undercoat layer treatment> Same treatment comparison with Example A1 Example A3(3)...Using steel A3 (cathodic electrolytic treatment) Using the same bath as Example A3(1), current density 4A/d
Cathode treatment at m ² for 4 seconds (bath temperature 40℃, Pb-Sn electrode used) <Undercoating layer treatment> Same treatment example as Example A3 (2) A4...Using steel A4 <Cathode electrolysis treatment> 200g/ Cathode treatment for 8 seconds at a current density of 30 A/dm ² in a H ₂ SO ₄ -210 g/NiSO ₄ 7H ₂ O aqueous solution (M/S = 8.2/50) (bath temperature 55°C, Pb-
(Using SnAg electrode) <Base coating layer treatment> 120g/NiSO ₄・7H ₂ O−180g/CoSO ₄・
7H ₂ O−12g/NiCl ₂・6H ₂ O−18g/
CoCl _2.6H ₂ O-boric acid 20g/(M/I=63%)
The current density was increased in a plating bath with a total Cl ^- ion concentration of 8.9 g/adjusted to pH 1.6 by adding sulfuric acid to the system bath.
Comparative example of Ni-60%Co alloy plating of 0.5μ at 30A/ ^dm2 A4...Using steel A4 <Cathodic electrolytic treatment> Same treatment as Example A4 <Undercoating layer treatment> 120g/NiSO ₄・7H ₂ O− 30g/ _NiCl2・
6H ₂ O-boric acid 30g/-250g/H ₂ SO ₄ (M/
Using a plating bath with pH < O.5 consisting of I = 11%),
Practical example of Ni plating of 0.1 μ at a current density of 30 A/dm ² A5...Steel A5 was used (cathode electrolytic treatment) 300 g/H ₂ SO ₄ -150 g/NiSO ₄ 7H ₂ O aqueous solution (M/S= 4.55/50) at a current density of 12.5 A/dm ² for 2.5 seconds (bath temperature 65 °C, Pb−
(Using Sn-Ir electrode) <Base coating layer treatment> 280g/NiSO ₄・7H ₂ O−35g/NiCl ₂・
6H ₂ O - 35 g/boric acid (M/I = 63.3%) in a plating bath with a total Cl ^- ion concentration of 10.4 g adjusted to pH 1.75 by adding H ₂ SO ₄ to the current density.
Comparative example of Ni plating of 0.08μ at 5A/ ^dm2 A5...Using steel A5 <Cathodic electrolytic treatment> Same treatment as Example A5 <Undercoating layer treatment> Same bath composition as Example A5, only PH 3.5 Ni plating with a thickness of 0.08μ was performed using a plating bath under the same conditions. The steel sheets produced in the above manner were evaluated for the uniform coverage of the plating layer, the adhesion of the plating layer, and the automobile exhaust system using the evaluation methods shown below. A performance evaluation was conducted regarding the corrosion resistance based on the intended use, and the results are shown in Table 2. The evaluation test method and evaluation criteria are as follows. [Evaluation test method and evaluation criteria] 1. Uniform coverage of the plating coating layer An Al-10.5%Si alloy plated steel plate with a plating amount of 60 g/m ² per side was manufactured at a line speed of 100 m/min, and The appearance was investigated and evaluated using the following evaluation criteria to examine its uniform coverage. ◎…The wettability of the plating bath is extremely good, and the appearance of the plating is very good.〇…The wettability of the plating bath is relatively good, and there is a flow pattern (the plating thickness is partially thick) on the evaluation surface of 10 ^dm2 . △...Due to the slightly poor wettability of the plating bath, a rough spot defect (more than 10 microscopic defects) occurred on the 10 ^dm2 evaluation surface ×...Plating bath Due to extremely poor wettability, a large number of rough point-like defects occurred on the 10 ^dm2 evaluation surface.2 Adhesion of plating layer An Al-8%Si alloy plating layer was applied to a 0.6 mm thick plate on one side. The plating layer was coated with a coating weight of 40 g/m ² , and after impact bending with the same radius of curvature as the board thickness, Cellotape (registered trademark) was applied and peeled off, and the peeling status of the plated layer was investigated. The evaluation criteria are as follows. ◎…No peeling of the plating layer, no peeling material adhering to Sellotape (registered trademark) 〇…Slight peeling of the surface of the plating layer, very slight peeling material adhering to Sellotape (registered trademark) △…Plating Partial peeling of the layer from the steel plate interface occurs, and adhesion of peeled substances to Sellotape (registered trademark) is clearly observed ×... Full peeling of the plating layer (1) Evaluation method A For a 100 x 100 mm size steel plate, high temperature At 700℃ in an exhaust gas atmosphere
A continuous heating test was conducted for 1000 hours and the occurrence of red rust was investigated. In other words, we evaluate the uniform coverage and high-temperature corrosion resistance of the plating layer by investigating the occurrence of red rust caused by plating defects (unmet areas) when exposed to a high-temperature exhaust gas atmosphere. did. The evaluation criteria are as follows. is Al
-6%Si40g/ ^m2 is Al-10%Si60g/ ^m2 . ◎…No red rust occurrence〇…Number of dotted red rust occurrences: 1 to 10 △…Number of dotted red rust occurrences: 11 or more or area-wise red rust occurrence areas: 3 or less ×…area-like red rust occurrence areas: 4 places Above (2) Evaluation method B 50×100mm evaluation material (NH ₄ ) ₂ SO ₄ 1000mg/
-NH ₄ NO ₃ 500mg/-NH ₄ Cl 1000mg/system aqueous solution adjusted to pH 3 with SO ₄ ^2- .
It was immersed at 80℃ for 500 hours and the occurrence of red rust was investigated. That is, the uniform coverage and corrosion resistance of the plating layer in a wet corrosive atmosphere targeting exhaust gas condensed water were evaluated. The evaluation criteria are as follows. is Al80g/m ² , is Al-8%Si-
0.5%Co50g/ ^m2 . ◎…Number of red rust spots: 5 or less 〇…Number of red rust spots: 6 to 10 or less △…Number of red rust spots: 11 to 30 ×…Number of red rust spots: 31 or more or areal red rust Occurrence (3) Evaluation method C SO ₄ ^2- (1000ppm) - NO ₃ ^- is used as a corrosion accelerating solution assuming the corrosive environment inside a car/muffler.
(150ppm) −Cl ^- (300ppm) −CO ₃ ^2- (4000ppm) −
_NH4 ⁺ (3000ppm)−HCOOH(1000ppm)−
A cycle test was conducted using a CH ₃ COOH (1000 ppm) aqueous solution adjusted to pH 8 under the following conditions. In other words, the evaluation material (30 x 50 mm) was heated to <350℃.
Heating for 60 minutes → Corrosion test liquid/semi-immersion test (using a sealed container, immerse 1/2 part of the evaluation material in the corrosion solution, 80
℃, 5 hours) → Drying (100℃, 24 hours) → Corrosion test solution/half-immersion test (80℃, 24 hours) → Drying (100℃, 24 hours) → Drying (100℃, 24 hours)
℃, 24 hours) → Corrosion test liquid/half immersion test (180℃,
24 hours)→indoor exposure (30℃, 56 hours)> was considered as one cycle, and the appearance corrosion status after 3 cycle tests was investigated, and corrosion was conducted in a wet corrosion and dry repeated corrosion atmosphere assuming corrosion inside the muffler. The effect of uniform coverage of the coating layer on corrosion resistance was evaluated. The evaluation criteria are as follows. teeth
Al-7%Si45g/ ^m2 , Al-10%Si70g/ ^m2
It is. ◎...The occurrence of red rust at the gas-liquid interface of the part immersed in the corrosive solution is 10 points or less of minute rust. 0...The occurrence of red rust is 11 points or more and 20 points or less, mainly at the gas-liquid interface of the part immersed in the corrosive solution, or the occurrence rate of red rust in
0.1% or less △...Significant red rust has occurred at the above gas-liquid interface or other parts ×...The red rust has occurred in the above △ situation, and there is significant perforation-like corrosion under the rust.

【表】【table】

〔評価試験方法及び評価基準〕[Evaluation test method and evaluation criteria]

１めつき被覆層の均一被覆性ラインスピード90ｍ／minで、片面当りのめつ
き量が110ｇ／m²のAl−３％Si合金めつき鋼板を
製造し、その外観を調査して、以下の評価基準で
評価して、その均一被覆性を検討した。 ◎…めつき浴の濡れ性極めて良好で、めつき外観
極めて良好〇…めつき浴の濡れ性比較的良好で、10dm²の評
価面に対して流れ模様（めつき厚さの部分的
に厚い部分）が２点以下発生 △…めつき浴の濡れ性若干劣るため、10dm²の評
価面にざらつき状の点状欠陥部（微小不めつ
きが10数点群発）が発生 ×…めつき浴の濡れ性著しく劣るため、10dm²の
評価面にざらつき状の点状欠陥部が多量に発
生２めつき層の密着性 0.6mmの板厚にAl−7.5％Si系合金めつき層を片
面当りの付着量で80ｇ／m²施施してから、100×
1000mmの評価材を長手方向に第１図に示す断面形
状のビツツバーグタイプにロツクフオーマー加工
を行い、曲げ加工部のめつき層の剥離状況を調査
した。尚、評価基準は以下の通りである。 ◎…めつき層に異常なく良好〇…めつき層に亀裂発生 △…極く一部にめつき剥離発生 ×…めつき層の剥離状況極めて大３評価法Ａ工業地帯で使用される建材を対象に、0.8mm板
厚、75×150mmサイズの評価材に押し出し高さ８
mmのエリクセン加工を施し、亜硫酸ガス濃度
25ppm、温度40℃、湿度95％の雰囲気下で７日間
曝露、その赤錆の発生状況を調査し、以下の評価
基準で性能を評価したはAl100ｇ／m²、はAl
−８％Si60ｇ／m²である。 ◎…赤錆の発生率0.1〜1.0％未満〇…赤錆の発生率0.1〜10％未満 △…赤錆の発生率１〜10％未満 ×…赤錆の発生率10％以上 (2) 評価法Ｂ板厚0.6mm、サイズ100×200mmの評価材の中央
部に長手方向に、板厚と同一の曲率半径の曲げ加
工を施してから、臨界工業地帯で５年間の大気曝
露試験を行い、その赤錆発生状況を調査し、以下
の評価基準で評価した。はAl−10％Si−0.5％
Mg80ｇ／m²、はAl−６％Si−１％Cr120ｇ／
m²である。 ◎…赤錆発生なし〇…赤錆発生率0.5％未満 △…赤錆発生率0.5〜５％未満 ×…赤錆発生率５％以上 1 Uniform coverage of the plating coating layer An Al-3%Si alloy plated steel plate with a plating amount of 110 g/m ² per side was manufactured at a line speed of 90 m/min, and its appearance was investigated. The uniform coverage was examined using evaluation criteria. ◎…The wettability of the plating bath is extremely good, and the appearance of the plating is very good.〇…The wettability of the plating bath is relatively good, and there is a flow pattern (the plating thickness is partially thick) on the evaluation surface of 10 ^dm2 . △...Due to the slightly poor wettability of the plating bath, a rough spot defect (more than 10 microscopic defects) occurred on the 10 ^dm2 evaluation surface ×...Plating bath Due to extremely poor wettability, a large number of rough point-like defects occurred on the 10 ^dm2 evaluation surface.2 Adhesion of the plating layer: An Al-7.5%Si alloy plating layer was applied to a 0.6 mm thick plate on one side. After applying 80g/ ^m2 with a coating weight of 100×
A 1000 mm evaluation material was subjected to lock former processing in the longitudinal direction into a Bitsburg type cross-sectional shape shown in Figure 1, and the peeling of the plated layer at the bent portion was investigated. The evaluation criteria are as follows. ◎…Good condition with no abnormalities in the plating layer〇…Cracks occurred in the plating layer △…Plating peeling occurred in a very small part ×…Peeling of the plating layer was extremely severe 3 Evaluation method A Building materials used in industrial areas The target was extrusion height 8 on evaluation material of 0.8 mm plate thickness and 75 x 150 mm size.
mm Erichsen processing, sulfur dioxide gas concentration
25ppm, exposed for 7 days in an atmosphere with a temperature of 40℃ and a humidity of 95%, the occurrence of red rust was investigated, and the performance was evaluated using the ^following evaluation criteria.
-8%Si60g/ ^m2 . ◎…Incidence rate of red rust 0.1 to less than 1.0%〇…Incidence rate of red rust 0.1 to less than 10% △…Incidence rate of red rust 1 to less than 10% ×…Incidence rate of red rust 10% or more (2) Evaluation method B Plate thickness A 0.6 mm, 100 x 200 mm evaluation material was bent in the longitudinal direction at the center with the same radius of curvature as the board thickness, and then subjected to a 5-year atmospheric exposure test in a critical industrial zone to determine the occurrence of red rust. was investigated and evaluated using the following evaluation criteria. is Al-10%Si-0.5%
Mg80g/ ^m2 , Al-6%Si-1%Cr120g/
^m2 . ◎…No red rust occurrence〇…Red rust occurrence rate less than 0.5% △…Red rust occurrence rate 0.5 to less than 5% ×…Red rust occurrence rate 5% or more

【表】【table】

【表】＊：成形不可のためテスト未実施
※：めつき層剥離のためテスト未実施
[Table] *: Not tested because molding is not possible.
*: Test not conducted due to peeling of plating layer

【図面の簡単な説明】[Brief explanation of the drawing]

第１図はピツツバーグタイプのロツクフオーマ
ー加工を示す図である。１…評価材。 FIG. 1 is a diagram showing Pittsburgh type lock former processing. 1...Evaluation material.

Claims

【特許請求の範囲】[Claims]

１ 25％以下のCrを含有する鋼板を、金属イオ
ンのNi²⁺、Co²⁺の１種又は２種が全SO₄ ^2-イオン
濃度に対する重量比率で１／50≦（金属イオン濃
度）／（全SO₄ ^2-イオン濃度）≦１／５、遊離硫
酸75〜350ｇ／を含有する水溶液中で7.5A／ｄ
m²以上の電流密度で１〜15秒間陰極電解処理し、
次いでNi²⁺、Co²⁺、Fe²⁺の１種又は２種以上の
金属イオンをSO₄ ^2-イオンとCl^-イオンの総和に
対する重量比率で50％以上含有しかつPH3.0以下
のめつき浴で0.01〜1μ厚さのNi、Co、Fe被覆層
或いはこれらの２種以上からなる合金被覆層を施
した後、該被覆層に溶融Al及びAl合金めつき層
を施すことを特徴とする均一被覆性及び被覆層の
密着性にすぐれた高耐食性Al及びAl合金めつき
Cr含有鋼板の製造法。1 A steel plate containing 25% or less of Cr is mixed with one or both of the metal ions Ni ²⁺ and Co ²⁺ at a weight ratio of 1/50≦(metal ion concentration)/to the total SO ₄ ^2- ion concentration. (Total SO ₄ ^2- ion concentration) ≦ 1/5, 7.5 A/d in an aqueous solution containing 75-350 g of free sulfuric acid/
Cathodic electrolysis treatment for 1-15 seconds at a current density of m2 or ^more ,
Next, it contains one or more metal ions of Ni ²⁺ , Co ²⁺ , and Fe ²⁺ in a weight ratio of 50% or more based on the total of SO ₄ ^2- ions and Cl ^- ions, and has a pH of 3.0 or less. After applying a Ni, Co, Fe coating layer or an alloy coating layer consisting of two or more of these in a soaking bath, a molten Al and Al alloy plating layer is applied to the coating layer. Highly corrosion resistant Al and Al alloy plating with excellent uniform coverage and coating layer adhesion.
Manufacturing method of Cr-containing steel plate.