JPH0510421B2

JPH0510421B2 -

Info

Publication number: JPH0510421B2
Application number: JP63013549A
Authority: JP
Inventors: Hiroaki Kawamura; Yoshiki Takei; Tsuneo Inui
Original assignee: Toyo Kohan Co Ltd
Current assignee: Toyo Kohan Co Ltd
Priority date: 1988-01-26
Filing date: 1988-01-26
Publication date: 1993-02-09
Also published as: JPH01191772A

Description

[Detailed description of the invention]

〔産業上の利用分野〕本発明は絞りしごき缶（Drawn ＆ Ironed
Can、DI缶）、絞り再絞り缶（Drawn ＆
Redrawn Can、DRD缶）、絞り缶および缶蓋な
ど厳しい加工を受ける缶用素材であるSn系めつ
き鋼板、Cr系めつき鋼板の素地鋼板として適し
た加工耐食性の優れた製缶用めつき素地鋼板の製
造方法に関する。〔従来の技術〕 Snめつき鋼板、いわゆるぶりき、および金属
Crとクロム水和酸化物の二層構造の皮膜で被覆
された鋼板、いわゆるテイン・フリー・スチール
（以下TFSと略す）は缶用素材として、広く使用
されている。近年、製缶用材料の分野にはアルミ
ニウムなどの競合材料の進出が著しく、安価で、
かつ加工耐食性の優れた缶用表面処理鋼板の開発
が要望されている。製缶用表面処理鋼板を安価に
する一方法として、めつき層を薄く、かつ緻密に
することが検討され、例えば薄Snめつき鋼板が
溶接缶の材料に使用されている。しかしながら、
めつき層が薄いため、加工部などの耐食性は通常
のぶりき、TFSより劣り、加工の厳しい用途に
使用するには、めつき素地鋼板自体の耐食性を改
良することが必要である。めつき素地鋼板自体の
耐食性を改良しようとする試みとして、製鋼時に
Crなどを添加する方法（特開昭61−6293、特開
昭61−177378、特開昭61−253377、特開昭62−
3089など）、鋼板表面にNiめつきを施し、非酸化
性雰囲気中で熱処理を行い、鋼板表面にNi拡散
層を形成させる方法（特開昭57−200592、特開昭
60−155685など）、鋼板表面にSnめつきあるいは
Sn−Ni合金めつきを施し、非酸化性雰囲気中で
熱処理を行い、鋼板表面にSnあるいはSnとNiの
拡散層を形成させる方法（特開昭60−5894、特開
昭60−89594）などが知られている。〔発明が解決しようとする課題〕確かに、特開昭62−3089などに示される製鋼時
にCrを添加する方法は鋼板自体の耐食性を著し
く改良する効果があるが、Cr添加による鋼板の
コストアツプだけでなく、熱間圧延後の脱スケー
ル性、Snなどのめつき性、製缶加工性などに
種々の問題を生じ、安価な製缶用めつき素地鋼板
として適した素材といいがたい。また特開昭60−
200592などに示されるNiめつきした鋼板を非酸
化性雰囲気中で熱処理し、鋼板表面にNi拡散層
を形成させる方法は未加工の場合の耐食性は改良
されるが、加工した場合、Ni拡散層にクラツク
が入る。このNi拡散層は果汁などの飲料中で素
地鉄より電位が貫であるため、このめつき素地鋼
板を飲料缶用材料に用いた場合、Ni拡散層のク
ラツクから素地鉄の腐食が促進され、孔食の危険
性がある。したがつて、この方法によつて得られ
ためつき素地鋼板は製缶用めつき鋼板の素地とし
て満足できるものでない。さらに特開昭60−
5894、特開昭60−89594に示されるSnあるいはSn
−Ni合金めつきした鋼板を非酸化性雰囲気中で
熱処理し、鋼板表面にSnあるいはSnとNiの拡散
層を形成させる方法で得られためつき素地鋼板も
Ni拡散層を形成させためつき素地鋼板と同様に
飲料中で素地鉄のカソードとして働き、これらの
拡散層のクラツクからの素地鉄の腐食が促進され
るので、製缶用めつき素地鋼板として十分なもの
でない。これらの問題点を解決し、安価で、特に
加工耐食性に対して効果があり、かつ冷間圧延以
降の工程において特別な問題点を生じないめつき
素地鋼板を開発することを目的として、種々検討
を重ねた結果、本発明に至つたものである。〔課題を解決するための手段〕本発明は冷間圧延、電解クリーニング後の鋼板
表面にCrめつきを施し、さらにSnめつきを施し
た後、鉄の非酸化性雰囲気中で熱処理を施し、鋼
板の表面層にCr−Sn−Feの三元系拡散層を形成
させることによつて、加工後の耐食性の優れため
つき素地鋼板を提供することにある。以下、本発明の方法について具体的に説明す
る。冷間圧延、電解クリーニング後の鋼板表面に
金属Cr量３〜150mg／m²のCrめつきを施し、つい
で、その上層にSn量20〜500mg／m²のSnめつきを
施した後、鉄の非酸化性雰囲気中で熱処理を施
し、鋼板の表面にめつきしたSn量の95％以上、
およびめつきしたCr量の１mg／m²以上を含み、
かつCr／Sn＋Crの重量比が0.02〜0.50であるCr
−Sn−Fe三元系拡散層を形成させるものである。次に、本願発明の製缶用めつき素地鋼板の製造
方法について説明する。最初に、冷間圧延、電解
クリーニング後の鋼板表面にCrめつきを施すが、
Crめつきするための浴として適量の助剤を添加
したクロム酸浴および硫酸クロム浴が考えられる
が、適量の助剤を添加したクロム酸浴が高速安定
生産の点から適している。このクロム酸浴には通
常Crめつきに使用されているサージエント浴を
はじめTFSの工業的な製造に使用されている適
量の硫酸とフツ素化合物を添加したクロム酸浴あ
るいはフツ素化合物のみを添加したクロム酸浴が
適している。クロム酸濃度については特に限定す
る必要はないが、金属Crの析出と同時に析出す
るクロム水和酸化物が多いと、次工程のSnめつ
きに支障をきたすので、高濃度クロム酸浴を用い
ることが好ましい。クロム酸濃度が100ｇ／以
下の低濃度クロム酸浴を用いた場合、多量のクロ
ム水和酸化物が金属Cr上に析出するので、次工
程のSnめつき前に、用いたクロム酸浴中に浸漬
し、表面のクロム水和酸化物皮膜を溶解除去する
ことが必要である。溶解後の残存するクロム水和
酸化物の量は理想的には０であることが好ましい
が、実用上クロム量として５mg／m²以下であれ
ば、次工程のSnめつきに支障をきたすことはな
い。めつきされる金属Cr量は３〜150mg／m²の範
囲がこのましいが、より好ましくは５〜70mg／m²
である。金属Cr量が３mg／m²以下であると、１
mg／m²以上のCrを鋼板表面に拡散させることは
出来ず、本発明の目的とする加工耐食性の優れた
めつき素地鋼板は得られない。金属Crは非常に
酸化されやすく、めつきされた金属Crの一部は
鉄の非酸化性雰囲気中での熱処理によつて酸化
Crになる。金属Crはこのように自己酸化して鉄
の酸化を防ぐとともに、鋼板中に含まれるＣの表
面濃化を防止する。また、溶接缶用鋼板のよう
に、鋼板とSn層の間にCrを介在させて、大気中
の加熱工程で酸化Crの形成等によりFe−Sn合金
化をおさえ、溶接性を改善させる方法があるが、
この場合Snの均一性は加熱によつて著しく悪く
なること、また、SnとFeの合金化も疎外され、
Snによる耐食性向上効果は得られない。本願発
明の目的は、CrとSnを鋼板表面に拡散させるこ
とが重要な要件であるが、そのために、酸化され
易いCrを最初にめつきし、後からSnめつきする
ことによつてCrの酸化をできるだけ押さえるこ
とを提案するものである。しかし、それでもCr
量が150mg／m²を越えると酸化Crも増加し、後で
行うSnめつき処理等の前処理では十分に除去で
きなくなり、均一なSnめつき等が得られず、め
つきによる耐食性向上効果を半減してしまう。さ
らに、金属Cr層上にめつきされたSnと素地鉄と
の拡散反応も抑制し、めつき素地鋼板の耐食性が
改良されないので好ましくない。つぎに、Crめ
つき後、施されるSnめつきには通常電気めつき
ぶりきの製造に使用されている公知のSnめつき
浴、例えばフエロスタン浴、硫酸浴およびハロゲ
ン浴などが用いられる。鋼板上にSnめつきする
場合と同様な条件でSnめつきを施すことができ
るが、金属Cr上に析出したクロム水和酸化物皮
膜を除去し、かつ均一なSnめつきを施すために、
Snイオン濃度を通常のぶりきの製造の場合に比
較し、約1/3以下に希釈し、Snのめつき効率を低
下させ、水素発生の多い浴を用いることが望まし
い。Crめつき後にめつきされたSnは鉄の非酸化
性雰囲気中での熱処理によつて、鋼板表層と容易
に拡散層を形成する元素であるが、Sn量が20
mg／m²以下では本発明の目的とする加工耐食性の
優れためつき素地鋼板は得られず、またSnめつ
き量が500mg／m²以上であると、鋼板表層に形成
されるCr−Sn−Feの三元系拡散層が脆くなり、
加工耐食性が改良されない。したがつて、金属
Cr層上にめつきされるSn量は20〜500mg／m²の範
囲、より好ましくは50〜200mg／m²の範囲が本発
明において適している。本発明においては最初に
Crめつきを施し、ついでSnめつきを施している
が、これは本発明の加工耐食性の優れためつき素
地鋼板を得るための必要条件である。すなわち、
金属Crは鋼板表面と直接接触していないと、熱
処理時に鋼板表層中への拡散は非常にむずかしい
ので、Crめつきを最初に施すのである。ついで
めつきされるSnは熱処理時における金属Crの酸
化を抑制し、金属Crの鋼板表層への拡散を助け
る効果をもつている。さらに素地鉄と拡散反応を
起こし、本発明の目的とする加工耐食性の改良に
寄与している。かりに、最初にSnめつきを施し、
ついでCrめつきを施した後、鉄の非酸化性雰囲
気中での熱処理を行つても、Sn−Feの二元系拡
散層は形成されるが、金属Crはほとんど鋼板表
層中に拡散されないので、加工耐食性、Snなど
のめつき性に優れためつき素地鋼板は得られな
い。本発明の方法で得られるめつき素地鋼板は製缶
用のぶりきなどのめつき素地鋼板であり、優れた
加工耐食性のほかに、製缶性の良い機械的特性も
兼ね備えていることが必須の条件である。したが
つて、ぶりきおよびTFSなどの缶用鋼板の素地
鋼板と同様な条件で熱処理を施すことによつて、
鋼板表層にCr−Sn−Feの三元系拡散層を形成さ
せることが本発明の前提である。すなわち、たと
えば水素６％、窒素94％の鉄の非酸化性雰囲気中
で520〜720℃の温度で、15〜30000秒の熱処理を
施すことによつて、めつきしたSnの95％以上、
めつきしたCrの１mg／m²以上を含み、かつCr／
Sn＋Crの重量比が0.02〜0.50であるCr−Sn−Fe
の三元系拡散層を形成させることが本発明におい
て不可欠である。すでに記した熱処理条件では、
めつきしたSnのほとんどは素地鉄と反応し、Sn
−Feの二元系拡散層を形成するが、金属Crの50
％以上を鋼板中に拡散させることはむずかしく、
めつきした金属Crの約15〜40％が拡散される。
したがつて、鋼板表層中に拡散させよううとする
Cr量の少なくとも2.5倍程度の金属Crを熱処理前
にめつきすることが必要である。この熱処理によ
つて形成されるCr−Sn−Feの三元系拡散層にお
いて、Cr／Sn＋Crの重量比が0.02以下であると、
鋼板中に拡散されたCr量が１mg／m²以上でも、
本発明の目的とする加工耐食性の優れためつき素
地鋼板は得られない。これは熱処理によつて形成
されるCr−Sn−Feの三元系拡散層中のCr量の僅
かの増加によつても、Sn量の著しい増加となり、
この拡散層が脆くなるためと考えられる。また、
Cr／Sn＋Crの重量比を0.50以上では、拡散層内
のCrが鋼板表面に露出した部分で酸化Crを形成
するが、その量が増加すること、また、すでに記
した熱処理条件下におけるめつきした金属Crの
拡散程度から考え、熱処理前にめつきされる金属
Cr量をSn量に対して増加させる必要があり、そ
の結果、金属Crはより酸化され熱処理後拡散せ
ずに残存した金属Crの酸化物が増加することに
より、Snめつきなどの前処理として施される電
解クリーニングで十分除去されず、Snなどの均
一めつき性およびSNなどの析出の電流効率を低
下させる危険性がある。したがつて、本発明にお
いて、熱処理で形成されるCr−Sn−Feの三元系
拡散層におけるCr／Sn＋Crの重量比は重要な因
子であり、0.02〜0.50の範囲が好ましく、0.05〜
0.20い。ぶりきなどの素地鋼板の熱処理条件で
は、本発明で限定した範囲のSnめつき量であれ
ば、すでに記したようにほとんど素地鉄と反応
し、金属Snあるいは酸化Snとして残ることはな
いが、かりに残存すると、Snめつき、TFS処理
などの前工程である調質圧延時に支障をきたす恐
れがあり、あえてめつきしたSn量の95％以上が
熱処理で形成されるCr−Sn−Feの三元系拡散層
に含まれるべきであると限定した。一方、本発明
において、鋼板表層中に拡散されるCr量の下限
は１mg／m²に限定したが、この下限は本発明の目
的とする加工耐食性の優れためつき素地鋼板を得
るために必要な不可欠の因子である。鋼板中に拡
散されるCr量が１mg／m²以下であると、たとえ
めつきしたCr量が３mg／m²以上でも、得られた
めつき素地鋼板の加工耐食性は改良されない。ま
た、本発明の方法で得られためつき素地鋼板は著
しく耐食性が改良されるので、Snなどのめつき
を施すことなしに、無塗装で、あるいは塗装した
後に缶用材料に使用することも可能である。（実施例）以下、本発明の実施例を比較例と対比し具体的
に説明する。実施例１板厚0.21mmの冷延鋼板を４％オルソケイ酸ソー
ダ水溶液中で、温度90℃、電流密度20A／ｄm²、
電解時間５秒の条件で、圧延油の脱脂処理を施
し、水洗後、(イ)に示す条件でCrめつきを施し、
同液に５秒浸漬した後水洗した。ついで、(ロ)に示
す条件でSnめつきを施し、水洗乾燥した。この
試料を鉄の非酸化性雰囲気（水素６％、窒素94
％）中で、温度520〜560℃で20秒熱処理を施し
た。熱処理後に於ける拡散層のCr／Sn＋Crは
0.093であつた。 (イ) Crめつき条件浴組成 CrO₃ 150ｇ／ NaF ５ｇ／ H₂SO₄ 0.8ｇ／浴温度 55℃ 陰極電流密度 40A／ｄm² 金属Cr量 10mg／m² 残存クロム水和酸化物量（Crとして）
２mg／m² (ロ) Snめつき条件浴組成 SnSO₄ 20ｇ／ H₂SO 20ｇ／エトキシ化ａ−ナフトール５ｇ／浴温度 45℃ 陰極電流密度 25A／ｄm² Snめつき量 30mg／m² 実施例２実施例１と同様の冷延鋼板を実施例１と同様の
前処理を施した後、実施例１の(イ)および(ロ)に示す
条件で、電解時間をかえてCrめつきおよびSnめ
つきを施し、水洗乾燥した。ついで、実施例１と
同じ非酸化性雰囲気中で、温度640〜680℃で８時
間箱型焼鈍炉を用いて熱処理を施した。熱処理後
に於ける拡散層のCr／Sn＋Crは0.08であつた。金属Cr量 127mg／m² 残存クロム水和酸化物量（Crとして）
３mg／m² Snめつき量 410mg／m² 比較例１実施例１と同様の冷延鋼板を実施例１と同様の
前処理を施し、水洗乾燥した。比較例２実施例１と同様の冷延鋼板を実施例１と同様の
前処理を施した後、実施例１の(イ)に示す条件で15
mg／m²のCrめつきを施した後、水洗乾燥した。
ついで、実施例１と同じ非酸化性雰囲気中で同様
に熱処理を施した。比較例３実施例１と同様の冷延鋼板を実施例１と同様の
前処理を施した後、実施例１の(ロ)に示す条件で
150mg／m²のSnめつきを施し、水洗乾燥した。つ
いで、実施例１と同じ非酸化性雰囲気中で同様に
熱処理を施した。実施例３実施例１と同様の冷延鋼板を実施例１と同様の
前処理を施した後、実施例１の(イ)および(ロ)に示す
条件で、それぞれ電解時間をかえてCrめつきお
よびSnめつきを施した後、水洗乾燥した。つい
で、実施例１と同じ非酸化性雰囲気中で、温度
620〜680℃で30秒熱処理を施した。この時、熱処
理後に於ける拡散層のCr／Sn＋Crが0.071である
鋼板を、さらに２％の調質圧延を施した。その
後、(イ)に示す条件でSnめつきを、さらに加熱溶
融処理を施した後、50℃で３％重クロム酸ソーダ
溶液で陰極電流密度15A／ｄm²で２秒電解し、水
洗乾燥した。 Crめつき量 50mg／m² 残存クロム水和酸化物量（Crとして）
３mg／m² Snめつき量 200mg／m² (イ) 熱処理、調質圧延後のSnめつき条件浴組成 SnSO₄ 60ｇ／フエノールスルホン酸（硫酸として）
15ｇ／エトキシ化α−ナフトール７ｇ／浴温度 45℃ 陰極電流密度 20A／ｄm² Snめつき量 2.7ｇ／m² 比較例４比較例１で得られた試料に２％の調質圧延を施
した後、実施例３の(イ)に示す条件で2.7ｇ／m²の
Snめつきを施し、加熱溶融処理後、実施例３に
示す条件で重クロム酸処理を施し、水洗乾燥し
た。比較例５比較例２で得られた試料に比較例４と同様に調
質圧延、Snめつき、加熱溶融処理および重クロ
ム酸処理を施し、水洗乾燥した。比較例６比較例３で得られた試料に比較例４と同様に調
質圧延、Snめつき、加熱溶融処理および重クロ
ム酸処理を施し、水洗乾燥した。実施例４実施例１で得られた試料に２％の調質圧延を施
した後、(イ)に示す条件で電解クロム酸処理
（TFS処理）を施し、水洗乾燥した。 (イ) 熱処理、調質圧延後の電解クロム酸処理条
件（TFS処理条件）浴組成 CrO₃ 80ｇ／ NaF ４ｇ／ H₂SO₄ 0.5ｇ／浴温度 40℃ 陰極電流密度 40A／ｄm² 金属Cr量 103mg／m² クロム水和酸化物量（Crとして） 15mg／m² 比較例７比較例１で得られた試料に２％の調質圧延を施
し、実施例４の(イ)に示す条件で電解クロム酸処理
を施した後、水洗乾燥した。比較例８比較例２で得られた試料に２％の調質圧延を施
し、実施例４の(イ)に示す条件で電解クロム酸処理
を施した後、水洗乾燥した。比較例９比較例３で得られた試料に２％の調質圧延を施
し、実施例４の(イ)に示す条件で電解クロム酸処理
を施した後、水洗乾燥した。以上の方法で得られた鋼板のめつき皮膜組成を
螢光Ｘ線法で測定後、無塗装での耐錆性、耐食性
および塗装後の加工耐食性を次に示す方法で調査
した。その結果を一括して第１表に示す。 (1) 熱処理によるCrおよびSnの鋼板中への拡散
量および率 [Industrial Application Field] The present invention is a Drawn & Ironed can.
Can, DI can), re-drawn can (Drawn &
A plating base for can making that has excellent process corrosion resistance and is suitable as a base steel sheet for Sn-based plated steel sheets and Cr-based plated steel sheets, which are materials for cans that undergo severe processing such as Redrawn Can, DRD can), drawn cans, and can lids. This invention relates to a method for manufacturing steel plates. [Prior art] Sn-plated steel plate, so-called tinplate, and metal
Steel sheets coated with a two-layered film of chromium and hydrated chromium oxide, so-called tein-free steel (hereinafter abbreviated as TFS), are widely used as materials for cans. In recent years, competitive materials such as aluminum have made significant advances in the field of can-making materials, and are inexpensive and
There is also a demand for the development of a surface-treated steel sheet for cans that has excellent processing corrosion resistance. As a way to reduce the cost of surface-treated steel sheets for can manufacturing, making the plating layer thinner and denser has been considered, and for example, thin Sn-plated steel sheets are being used as materials for welded cans. however,
Because the plating layer is thin, the corrosion resistance of processed parts is inferior to that of regular tinplate or TFS, and in order to use it in applications that require severe processing, it is necessary to improve the corrosion resistance of the plated base steel sheet itself. In an attempt to improve the corrosion resistance of the plated base steel sheet itself,
Method of adding Cr etc. (JP-A-61-6293, JP-A-61-177378, JP-A-61-253377, JP-A-62-
3089, etc.), a method in which Ni is plated on the surface of a steel sheet and heat treated in a non-oxidizing atmosphere to form a Ni diffusion layer on the surface of the steel sheet (JP-A-57-200592, JP-A-Sho.
60−155685, etc.), Sn plating or
A method of applying Sn-Ni alloy plating and heat treatment in a non-oxidizing atmosphere to form a Sn or Sn and Ni diffusion layer on the surface of the steel sheet (Japanese Patent Laid-Open No. 60-5894, Japanese Patent Laid-Open No. 60-89594), etc. It has been known. [Problem to be solved by the invention] It is true that the method of adding Cr during steel manufacturing as shown in JP-A-62-3089 etc. has the effect of significantly improving the corrosion resistance of the steel sheet itself, but the addition of Cr only increases the cost of the steel sheet. However, it causes various problems such as descaling properties after hot rolling, plating properties of Sn, etc., and can making processability, making it difficult to say that it is a suitable material as an inexpensive plated base steel sheet for can making. Also, JP-A-60-
200592, etc., in which a Ni-plated steel plate is heat-treated in a non-oxidizing atmosphere to form a Ni diffusion layer on the surface of the steel plate, corrosion resistance is improved when untreated, but when processed, the Ni diffusion layer is formed. There is a crack. This Ni diffusion layer has a higher potential than the base steel in drinks such as fruit juice, so when this plated base steel sheet is used as a material for beverage cans, corrosion of the base steel is accelerated due to cracks in the Ni diffusion layer. There is a risk of pitting corrosion. Therefore, the plated base steel sheet obtained by this method is not satisfactory as a base for a plated steel plate for can manufacturing. In addition, JP-A-1986-
5894, Sn or Sn shown in JP-A-60-89594
-A matte base steel sheet obtained by heat-treating a Ni alloy-plated steel sheet in a non-oxidizing atmosphere to form a Sn or Sn and Ni diffusion layer on the surface of the steel sheet.
Just like a galvanized base steel sheet with a Ni diffusion layer formed, it acts as a cathode for the base iron in beverages, and corrosion of the base iron from cracks in these diffusion layers is accelerated, so it is sufficient as a galvanized base steel sheet for can manufacturing. It's not something. Various studies were conducted with the aim of solving these problems and developing a plated base steel sheet that is inexpensive, particularly effective in terms of processing corrosion resistance, and does not cause any special problems in processes after cold rolling. As a result of repeated efforts, we have arrived at the present invention. [Means for Solving the Problems] The present invention applies Cr plating to the surface of a steel sheet after cold rolling and electrolytic cleaning, and then after applying Sn plating, heat treatment is performed in a non-oxidizing iron atmosphere, The object of the present invention is to provide a base steel sheet for tempering which has excellent corrosion resistance after working by forming a ternary diffusion layer of Cr-Sn-Fe on the surface layer of the steel sheet. The method of the present invention will be specifically explained below. After cold rolling and electrolytic cleaning, Cr plating with a metal Cr content of 3 to 150 mg/m ² is applied to the surface of the steel sheet, and then Sn plating with a Sn content of 20 to 500 mg/m ² is applied to the upper layer. Heat treatment is performed in a non-oxidizing atmosphere of 95% or more of the amount of Sn plated on the surface of the steel plate.
and a plated Cr amount of 1 mg/m ² or more,
and Cr whose weight ratio of Cr/Sn+Cr is 0.02 to 0.50
-Sn-Fe ternary diffusion layer is formed. Next, a method for manufacturing a plated base steel sheet for can manufacturing according to the present invention will be described. First, Cr plating is applied to the steel plate surface after cold rolling and electrolytic cleaning.
A chromic acid bath and a chromium sulfate bath to which an appropriate amount of auxiliary agent has been added can be considered as a bath for Cr plating, but a chromic acid bath to which an appropriate amount of auxiliary agent has been added is suitable from the viewpoint of high-speed and stable production. This chromic acid bath includes a sergeant bath that is normally used for chromium plating, a chromic acid bath that contains an appropriate amount of sulfuric acid and a fluorine compound, or only a fluorine compound that is used in the industrial production of TFS. A chromic acid bath is suitable. There is no need to specifically limit the chromic acid concentration, but if there is a large amount of chromium hydrated oxide that precipitates at the same time as metal Cr, it will interfere with the Sn plating in the next process, so a high concentration chromic acid bath should be used. is preferred. When using a low-concentration chromic acid bath with a chromic acid concentration of 100 g/less or less, a large amount of hydrated chromium oxide will precipitate on the metal Cr, so before the next step of Sn plating, It is necessary to dissolve and remove the chromium hydrated oxide film on the surface by immersion. Ideally, the amount of chromium hydrated oxide remaining after dissolution is preferably 0, but in practice, if the chromium amount is less than 5 mg/ ^m2 , it may interfere with the Sn plating in the next step. There isn't. The amount of metal Cr to be plated is preferably in the range of 3 to 150 mg/m ² , more preferably 5 to 70 mg/m ²
It is. When the amount of metal Cr is 3 mg/ ^m2 or less, 1
It is not possible to diffuse mg/m ² or more of Cr onto the surface of the steel sheet, and it is not possible to obtain a toughened base steel sheet with excellent processing corrosion resistance, which is the objective of the present invention. Cr metal is very easily oxidized, and some of the plated Cr metal is oxidized by heat treatment in a non-oxidizing atmosphere of iron.
Become a Cr. The metal Cr self-oxidizes in this way and prevents the oxidation of iron, and also prevents surface concentration of C contained in the steel sheet. In addition, as in the case of steel plates for welded cans, there is a method of interposing Cr between the steel plate and the Sn layer to suppress Fe-Sn alloying through the formation of Cr oxide during the heating process in the atmosphere, thereby improving weldability. Yes, but
In this case, the uniformity of Sn deteriorates significantly due to heating, and the alloying of Sn and Fe is also neglected.
The effect of improving corrosion resistance due to Sn cannot be obtained. The purpose of the present invention is to diffuse Cr and Sn onto the surface of the steel sheet. For this purpose, Cr, which is easily oxidized, is first plated, and then Sn is plated. It is proposed to suppress oxidation as much as possible. But still Cr
When the amount exceeds 150mg/ ^m2 , Cr oxide also increases and cannot be removed sufficiently by pre-treatment such as Sn plating that is carried out later, making it impossible to obtain uniform Sn plating, which reduces the effect of plating on improving corrosion resistance. will be halved. Furthermore, it is not preferable because it also suppresses the diffusion reaction between the Sn plated on the metal Cr layer and the base iron, and the corrosion resistance of the plated base steel sheet is not improved. Next, after Cr plating, Sn plating is performed using a known Sn plating bath that is normally used in the production of electroplated tin, such as a ferrostane bath, a sulfuric acid bath, or a halogen bath. Sn plating can be applied under the same conditions as when Sn plating is applied to steel sheets, but in order to remove the chromium hydrated oxide film deposited on the metal Cr and to apply uniform Sn plating,
It is desirable to dilute the Sn ion concentration to about 1/3 or less compared to the case of ordinary tinplate production, reduce the Sn plating efficiency, and use a bath that generates a large amount of hydrogen. Sn plated after Cr plating is an element that easily forms a diffusion layer with the surface layer of the steel sheet when iron is heat treated in a non-oxidizing atmosphere.
If the amount of Sn plating is less than 500 mg/ ^m2 , it will not be possible to obtain a toughened base steel sheet with excellent processing corrosion resistance, which is the objective of the present invention.If the amount of Sn plating is more than 500 mg/ ^m2 , Cr-Sn- The Fe ternary diffusion layer becomes brittle,
Processing corrosion resistance is not improved. Therefore, metal
In the present invention, the amount of Sn plated on the Cr layer is in the range of 20 to 500 mg/ ^m2 , more preferably in the range of 50 to 200 mg/ ^m2 . In the present invention, first
Cr plating is applied, and then Sn plating is applied, which is a necessary condition for obtaining the base steel plate with excellent process corrosion resistance of the present invention. That is,
If Cr metal is not in direct contact with the surface of the steel sheet, it is very difficult for it to diffuse into the surface layer of the steel sheet during heat treatment, so Cr plating is applied first. The Sn that is then plated has the effect of suppressing oxidation of the metal Cr during heat treatment and assisting the diffusion of the metal Cr into the surface layer of the steel sheet. Furthermore, it causes a diffusion reaction with the base iron, contributing to the improvement of processing corrosion resistance, which is the objective of the present invention. First, Sn plating is applied to the carp.
Even if heat treatment is performed in a non-oxidizing iron atmosphere after Cr plating, a Sn-Fe binary diffusion layer is formed, but the metallic Cr is hardly diffused into the surface layer of the steel sheet. , it is not possible to obtain a base steel plate with excellent processing corrosion resistance and plating properties such as Sn. The plated base steel sheet obtained by the method of the present invention is a plated base steel plate such as tin plate for can making, and it is essential that it has not only excellent processing corrosion resistance but also mechanical properties that are good for can making. This is the condition. Therefore, by applying heat treatment under the same conditions as the base steel sheets for can steel sheets such as tinplate and TFS,
The premise of the present invention is to form a ternary diffusion layer of Cr-Sn-Fe on the surface layer of the steel sheet. That is, by heat treating for 15 to 30,000 seconds at a temperature of 520 to 720°C in a non-oxidizing atmosphere of iron containing 6% hydrogen and 94% nitrogen, more than 95% of the plated Sn can be removed.
Contains 1mg/m2 or ^more of plated Cr, and Cr/
Cr−Sn−Fe with Sn+Cr weight ratio of 0.02 to 0.50
It is essential in the present invention to form a ternary diffusion layer. Under the heat treatment conditions already described,
Most of the plated Sn reacts with the base iron, and Sn
- Forms a binary diffusion layer of Fe, but 50% of metal Cr
It is difficult to diffuse more than % into the steel sheet.
Approximately 15-40% of the plated metal Cr is diffused.
Therefore, attempts are made to diffuse it into the surface layer of the steel sheet.
It is necessary to plate metal Cr in an amount of at least 2.5 times the amount of Cr before heat treatment. In the ternary diffusion layer of Cr-Sn-Fe formed by this heat treatment, when the weight ratio of Cr/Sn+Cr is 0.02 or less,
Even if the amount of Cr diffused into the steel sheet is 1mg/m2 ^or more,
A toughened base steel sheet with excellent processing corrosion resistance, which is the object of the present invention, cannot be obtained. This is because even a slight increase in the amount of Cr in the ternary diffusion layer of Cr-Sn-Fe formed by heat treatment results in a significant increase in the amount of Sn.
This is thought to be because this diffusion layer becomes brittle. Also,
When the weight ratio of Cr/Sn+Cr is 0.50 or more, Cr in the diffusion layer forms Cr oxide on the exposed parts of the steel sheet surface, but the amount increases, and the plating resistance under the heat treatment conditions mentioned above increases. Considering the degree of diffusion of metal Cr, metal plated before heat treatment
It is necessary to increase the amount of Cr relative to the amount of Sn, and as a result, the metal Cr becomes more oxidized and the amount of oxide of the metal Cr that remains without diffusing after heat treatment increases, making it difficult to use as a pre-treatment for Sn plating etc. There is a risk that the electrolytic cleaning that is carried out may not be sufficient to remove it, resulting in a decrease in the uniform plating of Sn, etc., and the current efficiency of depositing SN, etc. Therefore, in the present invention, the weight ratio of Cr/Sn+Cr in the ternary diffusion layer of Cr-Sn-Fe formed by heat treatment is an important factor, and is preferably in the range of 0.02 to 0.50, preferably 0.05 to
0.20. Under the heat treatment conditions for base steel plates such as tinplate, if the amount of Sn plating is within the range defined in the present invention, as already mentioned, it will almost react with the base iron and will not remain as metal Sn or Sn oxide. If it remains in the steel, it may cause trouble during temper rolling, which is a pre-process such as Sn plating and TFS treatment. It was limited that it should be included in the original diffusion layer. On the other hand, in the present invention, the lower limit of the amount of Cr diffused into the surface layer of the steel sheet was limited to 1 mg/m ² , but this lower limit is not necessary to obtain a tempered base steel sheet with excellent processing corrosion resistance, which is the objective of the present invention. It is an essential factor. If the amount of Cr diffused into the steel sheet is less than 1 mg/m ² , even if the amount of Cr plated is 3 mg/m ² or more, the processing corrosion resistance of the resulting dampened base steel sheet will not be improved. In addition, the corrosion resistance of the damped base steel sheet obtained by the method of the present invention is significantly improved, so it can be used as a material for cans without being coated or after being coated with Sn or other plating. It is. (Example) Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples. Example 1 A cold-rolled steel plate with a thickness of 0.21 mm was heated in a 4% sodium orthosilicate aqueous solution at a temperature of 90°C and a current density of 20 A/dm ² .
The rolling oil was degreased under the conditions of electrolysis time of 5 seconds, and after washing with water, Cr plating was applied under the conditions shown in (a),
After being immersed in the same solution for 5 seconds, it was washed with water. Next, Sn plating was applied under the conditions shown in (b), followed by washing with water and drying. This sample was heated in an iron non-oxidizing atmosphere (6% hydrogen, 94% nitrogen).
%) at a temperature of 520 to 560°C for 20 seconds. Cr/Sn+Cr of the diffusion layer after heat treatment is
It was 0.093. (a) Cr plating conditions Bath composition CrO ₃ 150g / NaF 5g / H ₂ SO ₄ 0.8g / Bath temperature 55℃ Cathode current density 40A/dm ^2Metal Cr amount 10mg/m ^2Residual chromium hydrated oxide amount (as Cr) )
2mg/m ² (b) Sn plating conditions Bath composition SnSO ₄ 20g/ H ₂ SO 20g/ Ethoxylated a-naphthol 5g/ Bath temperature 45℃ Cathode current density 25A/dm ² Sn plating amount 30mg/m ² Examples 2 The same cold-rolled steel sheet as in Example 1 was subjected to the same pretreatment as in Example 1, and then Cr plating and Sn It was plated, washed with water and dried. Then, heat treatment was performed in the same non-oxidizing atmosphere as in Example 1 at a temperature of 640 to 680° C. for 8 hours using a box-type annealing furnace. Cr/Sn+Cr of the diffusion layer after heat treatment was 0.08. Metallic Cr content 127mg/ ^m2 Residual chromium hydrated oxide content (as Cr)
3 mg/m ² Sn plating amount 410 mg/m ² Comparative Example 1 The same cold rolled steel sheet as in Example 1 was subjected to the same pretreatment as in Example 1, washed with water and dried. Comparative Example 2 A cold-rolled steel sheet similar to that in Example 1 was subjected to the same pretreatment as in Example 1, and then subjected to 15% treatment under the conditions shown in (a) of Example 1.
After applying Cr plating of mg/m ² , it was washed with water and dried.
Then, heat treatment was performed in the same non-oxidizing atmosphere as in Example 1. Comparative Example 3 A cold-rolled steel sheet similar to that in Example 1 was pretreated in the same manner as in Example 1, and then treated under the conditions shown in (b) of Example 1.
It was coated with 150 mg/m ² of Sn plating, washed with water, and dried. Then, heat treatment was performed in the same non-oxidizing atmosphere as in Example 1. Example 3 The same cold-rolled steel sheet as in Example 1 was subjected to the same pretreatment as in Example 1, and then Cr metallization was carried out under the conditions shown in (a) and (b) of Example 1, each with different electrolysis time. After applying plating and Sn plating, it was washed with water and dried. Then, in the same non-oxidizing atmosphere as in Example 1, the temperature was
Heat treatment was performed at 620-680°C for 30 seconds. At this time, the steel plate in which the Cr/Sn+Cr of the diffusion layer after heat treatment was 0.071 was further subjected to 2% temper rolling. Thereafter, Sn plating was further carried out under the conditions shown in (a), followed by heating and melting treatment, followed by electrolysis at 50°C with a 3% sodium dichromate solution at a cathode current density of 15 A/dm ² for 2 seconds, followed by washing with water and drying. . Cr plating amount 50mg/ ^m2 Residual chromium hydrated oxide amount (as Cr)
3mg/m ² Sn plating amount 200mg/m ² (a) Sn plating conditions after heat treatment and temper rolling Bath composition SnSO ₄ 60g/phenolsulfonic acid (as sulfuric acid)
15g/ Ethoxylated α-naphthol 7g/ Bath temperature 45℃ Cathode current density 20A/dm ² Sn plating amount 2.7g/m ² Comparative example 4 The sample obtained in Comparative example 1 was subjected to 2% temper rolling. After that, 2.7 g/m ² was applied under the conditions shown in Example 3 (a).
After Sn plating and heat melting treatment, dichromic acid treatment was performed under the conditions shown in Example 3, followed by washing with water and drying. Comparative Example 5 The sample obtained in Comparative Example 2 was subjected to temper rolling, Sn plating, heat melting treatment, and dichromic acid treatment in the same manner as in Comparative Example 4, and was washed with water and dried. Comparative Example 6 The sample obtained in Comparative Example 3 was subjected to temper rolling, Sn plating, heat melting treatment, and dichromic acid treatment in the same manner as in Comparative Example 4, and was washed with water and dried. Example 4 The sample obtained in Example 1 was subjected to 2% temper rolling, then subjected to electrolytic chromic acid treatment (TFS treatment) under the conditions shown in (a), washed with water, and dried. (b) Electrolytic chromic acid treatment conditions after heat treatment and temper rolling (TFS treatment conditions) Bath composition CrO ₃ 80g/ NaF 4g/ H ₂ SO ₄ 0.5g/ Bath temperature 40℃ Cathode current density 40A/dm ² Metallic Cr content 103 mg/m ² Amount of chromium hydrated oxide (as Cr) 15 mg/m ² Comparative Example 7 The sample obtained in Comparative Example 1 was subjected to 2% temper rolling and electrolyzed under the conditions shown in (a) of Example 4. After being treated with chromic acid, it was washed with water and dried. Comparative Example 8 The sample obtained in Comparative Example 2 was subjected to 2% temper rolling, subjected to electrolytic chromic acid treatment under the conditions shown in (a) of Example 4, and then washed with water and dried. Comparative Example 9 The sample obtained in Comparative Example 3 was subjected to 2% temper rolling, subjected to electrolytic chromic acid treatment under the conditions shown in (a) of Example 4, and then washed with water and dried. After measuring the composition of the plating film on the steel plate obtained by the above method using a fluorescent X-ray method, the rust resistance and corrosion resistance without painting and the processing corrosion resistance after painting were investigated using the following methods. The results are summarized in Table 1. (1) Amount and rate of diffusion of Cr and Sn into steel sheets due to heat treatment

〔Effect of the invention〕

本発明の方法で得られためつき素地鋼板は塗装
後の加工耐食性に優れ、かつSnなどのめつき性
にも優れているため、製缶用めつき素地鋼板とし
て用いられるだけでなく、そのまま缶用鋼板とし
ても用いることができ、産業上きわめて有用なも
のである。 The plated base steel sheet obtained by the method of the present invention has excellent processing corrosion resistance after painting and is also excellent in plating properties such as Sn, so it is not only used as a plated base steel plate for can manufacturing, but also can be used as is. It can also be used as a steel plate for industrial use, making it extremely useful industrially.

Claims

[Claims]

1 The metal Cr amount is 3 to 150 per side on the steel plate surface.
mg/m ² , the amount of chromium hydrated oxide is 5 as the amount of Cr
Cr plating with mg/m ² or less is applied, and the upper layer is
Sn plating with a Sn content of 20 to 500 mg/m ² is applied, followed by heat treatment in a non-oxidizing iron atmosphere, and the ternary diffusion layer of Cr-Sn-Fe is formed using Sn plated.
95% or more of the amount, and 1 of the amount of plated metal Cr
1. A method for producing a plated base steel sheet for can making having excellent process corrosion resistance, the method comprising a Cr/Sn+Cr weight ratio of 0.02 to ^0.50 .