JPS636629B2 - - Google Patents
Info
- Publication number
- JPS636629B2 JPS636629B2 JP57201998A JP20199882A JPS636629B2 JP S636629 B2 JPS636629 B2 JP S636629B2 JP 57201998 A JP57201998 A JP 57201998A JP 20199882 A JP20199882 A JP 20199882A JP S636629 B2 JPS636629 B2 JP S636629B2
- Authority
- JP
- Japan
- Prior art keywords
- galvanized steel
- dip galvanized
- alloyed hot
- steel sheet
- chromate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 claims description 56
- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 42
- 239000008397 galvanized steel Substances 0.000 claims description 42
- 238000011282 treatment Methods 0.000 claims description 32
- 230000007797 corrosion Effects 0.000 claims description 20
- 238000005260 corrosion Methods 0.000 claims description 20
- 239000011651 chromium Substances 0.000 claims description 12
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 8
- 229910052804 chromium Inorganic materials 0.000 claims description 8
- 229910000831 Steel Inorganic materials 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 claims description 7
- 239000010959 steel Substances 0.000 claims description 7
- 238000005246 galvanizing Methods 0.000 claims description 4
- 239000010408 film Substances 0.000 description 47
- 239000011701 zinc Substances 0.000 description 21
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 20
- 229910052725 zinc Inorganic materials 0.000 description 20
- 238000012360 testing method Methods 0.000 description 12
- 239000011248 coating agent Substances 0.000 description 10
- 238000000576 coating method Methods 0.000 description 10
- 239000003973 paint Substances 0.000 description 9
- 230000010287 polarization Effects 0.000 description 8
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 238000007747 plating Methods 0.000 description 7
- 238000000034 method Methods 0.000 description 5
- 238000010422 painting Methods 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 241001163841 Albugo ipomoeae-panduratae Species 0.000 description 3
- 238000005452 bending Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 230000002950 deficient Effects 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- DDFHBQSCUXNBSA-UHFFFAOYSA-N 5-(5-carboxythiophen-2-yl)thiophene-2-carboxylic acid Chemical compound S1C(C(=O)O)=CC=C1C1=CC=C(C(O)=O)S1 DDFHBQSCUXNBSA-UHFFFAOYSA-N 0.000 description 2
- 229920000298 Cellophane Polymers 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 239000002390 adhesive tape Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- -1 electrical equipment Substances 0.000 description 2
- 238000009713 electroplating Methods 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 description 2
- 229920000877 Melamine resin Polymers 0.000 description 1
- 206010027146 Melanoderma Diseases 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 229920000180 alkyd Polymers 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 238000004532 chromating Methods 0.000 description 1
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 1
- UFMZWBIQTDUYBN-UHFFFAOYSA-N cobalt dinitrate Chemical compound [Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O UFMZWBIQTDUYBN-UHFFFAOYSA-N 0.000 description 1
- 229910001981 cobalt nitrate Inorganic materials 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 235000005074 zinc chloride Nutrition 0.000 description 1
- 239000011592 zinc chloride Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/78—Pretreatment of the material to be coated
Description
本発明は合金化溶融亜鉛めつき鋼板の化成処理
のための製造方法に関するもので、合金化溶融亜
鉛めつき鋼板に極薄（0.01〜0.2μ）な電気亜鉛め
つきを施した後、引き続きクロメート皮膜を形成
させることにより合金化溶融亜鉛めつき鋼板に発
生しているクラツク若しくはクレーター内部にま
でクロメート皮膜を形成させ高耐食性とした合金
化溶融亜鉛めつき鋼板の製造方法に関するもので
ある。
合金化溶融亜鉛めつき鋼板は耐食性、塗装性な
ど他のめつき鋼板に見られない優れた特性を有し
ており、建材、車両、電気機器、鋼製家具、雑貨
など非常に多岐に渉つて使用されている。
現在は合金化溶融亜鉛めつき鋼板の化成処理と
して、リン酸塩或いはクロム酸塩系処理が行なわ
れている。
しかし、合金化溶融亜鉛めつき鋼板の欠点はめ
つき時に鋼板製造過程において層内部に直径数μ
のクレーターが発生し、またスキンパス、レベラ
−工程時には、めつき層にクラツク或いは表面に
不活性部分が発生する。之等を以下欠陥部と呼称
することとする。
之等の欠陥部に従来のクロメート処理を施して
も前述のクレーター部或いはクラツク部はクロメ
ート皮膜の欠陥部となる。また表面不活性部にお
いては充分な皮膜が形成されず、めつき欠陥部は
不均一な表面処理となる。
この様なことから、塗装を施さずに合金化溶融
亜鉛めつき鋼板をその儘の状態で海岸地帯や多湿
地帯などで使用された場合には必ずしも満足すべ
き耐食性は得られないのが現状である。
本発明者等は先に特公昭52−42135号（特許第
911167号）の合金化溶融亜鉛めつき鋼板に最適な
裸の耐食性と塗膜密着性及び塗装後の耐食性に優
れたクロメート処理浴組成物を提案した。しかし
この処理を行なつても前述のめつき表面のめつき
欠陥部に起因して塩水噴霧試験を行なうと72時間
経過時点から直径0.2〜１mmφの黒色斑点（以下、
微小黒サビと呼称する）が２〜５個／ｄm2発生す
る。之等の黒サビは240時間経過時点から同微小
黒サビを起点として白サビに転換する。
電気化学的手法で同黒サビ部を調査した結果で
は黒サビ部が電気化学的に貴な部分となり、周囲
とのマイクロセルを構成して亜鉛が溶解し非常に
緩慢ではあるが白サビ化する。この微小黒サビ点
が存在しなければ、塩水噴霧試験500時間でも何
等外観の変化が無く白サビが発生すること無く試
験前の美麗な外観と健全なめつき層を保持してい
る。
通常の処理条件によつて得られるクロメート皮
膜よりもより多量のクロメート皮膜を付与して
も、クロメート皮膜によつて表面の色調が黄色に
なり合金化溶融亜鉛めつき鋼板の美麗な外観特性
を損ねるばかりでなく、前述のめつき欠陥部に起
因する微小黒サビは全く解決出来ず、反つてステ
ンレスにおける孔食的な選択腐食の誘因ともな
る。
そこで本発明は之等の問題を一挙に解決したも
のである。
即ちクロメート処理時に消費溶出される亜鉛量
に相当する膜厚0.01〜0.2μの電気亜鉛めつきを施
した後、引き続きクロメート処理を行なつて、合
金化溶融亜鉛めつき鋼板において鋼素地にまで達
する微小クラツク、若しくはクレーター内の鋼表
面に純亜鉛めつき層が存在し、または存在しない
で合金化溶融亜鉛めつき鋼板の全表面にクロム量
（Cr）として60〜150mg／m2のクロメート皮膜層
が設けられている高耐食性合金化溶融亜鉛めつき
鋼板の製造方法に関するものである。
本発明は前述の問題点を解決したもので、合金
化溶融亜鉛めつき鋼板に対して、次工程のクロメ
ート処理時に溶出消費される亜鉛量に相当する短
時間で極薄（0.01〜0.2μ）の電気亜鉛めつきを施
した後クロメート処理を行ないクロム皮膜中のク
ロム量が60〜150mg／m2であるクロメート皮膜を
形成させることを特徴とするものである。
本発明の構成要件の一部である電気亜鉛めつき
浴組成は一般に公知の電気亜鉛めつき浴でよい。
合金化溶融亜鉛めつき鋼板に施す電気亜鉛めつ
きは、次工程のクロメート処理によつて溶出し消
費される亜鉛量に相当する量だけ、ないし若干多
目にめつきするものである。本クロメート処理は
めつきの組成にもよるが通常、合金化溶融亜鉛め
つきに対して高耐食性を保持させるに必要なクロ
ム量を有するクロメート皮膜を形成させるには後
述する様に少なくともクロム量として60〜150
mg／m2が必要であり、之等のクロム量を含有させ
たクロメート皮膜を形成させるには少なくとも消
費亜鉛量は凡そ0.01〜0.2μの膜厚が必要である。
0.01μ未満ではめつき欠陥部などで耐食性を付与
するだけの充分なクロメート皮膜が形成されず、
近傍の合金化溶融亜鉛めつき層に形成されたクロ
メート皮膜に比して極めて弱い皮膜となりローカ
ルセルが形成され易く不充分である。
また0.2μを超えた亜鉛皮膜を形成させるとクロ
メート処理液の組成にもよるが、一般に行なわれ
ている合金化溶融亜鉛めつき鋼板帯鋼の後処理で
は電気亜鉛が可成り存在し、合金化亜鉛の最大の
特長であるδ1層（Zn−10〜15％Fe）の表面を純
亜鉛で覆つて了うため高耐食性及び塗装性能が大
幅に低下し電気亜鉛めつきに近い特性を示すので
好ましくない。
本発明の最も特長とする点は電気亜鉛の亜鉛は
中間的な媒体であつてクロメート処理によつて完
全に溶解消失し、クロメート皮膜に転換させて了
う処にある。
即ち、電気めつき層を全く存在させないことが
最も望ましいが、現在の工業的製造技術上は難か
しい。若干のδ1層の上に純亜鉛層（クロメート処
理された）が存在しても差支えない。
モデル図の様に従来の合金化溶融亜鉛めつき鋼
板（第１図）にクロメート処理を行なうと第４図
に示した様にクレーター、クラツク、スキンパス
ロール接触部の不活性部などにクロメート皮膜が
形成されないが、本発明による電気亜鉛めつきを
行なうと表面は残す処なく非常に薄膜ではあるが
純亜鉛層で覆われてクレーター、クラツク、スキ
ンパスロール接触部の総べてに亜鉛が存在するこ
とになる（第２図）。この電気亜鉛めつき表面を
クロメート処理することによつてクロメート処理
時に純亜鉛層は完全に消費され電気亜鉛めつき層
が総べてないしは殆んどクロメート皮膜に転換す
る（第３図）。
この析出亜鉛が膜厚0.01〜0.2μの場合にはクロ
メート皮膜が形成されると同時に消失し、本来の
δ1層のみの合金化亜鉛めつき鋼板にクロメート処
理を施したものと同じ特性を示すことの証例を第
５図及び第６図に分極曲線の状態で示す。
図から明らかな様に膜厚0.2μの電気めつきを施
すことによつて自然電位は亜鉛の電位を示すが、
クロメート処理を施すことによつて完全に元の合
金化溶融亜鉛めつき鋼板の自然電位となつている
（第５図）
一方、電気亜鉛めつきを膜厚0.5μに施した後、
クロメート処理しても電気亜鉛めつき層の純亜鉛
層が可成り残存するため亜鉛に近い自然電位を示
している。このことからδ1特有の性質が損なわれ
耐食性も好ましくなく、且つ特に塗装後の塗膜の
密着性が極めて悪くなり合金化溶融亜鉛めつき鋼
板の最大の特長としている塗膜密着性が完全に損
なわれる。この理由のため本発明は析出亜鉛量を
クロメート皮膜を形成させるに必要充分ないし僅
かに多い目の亜鉛量に止めるものであり、現在の
クロメート処理浴組成や工業的規模からして0.01
〜0.2μ膜厚に亜鉛めつき厚さを限定したものであ
る。
また、電気亜鉛めつき後のクロメート処理は基
本的には本発明者等が先きに開示した特開昭49−
74640号に係るクロメート処理液（クロム酸−硝
酸コバルト−酸性フツ化アンモンなどの組成物）
で処理することが最も望ましいが、公知のクロメ
ート処理でも可能である。
クロム量（Cr）として60〜150mg／m2を含有す
るクロメート皮膜を形成させれば本発明の目的を
達成することが出来る。
クロメート処理方法はロールコート法、スプレ
ー法、浸漬法など従来公知の方法で処理すること
が出来る。
60mg／m2未満では均一なクロメート皮膜が形成
され難く、耐食性に乏しく充分でない。
一方、150mg／m2を超えるとクロメート皮膜の
影響で黄色化して商品価値が低下すると共に塗膜
の密着性及び塗装後の耐食性も悪くなる。
以下、本発明について実施例により詳細に説明
する。
板厚0.5mm、めつき付着量45g／m2の合金化溶融
亜鉛めつき鋼板に電気亜鉛めつき（注１）を施
し、引き続きクロメート処理（注２）を行ないク
ロメート皮膜を形成させ乾燥した後、耐食性の効
果を明確にするため塩水噴霧試験（注３）を行な
つて黒点状サビ発生状態を観察した。
（注１）：電気亜鉛めつき条件
めつき浴組成（塩化亜鉛200g／、
酢酸40ml／）。
温度〜30〜35℃
電流〜5A／ｄm2
時間〜（例0.2μは10秒）。
（注２）：クロメート処理条件
組成（クロム酸55g／、硝酸コバル
ト8g／、酸性フツ化アンモン2g／
）。
温度70℃、時間７秒。
（注３）：塩水噴霧試験条件（JISZ2371）。
塩水濃度5W／Ｖ％、試験室内温度35
±１℃
試験室内の相対湿度95〜98％
なお塗装性能を明確にするため板厚0.5mm、め
つき付着量45g／m2の合金化溶融亜鉛めつき鋼板
に（注１）、（注２）に示した条件で処理済みの試
片に塗装し、塗装確性試験を行なつて評価した。
その際の塗料は、メラミンアルキツド塗料（日
本ペイント製・ニユーオルガ100）をバーコータ
ーで乾燥塗膜厚さが30μになる様に塗布し130℃
の温度で10分間乾燥し試片を作成した。
確性試験はJISG3312（注３）に準拠する折り曲
げ試験とJISK5400（注４）に準拠するデユポン衝
撃試験とを行なつて塗膜の密着性を評価した。
（注３）：折り曲げ試験
180℃折り曲げ（折り曲げた部分の内側に試験
板と同じ厚さの板を２枚挾み込み万力で締め付け
る）を行なつた後、折り曲げ部をセロハン粘着テ
ープで剥離し、塗膜の剥ガレ状態を肉眼で観察し
た。
（注４）：デユポン衝撃試験
直径12.7mmの球状の先端を持つ撃心を試験面に
置き、500gのオモリを500mmの高さから落した
後、被衝撃部をセロハン粘着テープで剥離してか
ら塗膜の剥ガレ状態を肉眼で観察し評価した。
なお比較例として本発明によらない即ち合金化
溶融亜鉛めつき鋼板に電気めつきを施さないもの
及び本発明の特許請求の範囲外のものを用いて試
験も同様に行なつた。第１表に電気亜鉛めつき付
着量及びクロメート皮膜量、第２表にその結果を
夫々示す。
第２表より、本発明特許請求範囲内にある電気
亜鉛めつきを膜厚0.01〜0.2μに施し、更にクロメ
ート皮膜量60〜150mg／m2を形成させたものは何
れも良好な耐食性及び塗膜密着性が示されてい
る。本発明以外のもの、電気亜鉛めつき0.01μ未
満或いはクロメート皮膜量60mg／m2未満のものは
耐食性はよくない。
また、クロメート皮膜量が150mg／m2を超える
ものは耐食性は優れた性能を示すが表面の色調が
黄色になり合金化溶融亜鉛めつき鋼板の特性を損
なつていて好ましくない。
本発明によるものが良好な結果を示しているの
に対し、比較例のものは著しく耐食性が低下して
いる。
The present invention relates to a manufacturing method for chemical conversion treatment of alloyed hot-dip galvanized steel sheets. The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet that has high corrosion resistance by forming a chromate film even inside cracks or craters that occur in the alloyed hot-dip galvanized steel sheet. Alloyed hot-dip galvanized steel sheets have excellent properties not found in other galvanized steel sheets, such as corrosion resistance and paintability, and are used in a wide variety of applications such as building materials, vehicles, electrical equipment, steel furniture, and miscellaneous goods. It is used. Currently, phosphate or chromate-based treatments are used as chemical conversion treatments for alloyed hot-dip galvanized steel sheets. However, the drawback of alloyed hot-dip galvanized steel sheets is that during plating, the inside of the layer has a diameter of several μm during the steel sheet manufacturing process.
Craters occur in the plated layer or inactive areas appear on the surface during the skin pass and leveling processes. These will be hereinafter referred to as defective parts. Even if conventional chromate treatment is applied to these defective areas, the aforementioned crater areas or cracks will remain as defective areas in the chromate film. In addition, a sufficient film is not formed in the surface inactive areas, and plating defect areas result in non-uniform surface treatment. For this reason, the current situation is that if alloyed hot-dip galvanized steel sheets are used in coastal areas or humid areas without painting, satisfactory corrosion resistance cannot necessarily be obtained. be. The present inventors previously published Japanese Patent Publication No. 52-42135 (Patent No.
We have proposed a chromate treatment bath composition that has excellent bare corrosion resistance, paint film adhesion, and post-painting corrosion resistance that is ideal for alloyed hot-dip galvanized steel sheets (No. 911167). However, even with this treatment, black spots with a diameter of 0.2 to 1 mmφ (hereinafter referred to as
2 to 5 particles/ dm2 (referred to as microscopic black rust) occur. After 240 hours, the black rust starts to turn into white rust. The results of investigating the black rust part using an electrochemical method show that the black rust part becomes an electrochemically noble part, forms microcells with the surrounding area, dissolves zinc, and turns into white rust, albeit very slowly. . If these minute black rust spots do not exist, there will be no change in appearance even after 500 hours of salt spray testing, and the product will maintain its beautiful appearance and healthy plating layer before the test without any white rust. Even if a larger amount of chromate film is applied than that obtained under normal processing conditions, the chromate film will turn the surface yellow in color and impair the beautiful appearance characteristics of the alloyed hot-dip galvanized steel sheet. Not only that, the minute black rust caused by the plating defects described above cannot be resolved at all, and on the contrary, it may cause pitting-like selective corrosion in the stainless steel. Therefore, the present invention solves these problems all at once. In other words, after applying electrogalvanizing to a film thickness of 0.01 to 0.2μ corresponding to the amount of zinc consumed and eluted during chromate treatment, chromate treatment is subsequently performed to reach the steel base in alloyed hot-dip galvanized steel sheets. A chromate film layer with a chromium content (Cr) of 60 to 150 mg/m 2 on the entire surface of the alloyed hot-dip galvanized steel sheet with or without a pure galvanized layer on the steel surface in microcracks or craters. The present invention relates to a method for manufacturing a highly corrosion-resistant alloyed hot-dip galvanized steel sheet. The present invention solves the above-mentioned problems, and it can be applied to alloyed hot-dip galvanized steel sheets to make them extremely thin (0.01 to 0.2μ) in a short period of time, which is equivalent to the amount of zinc that is eluted and consumed during the next process of chromate treatment. The method is characterized in that a chromate treatment is performed after electrogalvanizing to form a chromate film having a chromium content of 60 to 150 mg/m 2 . The electrogalvanizing bath compositions that are part of the present invention may be generally known electrogalvanizing baths. Electrogalvanizing is applied to alloyed hot-dip galvanized steel sheets in an amount equivalent to or slightly more than the amount of zinc that is eluted and consumed in the next step of chromate treatment. This chromate treatment depends on the composition of the plating, but normally, in order to form a chromate film with the amount of chromium necessary to maintain high corrosion resistance against alloyed hot-dip galvanizing, the amount of chromium is at least 60 to 60%, as described below. 150
mg/m 2 is required, and in order to form a chromate film containing such an amount of chromium, a film thickness of at least 0.01 to 0.2 μ of zinc consumption is required.
If it is less than 0.01μ, a sufficient chromate film will not be formed to provide corrosion resistance at plating defects, etc.
This is an extremely weak film compared to the chromate film formed on the nearby alloyed hot-dip galvanized layer, and local cells are likely to be formed, which is insufficient. In addition, if a zinc film with a thickness exceeding 0.2μ is formed, although it depends on the composition of the chromate treatment solution, a considerable amount of electrolytic zinc is present in the commonly used post-treatment of alloyed hot-dip galvanized steel sheets and strips. Since the surface of the δ 1 layer (Zn - 10 to 15% Fe), which is the greatest feature of zinc, is covered with pure zinc, its high corrosion resistance and coating performance are significantly reduced, resulting in properties close to those of electrogalvanizing. Undesirable. The most distinctive feature of the present invention is that the zinc in electrolytic zinc is an intermediate medium and is completely dissolved and disappeared by chromate treatment, converting it into a chromate film. That is, it is most desirable to have no electroplated layer at all, but this is difficult in view of current industrial manufacturing technology. There may be a layer of pure zinc (chromated) on top of some of the δ 1 layer. As shown in the model diagram, when chromate treatment is applied to a conventional alloyed hot-dip galvanized steel sheet (Fig. 1), a chromate film forms in craters, cracks, and inert areas in contact with skin pass rolls as shown in Fig. 4. However, when electrogalvanizing according to the present invention is performed, the surface is covered with a pure zinc layer, albeit a very thin film, and zinc is present in all of the craters, cracks, and skin pass roll contact areas. (Figure 2). By chromating the electrogalvanized surface, the pure zinc layer is completely consumed during the chromate treatment, and the electrogalvanized layer is entirely or almost converted into a chromate film (Figure 3). If this precipitated zinc has a film thickness of 0.01 to 0.2μ, it disappears at the same time as the chromate film is formed, and exhibits the same characteristics as the original chromate treatment of an alloyed galvanized steel sheet with only one δ layer. An example of this is shown in the state of polarization curves in FIGS. 5 and 6. As is clear from the figure, by electroplating with a film thickness of 0.2μ, the natural potential shows the potential of zinc,
By applying chromate treatment, the potential is completely the same as that of the original alloyed hot-dip galvanized steel sheet (Figure 5).On the other hand, after electrogalvanizing to a film thickness of 0.5μ,
Even after chromate treatment, a considerable amount of the pure zinc layer of the electrogalvanized layer remains, so it exhibits a natural potential close to that of zinc. As a result, the unique properties of δ 1 are impaired, corrosion resistance is not desirable, and in particular, the adhesion of the paint film after painting is extremely poor, and the adhesion of the paint film, which is the greatest feature of alloyed hot-dip galvanized steel sheets, is completely lost. be damaged. For this reason, the present invention limits the amount of zinc precipitated to a level that is sufficient or slightly larger than necessary to form a chromate film.
The galvanizing thickness is limited to ~0.2μ film thickness. Furthermore, the chromate treatment after electrogalvanizing is basically the same as that disclosed in Japanese Unexamined Patent Application Publication No. 49-1983, which was previously disclosed by the present inventors.
Chromate treatment solution according to No. 74640 (composition such as chromic acid - cobalt nitrate - acidic ammonium fluoride)
Although treatment with chromate is most desirable, known chromate treatment is also possible. The object of the present invention can be achieved by forming a chromate film containing 60 to 150 mg/m 2 of chromium (Cr). The chromate treatment can be carried out by conventionally known methods such as roll coating, spraying, and dipping. If it is less than 60 mg/m 2 , it is difficult to form a uniform chromate film, resulting in poor corrosion resistance. On the other hand, if it exceeds 150 mg/m 2 , the chromate film will turn yellow and reduce its commercial value, as well as the adhesion of the paint film and the corrosion resistance after painting. Hereinafter, the present invention will be explained in detail with reference to Examples. Electrogalvanizing (Note 1) is applied to an alloyed hot-dip galvanized steel sheet with a thickness of 0.5 mm and a coating weight of 45 g/ m2 , followed by chromate treatment (Note 2) to form a chromate film and drying. In order to clarify the effect of corrosion resistance, a salt spray test (Note 3) was conducted to observe the appearance of black spot rust. (Note 1): Electrogalvanizing conditions Plating bath composition (zinc chloride 200g/,
Acetic acid 40ml/). Temperature ~30~35℃ Current ~5A/dm 2 hours~ (eg 0.2μ is 10 seconds). (Note 2): Chromate treatment condition composition (chromic acid 55g/, cobalt nitrate 8g/, acidic ammonium fluoride 2g/
). Temperature: 70℃, time: 7 seconds. (Note 3): Salt spray test conditions (JISZ2371). Salt water concentration 5W/V%, test room temperature 35
±1℃ Relative humidity in the test room 95-98% In order to clarify the coating performance, alloyed hot-dip galvanized steel sheets (Note 1) and (Note 2 ) with a thickness of 0.5 mm and a coating weight of 45 g/m2 were used. ) The treated specimens were coated under the conditions shown in ), and a coating accuracy test was conducted and evaluated. The paint used in this case was a melamine alkyd paint (New Olga 100 manufactured by Nippon Paint Co., Ltd.) applied with a bar coater to a dry film thickness of 30 μm at 130°C.
A specimen was prepared by drying at a temperature of 10 minutes. The adhesion of the paint film was evaluated by conducting a bending test in accordance with JISG3312 (Note 3) and a Dupont impact test in accordance with JISK5400 (Note 4). (Note 3): Bending test After bending at 180°C (insert two plates of the same thickness as the test plate inside the folded part and tighten them with a vise), peel off the folded part with cellophane adhesive tape. The state of peeling of the paint film was then observed with the naked eye. (Note 4): Dupont impact test Place the impact center with a spherical tip with a diameter of 12.7 mm on the test surface, drop a 500 g weight from a height of 500 mm, and then peel off the impact area with cellophane adhesive tape. The peeling state of the paint film was observed and evaluated with the naked eye. As a comparative example, tests were similarly conducted using alloyed hot-dip galvanized steel sheets not according to the present invention, which were not subjected to electroplating, and those which were outside the scope of the claims of the present invention. Table 1 shows the amount of electrogalvanized coating and the amount of chromate film, and Table 2 shows the results. From Table 2, it can be seen that electrogalvanizing within the claimed scope of the present invention is applied to a film thickness of 0.01 to 0.2μ, and a chromate film is formed in an amount of 60 to 150 mg/ m2 , all of which have good corrosion resistance and coating. Membrane adhesion is shown. Products other than those of the present invention, those with electrogalvanized coating of less than 0.01μ or those with a chromate coating amount of less than 60 mg/m 2 do not have good corrosion resistance. Further, a steel sheet having a chromate film amount exceeding 150 mg/m 2 exhibits excellent corrosion resistance, but the surface color becomes yellow, impairing the characteristics of the alloyed hot-dip galvanized steel sheet, which is not preferable. While the one according to the present invention shows good results, the one of the comparative example shows a marked decrease in corrosion resistance.
【表】【table】
【表】【table】
【表】【table】
第１図は通常の合金化溶融亜鉛めつき鋼板の断
面モデル図を示し、第２図は合金化溶融亜鉛めつ
き鋼板に電気亜鉛めつき（0.2μ）施したもの、第
３図は電気亜鉛めつきを膜厚0.2μ施した後、更に
クロメート処理を行なつた合金化溶融亜鉛めつき
鋼板の断面、第４図は合金化溶融亜鉛めつき鋼板
に直ちにクロメート処理を施した従来の合金化溶
融亜鉛めつき鋼板のクロメート処理品の断面を示
す。第５図は合金化溶融亜鉛めつき鋼板に電気亜
鉛めつきを膜厚0.2μ施した分極曲線を示し、第６
図は合金化溶融亜鉛めつき鋼板に電気亜鉛めつき
を膜厚0.5μ施した分極曲線を示す。
１……δ1層、２……Fe層、３……クラツク、
４……クレーター、５……スキンパスロール接触
部（表面圧延部）、６，６′，６″……電気亜鉛め
つき層（0.2μ）、７……クロメート皮膜、８……
合金化溶融亜鉛めつき鋼板の分極曲線、９……電
気亜鉛めつき0.2μ施した後の分極曲線、１０……
合金化溶融亜鉛めつき鋼板の自然電位、１１……
合金化溶融亜鉛めつき鋼板に電気亜鉛めつきを膜
厚0.2μ施した自然電位、１２……合金化溶融亜鉛
めつき鋼板に電気亜鉛めつきを0.2μ膜厚に施した
後、クロメート処理した時の分極曲線、１３……
合金化溶融亜鉛めつき鋼板に電気亜鉛めつきを
0.5μ膜厚に施した分極曲線、１４……合金化溶融
亜鉛めつき鋼板に電気亜鉛めつきを膜厚0.5μ施
し、更にクロメート処理を施した分極曲線、１５
……合金化溶融亜鉛めつき鋼板に電気亜鉛めつき
を膜厚0.5μ施した自然電位、１６……合金化溶融
亜鉛めつき鋼板に電気亜鉛めつきを膜厚0.5μ施
し、更にクロメート処理を行なつた場合の自然電
位。
Figure 1 shows a cross-sectional model diagram of a normal alloyed hot-dip galvanized steel sheet, Figure 2 shows a cross-sectional model of an alloyed hot-dip galvanized steel sheet subjected to electrogalvanizing (0.2μ), and Figure 3 shows an electrogalvanized steel sheet. Figure 4 shows a cross section of an alloyed hot-dip galvanized steel sheet that was plated to a thickness of 0.2μ and then further chromate-treated. A cross section of a chromate-treated hot-dip galvanized steel sheet is shown. Figure 5 shows the polarization curve of an alloyed hot-dip galvanized steel sheet subjected to electrogalvanizing with a film thickness of 0.2 μm.
The figure shows the polarization curve of an alloyed hot-dip galvanized steel sheet subjected to electrogalvanizing with a film thickness of 0.5 μm. 1...δ 1 layer, 2...Fe layer, 3...Crack,
4...Crater, 5...Skin pass roll contact area (surface rolled part), 6, 6', 6''...Electrogalvanized layer (0.2μ), 7...Chromate film, 8...
Polarization curve of alloyed hot-dip galvanized steel sheet, 9... Polarization curve after electrogalvanizing 0.2μ, 10...
Natural potential of alloyed hot-dip galvanized steel sheet, 11...
Natural potential of electrolytic galvanizing applied to alloyed hot-dip galvanized steel sheet to a film thickness of 0.2μ, 12... Electrogalvanizing was applied to alloyed hot-dip galvanized steel sheet to a film thickness of 0.2μ, followed by chromate treatment. Polarization curve of time, 13...
Electrogalvanizing on alloyed hot-dip galvanized steel sheets
Polarization curve applied to a film thickness of 0.5μ, 14... Polarization curve obtained by applying electrogalvanizing to a film thickness of 0.5μ on an alloyed hot-dip galvanized steel sheet, and further applying chromate treatment, 15
...Natural potential of an alloyed hot-dip galvanized steel sheet subjected to electrogalvanizing with a thickness of 0.5μ, 16...An alloyed hot-dip galvanized steel sheet subjected to electrolytic galvanization with a thickness of 0.5μ and further chromate treatment The natural potential when it is carried out.
Claims (1)
ート処理によつて消費されるのに対応する0.01〜
0.2μ膜厚の電気亜鉛めつきを施した後、クロム量
（Cr）として60〜150mg／m2のクロメート皮膜を
形成させることを特徴とする高耐食性合金化溶融
亜鉛めつき鋼板の製造方法。 ２ 合金化溶融亜鉛めつき鋼板に次工程のクロメ
ート処理によつて消費されるのに対応する量より
僅かに多い膜厚に電気亜鉛めつきを施して後、該
電気亜鉛めつき上にクロム量（Cr）として60〜
150mg／m2のクロメート皮膜を形成させることを
特徴とする高耐食性合金化溶融亜鉛めつき鋼板の
製造方法。[Claims] 1. 0.01 to 0.01, which corresponds to the amount consumed in the next step of chromate treatment on the alloyed hot-dip galvanized steel sheet.
A method for producing a highly corrosion-resistant alloyed hot-dip galvanized steel sheet, which comprises forming a chromate film with a chromium content (Cr) of 60 to 150 mg/m 2 after electrolytic galvanizing to a thickness of 0.2μ. 2. After applying electrogalvanizing to an alloyed hot-dip galvanized steel sheet to a film thickness slightly greater than the amount corresponding to that consumed in the next step of chromate treatment, an amount of chromium is added to the electrogalvanized steel sheet. (Cr) 60~
A method for producing a highly corrosion-resistant alloyed hot-dip galvanized steel sheet, which is characterized by forming a chromate film of 150 mg/m 2 .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP20199882A JPS5993884A (en) | 1982-11-19 | 1982-11-19 | Alloyed galvanized steel plate having high corrosion resistance and its production |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP20199882A JPS5993884A (en) | 1982-11-19 | 1982-11-19 | Alloyed galvanized steel plate having high corrosion resistance and its production |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5993884A JPS5993884A (en) | 1984-05-30 |
| JPS636629B2 true JPS636629B2 (en) | 1988-02-10 |
Family
ID=16450239
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP20199882A Granted JPS5993884A (en) | 1982-11-19 | 1982-11-19 | Alloyed galvanized steel plate having high corrosion resistance and its production |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5993884A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01268880A (en) * | 1988-04-15 | 1989-10-26 | Chubu Electric Power Co Inc | Surface treatment of iron metallic material and fitting for power transmission equipment subjected to surface treatment by this method |
| DE69625365T2 (en) * | 1996-06-06 | 2003-09-11 | Sumitomo Metal Ind | SURFACE TREATED STEEL SHEET WITH EXCELLENT CORROSION PROPERTIES AFTER PROCESSING |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56123359A (en) * | 1980-02-29 | 1981-09-28 | Sumitomo Metal Ind Ltd | Manufacture of alloyed steel sheet with superior corrosion resistance |
-
1982
- 1982-11-19 JP JP20199882A patent/JPS5993884A/en active Granted
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56123359A (en) * | 1980-02-29 | 1981-09-28 | Sumitomo Metal Ind Ltd | Manufacture of alloyed steel sheet with superior corrosion resistance |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5993884A (en) | 1984-05-30 |
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