Galvanized steel sheet and method for producing the same

Patent metadata

Field	Value
Publication number	US-10351960-B2
Application number	US-201515122036-A
Country	US
Kind code	B2
Filing date	Feb 27, 2015
Priority date	Feb 27, 2014
Publication date	Jul 16, 2019
Grant date	Jul 16, 2019

Abstract

Provided is a method for producing a galvanized steel sheet that includes an oxide layer forming step of bringing a galvanized steel sheet into contact with an acidic solution containing sulfate ions, then holding the galvanized steel sheet in contact for 1 to 60 seconds, and then washing the galvanized steel sheet with water; and a neutralization treatment step of holding a surface of an oxide layer, which has been formed in the oxide layer forming step, in contact with an alkaline aqueous solution for 0.5 seconds or longer, and then performing washing with water and drying. The alkaline aqueous solution contains 0.1 g/L or more of carbonate ions.

First claim

The invention claimed is:

1. A galvanized steel sheet comprising a steel sheet and a galvanized coating layer formed on the steel sheet,
wherein the coating layer includes an oxide layer in a surface layer, the oxide layer having an average thickness of 20 nm or more, and
the oxide layer consists of Zn, O, H, S, C, and unavoidable impurities, and contains 50 mg/m 2 or more of Zn, 5 mg/m 2 or more of S, and 0.2 mg/m 2 or more of C.

2. The galvanized steel sheet according to claim 1 , wherein a sulfate group, a carbonate group, and a hydroxyl group exist in the oxide layer.

3. The galvanized steel sheet according to claim 1 , wherein the oxide layer contains a crystal structure represented by Zn 4 (SO 4 ) 1-x (CO 3 ) x (OH) 6 ·nH 2 O,
where X is a real number in the range of 0<X <1 and n is a real number in the range of 0≤n≤10.

4. The galvanized steel sheet according to claim 2 , wherein the oxide layer contains a crystal structure represented by Zn 4 (SO 4 ) 1-x (CO 3 ) x (OH) 6 ·nH 2 O,
where X is a real number in the range of 0<X<1 and n is a real number in the range of 0≤n ≤10.

5. The galvanized steel sheet according to claim 1 , wherein the galvanized steel sheet is a hot-dip galvannealed steel sheet, a hot-dip galvanized steel sheet, or an electrogalvanized steel sheet.

6. The galvanized steel sheet according to claim 2 , wherein the galvanized steel sheet is a hot-dip galvannealed steel sheet, a hot-dip galvanized steel sheet, or an electrogalvanized steel sheet.

7. The galvanized steel sheet according to claim 3 , wherein the galvanized steel sheet is a hot-dip galvannealed steel sheet, a hot-dip galvanized steel sheet, or an electrogalvanized steel sheet.

8. The galvanized steel sheet according to claim 4 , wherein the galvanized steel sheet is a hot-dip galvannealed steel sheet, a hot-dip galvanized steel sheet, or an electrogalvanized steel sheet.

9. A method for producing the galvanized steel sheet according to claim 1 , the method comprising:
an oxide layer forming step of bringing a galvanized steel sheet into contact with an acidic solution containing 0.3 g/L or more of sulfate ions, then holding the galvanized steel sheet in contact for 1 to 60 seconds, and then washing the galvanized steel sheet with water; and
a neutralization treatment step of holding a surface of an oxide layer, which has been formed in the oxide layer forming step, in contact with an alkaline aqueous solution having a pH of 9 to 12 for 0.5 seconds or longer, and then performing washing with water and drying,
wherein the alkaline aqueous solution contains 0.1 g/L or more of carbonate ions.

10. The method for producing the galvanized steel sheet according to claim 9 , wherein the alkaline aqueous solution has a temperature of 20° C. to 70° C.

11. The method for producing the galvanized steel sheet according to claim 9 , wherein the acidic solution has a pH buffering action and has a pH-increasing property in the range of 0.003 to 0.5, where the pH-increasing property is defined by an amount (L) of a 1.0 mol/L sodium hydroxide solution needed to increase a pH of 1 L of the acidic solution from 2.0 to 5.0.

12. The method for producing the galvanized steel sheet according to claim 9 , wherein the acidic solution contains a total of 5 to 50 g/L of at least one salt selected from an acetate, a phthalate, a citrate, a succinate, a lactate, a tartrate, a borate, and a phosphate, and has a pH of 0.5 to 5.0 and a temperature of 20° C. to 70° C.

13. The method for producing the galvanized steel sheet according to claim 9 , wherein, in the oxide layer forming step, an acidic solution coating weight on a steel sheet surface after contacting the acidic solution is 15 g/m 2 or less.

14. The method for producing the galvanized steel sheet according to claim 9 , wherein the galvanized steel sheet is a hot-dip galvannealed steel sheet.

15. The method for producing the galvanized steel sheet according to claim 9 , wherein the galvanized steel sheet is a hot-dip galvanized steel sheet.

16. The method for producing the galvanized steel sheet according to claim 9 , wherein the galvanized steel sheet is an electrogalvanized steel sheet.

17. The method for producing the galvanized steel sheet according to claim 9 , wherein a surface of the galvanized steel sheet is activated by bringing the surface of the galvanized steel sheet into contact with an alkaline aqueous solution before the oxide layer forming step.

18. The method for producing the galvanized steel sheet according to claim 9 , wherein the galvanized steel sheet is temper rolled before the oxide layer forming step.

Assignees

• Jfe Steel Corp

Inventors

• Hoshino Katsuya
• Taira Shoichiro
• Nagoshi Masayasu
• Hanada Kazutoshi

Classifications

• C23C28/3225

  with at least one zinc-based layer · CPC title

• C23C22/83

  Chemical after-treatment · CPC title

• B32B15/04

  comprising metal as the main or only constituent of a layer, {which is} next to another layer of {the same or of} a {different material (next to a bituminous or tarry layer B32B11/08; next to a water-setting substance layer B32B13/06; next to a glass layer B32B17/061; next to a cellulosic plastic layer B32B23/042)} · CPC title

• C23C2/405

  Plates of specific length · CPC title

• B32B15/18

  comprising iron or steel {(B32B15/011, B32B15/012 and B32B15/013 take precedence)} · CPC title