Title:
HOT-DIP GALVANNEALED STEEL SHEET MANUFACTURING METHOD
Document Type and Number:
WIPO Patent Application WO/2023/181390
Kind Code:
A1
Abstract:
The present invention provides a hot-dip galvannealed steel sheet that has a beautiful external appearance without defects such as bare spots, has excellent plating adhesion, and also has excellent hydrogen embrittlement resistance. A manufacturing method for this hot-dip galvannealed steel sheet involves: heating a steel sheet having a composition containing, in mass percentages, 0.10-2.00%, inclusive, of Si and 1.0-5.0%, inclusive, of Mn to at least 600°C in an oxidation atmosphere including 1000-30000 volumetric ppm, inclusive, of O2; holding the steel sheet after the oxidation step for at least 20 s in a reduction atmosphere having a hydrogen concentration that is greater than 8 vol% and at most 30 vol%, at 700°C or higher; holding the steel sheet for 20-300 s, inclusive, in an isothermal atmosphere having a hydrogen concentration of 0.2-8 vol%, inclusive, at 750°C or higher; cooling the steel sheet; immersing the steel sheet in a molten zinc bath to obtain a hot-dip galvanized steel sheet; performing an alloying process on the hot-dip galvanized steel sheet to obtain a hot-dip galvannealed steel sheet; and, after cooling the hot-dip galvannealed steel sheet to a cooling stop temperature that is at most a Ms point, holding the steel sheet for at least 30 s at a temperature that is at least the cooling stop temperature and is 100-450°C, inclusive, in a reheating atmosphere having a hydrogen concentration of at most 0.2 vol%.
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Inventors:
TERASHIMA SHOTARO (JP)
NAKAGAITO TATSUYA (JP)
YOSHITOMI HIROMI (JP)
HOSHINO KATSUYA (JP)
OKUMURA YUSUKE (JP)
NAKAGAITO TATSUYA (JP)
YOSHITOMI HIROMI (JP)
HOSHINO KATSUYA (JP)
OKUMURA YUSUKE (JP)
Application Number:
PCT/JP2022/014582
Publication Date:
September 28, 2023
Filing Date:
March 25, 2022
Export Citation:
Assignee:
JFE STEEL CORP (JP)
International Classes:
C23C2/06; C21D3/06; C21D9/46; C21D9/56; C23C2/02; C23C2/26; C23C2/28; C23C2/40
Domestic Patent References:
| WO2020170542A1 | 2020-08-27 | |||
| WO2021166350A1 | 2021-08-26 | |||
| WO2015087549A1 | 2015-06-18 | |||
| WO2019106894A1 | 2019-06-06 |
Foreign References:
| JP2013142198A | 2013-07-22 |
Attorney, Agent or Firm:
SUGIMURA Kenji (JP)
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