Alloyed hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet production method

Patent metadata

Field	Value
Publication number	US-11408047-B2
Application number	US-201917040348-A
Country	US
Kind code	B2
Filing date	Mar 12, 2019
Priority date	Mar 28, 2018
Publication date	Aug 9, 2022
Grant date	Aug 9, 2022

Abstract

In one aspect of the present invention, a hot-dip galvannealed steel sheet includes a steel sheet and a hot-dip galvannealed layer on the surface of the steel sheet. The steel sheet has a predetermined composition and has an average oxygen concentration of 0.10 mass % or less in the region of 1 μm from the interface between the steel sheet and the hot-dip galvannealed layer toward the steel sheet. The metal microstructure of the steel sheet at a position of t/4 where t represents the sheet thickness of the hot-dip galvannealed steel sheet includes 50 to 85 area % of martensite, 15 to 50 area % of bainite, and 5 area % or less of ferrite.

First claim

The invention claimed is:

1. A hot-dip galvannealed steel sheet comprising:
a steel sheet; and
a hot-dip galvannealed layer on a surface of the steel sheet,
wherein the steel sheet comprises, in mass %,
C: 0.10% or more and 0.25% or less,
Si: more than 0% and 0.50% or less,
Mn: more than 2.0% and 3.5% or less,
P: more than 0% and 0.1% or less,
S: more than 0% and 0.05% or less,
Al: 0.01% or more and 0.10% or less,
Ti: more than 0% and 0.1% or less,
B: 0.0020% or more and 0.0050% or less,
N: more than 0% and 0.01% or less,
Cr: more than 0% and 0.5% or less, and
Mo: more than 0% and 0.5% or less,
wherein the steel sheet has an average oxygen concentration of 0.10 mass % or less in a region of 1 μm from an interface between the steel sheet and the hot-dip galvannealed layer toward the steel sheet, wherein the interface is a face where a mass concentration of Fe is the same as a mass concentration of Zn, and
wherein a metal microstructure of the steel sheet at a position of t/4, where t represents a sheet thickness of the hot-dip galvannealed steel sheet, comprises 50 to 85 area % of martensite, 15 to 50 area % of bainite, and 5 area % or less of ferrite.

2. A method for manufacturing the hot-dip galvannealed steel sheet of claim 1 , the method comprising:
soaking a steel having a composition of the steel sheet at 1100° C. to 1300° C., hot-rolling the steel at a finishing temperature of 850° C. to 950° C., and coiling the hot-rolled steel at 630° C. to 680° C., to provide a hot-rolled material;
pickling the hot-rolled material using 3 to 20 mass % hydrochloric acid under a condition of 60° C. to 90° C. for 35 to 200 seconds;
cold-rolling the hot-rolled material after pickling, to provide a cold-rolled material;
annealing the cold-rolled material by soaking the cold-rolled material at an Ac 3 point or higher and lower than 880° C. under a condition of a dew point of −25° C. or lower, to provide a soaked material;
cooling the soaked material to a cooling finishing temperature of 380° C. to 500° C. at 3.0° C./s or more, to provide a cooled material;
maintaining the cooled material at the cooling finishing temperature for 15 seconds or longer, to provide the steel sheet; and
subjecting the steel sheet to a plating process, to form the hot-dip galvannealed layer on the steel sheet.

Assignees

• Kobe Steel Ltd

Inventors

• Hoshika Tetsuji
• Ikeda Muneaki
• Nakaya Michiharu

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C23C2/40

  Plates; Strips · CPC title

• C23C2/06

  Zinc or cadmium or alloys based thereon · CPC title

• C21D6/008

  containing Si · CPC title