High-strength hot-dip galvanized steel sheet having excellent surface quality and spot weldability, and manufacturing method therefor

Patent metadata

Field	Value
Publication number	US-12559814-B2
Application number	US-202118267364-A
Country	US
Kind code	B2
Filing date	Dec 7, 2021
Priority date	Dec 21, 2020
Publication date	Feb 24, 2026
Grant date	Feb 24, 2026

Abstract

According to one aspect of the present invention, a high-strength hot-dip galvanized steel sheet having an excellent surface quality and spot weldability, and a manufacturing method therefor may be provided.

First claim

The invention claimed is:

1 . A galvanized steel sheet, comprising:
a base steel sheet; and a zinc-based plating layer provided on a surface of the base steel sheet, wherein the base steel sheet includes: a first surface layer region that is a region corresponding to a depth of 25 μm in a thickness direction of the base steel sheet from an interface between the base steel sheet and the zinc-based plating layer; and a second surface layer region that is adjacent to the first surface layer region and corresponds to a depth of 25 μm to 50 μm in the thickness direction of the base steel sheet, and a fraction of ferrite contained in the first surface layer region is 55 area % or more, and an average grain size of ferrite contained in the first surface layer region is 2 to 10 μm, and a fraction of ferrite contained in the second surface layer region is 30 area % or more, and an average grain size of ferrite contained in the second surface layer region is 1.35 to 7 μm.

2 . The galvanized steel sheet of claim 1 , wherein a ratio of an average hardness of the first surface layer region to an average hardness of a central portion of the base steel sheet is 90% or less, and a ratio of an average hardness of the second surface layer region to the average hardness of the central portion of the base steel sheet is 95% or less.

3 . The galvanized steel sheet of claim 1 , wherein a plating adhesion amount of the zinc-based plating layer is 30 to 70 g/m 2 .

4 . The galvanized steel sheet of claim 1 , wherein the base steel sheet contains a composition containing, by wt %, C: 0.05 to 1.5%, Si: 2.5% or less, Mn: 1.5 to 20.0%, S—Al (acid-soluble aluminum): 3.0% or less, Cr: 2.5% or less, Mo: 1.0% or less, B: 0.005% or less, Nb: 0.2% or less, Ti: 0.2% or less, Sb+Sn+Bi: 0.1% or less, N: 0.01% or less, and a balance of Fe and unavoidable impurities.

5 . The galvanized steel sheet of claim 4 , wherein a tensile strength of the galvanized steel sheet is 900 MPa or more.

6 . The galvanized steel sheet of claim 4 , wherein a surface layer portion of the base steel sheet contains oxide containing at least one of Si, Mn, Al, and Fe.

7 . The galvanized steel sheet of claim 1 , wherein a thickness of the base steel sheet is 1.0 to 2.0 mm.

8 . A method for manufacturing a galvanized steel sheet, comprising:
reheating a steel slab to a temperature range of 950 to 1300° C.; providing a hot-rolled steel sheet by hot rolling the reheated slab at a finish rolling start temperature of 900 to 1150° C. and a finish rolling end temperature of 850 to 1050° C.; coiling the hot-rolled steel sheet in a temperature range of 590 to 750° C.; heating the hot-rolled steel sheet in a heating zone at a heating rate of 1.3 to 4.3° C./s; annealing the hot-rolled steel sheet in a soaking zone having a dew point temperature of −10 to +30° C., an atmosphere gas of N 2 -5 to 10% H 2 , and a temperature range of 650 to 900° C.; slowly cooling the annealed hot-rolled steel sheet in a slow cooling zone in a temperature range of 550 to 700° C.; quenching the slowly cooled hot-rolled steel sheet in a quenching zone in a temperature range of 270 to 550° C.; forming a zinc-based plating layer by reheating the quenched hot-rolled steel sheet and then immersing the reheated quenched hot-rolled steel sheet in a zinc-based plating bath at a lead in temperature of 420 to 550° C.; and optionally alloying the steel sheet, on which the zinc-based plating layer is formed, by heating the steel sheet to a temperature range of 480 to 560° C.

9 . The method of claim 8 , wherein a threading speed is 40 to 130 mpm during the annealing.

10 . The method of claim 8 , wherein the steel slab contains a composition containing, by wt %, C: 0.05 to 0.30%, Si: 2.5% or less, Mn: 1.5 to 10.0%, S-AI (acid-soluble aluminum): 1.0% or less, Cr: 2.0% or less, Mo: 0.2% or less, B: 0.005% or less, Nb: 0.1% or less, Ti: 0.1% or less, Sb+Sn+Bi: 0.05% or less, N: 0.01% or less, and a balance of Fe and unavoidable impurities.

Assignees

• Posco Co Ltd

Inventors

• Kang Ki-Cheol
• Kang Dae-Young
• Kim Nam-A
• Kim Myung-Soo

Classifications

• C21D8/02

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

• C23C2/40

  Plates; Strips · CPC title

• C23C2/06

  Zinc or cadmium or alloys based thereon · CPC title

• C22C38/60

  containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur · CPC title

• C22C38/38

  with more than 1.5% by weight of manganese · CPC title