# US 2023/0407429 A1 · Plated steel sheet having excellent strength, formability and surface quality, and manufacturing method therefor

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- Number: US 2023/0407429 A1
- Document ID: US20230407429A1
- Status: Published application
- Kind: A1
- Application number: 18/036,876
- Filed: 2021-11-10
- Published: 2023-12-21
- Earliest claimed: 2020-11-18
- Assignees: Posco
- Applicants: Posco Co., Ltd
- Inventors: Yu-Mi HA; Jun-Sung YEOM
- Web page: https://patentgrep.com/patent/US20230407429A1

## CPC

- C21D 9/46: for sheet metals
- B32B 15/013: {one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium}
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/021: involving particular fabrication steps or treatments of ingots or slabs
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0242: {Flattening; Dressing; Flexing}
- C21D 8/0263: {following hot rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- C21D 8/0278: involving a particular surface treatment (C21D8/0294 takes precedence)
- C22C 18/00: Alloys based on zinc
- C22C 18/04: with aluminium as the next major constituent
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/004: {Very low carbon steels, i.e. having a carbon content of less than 0,01%}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/20: with copper
- C23C 2/022: {by heating}
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/28: Thermal after-treatment, e.g. treatment in oil bath
- C23C 2/40: Plates; Strips
- C21D 2211/005: Ferrite
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- 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 (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)

## Abstract

Provided is a plated steel sheet and a method for manufacturing the same, and more particularly, to a zinc-based plated steel sheet having high strength and high formability that may be suitably applied as a material for an automotive outer panel and a method for manufacturing the same.

## Claims

### Claim 1

A plated steel sheet comprising:
a base steel sheet; and
a plating layer formed on the base steel sheet,
wherein the base steel sheet contains, by wt %, 0.003 to 0.009% of C, 0.05% or less of Si, 0.4 to 1.0% of Mn, 0.04 to 0.09% of P, 0.01% or less of S, 0.005% or less of N, 0.1% or less of S.Al, 0.03 to 0.08% of Mo, 0.005 to 0.03% of Ti, 0.02 to 0.045% of Nb, 0.06 to 0.15% of Cu, 0.003% or less of B, and a balance of Fe and unavoidable impurities, and
the plated steel sheet satisfies the following Relational Expression 1:
1.6≤Mt/Ms≤6 [Relational Expression 1]
(in Relational Expression 1, Mt represents an average content wt % of Mo at a point spaced apart from a surface of the base steel sheet in a thickness direction of the base steel sheet by 0.1 μm, Ms represents an average content wt % of Mo at a ¼t point from the surface of the base steel sheet in the thickness direction of the base steel sheet, and t represents a total average thickness of the base steel sheet and is in a range of 0.8 to 1 mm).

### Claim 2 (depends on 1)

The plated steel sheet of claim 1, wherein a microstructure of the base steel sheet contains, by an area fraction, 99% or more of ferrite and a balance of pearlite.

### Claim 3 (depends on 2)

The plated steel sheet of claim 2, wherein an average grain size of the ferrite is 5 to 15 μm.

### Claim 4 (depends on 1)

The plated steel sheet of claim 1, wherein the plated steel sheet has a tensile strength of 390 MPa or more and an elongation of 28 to 43%.

### Claim 5 (depends on 4)

The plated steel sheet of claim 4, wherein the plated steel sheet has a yield strength of 205 MPa or more.

### Claim 6 (depends on 1)

The plated steel sheet of claim 1, wherein the plating layer contains, by wt %, 8 to 13% of Fe and a balance of Zn and unavoidable impurities.

### Claim 7 (depends on 1)

The plated steel sheet of claim 1, wherein the plated steel sheet satisfies the following Relational Expression 2:
[P]/[Mo]≤1.162 [Relational Expression 2]
(in Relational Expression 2, [P] represents an average content wt % of P in the base steel sheet, and [Mo] represents an average content wt % of Mo in the base steel sheet).

### Claim 8

A method for manufacturing a plated steel sheet, the method comprising:
performing continuous casting on steel containing, by wt %, 0.003 to 0.009% of C, 0.05% or less of Si, 0.4 to 1.0% of Mn, 0.04 to 0.09% of P, 0.01% or less of S, 0.005% or less of N, 0.1% or less of S.Al, 0.03 to 0.08% of Mo, 0.005 to 0.03% of Ti, 0.02 to 0.045% of Nb, 0.06 to 0.15% of Cu, 0.003% or less of B, and a balance of Fe and unavoidable impurities;
reheating a slab obtained by the continuous casting;
providing a hot-rolled steel sheet by hot rolling the reheated slab;
coiling the hot-rolled steel sheet;
providing a cold-rolled steel sheet by cold rolling the hot-rolled steel sheet;
annealing the cold-rolled steel sheet; and
hot-dip galvanizing the annealed cold-rolled steel sheet by immersing the annealed cold-rolled steel sheet in a zinc-based plating bath,
wherein the continuous casting satisfies the following Relational Expression 3:
1≤Vc≤5−[P]/[Mo] [Relational Expression 3]
(in Relational Expression 2, Vc represents an average casting velocity during the continuous casting and a unit thereof is m/min, [P] represents an average content wt % of P in the slab, and [Mo] represents an average content wt % of Mo in the slab).

### Claim 9 (depends on 8)

The method for manufacturing a plated steel sheet of claim 8, wherein a temperature for reheating the slab is 1,180 to 1,230° C.,
a temperature of the hot rolling is 880 to 970° C.,
a temperature for coiling the hot-rolled steel sheet is 600 to 640° C.,
a reduction ratio during the cold rolling is 70 to 83%, and
a temperature for annealing the cold-rolled steel sheet is 740 to 830° C.

### Claim 10 (depends on 8)

The method for manufacturing a plated steel sheet of claim 8, wherein in the continuous casting, cooling is performed with the amount of cooling water of 0.80 to 3.0 L/kg.

### Claim 11 (depends on 8)

The method for manufacturing a plated steel sheet of claim 8, further comprising performing skin pass rolling on the alloyed heat-treated steel sheet using a skin pass roll having a roughness Ra of 1.0 to 1.6 μm.

### Claim 12 (depends on 11)

The method for manufacturing a plated steel sheet of claim 11, wherein the skin pass rolling is performed at a reduction ratio of 0.6 to 1.2%.

### Claim 13 (depends on 8)

The method for manufacturing a plated steel sheet of claim 8, further comprising, after the hot-dip galvanizing, performing an alloying heat treatment at 500 to 560° C.