# US 11,299,793 B2 · Steel sheet having excellent resistance to liquid metal embrittlement cracks and method for manufacturing the same

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- Number: US 11,299,793 B2
- Document ID: US11299793B2
- Status: Granted
- Kind: B2
- Application number: 16/609,017
- Filed: 2018-06-22
- Published: 2020-05-07
- Granted: 2022-04-12
- Earliest claimed: 2017-06-30
- Assignees: Posco
- Applicants: Posco
- Inventors: Sea-Woong Lee; Kyoo-Young Lee; Joo-Hyun Ryu; Ki-Cheol Kang
- Web page: https://patentgrep.com/patent/US11299793B2

## CPC

- C21D 9/46: for sheet metals
- B32B 15/012: {one layer being formed of an iron alloy or steel, another layer being formed of aluminium or an aluminium alloy}
- 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 1/26: Methods of annealing
- C21D 6/002: {containing Cr (C21D6/004 takes precedence)}
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0263: {following hot rolling}
- C21D 8/0273: {Final recrystallisation annealing}
- 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 38/02: 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 38/38: with more than 1.5% by weight of manganese
- C23C 2/02: Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence)
- C23C 2/0224: {Two or more thermal pretreatments}
- C23C 2/024: {by cleaning or etching}
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/12: Aluminium or alloys based thereon
- C23C 2/40: Plates; Strips
- C23C 14/16: on metallic substrates or on substrates of boron or silicon
- C21D 2211/001: Austenite
- C21D 2211/002: Bainite
- C21D 2211/008: Martensite
- 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 steel sheet having excellent resistance to liquid metal embrittlement cracks and a method for manufacturing the same. The steel sheet includes, by weight %, 0.04% to 0.35% of C, 0.99% or less of Al+Si, 3.5% to 10% of Mn, 0.05% or less of P (excluding 0%), 0.02% or less of S (excluding 0%), and 0.02% or less of N (excluding 0%) with a remainder of Fe and other inevitable impurities, wherein the steel sheet comprises a microstructure comprising at least 10% of residual austenite, at least 60% of annealed martensite and 20% or less of alpha martensite and epsilon martensite, by volume fraction, and an average thickness of a Mn-depleted layer is at least 0.5 μm from a product surface.

## Claims

### Claim 1

A steel sheet having excellent resistance to liquid metal embrittlement cracks, the steel sheet comprising:
by weight %, 0.04% to 0.35% of C, 0.99% or less of Al+Si, 3.5% to 10% of Mn, 0.05% or less of P (excluding 0%), 0.02% or less of S (excluding 0%), and 0.02% or less of N (excluding 0%) with a remainder of Fe and other inevitable impurities;
a microstructure comprising: at least 10% by volume fraction of residual austenite, at least 60% by volume fraction of annealed martensite, and 20% or less by volume fraction of alpha martensite and epsilon martensite; and
a Mn-depleted layer having an average thickness of at least 0.5 μm from a surface of the steel sheet.

### Claim 2 (depends on 1)

The steel sheet of claim 1, further comprising: at least one selected from the group consisting of 0.15% or less of Ti, 0.5 or less of Nb, 0.5 or less of V and 0.5 or less of Mo.

### Claim 3 (depends on 1)

The steel sheet of claim 1, further comprising: at least one of 0.001% to 0.1% of Zr and 0.001% to 0.5% of W.

### Claim 4 (depends on 1)

The steel sheet of claim 1, further comprising: at least one selected from the group consisting of 1% or less of Ni, 1.5% or less of Cr and 0.5% or less of Cu.

### Claim 5 (depends on 1)

The steel sheet of claim 1, further comprising: at least one selected from the group consisting of 0.1% or less of Sb, 0.01% or less of Ca and 0.01% or less of B.

### Claim 6 (depends on 1)

The steel sheet of claim 1, wherein the steel sheet is one of a cold-rolled steel sheet, a hot-dip galvanized steel sheet, a hot-dip galvannealed steel sheet, an electrolytic galvanized steel sheet, a PVD galvanized steel sheet and a hot-dip aluminum-plated steel sheet.

### Claim 7

A method of manufacturing a steel sheet having excellent resistance to liquid metal embrittlement cracks, the method comprising:
reheating a steel slab comprising: 0.04% to 0.35% of C, 0.99% or less of Al+Si, 3.5% to 10% of Mn, 1.5% or less of Cr (excluding 0%), 0.05% or less of P (excluding 0%), 0.02% or less of S (excluding 0%), and 0.02% or less of N (excluding 0%) with a remainder of Fe and other inevitable impurities, by weight %, at a temperature of 1100° C. to 1300° C.;
finish-hot-rolling the reheated steel slab at a temperature of Ar3 to 1000° C. to obtain a hot-rolled steel sheet;
coiling the hot-rolled steel sheet at a temperature of 720° C. or less;
heat-treating the coiled hot-rolled steel sheet at a temperature in a range of Ac1 to Ac1+(Ac3−Ac1)/2 for at least 30 minutes;
pickling the heat-treated hot-rolled steel sheet for at least 5 seconds;
cold-rolling the pickled hot-rolled steel sheet to obtain a cold-rolled steel sheet; and
two-phase annealing the cold-rolled steel sheet a temperature in the range of 580° C. to 900° C. for 10 seconds to 5 minutes.

### Claim 8 (depends on 7)

The method of claim 7, wherein the steel slab further comprises: at least one selected from the group consisting of 0.15% or less of Ti, 0.5% or less of Nb, 0.5% or less of V and 0.5% or less of Mo.

### Claim 9 (depends on 7)

The method of claim 7, wherein the steel slab further comprises: at least one of 0.001% to 0.1% of Zr and 0.001% to 0.5% of W.

### Claim 10 (depends on 7)

The method of claim 7, wherein the steel slab further comprises: at least one selected from the group consisting of 1% or less of Ni, 1.5% or less of Cr and 0.5% or less of Cu.

### Claim 11 (depends on 7)

The method of claim 7, wherein the steel slab further comprises: at least one selected from the group consisting of 0.1% or less of Sb, 0.01% or less of Ca and 0.01% or less of B.

### Claim 12 (depends on 7)

The method of claim 7, further comprising: annealing the cold-rolled steel sheet at a temperature of at least Ac3 for at least 30 seconds and cooling the annealed cold-rolled steel sheet, before the two-phase annealing.

### Claim 13 (depends on 7)

The method of claim 7, further comprising: plating the two-phase-annealed cold-rolled steel sheet.

### Claim 14 (depends on 13)

The method of claim 13, wherein the plating is at least one of hot-dip galvanization, hot-dip galva-annealing, electrolytic galvanization, PVD galvanization and hot-dip aluminum plating.

### Claim 15 (depends on 14)

The method of claim 14, wherein the hot-dip galvanization is achieved by immersing the two-phase-annealed cold-rolled steel sheet in at least one of a Zn plating bath, a Zn—Al plating bath, an Al—Si plating bath, an Al—Si—Mg plating bath and a Zn—Mg—Al plating bath.

### Claim 16 (depends on 14)

The method of claim 14, wherein the PVD galvanization is achieved using an electromagnetic levitation physical vapor deposition (EML-PVD) method.