# US 2017/0283902 A1 · Hot dip galvanized and galvannealed steel sheet having excellent elongation properties

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- Number: US 2017/0283902 A1
- Document ID: US20170283902A1
- Status: Published application
- Kind: A1
- Application number: 15/622,794
- Filed: 2017-06-14
- Published: 2017-10-05
- Earliest claimed: 2014-12-24
- Assignees: Posco
- Applicants: Posco
- Inventors: Sang Ho HAN; Seong Ho HAN
- Web page: https://patentgrep.com/patent/US20170283902A1

## 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}
- B32B 15/017: {one layer being formed of aluminium or an aluminium alloy, another layer being formed of an alloy based on a non ferrous metal other than aluminium}
- B32B 15/04: comprising metal as the main or only constituent of a layer, {which is} next to another layer of {the same or of} a {different material (next to a bituminous or tarry layer B32B11/08; next to a water-setting substance layer B32B13/06; next to a glass layer B32B17/061; next to a cellulosic plastic layer B32B23/042)}
- B32B 15/043: {of metal (B32B15/01 takes precedence)}
- B32B 15/18: comprising iron or steel {(B32B15/011, B32B15/012 and B32B15/013 take precedence)}
- 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 8/0278: involving a particular surface treatment (C21D8/0294 takes precedence)
- C21D 8/0426: {Hot rolling}
- C21D 8/0436: {Cold rolling}
- C21D 8/0473: {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 38/18: containing chromium
- C22C 38/22: with molybdenum or tungsten
- C22C 38/32: with boron
- 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 2/04: characterised by the coating material
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/12: Aluminium or alloys based thereon
- C23C 2/285: {for remelting the coating}
- C23C 2/29: {Cooling or quenching}
- C23C 2/40: Plates; Strips
- C23C 28/021: {including at least one metal alloy layer}
- C23C 28/023: {only coatings of metal elements only}
- C23C 30/00: Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process (C23C26/00, C23C28/00 take precedence)
- C23C 30/005: {on hard metal substrates}
- Y10T 428/12757: Fe
- Y10T 428/12792: Zn-base component
- Y10T 428/12972: Containing 0.01-1.7% carbon [i.e., steel]
- 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)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

There is provided a hot-dip galvanized steel sheet and a hot-dip galvannealed steel sheet, which have excellent elongation properties, and methods for manufacturing the hot-dip galvanized steel sheet and the hot-dip galvannealed steel sheet. The present disclosure relates to a hot-dip galvanized steel sheet in which a hot-dip galvanized layer is formed on a surface of abase steel sheet, the hot-dip galvanized steel sheet having excellent elongation properties and being characterized by the composition and the microstructure thereof.

## Claims

### Claim 1 (depends on 1)

A method for manufacturing a hot-dip galvanized steel sheet having excellent elongation properties, the method comprising:
preparing a steel slab having compositional components of claim 1, and thereafter reheating the steel slab;
performing finish hot-rolling on the reheated steel slab in a temperature range of Ar3+50° C.-950° C., and thereafter coiling the finish hot-rolled steel sheet at 450-700° C.;
performing cold-rolling on the coiled hot-rolled steel sheet with a reduction ratio of 40-80%, and thereafter performing continuous annealing on the cold-rolled steel sheet in a temperature range of 760-850° C.;
performing a first cooling on the continuous annealed steel sheet to a temperature range of 630-670° C. at an average cooling rate of 2-8° C./s, and thereafter performing a second cooling on the first cooled steel sheet to a temperature range of Ms+20° C. to Ms+50° C. at an average cooling rate of 3-10° C./s; and
performing hot-dip galvanizing on the second cooled steel sheet in a temperature range of 440-480° C., and thereafter cooling the hot-dip galvanized steel sheet to a temperature of Ms−100° C. or lower at an average cooling rate of 4° C./s or higher.

### Claim 2 (depends on 1)

The method of claim 1, wherein a base steel sheet of the hot-dip galvanized steel sheet,
has a microstructure including 90% or more of ferrite, and a remainder of martensite and 3% or less of bainite, as defined by Equation 1;
contains a percentage of martensite (M %) having an average particle diameter of 5 μm or less occupying space in ferrite grain boundaries (including grain boundary triple points) of 90% or higher, as defined by Equation 2; and
at ¼t based on the thickness (t) of the sheet, the ratio of a C concentration (a) in the ferrite phase to a C concentration (b) in the martensite phase, i.e., (a)/(b), is 0.7 or less, and the ratio of an Mn concentration (c) in the ferrite phase to an Mn concentration (d) in the martensite phase, i.e., (c)/(d), is 0.8 or less,
B(%)={BA/(MA+BA)}×100 [Equation 1]
where BA is the area occupied by bainite, and MA is the area occupied by martensite,
M (%)={Mgb/(Mgb+Min)}×100 [Equation 2]
where Mgb is the amount of martensite in ferrite grain boundaries, and Min is the amount of martensite within ferrite grains, the martensite having an average particle diameter of 5 μm or less.

### Claim 3 (depends on 1)

The method of claim 1, wherein, in a base steel sheet of the hot-dip galvanized steel sheet, the ferrite phase has an average grain size of 4 μm or greater, and the area occupied by the ferrite phase having an average grain size of 7 μm or greater in the entire ferrite phase is 10% or higher.