# US 2014/0193665 A1 · Galvannealed layer and steel sheet comprising the same, and method for producing the same

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- Number: US 2014/0193665 A1
- Document ID: US20140193665A1
- Status: Published application
- Kind: A1
- Application number: 14/235,155
- Filed: 2012-07-27
- Published: 2014-07-10
- Earliest claimed: 2011-07-29
- Assignees: Nippon Steel Corporation
- Applicants: Nippon Steel Corporation
- Inventors: Hiroyuki Kawata; Naoki Maruyama; Akinobu Murasato; Akinobu Minami; Takeshi Yasui
- Web page: https://patentgrep.com/patent/US20140193665A1

## CPC

- C23C 2/28: Thermal after-treatment, e.g. treatment in oil bath
- 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 8/0473: {Final recrystallisation annealing}
- C21D 8/0484: {Application of a separating or insulating coating}
- C22C 18/00: Alloys based on zinc
- 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
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C21D 8/041: {involving a particular fabrication or treatment of ingot or slab}
- C21D 2211/001: Austenite
- C21D 2211/002: Bainite
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- Y10T 428/12611: Oxide-containing component
- Y10T 428/12618: Plural oxides
- Y10T 428/12799: Next to Fe-base component [e.g., galvanized]
- 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)
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- 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)
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Provided are: a galvannealed steel sheet, reliably and sufficiently improved in the adhesiveness of a plated layer with a base steel sheet, as a galvannealed steel sheet, prepared by using a high-strength steel sheet as a base material; and a method for producing the galvannealed steel sheet. The galvannealed steel sheet wherein a galvannealed layer is formed on a base steel sheet including a high-strength steel having predetermined component composition; the average amount of Fe in the galvannealed layer is in a range of 8.0 to 12.0%; and the absolute value ΔFe of a difference between the amount of Fe in the vicinity of an interface with the base steel sheet (the amount of Fe in the vicinity of an internal side) and the amount of Fe in the vicinity of the external surface of the plated layer (the amount of Fe in the vicinity of an external side) in the plated layer is in a range of 0.0 to 3.0%. Further, in a method for producing the galvannealed steel sheet, intra-plated-layer diffusion treatment for flattening the concentration gradient of Fe in the plated layer is performed after finishing hot dip galvanizing and alloying treatment.

## Claims

### Claim 1

A galvannealed layer formed on a surface of a base steel sheet, wherein the average amount of Fe in the galvannealed layer is in a range of 8.0 to 12.0%; and the absolute value of a difference ΔFe between the amount of Fe at a position of ⅛ of the thickness of the galvannealed layer and the amount of Fe at a position of ⅞ of the thickness of the galvannealed layer in the galvannealed layer, the thickness being from an interface between the galvannealed layer and the base steel sheet to the external surface of the galvannealed layer, is in a range of 0.0 to 3.0%.

### Claim 2 (depends on 1)

A galvannealed steel sheet, wherein the galvannealed layer according to claim 1 is formed on a surface of a base steel sheet comprising, in mass %,
C: 0.050 to 0.300%,
Si: 0.10 to 2.50%,
Mn: 0.50 to 3.50%,
P: 0.001 to 0.030%,
S: 0.0001 to 0.0100%,
Al: 0.005 to 1.500%,
O: 0.0001 to 0.0100%,
N: 0.0001 to 0.0100%, and
the balance of Fe and unavoidable impurities.

### Claim 3 (depends on 2)

The galvannealed steel sheet according to claim 2, wherein the base steel sheet further comprises, in mass %, one or two or more selected from
Cr: 0.01 to 2.00%,
Ni: 0.01 to 2.00%,
Cu: 0.01 to 2.00%,
Ti: 0.005 to 0.150%,
Nb: 0.005 to 0.150%,
V: 0.005 to 0.150%,
Mo: 0.01 to 1.00%, and
B: 0.0001 to 0.0100%.

### Claim 4 (depends on 2, 3)

The galvannealed steel sheet according to any one of claim 2 and claim 3, wherein the base steel sheet further comprises 0.0001 to 0.5000% in total of one or two or more selected from Ca, Ce, Mg, Zr, Hf, and REM.

### Claim 5 (depends on 2, 4)

The galvannealed steel sheet according to any one of claim 2 to claim 4, wherein a coating comprising a P oxide and/or a complex oxide containing P is formed on a surface of the galvannealed layer.

### Claim 6

A method for producing a galvannealed layer, comprising:
a hot dip galvanizing step for subjecting a surface of a base steel sheet to hot dip galvanizing to obtain a hot dip galvanized steel sheet;
an alloying treatment step for heating a hot dip galvanized layer, formed in the hot dip galvanizing step, to a temperature in a range of 470 to 650° C. to form a galvannealed layer and to produce a galvannealed steel sheet; and
an intra-galvannealed-layer diffusion treatment step for, after the alloying treatment step, allowing the galvannealed steel sheet to stay at a temperature in a range of 250 to 450° C. and subjecting the galvannealed steel sheet to one or more times of bending-unbending working in the temperature range to diffuse Fe in the galvannealed layer.

### Claim 7 (depends on 6)

The method for producing a galvannealed layer according to claim 6, wherein the galvannealed steel sheet is obtained, in which, after the intra-galvannealed-layer diffusion treatment step, the average amount of Fe in the galvannealed layer is in a range of 8.0 to 12.0%; and the absolute value of a difference ΔFe between the amount of Fe at a position of ⅛ of the thickness of the galvannealed layer and the amount of Fe at a position of ⅞ of the thickness of the galvannealed layer in the galvannealed layer, the thickness being from an interface between the galvannealed layer and the base steel sheet to the external surface of the galvannealed layer, is in a range of 0.0 to 3.0%.

### Claim 8 (depends on 6, 7)

The method for producing a galvannealed layer according to any one of claim 6 and claim 7, wherein in the intra-galvannealed-layer diffusion treatment step, the bending working is performed so that a maximum tensile strain amount in a surface of the steel sheet ranges from 0.0007 to 0.0910.

### Claim 9 (depends on 6, 8)

The method for producing a galvannealed layer according to any one of claim 6 to claim 8, wherein a surface of the galvannealed layer is subjected to phosphate coating treatment for forming a coating comprising a P oxide and/or a complex oxide containing P after the intra-galvannealed-layer diffusion treatment step.

### Claim 10 (depends on 6, 9)

The method for producing a galvannealed layer according to any one of claim 6 to claim 9, wherein a base steel sheet comprising, in mass %,
C: 0.050 to 0.300%,
Si: 0.10 to 2.50%,
Mn: 0.50 to 3.50%,
P: 0.001 to 0.030%,
S: 0.0001 to 0.0100%,
Al: 0.005 to 1.500%,
O: 0.0001 to 0.0100%,
N: 0.0001 to 0.0100%, and
the balance of Fe and unavoidable impurities is used as the base steel sheet.

### Claim 11 (depends on 10)

The method for producing a galvannealed layer according to claim 10, wherein the steel sheet further comprising, in mass %, one or two or more selected from
Cr: 0.01 to 2.00%,
Ni: 0.01 to 2.00%,
Cu: 0.01 to 2.00%,
Ti: 0.005 to 0.150%,
Nb: 0.005 to 0.150%,
V: 0.005 to 0.150%,
Mo: 0.01 to 1.00%, and
B: 0.0001 to 0.0100%
is used as the base steel sheet.

### Claim 12 (depends on 10, 11)

The method for producing a galvannealed layer according to any one of claims 10 to 11, wherein the steel sheet further comprises, in mass %, 0.0001 to 0.5000% in total of one or two or more selected from Ca, Ce, Mg, Zr, Hf, and REM is used as the base steel sheet.