# US 2020/0399730 A1 · Cold rolled steel sheet and method for manufacturing the same

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- Number: US 2020/0399730 A1
- Document ID: US20200399730A1
- Status: Published application
- Kind: A1
- Application number: 16/975,227
- Filed: 2019-02-26
- Published: 2020-12-24
- Earliest claimed: 2018-02-28
- Assignees: Jfe Steel Corporation
- Applicants: JFE Steel Corporation
- Inventors: Lingling Yang; Tatsuya Nakagaito
- Web page: https://patentgrep.com/patent/US20200399730A1

## 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 6/002: {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 8/0273: {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 38/004: {Very low carbon steels, i.e. having a carbon content of less than 0,01%}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/008: {containing tin}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/08: containing nickel {(C22C38/105 takes precedence)}
- C22C 38/10: containing cobalt
- C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/28: with titanium or zirconium
- C22C 38/32: with boron
- C22C 38/38: with more than 1.5% by weight of manganese
- C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
- 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

A cold rolled steel sheet of the present invention has a specific chemical composition and a steel microstructure in which the average aspect ratio of ferrite crystal grains is 2.0 or less; an rave value that is the average value of values obtained by measuring the r-value represented by a first predetermined formula in three places apart with spacings of 200 mm in the sheet width direction is 1.20 or more, and |Δrave| that is the average value of values obtained by measuring, in three places apart with spacings of 200 mm in the sheet width direction, |Δr| that is the absolute value of Δr represented by a second predetermined formula is 0.40 or less and the difference between the largest value and the smallest value of |Δr| among the three places is 0.15 or less.

## Claims

### Claim 1

A cold rolled steel sheet comprising a chemical composition containing, in mass %,
C: 0.0003 to 0.010%,
Si: 0.01 to 1.0%,
Mn: 0.10 to 3.0%,
P: 0.005 to 0.15%,
S: 0.020% or less,
Al: 0.01 to 1.00%, and
N: 0.005% or less,
further containing any one or more of
Nb: 0.005 to 0.10%,
Ti: 0.01 to 0.10%, and
B: 0.0001 to 0.0030%, and a balance being iron and incidental impurities, and
having a steel microstructure in which an average aspect ratio of ferrite crystal grains is 2.0 or less,
wherein an rave value that is an average value of values obtained by measuring an r-value represented by Formula (1) below in three places apart with spacings of 200 mm in a sheet width direction is 1.20 or more, and
|Δrave| that is an average value of values obtained by measuring, in three places apart with spacings of 200 mm in the sheet width direction, |Δr| that is an absolute value of Δr represented by Formula (2) below is 0.40 or less and a difference between a largest value and a smallest value of |Δr| among the three places is 0.15 or less,
r-value=(r0+2r45+r90)/4 Formula (1):
Δr=(r0−2r45+r90)/2 Formula (2):
in Formula (1) and Formula (2) above, r0, r45, and r90 being Lankford values in directions of 0°, 45°, and 90°, respectively, based on a rolling direction of the steel sheet.

### Claim 2 (depends on 1)

The cold rolled steel sheet according to claim 1, wherein the chemical composition further contains any one or more of Cr, Cu, Ni, Sn, As, Sb, Ca, Mg, Pb, Co, Ta, W, REMs, Zn, Sr, Cs, Hf, and V at 1% or less in mass % in total.

### Claim 3 (depends on 1)

The cold rolled steel sheet according to claim 1, comprising a coating layer on a surface.

### Claim 4 (depends on 3)

The cold rolled steel sheet according to claim 3, wherein the coating layer is a hot-dip galvanizing layer or a galvannealing layer.

### Claim 5 (depends on 1)

A method for manufacturing a cold rolled steel sheet, the method comprising: a hot rolling step of hot rolling a steel raw material having the chemical composition according to claim 1 and performing coiling under a condition where a difference in coiling temperature in a sheet width direction is 40° C. or less;
a cold rolling step of cold rolling a hot rolled steel sheet obtained by the hot rolling step at a cold rolling reduction rate of 30 to 75%; and
an annealing step of heating a cold rolled steel sheet obtained by the cold rolling step at an average heating rate of 35° C./s or more through a range of 350 to 650° C. in a continuous annealing facility including a pre-heating section, a heating zone, a soaking section, and a cooling zone and performing soaking at a soaking temperature of 700 to 900° C. and for a soaking time of 1 to 200 seconds, and performing, in the soaking, reverse bending four times or more in total with a roll having a radius of 100 mm or more.

### Claim 6 (depends on 5)

The method for manufacturing a cold rolled steel sheet according to claim 5, comprising, after the annealing step, a coating step of performing coating treatment.

### Claim 7 (depends on 6)

The method for manufacturing a cold rolled steel sheet according to claim 6, wherein the coating treatment is a coating treatment that forms a hot-dip galvanizing layer or a coating treatment that forms a galvannealing layer.

### Claim 8 (depends on 2)

The cold rolled steel sheet according to claim 2, comprising a coating layer on a surface.

### Claim 9 (depends on 8)

The cold rolled steel sheet according to claim 8, wherein the coating layer is a hot-dip galvanizing layer or a galvannealing layer.

### Claim 10 (depends on 2)

A method for manufacturing a cold rolled steel sheet, the method comprising: a hot rolling step of hot rolling a steel raw material having the chemical composition according to claim 2 and performing coiling under a condition where a difference in coiling temperature in a sheet width direction is 40° C. or less;
a cold rolling step of cold rolling a hot rolled steel sheet obtained by the hot rolling step at a cold rolling reduction rate of 30 to 75%; and
an annealing step of heating a cold rolled steel sheet obtained by the cold rolling step at an average heating rate of 35° C./s or more through a range of 350 to 650° C. in a continuous annealing facility including a pre-heating section, a heating zone, a soaking section, and a cooling zone and performing soaking at a soaking temperature of 700 to 900° C. and for a soaking time of 1 to 200 seconds, and performing, in the soaking, reverse bending four times or more in total with a roll having a radius of 100 mm or more.

### Claim 11 (depends on 10)

The method for manufacturing a cold rolled steel sheet according to claim 10, comprising, after the annealing step, a coating step of performing coating treatment.

### Claim 12 (depends on 11)

The method for manufacturing a cold rolled steel sheet according to claim 11, wherein the coating treatment is a coating treatment that forms a hot-dip galvanizing layer or a coating treatment that forms a galvannealing layer.