# US 12,215,397 B2 · High-yield-ratio cold-rolled dual-phase steel and manufacturing method therefor

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- Number: US 12,215,397 B2
- Document ID: US12215397B2
- Status: Granted
- Kind: B2
- Application number: 17/295,942
- Filed: 2019-11-22
- Published: 2022-01-13
- Granted: 2025-02-04
- Earliest claimed: 2018-11-23
- Assignees: Baoshan Iron & Steel Co., Ltd.
- Applicants: Baoshan Iron & Steel Co., Ltd.
- Inventors: Wei Li; Xiaodong Zhu; Peng Xue
- Web page: https://patentgrep.com/patent/US12215397B2

## CPC

- C21D 1/19: by interrupted quenching
- C21D 8/0263: {following hot rolling}
- C21D 1/26: Methods of annealing
- C21D 6/00: Heat treatment of ferrous alloys
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C21D 6/02: Hardening by precipitation
- C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence)
- C21D 8/0226: {Hot rolling}
- C21D 8/0236: {Cold rolling}
- C21D 8/0247: characterised by the heat treatment
- C21D 9/46: for sheet metals
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- 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
- C21D 2211/004: Dispersions; Precipitations
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- Y02P 10/20: Recycling
- 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)
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

Disclosed is a high-yield-ratio cold-rolled dual-phase steel, having the following chemical elements in percentage by mass: 0.05%-0.08% of C, 0.9%-1.2% of Mn, 0.1%-0.6% of Si, 0.030%-0.060% of Nb, 0.030%-0.060% of Ti, 0.015%-0.045% of Al, and the balance being Fe and other inevitable impurities. A manufacturing method for the high-yield-ratio cold-rolled dual-phase steel, comprising: (1) smelting and casting; (2) hot rolling, wherein a casting blank is controlled and soaked at a temperature of 1200° C.-1250° C.; rolled with the finish rolling temperature being 840° C.-930° C.; cooled at a speed of 20° C./s-70° C./s, and then wound at the winding temperature being 570° C.-630° C.; (3) cold rolling; (4) annealing at the soaking temperature being 750° C.-790° C. for 40 s-200 s, cooling at a speed of 30° C./s-80° C./s, the start temperature of cooling is 650° C. to 730° C., the aging temperature is 200° C. to 260° C., and the overaging time is 100 s to 400 s; and (5) leveling.

## Claims

### Claim 1

A cold-rolled dual-phase steel having a high yield ratio, comprising the following chemical elements in mass percentages:
C: 0.05-0.08%, Mn: 0.9-1.2%, Si: 0.1-0.6%, Nb: 0.030-0.060%, Ti: 0.030-0.060%, Al: 0.015-0.045%, and a balance of Fe and other unavoidable impurities,
wherein the steel has a microstructure which is a complex phase structure of martensite+ferrite+[NbxTiy(C,N)z] carbonitride,
wherein the martensite has a phase proportion of 20-30%, and the martensite is in the shape of long strip-islands,
wherein the [NbxTiy(C,N)z] carbonitride has an irregular spherical shape and is uniformly distributed in ferrite grains, and the [NbxTiy(C,N)z] carbonitride has a phase proportion of 5-10%, and
wherein the steel has a yield ratio of greater than 0.8.

### Claim 2 (depends on 1)

The cold-rolled dual-phase steel having a high yield ratio according to claim 1, wherein the [NbxTiy(C,N)z] carbonitride has a size of less than 2 μm.

### Claim 3 (depends on 1)

The cold-rolled dual-phase steel having a high yield ratio according to claim 1, wherein among the other unavoidable impurities, mass percentages of the P, S and N elements meet at least one of the following: P≤0.015%; S≤0.005%; N≤0.005%.

### Claim 4 (depends on 1)

The cold-rolled dual-phase steel having a high yield ratio according to claim 1, wherein the steel has a yield strength of 550-660 MPa, a tensile strength of ≥660 MPa, and an elongation at break of ≥15%.

### Claim 5 (depends on 1)

A manufacturing method for the cold-rolled dual-phase steel having a high yield ratio according to claim 1, wherein the method comprises the following steps:
(1) Smelting and casting;
(2) controlling a cast blank for soaking at a temperature of 1200-1250° C.; rolling with a finish rolling temperature being controlled at 840-930° C.; cooling at a rate of 20-70° C./s after the rolling; then coiling with a coiling temperature being controlled at 570-630° C.;
(3) Cold rolling;
(4) annealing at an annealing soaking temperature of 750-790° C. for an annealing time of 40-200 s; and then cooling at a rate of 30-80° C./s, wherein the cooling begins at a temperature of 650-730° C., an aging temperature is 200-260° C., and an over-aging time is 100-400 s; and
(5) Temper rolling.

### Claim 6 (depends on 5)

The manufacturing method according to claim 5, wherein in Step (3), a cold rolling reduction rate is controlled to be 50-70%; and/or in Step (5), a temper rolling reduction rate is controlled to be 0.3-1.0%.

### Claim 7 (depends on 5)

The manufacturing method according to claim 5, wherein in Step (2), a soaking time is 5-6 hours; the steel is cooled to 570-630° C. after the rolling; and then the coiling is performed.

### Claim 8 (depends on 5)

The manufacturing method according to claim 5, wherein the steel has a microstructure which is a complex phase structure of martensite+ferrite+[NbxTiy(C,N)z] carbonitride.

### Claim 9 (depends on 5)

The manufacturing method according to claim 5, wherein the [NbxTiy(C,N)z] carbonitride has a size of less than 2 μm.

### Claim 10 (depends on 5)

The manufacturing method according to claim 5, wherein among the other unavoidable impurities of the cold-rolled dual-phase steel, mass percentages of the P, S and N elements meet at least one of the following: P≤0.015%; S≤0.005%; N≤0.005%.

### Claim 11 (depends on 5)

The manufacturing method according to claim 5, wherein the steel has a yield strength of 550-660 MPa, a tensile strength of ≥660 MPa, and an elongation at break of ≥15%.