Low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plate and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-11339451-B2
Application number	US-201816624270-A
Country	US
Kind code	B2
Filing date	Jun 26, 2018
Priority date	Jun 30, 2017
Publication date	May 24, 2022
Grant date	May 24, 2022

Abstract

A low-cost and high-formability 1180 MPa grade cold-rolled annealed dual-phase steel plate and a manufacturing method thereof are provided. The dual-phase steel plate has the following chemical composition by mass percentages: C: 0.1%-0.125%, Si: 0.4%-0.8%, Mn: 2.6%-2.9%, Al: 0.01%-0.05%, Nb: 0.01%-0.03%, and Ti: 0.01%-0.03%, the remainder being Fe and unavoidable impurities. By reasonable design of alloy elements and manufacturing processes, the dual-phase steel plate of the invention achieves a strength of 1180 MPa grade at a low cost, obtains a fine and uniform martensite-ferrite dual-phase structure that ensures excellent elongation rate and cold bending performance, and has good formability. The dual-phase steel plate has a yield strength of more than 850 MPa, a tensile strength of more than 1180 MPa, an elongation rate of 8% or more, and a parameter (R/t), characterizing the 90-degree cold bending performance, of 2.5 or less.

First claim

The invention claimed is:

1. A 1180 MPa grade cold-rolled annealed dual-phase steel plate, consisting of following chemical composition by mass percentages:
C: 0.1%-0.125%,
Si: 0.4%-0.8%,
Mn: 2.6%-2.9%,
Al: 0.01%-0.05%,
Nb: 0.01%-0.03%, and
Ti: 0.01%-0.03%,
a remainder being Fe and unavoidable impurities,
wherein C, Mn and Si contents satisfy that 1.73×[C]×[Mn]+[Si]≥1, and Nb and Ti contents satisfy that [Nb]+[Ti]×3≥0.047.

2. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the C content is from 0.11% to 0.125%.

3. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the Si content is from 0.5% to 0.7%.

4. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the Mn content is from 2.7% to 2.85%.

5. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the Al content is from 0.015% to 0.045%.

6. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the Nb content is from 0.015% to 0.025%.

7. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the Ti content is from 0.015% to 0.025%.

8. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the dual-phase steel plate has a fine and uniform martensite-ferrite dual-phase structure, and
wherein the dual-phase steel plate contains at least 75% of martensite, and a rest is ferrite the martensite has a grain size of not more than 5 micrometers, and the ferrite has a grain size of not more than 5 micrometers.

9. The 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the dual-phase steel plate has a yield strength of more than 850 MPa, a tensile strength of more than 1180 MPa, an elongation rate of 8% or more, and a parameter (R/t), characterizing 90° cold bending performance, of 2.5 or less, wherein R is bend radius, and t is plate thickness in mm.

10. A method for manufacturing the 1180 MPa grade cold-rolled annealed dual-phase steel plate as claimed in claim 1 , wherein the method comprises:
1) smelting and casting into a slab having a chemical composition claimed in claim 1 ;
2) hot rolling including firstly, heating to 1100° C.-1230° C. and holding for 0.6 hours or more, and then hot rolling at a temperature of Ar3 or more, after rolling, rapidly cooling at a rate of 30° C./s-100° C./s coiling at a temperature of 400° C.-500° C., after coiling, slowly cooling to 370° C. or less at a cooling rate of not more than 0.3° C./s;
3) cold rolling that is controlled at a reduction rate of 50%-70%;
4) annealing at a soaking temperature of 790° C.-840° C., then cooling at a rate of v=3° C./s-20° C./s to a rapid cooling start temperature T, wherein the rapid cold start temperature satisfies T≥800-30×v, and then cooling to 200° C.-270° C. at a rate of 30° C./s-100° C./s;
5) tempering at a temperature of 200° C.-270° C. for 100 s-400 s; and
6) leveling to a degree of 0%-0.3%.

11. A 1180 MPa grade cold-rolled annealed dual-phase steel plate, comprising following chemical composition by mass percentages:
C: 0.1%-0.125%,
Si: 0.4%-0.8%,
Mn: 2.6%-2.9%,
Al: 0.01%-0.05%,
Nb: 0.01%-0.03%, and
Ti: 0.01%-0.03%,
a remainder being Fe and unavoidable impurities,
wherein C, Mn and Si contents satisfy that 1.73×[C]×[Mn]+[Si]≥1, and Nb and Ti contents satisfy that [Nb]+[Ti]×3≥0.047, and
wherein the steel plate does not contain Mo and does not contain Cr.

Assignees

• Baoshan Iron & Steel

Inventors

• Xue Peng
• Zhu Xiaodong
• Li Wei

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• Y02P10/20

  Recycling · CPC title

• C22C38/04 Primary

  containing manganese · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C21D2211/008

  Martensite · CPC title