Low-yield-ratio ultra-high-strength hot-rolled QandP steel and production method therefor

Patent metadata

Field	Value
Publication number	US-11180822-B2
Application number	US-201515536787-A
Country	US
Kind code	B2
Filing date	Nov 24, 2015
Priority date	Dec 19, 2014
Publication date	Nov 23, 2021
Grant date	Nov 23, 2021

Abstract

Disclosed is provided a low yield ratio and superhigh-strength hot-rolled Q&P steel and a method for manufacturing the same, having the following chemical composition in weight percentage: C: 0.2-0.3%, Si: 1.0-2.0%, Mn: 1.5-2.5%, P: ≤0.015%, S: ≤0.005%, Al: 0.5-1.0%, N: ≤0.006%, Nb: 0.02-0.06%, Ti: ≤0.03%, O: ≤0.003%, and the balance being Fe and inevitable impurities. The manufacture method comprises a stepped cooling process to finally obtain the steel with a three-phase structure containing a certain volume fraction of proeutectoid ferrite; martensite; and residual austenite, and having an excellent comprehensive performance with a yield strength of ≥600 MPa, a tensile strength of ≥1300 MPa, a good elongation, and a low yield ratio. The obtained Q&P steel also shows an excellent match of high plasticity suitable for easy deformabilities and wear-resistances.

First claim

The invention claimed is:

1. A low yield ratio and superhigh-strength hot-rolled Q&P steel, having the following chemical composition in weight percentage:
C: 0.2-0.3%, Si: 1.3-2.0%, Mn: 1.5-2.5%, P: ≤0.015%, S: ≤0.005%, Al: 0.75-1.0%, N: ≤0.006%, Nb: 0.02-0.06%, Ti: ≤0.03%, O: ≤0.003%, and the balance being Fe and inevitable impurities, and Ti/N≤3.42,
wherein said Q&P steel has a yield strength of 600 MPa, a tensile strength of ≥1300 MPa, and a yield ratio of ≤0.5, and
wherein the microstructure of said Q&P steel is a three-phase structure consisting of 10-25% (v/v) of proeutectoid ferrite, 65-85% (v/v) of martensite, and 5-10% (v/v) of residual austenite.

2. The low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 1 , characterized in that said chemical composition, the content of Si is in the range of 1.3-1.7%.

3. The low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 1 , characterized in that the content of Mn is in the range of 1.8-2.2% in weight percentage.

4. The low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 1 , characterized in that the content of Al is in the range of 0.8-1.0% in weight percentage.

5. The low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 1 , characterized in that the content of N is in the range of ≤0.004% in weight percentage.

6. The low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 1 , characterized in that said chemical composition, the content of Nb is in the range of 0.03-0.05%.

7. A method for manufacturing the low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 1 , characterized by comprising the following steps:
1) smelting, secondary refining, and casting
smelting by using a rotary furnace or electric furnace, secondary refining by using a vacuum furnace, and casting to form a cast slab or cast ingot, according to the following chemical composition in weight percentage: C: 0.2-0.3%, Si: 1.3-2.0%, Mn: 1.5-2.5%, P: ≤0.015%, S: ≤0.005%, Al: 0.75-1.0%, N: ≤0.006%, Nb: 0.02-0.06%, Ti: ≤0.03%, O: ≤0.003%, and the balance being Fe and inevitable impurities, with Ti/N≤3.42;
2) heating and hot rolling
heating the cast slab or cast ingot to 1100-1200° C. and holding for 1-2 h, with a rolling starting temperature of 1000-1100° C. and an accumulative deformation amount of ≥50% after multi-pass large reduction at a non-recrystallization temperature T nr or higher to obtain an intermediate slab containing fine equiaxed austenite grains; and then rolling for 3-5 passes with an accumulative deformation amount of 70% after the temperature of the intermediate slab reaches a temperature in the range of T nr or less to 800° C. to obtain a hot-rolled piece; wherein the non-recrystallization temperature T nr is determined according to the following formula, in which various element symbols respectively represent the corresponding contents in weight percentage of the elements;
T nr =887+464C+(6445Nb−644Nb 1/2 )+(732V−230V 1/2 )+890Ti+363Al−357Si; and

3) stepped cooling
rapidly water-cooling the hot-rolled piece from a temperature above a starting temperature of ferrite precipitation to 600-700° C. at a cooling rate of >30° C./s, air-cooling for 5-10 s, and continuing the cooling to a temperature between 150-300° C. at a cooling rate of >30° C./s, then coiling and slowly cooling to room temperature to obtain said low yield ratio and superhigh-strength hot-rolled Q&P steel.

8. The method for manufacturing the low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 7 , characterized in that the low yield ratio and superhigh-strength hot-rolled Q&P steel obtained by the manufacturing method has an elongation of ≥10%.

9. The low yield ratio and superhigh-strength hot-rolled Q&P steel according to claim 1 , wherein said Q&P steel has an elongation of ≥10%.

Assignees

• Baoshan Iron & Steel

Inventors

• Wang Huanrong
• Yang Ana
• Wang Wei

Classifications

• C21D8/02

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

• Y02P10/20

  Recycling · CPC title

• C22C38/001

  containing N · CPC title

• C21D2211/005

  Ferrite · CPC title

• C22C38/14 Primary

  containing titanium or zirconium · CPC title