700Mpa-level high-strength hot rolling Q and P steel and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-10023928-B2
Application number	US-201414769647-A
Country	US
Kind code	B2
Filing date	Mar 13, 2014
Priority date	Apr 9, 2013
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

A 700 Mpa-level high-strength hot rolling Q&P steel and the method of manufacturing the same, which steel has the chemical compositions in weight percentage as follows: C: 0.15%˜0.40%; Si: 1.0%˜2.0%; Mn: 1.5%˜3.0%; P: less than or equal to 0.015%; S: less than or equal to 0.005%; Al: 0.3%˜1.0%; N: less than or equal to 0.006%; Ti: 0.005%˜0.015%, the remainders being Fe; it having a yield strength of more than or equal to 700 Mpa, a tensile strength of more than or equal to 1300 Mpa and an elongation rate of more than 10%. Through reasonable design on the compositions and on the basis of the compositions of common C—Mn steel, the present invention improves the content of Si to restrict the precipitation of cementite, performs the micro-Ti treatment to refine the austenite grains, and improves the content of Al to quicken the austenite transformation dynamics during the air cooling process; at the same time, combines the hot rolling process with the staged cooling process to obtain the structures of proeutectoid ferrite plus martensite plus retained austenite and reduces the cost of alloy elements substantially.

First claim

What is claimed is:

1. A 700 MPa-level high-strength hot rolling quenching-partitioning steel, consisting of a chemical composition in weight percentage as follows: C: 0.15%˜0.40%; Si: 1.0%˜2.0%; Mn: 1.5%˜3.0%; P: less than or equal to 0.015%; S: less than or equal to 0.005%; Al: 0.3%˜1.0%; N: less than or equal to 0.006%; Ti: 0.005%˜0.015%, the balance being Fe and other unavoidable impurities; wherein the hot rolling quenching-partitioning steel has a yield strength of more than or equal to 700 Mpa, a tensile strength of more than or equal to 1300 Mpa and an elongation rate of more than 10%; and wherein the structure of the hot rolling quenching-partitioning steel is of proeutectoid ferrite plus martensite plus retained austenite, and the volume fraction of the proeutectoid ferrite is 10˜20%, while the volume fraction of the retained austenite is more than 5% and less than 10%, wherein the ratio between the content of Ti to the content of N is less than 3.42.

2. The 700 MPa-level high-strength hot rolling quenching-partitioning steel according to claim 1 , wherein the hot rolling quenching-partitioning steel comprises the chemical compositions in weight percentage: Si: 1.3˜1.7 wt %; Mn: 1.8˜2.5 wt %; N: less than or equal to 0.004 wt %; Ti: 0.0080.012 wt %; 0: less than or equal to 30 ppm.

3. A method of manufacturing the 700 MPa-level high-strength hot rolling quenching-partitioning steel according to claim 2 , comprising specifically the following stages:
1) smelting, secondary refining, and casting:
smelting in a converter or electric furnace as the following compositions, secondary refining in a vacuum furnace, and casting to form a casting blank or casting ingot, wherein the chemical compositions in weight percentage are: C: 0.15%˜0.40%, Si: 1.0%˜2.0%, Mn: 1.5%˜3.0%, P: less than or equal to 0.015%, S: less than or equal to 0.005%, Al: 0.3%˜1.0%, N: less than or equal to 0.006%, Ti: 0.005%˜0.015%, the balance being Fe and other unavoidable impurities;
2) heating, and hot rolling:
heating the casted blank or casted ingot obtained by the stage 1) up to 1100˜1200° C., and preserving heat for 1˜2 h; with the bloom rolling temperature of 1000˜1100° C., performing the multi-pass rolling and the accumulating deforming amount being more than or equal to 50%; subsequently, when the intermediate billet temperature falls to 900˜950° C., performing 3˜5 passes of rolling and the accumulating deforming amount being more than or equal to 70%;
3) staged cooling:
the rolled piece at the temperature between 800˜900° C. after hot rolling being rapidly water cooled to 500˜600° C. in a cooling speed of more than 50° C./s, then air cooled for 5˜10 s, and subsequently cooled to a temperature between 100∫300° C. (i.e. between Ms-Mf) in a cooling speed of more than 50° C./s, to obtain the structures of proeutectoid ferrite plus martensite plus retained austenite, finally cooled slowly to the room temperature after reeling, thereby obtaining the 700 MPa-level high-strength hot rolling quenching-partitioning steel.

4. A method of manufacturing the 700 MPa-level high-strength hot rolling quenching-partitioning steel according to claim 1 , comprising specifically the following stages:
1) smelting, secondary refining, and casting:
smelting in a converter or electric furnace as the following compositions, secondary refining in a vacuum furnace, and casting to form a casting blank or casting ingot, wherein the chemical compositions in weight percentage are: C: 0.15%˜0.40%, Si: 1.0%˜2.0%, Mn: 1.5%˜3.0%, P: less than or equal to 0.015%, S: less than or equal to 0.005%, Al: 0.3%-1.0%, N: less than or equal to 0.006%, Ti: 0.005%˜0.015%, the balance being Fe and other unavoidable impurities;
2) heating, and hot rolling:
heating the casted blank or casted ingot obtained by the stage 1) up to 1100˜1200° C., and preserving heat for 1˜2 h; with the bloom rolling temperature of 1000˜1100° C., performing the multi-pass rolling and the accumulating deforming amount being more than or equal to 50%; subsequently, when the intermediate billet temperature falls to 900˜950° C., performing 3˜5 passes of rolling and the accumulating deforming amount being more than or equal to 70%;
3) staged cooling:
the rolled piece at the temperature between 800˜900° C. after hot rolling being rapidly water cooled to 500˜600° C. in a cooling speed of more than 50° C./s, then air cooled for 5˜10 s, and subsequently cooled to a temperature between 100∫300° C. (i.e. between Ms-Mf) in a cooling speed of more than 50° C./s, to obtain the structures of proeutectoid ferrite plus martensite plus retained austenite, finally cooled slowly to the room temperature after reeling, thereby obtaining the 700 MPa-level high-strength hot rolling quenching-partitioning steel.

5. The method of manufacturing the 700 MPa-level high-strength hot rolling quenching-partitioning steel according to claim 4 , wherein the multi-pass rolling in the stage 2) is 5˜7 passes of rolling; the speed of slow cooling after reeling in the stage 3) is 8˜12° C./h.

Assignees

• Baoshan Iron & Steel

Inventors

• Wang Huanrong
• Li Zigang
• Wang Wei
• Zhang Jiansu
• Li Jianye

Classifications

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C21D6/005

  containing Mn · CPC title

• C21D1/84 Primary

  Controlled slow cooling (cooling-beds for metal rolling B21B43/00) · CPC title

• C21D2211/008

  Martensite · CPC title

• C21D8/0263

  following hot rolling · CPC title