Cold rolled and heat treated steel sheet, method of production thereof and use of such steel to produce vehicle parts

Patent metadata

Field	Value
Publication number	US-11549163-B2
Application number	US-201816772379-A
Country	US
Kind code	B2
Filing date	Dec 18, 2018
Priority date	Dec 19, 2017
Publication date	Jan 10, 2023
Grant date	Jan 10, 2023

Abstract

A cold rolled and heat treated steel sheet having a composition including the following elements, expressed in % by weight:0.1%≤carbon≤0.6%4%≤manganese≤20%5%≤aluminum≤15%0≤silicon≤2%aluminium+silicon+nickel≥6.5%and can possibly contain one or more of the following optional elements:0.01%≤niobium≤0.3%,0.01%≤titanium≤0.2%0.01%≤vanadium≤0.6%0.01%≤copper≤2.0%0.01%≤nickel≤2.0%cerium≤0.1%boron≤0.01%magnesium≤0.05%zirconium≤0.05%molybdenum≤2.0%tantalum≤2.0%tungsten≤2.0%the remainder being composed of iron and unavoidable impurities caused by processing, wherein the microstructure of said steel sheet includes in area fraction, 10 to 50% of austenite, the austenite phase optionally including intragranular kappa carbides, the remainder being regular ferrite and ordered ferrite of D03 structure (Fe,Mn,X)3Al, optionally including up to 2% of intragranular kappa carbides (Fe,Mn)3AlCx said steel sheet presenting a ultimate tensile strength higher than or equal to 900 MPa. It also deals with a manufacturing method and with use of such grade for making vehicle parts.

First claim

What is claimed is:

1. A cold rolled and heat treated steel sheet having a composition comprising the following elements, expressed in percent by weight:
0.10%≤carbon≤0.6%
4%≤manganese≤20%
5%≤aluminum≤15%
0≤silicon≤2%
aluminium+silicon+nickel≥6.5%

and optionally at least one of the following optional elements:
0.01%≤niobium≤0.3%,
0.01%≤titanium≤0.2%
0.01%≤vanadium≤0.6%
0.01%≤copper≤2.0%
0.01%≤nickel≤2.0%
cerium≤0.10%
boron≤0.01%
magnesium≤0.05%
zirconium≤0.05%
molybdenum≤2.0%
tantalum≤2.0% and
tungsten≤2.0%;

a remainder being composed of iron and unavoidable impurities, wherein a microstructure of the steel sheet includes in area fraction, 10 to 50% of austenite, the austenite phase optionally including intragranular kappa carbides, a microstructure remainder being regular ferrite and a minimum of 0.1% of ordered ferrite of D0 3 structure (Fe,Mn,X) 3 Al, optionally including up to 2% of intragranular kappa carbides (Fe,Mn) 3 AlC x , the steel sheet having a ultimate tensile strength higher than or equal to 900 MPa.

2. The cold rolled and heat treated steel sheet as recited in claim 1 wherein the aluminium, manganese and carbon amounts are such that 0.3<(Mn/(2×Al))×exp(C)<2.

3. The cold rolled and heat treated steel sheet as recited in claim 1 wherein the steel sheet has a density of less than or equal to 7.4 g/cm 3 and a uniform elongation higher than or equal to 9%.

4. A method of production of the cold rolled and heat treated steel sheet according to claim 1 comprising the following steps:
providing a cold rolled steel sheet with a composition comprising the following elements, expressed in percent by weight:
0.10%≤carbon≤0.6%
4%≤manganese≤20%
5%≤aluminum≤15%
0≤silicon≤2%
aluminium+silicon+nickel≥6.5%

and optionally at least one of the following optional elements:
0.01%≤niobium≤0.3%,
0.01%≤titanium≤0.2%
0.010%≤vanadium≤0.6%
0.01%≤copper 2.0%
0.01%≤nickel≤2.0%
cerium≤0.10%
boron≤0.01%
magnesium≤0.05%
zirconium≤0.05%
molybdenum≤2.0%
tantalum≤2.0% and
tungsten≤2.0%;

a remainder being composed of iron and unavoidable impurities;
heating the cold rolled steel sheet up to a soaking temperature between 750 and 950° C. during less than 600 seconds, then cooling the sheet down to room temperature;
reheating the steel sheet to a soaking temperature of 150° C. to 600° C. during 10 s to 1000 h, then further cooling the sheet so as to the obtain the cold rolled and heat treated steel sheet as recited in claim 1 .

5. A method for the manufacture of structural or safety parts of a vehicle comprising using the cold rolled and heat treated steel sheet as recited in claim 1 .

6. The method as recited in claim 5 further comprising flexibly rolling the cold rolled and heat treated steel sheet.

7. A vehicle part comprising the cold rolled and heat treated steel sheet as recited in claim 1 .

8. A vehicle comprising the vehicle part as recited in claim 7 .

9. The method as recited in claim 4 wherein the cooling of the sheet is at a cooling rate of greater than 30 degrees C./s.

Assignees

• Arcelormittal

Inventors

• Barges Patrick
• Zuazo Rodriguez Ian Alberto

Classifications

• C21D6/005 Primary

  containing Mn · CPC title

• C22C38/06

  containing aluminium · CPC title

• C21D8/0268

  between cold rolling steps · CPC title

• C22C38/02 Primary

  containing silicon · CPC title

• C22C38/08 Primary

  containing nickel {(C22C38/105 takes precedence)} · CPC title