Very high-strength, cold-rolled, dual steel sheets

Patent metadata

Field	Value
Publication number	US-2019106765-A1
Application number	US-201816213455-A
Country	US
Kind code	A1
Filing date	Dec 7, 2018
Priority date	May 21, 2008
Publication date	Apr 11, 2019
Grant date	—

Abstract

The present invention provides a cold-rolled and annealed Dual-Phase steel sheet having a tensile strength from 980 to 1100 MPa. The composition includes the contents being expressed by weight: 0.055%≤C≤0.095%, 2%≤Mn≤2.6%, 0.005%≤Si≤0.35%, S≤0.005%, P≤0.050%, 0.1≤Al≤0.3%, 0.05%≤Mo≤0.25%, 0.2%≤Cr≤0.5%, Cr+2 Mo≤0.6%, Ni≤0.1%, 0.010≤Nb≤0.040%, 0.010≤Ti≤0.050%, 0.0005≤B≤0.0025%, and 0.002%≤N≤0.007%. The remainder of the composition includes iron and inevitable impurities resulting from the smelting. A microstructure of the steel sheet is 40 to 65% ferrite, 35 to 50% martensite and 0 to 10% bainite. A non-recrystallized ferrite fraction is less than or equal to 15%.

First claim

What is claimed is:

1 . A cold-rolled and annealed Dual-Phase steel sheet comprising:
a composition comprising, the contents being expressed by weight:
0.055%≤C≤0.095%;
2%≤Mn≤2.6%;
0.005%≤Si≤0.35%;
S≤0.005%;
P≤0.050%;
0.1≤Al≤0.3%;
0.05%≤Mo≤0.25%;
0.2%≤Cr≤0.5%;
Cr+2Mo≤0.6%;
Ni≤0.1%;
0.010≤Nb≤0.040%;
0.010≤Ti≤0.050%;
0.0005≤B≤0.0025%; and
0.002% ≤N≤0.007%;
a remainder of the composition comprising iron and the inevitable impurities resulting from smelting;
a tensile strength between 980 and 1100 MPa; and a microstructure consisting of 40 to 65% ferrite, 35 to 50% martensite and 0 to 10% bainite, a non-recrystallized ferrite fraction being less than or equal to 15%.

2 . The steel sheet as recited in claim 1 , wherein the composition of the steel contains, the content being expressed by weight: 0.12%≤Al≤0.25%.

3 . The steel sheet as recited in claim 1 , wherein the composition of the steel contains, the content being expressed by weight: 0.10%≤Si≤0.30%.

4 . The steel sheet as recited in claim 1 , wherein the composition of the steel contains, the content being expressed by weight: 0.15%≤Si≤0.28%.

5 . The steel sheet as recited in claim 1 , wherein the composition of the steel contains, the content being expressed by weight: P≤0.015%.

6 . The steel sheet as recited in claim 1 , wherein a microstructure of the steel sheet includes a surface area fraction of 35 to 50% martensite.

7 . The steel sheet as recited in claim 6 , wherein a remainder of the microstructure consists of a surface area fraction of 50 to 65% ferrite.

8 . The steel sheet as recited in claim 6 , wherein a remainder of the microstructure consists of surface area fractions of 1 to 10% bainite and 40 to 64% ferrite.

9 . The steel sheet as recited in claim 1 , wherein a remainder of the microstructure consists of martensite and ferrite.

10 . The steel sheet as recited in claim 1 , wherein a ratio of yield strength Re to strength Rm is such that: 0.6≤Re/Rm≤0.8.

11 . The steel sheet as recited in claim 1 , wherein the steel sheet is continuously galvanized.

12 . The steel sheet as recited in claim 1 , further comprising a galvannealed coating.

13 . A structural or safety part for a motor vehicle comprising:
the steel sheet as recited in claim 1 .

14 . The steel sheet as recited in claim 1 , wherein the remainder of the composition consists of iron and inevitable impurities.

Assignees

• Arcelormittal

Inventors

• Moulin Antoine
• Sardoy Veronique
• Vinci Catherine
• Restrepo Gacess Gloria
• Watershoot Tom
• Goune Mohamed

Classifications

• C21D8/02

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

• C23C2/06

  Zinc or cadmium or alloys based thereon · CPC title

• C21D9/46 Primary

  for sheet metals · CPC title

• C22C38/54

  with boron · CPC title

• C21D8/021

  involving particular fabrication steps or treatments of ingots or slabs · CPC title