High strength cold rolled steel sheet

Patent metadata

Field	Value
Publication number	US-10106874-B2
Application number	US-201314380941-A
Country	US
Kind code	B2
Filing date	Apr 2, 2013
Priority date	Mar 30, 2012
Publication date	Oct 23, 2018
Grant date	Oct 23, 2018

Abstract

The present invention relates to high strength cold rolled steel sheet suitable for applications in automobiles, construction materials and the like, specifically high strength steel sheet excellent in formability. In particular, the invention relates to cold rolled steel sheets having a tensile strength of at least 980 MPa and a method for producing such steel sheet.

First claim

The invention claimed is:

1. A high strength cold rolled TRIP steel sheet with a matrix of bainitic ferrite having,
a) a composition consisting of the following elements, in wt. %:

C
 0.1-0.19

Mn
2.0-3.0

Si
0.4-0.9

Cr
0.2-0.6

Si + Cr
0.9-1.3

Si/Cr
>2

Al
≤0.06

Nb
<0.1

Mo
<0.3

Ti
<0.2

V
<0.2

Cu
<0.5

Ni
<0.5

B
<0.005

Ca
<0.005

Mg
<0.005

REM
<0.005

S
<0.01

P
<0.02

N
<0.02

 balance Fe apart from impurities,
b) a multiphase microstructure comprising, in vol. %

retained austenite
5-20

bainitic ferrite
>50

bainite + bainitic ferrite + tempered martensite
≥80

polygonal ferrite
≤10

wherein the maximum size of martensite-austenite particles (MA) is ≤6 μm,
c) at least one of the following mechanical properties

a tensile strength (R m )
980-1200 MPa

an elongation (A 80 )
 ≥6%

a hole expanding ratio (λ)
≥40%

 and fulfilling the following conditions

R m × A 80
≥13 000
MPa %

R m × λ
≥40 000
MPa %.

2. The high strength cold rolled TRIP steel sheet according to claim 1 wherein at least one of the following elements is in the composition, in wt. %:

C
0.15-0.19

Mn
2.0-2.6

Si
 0.6-0.9.

3. The high strength cold rolled TRIP steel sheet according to claim 1 , wherein at least one of the following elements is in the composition, in wt. %:

Nb
 0.02-0.08

Mo
0.05-0.3

Ti
 0.02-0.08

V
0.02-0.1

Cu
0.05-0.4

Ni
0.05-0.4

B
0.0005-0.003

Ca
0.0005-0.005

Mg
0.0005-0.005

REM
 0.0005-0.005.

4. The high strength cold rolled TRIP steel sheet according to claim 1 , wherein:
Ti>3.4N.

5. The high strength cold rolled TRIP steel sheet according to according to claim 1 , wherein the maximum size of martensite-austenite particles (MA) is ≤3 μm.

6. The high strength cold rolled TRIP steel sheet according

Assignees

• Voestalpine Stahl Gmbh
• Kobe Steel Ltd

Inventors

• Paul Stefan
• Krizan Daniel
• Pichler Andreas
• Nakaya Michiharu

Classifications

• C21D1/26

  Methods of annealing · CPC title

• C22C38/50

  with titanium or zirconium · CPC title

• C21D1/20

  Isothermal quenching, e.g. bainitic hardening · CPC title

• C22C38/02

  containing silicon · CPC title

• C21D6/008

  containing Si · CPC title