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US 12,753,461 B2Granted
Hot rolled high strength steel strip having high hole expansion ratio
AssigneeTata Steel Ijmuiden B.V.
InventorsRolf Arjan Rijkenberg, Shangping Chen, Maxim Peter Aarnts
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Abstract
A high strength steel with a careful selection of the normal alloying elements C, Mn, Si and Al, together with micro-element addition. This a steel with a high strength and high hole expansion ratio can be produced. The invention also relates to the method to manufacture this high strength steel.
Claims21
A hot rolled high strength steel strip consisting of:
- 0.02-0.13 wt. % C;
- 1.20-2.20 wt. % Mn;
- 0.10-1.00 wt. % Si;
- 0.01-0.10 wt. % Al;
- 0.09-0.18 wt. % Ti;
- 0.001-0.010 wt. % N;
- 0.005-0.2 wt. % Mo;
- 0-0.10 wt. % P;
- 0-0.01 wt. % S;
- 0-1.5 wt. % Cu;
- 0-1.0 wt. % Cr;
- 0-0.50 wt. % Ni;
- 0-0.30 wt. % V;
- 0-0.04 wt. % Nb;
- wherein Ti+Nb≤0.25 wt. %,
- wherein Cr+Mo≤1.0 wt. %,
- remainder iron and inevitable impurities,
- the steel having a microstructure consisting of (in volume %):
- at least 85% bainite,
- at most 10% martensite plus retained austenite,
- more than 0.01% and at most 5% cementite,
- inevitable amounts of inclusions,
- the sum adding up to 100 volume %;
- wherein the bainite consists of at least one member of the group consisting of Ferritic Bainite (FB), Granular Bainite (GB), Upper Bainite (UB), and Cementite-Free Bainite (CFB), and
- wherein the cementite is related to the presence of the Upper Bainite;
- and
- wherein the steel strip microstructure contains at least 60% lath-like bainitic ferrite and at most 40% irregular-shaped bainitic ferrite;
- wherein the steel strip has the following mechanical properties:
- a tensile strength of at least 760 and at most 960 MPa,
- a total elongation (A50) of at least 10%,
- a hole expansion ratio (λ) value of at least 50%, or
- wherein the steel strip has the following mechanical properties:
- a tensile strength of at least 960 and at most 1380 MPa,
- a total elongation (A50) of at least 9%,
- a hole expansion ratio (λ) value of at least 40%;
- wherein the equation
- C
- /
- 12
- (
- Ti_sol
- /
- 48
- +
- Nb
- /
- 93
- +
- V
- /
- 51
- +
- Mo
- /
- 96
- )
- has a lower limit of 0.45 and an upper limit of 2.2,
- wherein Ti_sol is defined as
- Ti
- _
-
- sol
- =
- Ti
- -
- (
- 4
-
- 8
- 1
-
- 4
- )
- ×
- N
- .
73 more elements
A hot rolled high strength steel strip consisting of:
- 0.03-0.12 wt. % C;
- 1.50-2.20 wt. % Mn;
- 0.20-0.95 wt. % Si;
- 0.01-0.10 wt. % Al;
- 0.10-0.18 wt. % Ti;
- 0.001-0.010 wt. % N;
- 0.005-0.2 wt. % Mo;
- 0-0.10 wt. % P;
- 0-0.01 wt. % S;
- 0.0010-0.005 wt. % B;
- 0-0.5 wt. % Cu;
- 0-0.9 wt. % Cr;
- 0-0.2 wt. % Ni;
- 0-0.18 wt. % V;
- 0-0.04 wt. % Nb;
- wherein Ti+Nb≤0.25 wt. %,
- wherein Cr+Mo≤1.0 wt. %,
- wherein Mn+Cr+2 Mo≥2.3wt. %,
- remainder iron and inevitable impurities,
- the steel strip having a microstructure consisting of (in volume %):
- at least 90% bainite,
- at most 5% martensite plus retained austenite,
- more than 0.01% and at most 5% cementite,
- inevitable amounts of inclusions,
- the sum adding up to 100 volume %;
- wherein the steel strip contains at least 60% lath-like bainitic ferrite and at most 40% irregular-shaped bainitic ferrite.
23 more elements
Dependencies are inferred from the claim text.