US 11,884,990 B2
High strength hot rolled or cold rolled and annealed steel and method of producing it
Joost Willem Hendrik Van Krevel, Beverwijk (NL); and Nieves Cabanas Poy, Haarlem (NL)
Assigned to TATA STEEL NEDERLAND TECHNOLOGY B.V., Velsen-Noord (NL)
Appl. No. 16/967,233
Filed by TATA STEEL NEDERLAND TECHNOLOGY B.V., Velsen-Noord (NL)
PCT Filed Feb. 5, 2019, PCT No. PCT/EP2019/052809
§ 371(c)(1), (2) Date Aug. 4, 2020,
PCT Pub. No. WO2019/154819, PCT Pub. Date Aug. 15, 2019.
Claims priority of application No. 18155630 (EP), filed on Feb. 7, 2018.
Prior Publication US 2021/0025024 A1, Jan. 28, 2021
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/52 (2006.01); C21D 9/46 (2006.01); C21D 8/02 (2006.01); C21D 6/00 (2006.01); C22C 38/14 (2006.01); C22C 38/06 (2006.01); C22C 38/04 (2006.01); C22C 38/02 (2006.01); C22C 38/00 (2006.01); C22C 38/12 (2006.01)
CPC C21D 9/52 (2013.01) [C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0263 (2013.01); C21D 9/46 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/008 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/008 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A hot-rolled, cold-rolled and annealed, or cold-rolled, annealed and temper rolled steel strip or sheet having a complex phase steel microstructure comprising:
0.16-0.21 wt. % C;
2.3-4.00 wt. % Mn;
5-50 ppm B;
5-100 ppm N;
0.019-1.10 wt. % Al tot which is the sum of aluminum present as alumina and any other aluminum;
0.05-1.10 wt. % Si;
0-0.04 wt. % Ti, wherein if Al is below 0.030 wt. % Ti is 0.010-0.04 wt. %;
0-0.10 wt. % Cu;
0-0.10 wt. % Mo;
0-0.10 wt. % Ni;
0-0.20 wt. % V;
0-0.05 wt. % P;
0-0.05 wt. % S;
0-0.10 wt. % Sn;
0-0.025 wt. % Nb
0-0.025 wt. % Ca;
remainder iron and inevitable impurities,
wherein the steel has a cracking parameter value, Pc, of at most 0.365, wherein

OG Complex Work Unit Math
and wherein the alloying contents are given in wt. % and the plate thickness d, is given in mm,
wherein the steel strip or sheet after hot-rolling has a yield strength of at least 500 MPa and a tensile strength of at least 850 MPa, or
wherein the steel strip or sheet after cold-rolling and annealing has a yield strength of at least 550 MPa and a tensile strength of at least 1000 MPa, or
wherein the steel strip or sheet after cold-rolling and annealing and temper rolling has a yield strength of at least 600 MPa and a tensile strength of at least 1200 MPa,
wherein the steel microstructure consists of a mixture of martensite with retained austenite, and a remainder being carbide free bainite consisting of bainite with retained austenite without the presence of cementite,
wherein the martensite is at least one member selected from the group consisting of tempered martensite and untempered martensite,
wherein the steel microstructure is between 0 and 50 vol. % tempered martensite, and
wherein the steel microstructure is free from ferrite and free from pearlite.