HIGH-STRENGTH MULTI-PHASE STEEL, METHOD FOR ITS PREPARATION AND APPLICATION Russian patent published in 2018 - IPC C21D8/02 C22C38/00 C21D9/46 C23C2/00 

FIELD: metallurgy.

SUBSTANCE: to ensure a tensile strength of 980 MPa, a yield strength greater than or equal to 500 MPa, a full elongation greater than or equal to 8 %, cold-rolled sheet steel contains in wt. % 0.05≤C≤0.15, 2≤Mn≤3 %, Al≤0.1, 0.3≤Si≤1.5, Nb≤0.05, N≤0.02, 0.1≤Cr+Mo≤1, 0.0001≤B≤0.0025, 3.4×N≤Ti≤0.5, V≤0.1, S≤0.01, P≤0.05, iron and unavoidable impurities – the rest, has a microstructure in the surface fraction of between 50 and 95 % martensite and between 5 and 50 % of the sum of ferrite and bainite, the size of the ferritic grain is less than 10 microns and the aspect ratio of the ferritic grain is between 1 and 3.

EFFECT: steel according to the invention is oxidized and then reduced during annealing during the heating, holding and cooling steps.

20 cl, 1 dwg, 5 tbl