EXTRA HIGH STRENGTH MULTIPHASE STEEL AND METHOD FOR PRODUCTION OF COLD-ROLLED STEEL STRIP FROM IT Russian patent published in 2019 - IPC C21D8/02 C22C38/58 C23C2/00 C21D9/48 

FIELD: metallurgy.

SUBSTANCE: to provide homogeneous mechanical properties and minimum tensile strength of 980 MPa, obtaining multiphase steel containing the following, wt. %: C from 0.075 to 0.115, Si from 0.400 to 0.500, Mn from 1.900 to 2.350, Cr from 0.250 to 0.400, Al from 0.005 to 0.060, N from 0.0020 to 0.0120, S is less than or equal to 0.0020, Nb from 0.005 to 0.060, Ti from 0.005 to 0.060, B from 0.0005 to 0.0010, Mo from 0.200 to 0.300, Ca from 0.0010 to 0.0060, Cu is less than or equal to 0.050, Ni is less than or equal to 0.050, the rest is iron and unavoidable impurities, wherein total content of Mn + Si + Cr ranges from 2.500 to 3.250 wt. %. To produce steel strip from multiphase steel, hot-rolled strip is made, which is subjected to cold rolling to thickness of 0.50 to 3.00 mm, then continuous annealing is performed, wherein cold-rolled steel strip is heated to 700–950 °C and cooled from annealing temperature at cooling rate of about 15–100 °C/s first to first intermediate temperature of about 300–500 °C, then at cooling rate of about 15–100°C to second intermediate temperature of about 160–250°C, and then with air at cooling rate of about 2–30 °C/s. Coating is applied at annealing temperature.

EFFECT: invention relates to metallurgy, particularly to multiphase steel used for light-duty vehicles.

35 cl, 13 dwg, 5 ex