ULTRAHIGH-STRENGTH AIR-HARDENING MULTI-PHASE STEEL COMPRISING EXCELLENT PROCESSING PROPERTIES AND METHOD FOR PRODUCTION OF STEEL STRIP FROM SAID STEEL Russian patent published in 2019 - IPC C21D8/02 C22C38/58 C21D9/46 C23C2/06 

FIELD: metallurgy.

SUBSTANCE: to provide tensile strength in non-hardened condition of at least 750 MPa, cold-rolled or hot-rolled strip is obtained from steel containing, wt. %: C from 0.075 to 0.115, Si from 0.600 to 0.750, Mn from 1.000 to 1.950, Cr from 0.200 to 0.600, Al from 0.010 to 0.060, N from 0.0020 to 0.0120, S ≤ 0.0030, Mo ≥ 0.0200, Nb from 0.005 to 0.040, Ti from 0.005 to 0.030, B from 0.0005 to 0.0030, Ca from 0.0005 to 0.0060, Cu ≤ 0.050, Ni ≤ 0.050, iron and unavoidable impurities remaining, wherein total content of elements (Mn + Si + Cr + Mo) is in following dependence on thickness of obtained strip: at strip thickness of up to 1.00 mm, sum of elements ranges from 2.450 to 2.800 wt. %, at thickness of 1.00 to 2.00 mm, the sum of elements ranges from 2.600 to 3.150 wt. %, at thickness of more than 2.00 mm, sum of elements ranges from 3.000 to 3.450 wt%. Cold-rolled or hot-rolled steel strip is heated to an annealing temperature of 700 to 950 °C and cooled from annealing temperature to first intermediate temperature from 300 to 500 °C with cooling rate of 15–100 °C/s with further cooling to the second temperature from 160 to 250°C at cooling rate of 15–100°C / s, then steel strip is cooled to room temperature at cooling rate from 2 to 30°C/s or cooled from first intermediate temperature to room temperature while maintaining cooling rate of 15–100°C/s.

EFFECT: resulting steel strip has given hole distribution values in accordance with ISO 16630 and bending angle in accordance with VDA 238-100.

41 cl, 6 dwg