METHOD FOR PRODUCING COLD-ROLLED TWO-PHASE FERRITE-MARTENSITE AUTOMOBILE BODY SHEET STEEL Russian patent published in 2017 - IPC C21D8/04 C21D9/46 C22C38/04 

FIELD: metallurgy.

SUBSTANCE: method includes steel melting containing, wt %: C 0.10-0.15, Si 0.10 -0.40, Mn 1.8-2.4, Cr 0.20-0.40, Mo 0.10-0.40, Al 0.02-0.08, P no more than 0.02, S no more than 0.02, Fe and unavoidable impurities, hot rolling at beginning temperature from 1050 to 1200°C and the ending at 800-890°C, coiling the sheet into a roll at 580-650°C, cold rolling with total reduction of 45-70% for thickness 0.9-1.5 mm and heat treatment in continuous-action unit by heating to annealing temperature 730-790°C, soaking, slow cooling to temperatures below A_r1, accelerated cooling to 250-330°C and ageing at said temperature. The sheet is moved in the unit at a speed provided that: V_smr=[(T_an-680°C/k-10m/min]÷[(T_an-680°C/k+10 m/min], where V_smr- strip movement rate, m/min, k=1×min×°C/m, T_an - annealing temperature, °C.

EFFECT: provision of required level of BH-effect and capacity to crush the hole with preservation of mechanical properties, with strength class of 780 mpa of ferrite-martensite steel.

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