Sheet steel with very high mechanical characteristics of strength and formability, manufacturing process and use of these plates

摘要

Steel sheet cold rolled and annealed with a mechanical or strength greater than or equal to 900 MPa, with a uniform than or equal to 12% over 700 MPa yield strength and elongation which composition comprises the amounts being expressed in percentage by weight, 0.26% = C = 0.45% 1.0% = Mn = 3.0% 1.0% = Si = 3.0% Al = 0.1% Cr = 1 , 5% S = 0.005% P = 0.020% Nb = 0.1% Ti = 0.02% V = 0.015% N = 0.01%, the balance of the composition consists of iron and unavoidable impurities resulting from the smelting, it being understood that 256xC + 47xMn + 150xCr + 2260xNb 142, the microstructure being composed, in proportions of surface, from 13 to 25% residual austenite, from 13 to 30% of islets of martensite and residual austenite, the remainder consisting of bainite and ferrite being occasionally.