COLD-ROLLED STEEL SHEET AND METHOD OF ITS FABRICATION

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FIELD : metallurgy. SUBSTANCE : sheet is made of steel containing in wt % : C - 0.150-0.300, Si - 0.010-1.000, Mn - 1.50-2.70, P - 0.001-0.060, S - 0.001-0.010, N - 0.0005-0.0100, Al - 0.010-0.050 and, optionally, one or several of the following elements : B - 0.0005-0.0020, Mo - 0.01-0.50, Cr - 0.01-0.50, V - 0.001-0.100, Ti - 0.001-0.100, Nb - 0.001-0.050, Ni - 0.01-1.00, Cu - 0.01-1.00, Ca - 0.0005-0.0050, rare-earth metals - 0.0005-0.0050, Fe and unavoidable impurities making the rest. Metallographic structure after hot forming comprise up to 40%-90% of ferrite and 10%-60% of martensite and, additionally, one or several of the following phases : 10% or less of pearlite, 5% or less of residual austenite in relative volume and less than 20% of bainite. The product TS×λ of stretching strength TS and opening expansion factor λ makes 50000 MPa·% or more. EFFECT : higher stretching strength and opening expansion factor. 19 cl, 8 dwg, 8 tbl, 1 ex