THICK-WALL HIGH-STRENGTH HOT-ROLLED STEEL SHEET THAT FEATURES HIGH RESISTANCE TO CRACKING INDUCED BY

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FIELD : metallurgy. SUBSTANCE : thick-wall hot-rolled steel sheet contains the following components in wt % : 0.02 to 0.08 of Ca, 1 or less Si, 0.50 to 1.85 of Mn, 0.03 to 0.10 of Nb, 0.001 to 0.05 of Ti, 0.0005 or less, so that the following relation is satisfied (Ti+Nb/2)/C<4. Besides, it includes one, two or more of 0.010% Ca, 0, 02% or less of rear-earth metals and in balance Fe and features structure formed by bainite-ferrite phase or bainite phase. Steel sheet formed by bainite-ferrite phase or bainite phase is produced by sheet steel hot rolling and cooling in three steps at preset cooling rate at every said step. EFFECT : high cracking resistance, tensile strength of up to 520 MPa and higher, surface layer hardness of HV 230 or lower. 13 cl, 12 tbl, 2 ex