THICK-WALL HIGH-STRENGTH HOT-ROLLED STEEL SHEET WITH HIGH TENSILE STRENGTH, HIGH-TEMPERATURE TOUGHNESS, AND METHOD OF ITS PRODUCTION Russian patent published in 2013 - IPC C21D8/02 C22C38/00 C22C38/54 C22C38/58 

FIELD: metallurgy.

SUBSTANCE: thick-wall hot-rolled steel sheet contains the following components in wt %: 0.02 to 0.08 of C, 0.01 to 0.50 of Si, 0.5 to 1.8 of Mn, 0.025 or less of P, 0.005 or less of S, 0.005 to 0.10 of A1, 0.01 to 0.10 of Nb, 0.001 to 0.05 of Ti, Fe and unavoidable impurities making the rest. Note here that contains C, Ti and Nb in amounts the following relation is satisfied (Ti+Nb/2)/C<4.Note here that steel sheet features structure wherein structure primary phase at 1 mm from sheet surface represents phase selected from the group consisting of ferrite phase, annealed martensite and structure mixed thereof. Note also that structure primary phase at the center of sheep depth is formed by ferrite phase while difference ΔV between structural fraction (in vol. %) of secondary phase at 1 mm from sheet surface and structural fraction of secondary phase at sheep depth center makes 2% or less.

EFFECT: high cracking resistance, tensile strength of up to 520 MPa and higher, surface layer hardness of HV 230 or lower.

19 cl, 5 dwg, 13 tbl, 3 ex