METHOD OF PRODUCING THICK-SHEET STEEL AND STEEL TUBES FOR SUPER STRONG PIPELINE Russian patent published in 2012 - IPC C21D8/02 C21D8/10 C21D9/08 C21D9/50 C22C38/14 

FIELD: metallurgy.

SUBSTANCE: proposed steel contains following substances, in wt %: C 0.03-0.06, Si 0.01-0.50, Mn 1.5-2.5, P 0.01 or less, S 0.0030 or less, Nb 0.0001- 0.20, Al 0.0005-0.03, Ti 0.003-0.030, B 0.0003-0.0030, N 0.0010-0.0050, O 0.0050 or less, Fe and unavoidable impurities making the rest. Fused steel is cast into slab to be rolled into thick-sheet steel and water-cooled to preset surface temperature exceeding that of M_s point martensite conversion start. Thick-sheet steel surface is, then, cooled by reiteration of processing whereat heat is recovered one or more times to cool is finally to M_s point or lower. UO-press is used to form tube from sheet. Sheet adjoining edges are arc-welded at flux using welding wire and agglomerated or fused flux to expand the tube.

EFFECT: tensile strength increased to 915 MPa, excellent low-temperature toughness.

10 cl, 3 tbl, 3 dwg