HIGH-STRENGTH WELDED STEEL PIPE Russian patent published in 2009 - IPC B21C37/08 C22C38/00 B23K101/06 B23K101/10 

FIELD: metallurgy.

SUBSTANCE: invention relates to manufacturing of high-strength welded steel pipe, which basis metal is steel of grade no less than API X100 and allows ultimate tensile strength at least 760 MPa, and welded joint consists of internal and external joints and allows ultimate tensile strength at least 780 MPa. Effective diametre of elementary austenite grain in metal of internal welded joint is at least 90 micrometre and not more than 150 micrometre. Basic metal of pipe except iron and admixtures contains in wt %: carbon 0.02-0.12, silicon 0.01-0.50, manganese 0.4-2.5, phosphor not more 0.015, sulphur not more 0.003, niobium 0.005-0.10, aluminium 0.005-0.06, and at least one of copper, nickel, chrome, molybdenum, vanadium and boron. Metal of internal joint except iron and admixtures contains in wt %: carbon 0.02-0.12, silicon 0.05-0.50, manganese 0.4-2.5, chrome, molybdenum and nickel 0.1-3.0% of each, titanium 0.005-0.050 and aluminium 0.005-0.050.

EFFECT: it is provided increasing of metal stability of welded joint to transversal cracking without implementation of preheating or heating of welded joints after welding.

5 cl, 6 tbl, 1 ex