FIELD: metallurgy.
SUBSTANCE: part of basic material contains the following, wt %: C more than 0.03-0.08, Si 0.01-0.5, Mn 1.5-3.0, P ≤ 0.015, S ≤ 0.005, Al 0.01-0.08, Nb 0.005-0.025, Ti 0.005-0.025, N 0.001-0.010, 0 ≤ 0.005, B 0.0003-0.0020, in addition: includes one or more of the elements: Cu, Ni, Cr, Mo and V, the rest is Fe and inevitable impurities. Tensile strength is 760-930 MPa, relative elongation is 5% or more and ratio of yield strength to tensile strength is 85% or less. Part of weld metal contains the following, wt %: C more than 0.03-0.08, Si < 0.5, Mn 1.5-3.0, P ≤ 0.015, S ≤ 0.005, Al ≤ 0.05, Nb 0.005-0.05, Ti 0.005-0.03, N ≤ 0.010, 0 0.015-0.045, B 0.0003-0.0020, in addition it includes one or more of the elements: Cu, Ni, Cr, Mo and V, the rest is Fe and inevitable impurities. In microstructure of heat-affected zone upon welding size of primary austenitic grain is 50 mcm or more, and structure consists of lower bainite or multiphase structure containing lower bainite with fraction part of 50% or more and upper bainite and/or martensite.
EFFECT: improving pipe strength upon buckle and impact strength of heat-affected zone upon welding.
19 cl, 1 dwg, 8 tbl, 2 ex
