STEEL FOR HIGH-DEFINITION PIPES OF MAJOR PIPELINES WITH STRESS AGING AND HYDROGEN ATTACK HIGH RESISTANCE, METHOD FOR THEIR MANUFACTURING AND WELDED STEEL PIPE

摘要

FIELD: metallurgy.;SUBSTANCE: invention relates to the field of metallurgy, namely to steel plate material used for the manufacture of major pipeline pipes. Material has a chemical composition containing, mass %: C: 0.030–0.100, Si: 0.01–0.50, Mn: 0.5–2.5, P: 0.015 or less, S: 0.002 or less, Cu: 0.20–1.00, Mo: 0.01 or less, Nb: 0.005–0.05, Ti: 0.005–0.040, Al: 0.10 or less, N: 0.007 or less, Fe and unavoidable impurities – the rest, and the metallographic structure, consisting mainly of ferrite and bainite, in which the total share of the ferrite and bainite area is 90 % or more, and the difference in hardness between ferrite and bainite is 70 or more in units of Vickers hardness.;EFFECT: high resistance to stress aging and hydrogen attack, a uniform elongation of 9 % or more, and a yield strength to strength ratio of 90 % or less are provided.;6 cl, 1 ex, 3 tbl