THICK-WALL WELDED STEEL PIPE WITH EXCELLENT LOW-TEMPERATURE IMPACT STRENGTH, MANUFACTURING METHOD OF THICK-WALL WELDED STEEL PIPE WITH EXCELLENT LOW-TEMPERATURE IMPACT STRENGTH, AND STEEL PLATE FOR PRODUCTION OF THICK-WALL WELDED STEEL PIPE

摘要

FIELD: metallurgy.;SUBSTANCE: pipe is made from a parent material of a steel plate folded into a pipe-shaped form and welded by seam welding so that a weld and a large-grained heat-affected zone (HAZ) are formed. The parent material of the steel plate has the following chemical composition, wt %: C 0.03 to 0.085, Mn 1.45 to 1.85, Ti 0.005 to 0.020, Nb 0.005 to 0.050, O 0.0005 to 0.005, Si 0.15 or less, Al 0.015 or less, P 0.02 or less, S 0.005 or less, Mo 0.20 or less, Fe and inevitable impurities are the rest. The structure of metal of the parent material of the steel plate consists of ferrite with a fraction of the area of 30 to 95%, martensite, bainite and martensitic-austenitic component (MA) is the rest, and for the metal structure of the large-grained HAZ the fraction of the area of the grain boundary ferrite is 1.5% or more, the total fraction of the area of the grain boundary ferrite and intragranular ferrite is at least 11%, but not more than 90%, the fraction of the MA area is 10% or less, and bainite is the rest.;EFFECT: improvement of characteristics.;13 cl, 10 dwg, 4 tbl, 1 ex