And a method of manufacturing the line pipe for high-strength steel sheet excellent in weld heat-affected zone toughness and HIC resistance characteristics

摘要

PROBLEM TO BE SOLVED: To provide a steel sheet having a strength of an API X65 grade or higher for a line pipe, which has superior HIC resistance for HIC generated at a central segregation part and HIC that initiates from the vicinity of the surface and inclusions, and superior toughness in a weld heat-affected zone, at a low cost without adding a large quantity of alloy elements.;SOLUTION: The high-strength steel sheet for the line pipe comprises, by mass%, 0.02-0.08% C, 0.01-0.5% Si, 0.5-2% Mn, 0.01% or less P, 0.002% or less S, 0.05-0.5% Mo, 0.005-0.025% Ti, 0.07% or less Al, 0.004-0.006% N, while controlling C/(Mo+Ti) to 0.5-3 and Ti/N to 2-4, and the balance substantially Fe; and has a metallographic structure of a two-phase structure consisting substantially of ferrite and bainite, in which fine precipitates containing Ti and Mo are dispersingly precipitated.;COPYRIGHT: (C)2005,JPO&NCIPI