STEEL SHEET FOR THICK-WALLED HIGH-STRENGTH LINE PIPE HAVING EXCEPTIONAL SOURING RESISTANCE CRUSH RESISTANCE PROPERTIES AND LOW-TEMPERATURE DUCTILITY AND LINE PIPE

摘要

A steel sheet for a high strength and high strength line pipe excellent in resistance to sagging, crushing resistance and low temperature toughness, and a process for producing the same. _Wherein the metal structure of the surface layer portion comprises not more than 5% of the processed ferrite and not more than 1% of S _{fe determined} by the following formula 1a, and the martensite-austenite hybrid (MA): 8% or less, the remainder, polygonal ferrite and / or bainite, and the metal structure at the center of the plate thickness is 5% or less of processed ferrite and 5% or less of MA, And / or bainite, and the average value of the effective grain size at the surface layer portion and the central portion of the plate thickness is 20 占 퐉 or less. T _H : plate thickness of steel plate