METHOD FOR MANUFACTURING STEEL SHEET AND STEEL PIPE FOR ULTRAHIGH-STRENGTH LINE PIPE SUPERIOR IN DEFORMABILITY AND LOW-TEMPERATURE TOUGHNESS

摘要

PROBLEM TO BE SOLVED: To provide a method for manufacturing a steel sheet and a steel pipe of which the base metal has superior strength, low-temperature toughness and deformability, for an ultrahigh-strength line pipe that can be easily welded on the actual place and has a tensile strength of 900 MPa or higher (X120 or higher in the API standards).;SOLUTION: This manufacturing method comprises the steps of: smelting a steel containing C, Si, Mn, Mo, Nb, Al and Ti; then, hot-rolling the steel; cooling it with water to a temperature between (the γ/α transformation starting point-50) (°C) and the γ/α transformation starting point (°C); reheating it; and subsequently cooling it with water. Due to the above effect, the method can enhance strength, low-temperature toughness and deformability before and after strain ageing, and greatly improve the safety of the line pipe.;COPYRIGHT: (C)2009,JPO&INPIT