Patent ID: 8038811
Filing Date: 2011-10-18
Classification: C21D,C22C

Abstract:
1. A process for producing a bent pipe for a line pipe, comprising the steps of: preparing a straight steel pipe containing, by mass, at most 0.009% C, at most 1.0% Mn, at most 1.0% Si, at most 0.04% P, at most 0.005% S, 0.01 to 0.2% Ti, 0.01 to 0.10% V, 0.001 to 0.1% Al, at most 0.1% N, 4.0 to 8.0% Ni, 9.0 to 15.0% Cr, and 1.5 to 7.0% Mo, the balance being Fe and impurities; bending the straight steel pipe into a bent pipe; quenching the bent pipe at a quenching temperature of 850° C. to lower than 950° C.; and tempering the quenched bent pipe at a tempering temperature of 600° C. to 700° C. to produce the bent pipe having a yield strength of 550 MPa to 725 MPa.