Patent ID: 9540717
Date: 2017-01-10
CPC Classifications: C21D,C22C,F16L

Claim:
1. A thick high-strength hot-rolled steel sheet for electric resistance welded line pipe having excellent sour resistance, the thick high-strength hot-rolled steel sheet having a composition containing 0.01% to 0.07% C, 0.40% or less Si, 0.5% to 1.4% Mn, 0.015% or less P, 0.003% or less S, 0.1% or less Al, 0.01% to 0.15% Nb, 0.1% or less V, 0.03% or less Ti, 0.3% or less Mo, 0.5% or less Cu, 0.5% or less Ni, and 0.008% or less N on a mass basis, the remainder being Fe and inevitable impurities; Nb, V, and Ti satisfying the following inequality (1); Cm defined by the following equation (2) satisfying 0.12 or less; the thick high-strength hot-rolled steel sheet having a microstructure containing a bainite phase or bainitic ferrite phase at an area fraction of 95% or more, a thickness-wise maximum hardness of 220 HV or less, and a yield strength of 450 MPa or more: where Nb, V, Ti, C, Si, Mn, Cu, Ni, Mo, and V are the content (mass percent) of each element.