Patent ID: 9551047
Date: 2017-01-24
CPC Classifications: B21C,B23K,B32B,C21D,C22C,F16L,Y10T

Claim:
1. A high strength electric resistance welded pipe having a longitudinally extending seam of an electric resistance weld zone, a base metal of the pipe having a chemical composition containing, by mass %, C: 0.025% or more and 0.084% or less, Si: 0.10% or more and 0.30% or less, Mn: 0.70% or more and 1.90% or less, P: 0.018% or less, S: 0.0029% or less, Al: 0.01% or more and 0.10% or less, Nb: 0.001% or more and 0.070% or less, V: 0.001% or more and 0.065% or less, Ti: 0.001% or more and 0.033% or less, Ca: 0.0001% or more and 0.0035% or less, N: 0.0050% or less, O: 0.0030% or less and the balance being Fe and inevitable impurities, in which a condition that Pcm defined by equation (1) below is 0.20 or less is satisfied, having a microstructure in the base metal portion including, in terms of volume percentage, 90% or more of a quasi-polygonal ferrite phase as a main phase and the balance being hard phases other than the quasi-polygonal ferrite phase in which the quasi-polygonal ferrite phase has an average grain diameter of 10 μm or less, having a microstructure in an electric resistance weld zone including, in terms of volume percentage, 90% or more of a quasi-polygonal ferrite phase as a main phase and the balance being hard phases other than the quasi-polygonal ferrite phase, in which the quasi-polygonal ferrite phase has an average grain diameter of 10 μm or less, and having a yield strength YS of 450 MPa or more: where C, Si, Mn, Cu, Ni, Cr, Mo, V and B represent the contents (mass %) of chemical elements respectively represented by the corresponding atomic symbols.