Patent ID: 8974610
Filing Date: 2015-03-10
Classification: B23K,C21D,C22C,Y10S

Abstract:
1. A high-strength welded steel pipe obtained by welding a seam weld portion of a steel plate into forming a pipe shape, wherein a base metal of the steel plate includes, by mass %, C: 0.010% to 0.080%, Si: 0.01% to 0.50%, Mn: 0.50% to 2.00%, S: 0.0001% to 0.0050%, Ti: 0.003% to 0.030%, Mo: 0.05% to 1.00%, B: 0.0003% to 0.0100%, O: 0.0001% to 0.0080%, N: 0.006% to 0.0118%, P: limited to 0.050% or less, Al: limited to 0.008% or less, and a balance of iron and inevitable impurities, wherein a Ceq that is obtained from a following equation <7> is 0.30 to 0.53, a Pcm that is obtained from a following equation <8> is 0.10 to 0.20, the [N] and the [Ti] satisfy a following equation <9>, wherein an average grain size of prior γ grains in a heat affected zone in the steel plate is 250 μm or less, and the prior γ grains include bainite and intragranular bainite, wherein [C], [Si], [Mn], [Ni], [Cu], [Cr], [Mo], [V], [B], [N], and [Ti] are defined as the amounts of C, Si, Mn, Ni, Cu, Cr, Mo, V, B, N, and Ti in mass %, respectively.