Patent ID: 7754344

Claim:
Ferritic stainless steel welded pipe having one or both of Ti and Nb in an amount of 0.05 to 0.5 wt % and superior in expandability by a multi-step process, said ferritic stainless steel consisting of a matrix and a welded zone, said ferritic stainless steel welded pipe characterized in that after forming, welding, and sizing, the matrix of the welded pipe has an elongation in the circumferential direction of 15% or more, and a hardness difference ΔHV (=HV W −HV M ) between the Vicker's hardness HV W of the weld zone and the Vicker's hardness HV M of the matrix is 10 to 40 in range; and in that a ratio RT (=T W /T M ) between a bead thickness T W of the weld zone and a thickness T M of the matrix is 1.05 to 1.3.