Patent ID: 8168008

Claim:
A martensitic stainless steel seamless pipe containing: less than 0.0100% of C and less than or equal to 0.0050% of C sol ; less than 0.0100% of N; about 10% to about 14% of Cr; about 4% to about 7% of Ni; about 0.05% to about 1.0% of Si; about 0.1% to about 2.0% of Mn; about 0.3% or less of P; about 0.010% or less of S; about 0.001% to about 0.10% of Al; 0.02% to 0.1% of V; one or more selected from the group consisting of about 4% or less of Cu, about 4% or less of Co, about 4% or less of Mo, and about 4% or less of W; and one or more selected from the group consisting of about 0.15% or less of Ti, about 0.10% or less of Nb, about 0.10% or less of Zr, about 0.20% or less of Hf, and about 0.20% or less of Ta on a mass basis, the remainder being Fe and unavoidable impurities, wherein C sol is determined by equation (1): C sol =C−⅓×C pre (1) where C pre =12.0 {Ti/47.9+½(Nb/92.9+Zr/91.2)+⅓(V/50.9+Hf/178.5+Ta/180.9)−N/14.0} or C pre =0 when C pre <0, where C represents the carbon content, Ti represents the titanium content, Nb represents the niobium content, Zr represents the zirconium content, V represents the vanadium content, Hf represents the hafnium content, Ta represents the tantalum content, and N represents the nitrogen content on a mass basis, and martensite in a weld heat affected zone of the steel pipe is substantially free of Cr depleted zones.