High-strength seamless stainless steel pipe and method of manufacturing high-strength seamless stainless steel pipe

Abstract

A high-strength seamless stainless steel pipe has a composition including, by mass %, 0.05% or less C, 1.0% or less Si, 0.1 to 0.5% Mn, 0.05% or less P, 0.005% or less S, more than 16.0% to 18.0% or less Cr, more than 2.0% to 3.0% or less Mo, 0.5 to 3.5% Cu, 3.0% or more and less than 5.0% Ni, 0.01 to 3.0% W, 0.01 to 0.5% Nb, 0.001 to 0.3% Ti, 0.001 to 0.1% Al, less than 0.07% N, 0.01% or less O, and Fe and unavoidable impurities as a balance, wherein the steel pipe has a microstructure including a tempered martensite phase forming a main phase, 20 to 40% of a ferrite phase in terms of volume ratio, and 25% or less of a residual austenite phase in terms of volume ratio, an average grain size of the ferrite phase is 40 μm or less, and a sum of amounts of Ti and Nb precipitated as precipitates having a grain size of 2 μm or less is 0.06 mass % or more, whereby the steel pipe has high strength where yield strength YS is 758 MPa or more and high toughness where an absorbing energy value vE−10 in a Charpy impact test at a test temperature of −10° C. is 40 J or more.

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