Abstract: A high strength martensitic stainless steel contains:0.06 wt. % or less C, 12 to 16 wt. % Cr, 1 wt. % or less Si, 2 wt. % or less Mn, 0.5 to 8 wt. % Ni, 0.1 to 2.5 wt. % Mo, 0.3 to 4 wt. % Cu, 0.05 wt. % or less N, and the balance being Fe and inevitable impurities;said steel having an area ratio of .delta.-ferrite phase of at most 10%; andsaid steel having fine copper precipitates dispersed in a matrix.And further a method for making the stainless steel comprises austenitizing, cooling and tempering.

Abstract: A martensitic stainless steel having good corrosion resistance suitable for use in an oil well having 0.08 to 0.25 wt. % C, 14 to 16 wt. % Cr, 1.0 wt. % or less Si, 2.0 wt. % or less Mn, 0.5 to 3.0 wt. % Ni, 0.03 to 0.10 wt. % N, 0.04 wt. % or less P, 0.01 wt. % or less S, 0.1 to 1.0 wt. % Mo, the balance being Fe and inevitable impurities. The Cr, C, Ni and N being in amounts such that 20 wt. % .gtoreq.Cr-12C+0.75 Ni+10N.gtoreq.13 wt. %. The martensitic stainless steel having a content of .delta.-ferrite of 10% or less. The martensitic stainless steel can contain at least one of 0.05 to 0.30 wt. % V and 0.01 to 0.1 wt. % Nb. Also the martensitic stainless steel can contain 0.5 to 3.0 wt. % Cu. Further the martensitic stainless steel can contain 0.5 to 3.0 wt. % Cu, and at least one of 0.05 to 3.0 wt. % V and 0.01 to 0.1 wt. % Nb.

Abstract: The austenite alloy tube has a composition of 15.about.26% of Cr, 8.about.35% of Ni, 1.0% or less of Si, 2.0% or less of Mn and less than 0.25% of N and the balance of iron and impurities. The nitrogen content on the inner surface of the tube is at least 0.25%. If desired, one or more of 0.6% or less of Ti, 0.6% or less of Al, 3.0% or less of Mo and 1.0% or less of Nb may be incorporated.