Abstract: The invention provides a steel pipe excellent in deformation characteristics, most notably a steel pipe for expandable-pipe oil well and a low-yield-ratio line pipe, and a method of producing the same without conducting water cooling requiring large-scale heat treatment equipment, namely a method of producing a steel pipe excellent in deformation characteristics whose microstructure is a two-phase structure including a martensite-austenite constituent at an area fraction of 2 to 10% and a soft phase, which method comprises: heating at Ac1+10° C. to Ac1+60° C. and thereafter cooling a precursor steel pipe which contains, in mass %, C: 0.04 to 0.10% and Mn: 1.00 to 2.50%, is limited to Si: 0.80% or less, P: 0.03% or less, S: 0.01% or less, Al: 0.10% or less and N: 0.01% or less, further contains one or more of Ni: 1.00% or less, Mo: 0.60% or less, Cr: 1.00% or less and Cu: 1.00% or less, where content of Mn and content of one or more of Cr, Ni, Mo and Cu satisfy Mn+Cr+Ni+2Mo+Cu?2.

Abstract: A high-corrosion-resistant martensitic stainless steel possessing excellent weldability and SSC resistance, having a tempered martensitic structure, characterized by comprising steel constituents satisfying by weight C: 0.005 to 0.035%, Si: not more than 0.50%, Mn: 0.1 to 1.0%, P: not more than 0.03%, S: not more than 0.005%, Mo: 1.0 to 3.0%, Cu: 1.0 to 4.0%, Ni: 1.5 to 5.0%, Al: not more than 0.06%, N: not more than 0.01%, and Cr satisfying a requirement represented by the formula 13>Cr+1.6Mo.gtoreq.8,C+N.gtoreq.0.03,40C+34N+Ni+0.3Cu-1.1Cr-1.8 Mo.gtoreq.10,or further comprising at least one element selected from the group consisting of Ti: 0.05 to 0.1%, Zr: 0.01 to 0.2%, Ca: 0.001 to 0.02%, and REM: 0.003 to 0.4%, with the balance consisting essentially of Fe. A process for producing a martensitic stainless steel, comprising the steps of: subjecting a steel plate, produced by hot-rolling a stainless steel slab having the above composition, to austenitization at a temperature of Ac.sub.3 point to 1000.