HIGH STRENGTH MARTENSITIC STAINLESS STEEL PIPE FOR OIL WELL EXCELLENT IN BALANCE OF STRENGTH-TOUGHNESS AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a high strength martensitic stainless steel pipe for an oil well having high strength of YS: ≥758 MPa (110 ksi) and high toughness in which Charpy absorbed energy v E-10 at -10°C is ≥50 J and excellent in a balance of strength-toughness and to provide its production method.;SOLUTION: A steel pipe having a composition containing, by mass, 0.17 to 0.22% C, ≤1.0% Si, 0.25 to 1.0% Mn, 12 to 14% Cr, 0.01 to 0.5% Ni, 0.001 to 0.06% N and 0.01 to 0.07% Nb is subjected to quenching treatment so as to be austenitized at a temperature in the range of (the Ac3 transformation point) to 1,100°C for a time in the range of 60 to 1,800 s also as a heating temperature T (°C) and for a holding time t(s) satisfying T+100 log (t/60)-500 (C+N)-4,000 Nb≤880 and thereafter be cooled and is next subjected to tempering treatment at the Ac1 transformation point or lower.;COPYRIGHT: (C)2002,JPO