Patent ID: 7476282

Claim:
A high-strength martensitic stainless steel pipe, excellent in toughness and hot workability, which comprises by mass percent, C: 0.18 to 0.22%, Si: 0.1 to 0.5%, Mn: 0.40 to 1.00%, P: 0.011 to 0.018%, S: 0.003% or less, Cr: 11.50 to 13.50%, Ni: 0.5% or less, Al: 0.0005 to 0.003%, N: 0.012 to 0.040%, Cu: 0.25% or less, Ti: 0.05% or less, V: 0.02 to 0.18%, Mo: 0 to 0.05%, Nb: 0.001 to 0.009%, B: 0.0010% or less, and Ca: 0.0050% or less, with the balance being Fe and impurities, and having a value of fn represented by the following formula (A) satisfying 15 to 80, a yield strength of 650 MPa or more and a toughness exceeding 70 J/cm 2 by impact value in the Charpy impact test at 0 degrees C. using V-notch test pieces; fn= 50Mo+500( V− 0.04)+5000Nb (A), wherein an element symbol appearing in the formula (A) represents the content by mass percent of the corresponding element included in the steel.