Patent ID: 8747575

Claim:
A 655 MPa grade martensitic stainless steel without containing Nb, having high toughness, comprising C: 0.029-0.05%, Si: 0.1-0.5%, Mn: 0.1-2.0%, P: 0.05% or less, S: 0.005% or less, Cr: 10.0-12.5%, Mo: 0.1-0.5%, Ni: 2.2-3.0%, N: 0.02% or less, Al: 0.01-0.1% by weight, wherein the 655 MPa grade martensitic stainless steel has an FI value, defined by the formula [FI=Cr+Mo−Ni−30 (C+N)], of 7.93 to 8.45 and a balance of substantially Fe, wherein the 655 MPa grade martensitic steel is characterized by having a single phase martensite with a delta ferrite of below 0.13%.