Patent ID: 8333849

Claim:
A low-carbon martensitic chromium-containing steel comprising: 0.02% to 0.10% by mass of carbon and 0.02% to 0.10% by mass of nitrogen, the total content of carbon and nitrogen being 0.08% to 0.16% by mass; 0.5% by mass or less of silicon; 0.1% by mass or less of aluminum; 0.3% to 3.0% by mass of manganese; 10.5% to 13.5% by mass of chromium; 0.05% to 0.60% by mass of niobium and 0.15% to 0.80% by mass of vanadium, the total content of niobium and vanadium being 0.25% to 0.95% by mass; 0.02% to 2.0% by mass of nickel; and less than 0.5% by mass of copper; the balance comprising iron and incidental impurities; the steel having an Fp value of 80.0 to 96.0, a hardness after quenching of HRC 31 to 40, and a hardness after tempering at 700° C. for one hour of HRC 31 or more, the Fp value represented by equation (1): Fp value=−230C+5Si−5Mn−6Cu+10Cr−12Ni+32Nb+22V+12Mo+8W+10Ta+40Al−220N (1) wherein the element symbols denote the contents of the respective elements (% by mass).