Martensitic stainless steels are essentially Fe-Cr-C alloys. They are ferromagnetic, hardenable by heat treating, and generally resistant to corrosion only in relatively mild environments. Chromium content is generally in the range of 10.5 to 18%, and carbon content can exceed 1.2%. The most commonly used alloy within the martensitic stainless steel family is type 410, which contains approximately 12 wt% Cr and 0.1 wt% C to provide strength. The carbon level and, consequently, strength increase in the 420, 440A, 440B, and 440C alloy series. In the annealed condition, martensitic stainless steels have a tensile yield strength of approximately 275 MPa (40 ksi) and can be moderately hardened by cold working. However, martensitic alloys are typically heat treated by both hardening and tempering to yield strength levels up to 1900 MPa (275 ksi), depending primarily on carbon level. These alloys have good ductility and toughness properties, which decrease as strength increases. Martensitic stainless steels are specified when the application requires good tensile strength, creep, and fatigue strength properties, in combination with moderate corrosion resistance and heat resistance up to approximately 650° C (1200° F).