What largely determines the hardness of martensitic stainless steels?

The hardness of martensitic stainless steels is largely determined by the carbon content. In these types of stainless steels, martensite is formed through a heat treatment process that involves quenching. The carbon present in the alloy plays a critical role in the formation of martensite during this transformation.

Higher carbon levels increase the ability of the steel to harden when it undergoes quenching, as carbon acts to restrict dislocation movement within the crystal structure of the iron, thereby enhancing hardness. Martensitic stainless steels typically have a carbon content that can range from about 0.1% to over 1.0%, with greater amounts of carbon leading to increased hardness levels after quenching.

While chromium, nickel, and manganese are important alloying elements that contribute to the overall properties of the steel (like corrosion resistance and toughness), it is the carbon content that has the most significant impact on hardness in martensitic structures. Therefore, in the context of martensitic stainless steels, carbon content is the key factor influencing hardness.