440C

440C is a martensitic stainless steel in the 440 series. It is characterized by relatively high carbon content and a chromium level typically in the range of 16–18%, which together allow heat treatment to produce high hardness while maintaining corrosion resistance for a stainless steel alloy. The nominal composition commonly cited is approximately carbon 0.95–1.20% and chromium 16–18%, with small amounts of manganese and silicon and very low levels of phosphorus and sulfur.

Heat treatment and properties

440C is designed to be hardened. Typical heat-treatment practice involves austenitizing around 1010–1050°C, followed by oil quenching and tempering to achieve the desired hardness. Hardened microstructures give high wear resistance. In practical applications, hardness after heat treatment is often in the range of about 58–60 HRC, with optimization capable of reaching roughly 60–62 HRC under controlled conditions. The alloy balances hardness with reasonable toughness for a high-carbon stainless steel.

Corrosion resistance and machinability

As a stainless steel, 440C offers better corrosion resistance than plain carbon steels, but it is not as corrosion resistant as many austenitic stainless steels. Its corrosion performance depends strongly on heat-treatment quality and subsequent maintenance. Machinability is moderate to difficult, particularly after hardening; machining is easier in the annealed condition, and carbide tooling is typically recommended for hardened workpieces.

Applications

440C is widely used for knife blades, where high edge retention and corrosion resistance are valued, as well as for surgical instruments and certain bearing components where hardness and wear resistance are important. It remains a common choice where a tough, wear-resistant stainless steel is needed.