Colossal carbon supersaturation in austenitic stainless steels carburized at low temperature Original Research Article

A novel, low-temperature (470 °C) gas-phase carburization treatment, developed by the Swagelok Company, increases the surface hardness of 316 austenitic stainless steels from ≈200 to ≈1000 HV25 and improves the corrosion resistance. While normally the precipitation of carbides restricts the carbon concentration in the austenite of 316 steels to <0.015 at%, the Swagelok treatment generates a colossal supersaturation of up to 12 at% carbon in solid solution. Only upon extended treatment, does carbide precipitation eventually occur, but the colossal carbon supersaturation of the austenite is maintained. Unusual for austenitic stainless steels, the precipitates are Hägg carbide (M5C2).