Carbides in low-temperature-carburized stainless steels

Abstract A novel, low-temperature (470 °C) gas-phase carburization treatment, developed by the Swagelok Company, increases the surface hardness of 316-type austenitic stainless steels from ≈200 to ≈1000HV25 via a colossal supersaturation of up to 12 at.% carbon in solid solution. Upon extended treatment, carbide precipitation does eventually occur. Transmission electron microscopy of carburized bulk, foil, and powder samples has revealed two different carbides: M 5 C 2 (“Hagg” or “χ” carbide) and M 7 C 3 . The particles of both carbides have the shape of long needles or laths, contain a high density of planar defects normal to the particle axis, and adopt special topotaxial orientation relationships with the austenite matrix.