The heat treatment of fasteners falls into three categories of material selection.  Medium strength and ductility properties can be achieved with carbon and alloy steel heat treated by oil quench harden and temper.  The same properties can be achieved by hardening 400 series stainless steel.  The carbon and alloy steel hardening is typically performed in continuous atmosphere oil quench furnaces for small parts and in atmosphere batch furnaces for large parts.  The stainless steel bright hardening is typically performed in hydrogen atmosphere continuous belt furnaces for small parts and in vacuum furnaces for large parts.

Fasteners may also achieve self tapping properties with light case carbonitriding of carbon steel parts.  This treatment may be performed in batch or continuous atmosphere furnaces.  The resulting microstructure is typically 0.001” to 0.003” file hard case and core hardness in the range of Rc 20 to Rc 40, depending on material selection and final application requirements.