gascarburizing

Gas carburizing is a heat treatment process used to harden the outer surface of steel while leaving the core relatively soft and tough. By exposing steel to a carbon-rich atmosphere at high temperatures, carbon diffuses into the surface to form a hardened diffusion layer or “case.” Typical alloy steels treated this way develop case depths ranging from fractions of a millimeter to a few millimeters, depending on time, temperature, and carbon potential.

The process is carried out in a furnace where a controlled carburizing atmosphere is maintained. Common atmospheres are hydrocarbon-based gases (such as natural gas, methane, or propane) diluted with nitrogen and hydrogen, or endothermic gas generated from a hydrocarbon/air reaction. The carbon potential of the atmosphere is adjusted to achieve the desired case depth while minimizing decarburization or excessive scale. Parts are held at temperatures around 900–980°C (about 1650–1800°F) for a period that yields the target case thickness, then rapidly quenched to obtain a martensitic hardened surface.

Post-carburizing treatments typically include quenching followed by tempering to achieve the required balance of hardness, strength, and toughness. The hardened case improves wear resistance, fatigue life, and load-carrying capability, especially for gears, camshafts, crankshafts, bearings, and other components subjected to surface contact and friction.

Variants of carburizing include vacuum or sealed-atmosphere carburizing and continuous or batch processes. Gas carburizing is valued for its ability to produce uniform, well-controlled cases with good dimensional stability and suitability for complex shapes.