Carburized

Carburized is a term used in metallurgy to describe steel or iron that has undergone carburization, a heat-treatment process in which carbon diffuses into the surface layer to form a hard, wear-resistant case while preserving a softer core.

During carburizing, the workpiece is heated to high temperatures in a carbon-rich environment. Carbon atoms diffuse into the surface, increasing the carbon content near the surface. After carburizing, the part is commonly quenched to harden the case and may be tempered to balance hardness with toughness.

Common methods include gas carburizing, pack carburizing, vacuum carburizing, and liquid carburizing. Gas carburizing uses a controlled hydrocarbon atmosphere; pack carburizing packs the parts in a carbonaceous material; vacuum carburizing uses low pressure with a carbon source; liquid carburizing employs molten salt or similar baths. Each method yields different case depths and surface compositions and is chosen based on geometry, material, and production requirements.

The resulting microstructure typically features a hardened case of martensite over a softer core. Case depths can range from a few tenths of a millimeter to several millimeters, and surface hardness commonly exceeds 60 HRC, depending on alloy composition and process parameters. Post-carburizing quenching and tempering further tailor hardness, residual stresses, and toughness.

Carburized steel is widely used for gears, camshafts, crankshafts, bearing races, and other wear-bearing components where a hard surface and tough core improve fatigue life and wear resistance. Process control is important to minimize distortion and residual stresses, and carburized parts may require finishing and straightening after treatment.