Carburizing

Carburizing is a case hardening heat treatment used to harden the surface of low- to medium-carbon steels while preserving a tougher, more ductile core. The process introduces carbon into the surface by exposing the steel to a carbon-rich environment at elevated temperatures, typically 875–980°C (1600–1800°F). Methods include pack carburizing, gas carburizing, vacuum carburizing, and liquid carburizing. Pack carburizing uses a carbonaceous material surrounding the workpiece; gas carburizing relies on a carbon-bearing atmosphere; vacuum carburizing applies a controlled carbon potential under vacuum; liquid carburizing uses a salt bath.

During treatment, carbon diffuses into the surface to create a higher carbon case. After diffusion, the part is often quenched to transform the retained austenite and carbon-rich layer into martensite, producing a hard, wear-resistant surface. A tempering step is commonly applied to reduce residual stresses and brittleness.

Typical case depths range from roughly 0.25 to 3 mm, depending on alloy, temperature, and time. Carburized parts are commonly tempered to achieve target hardness and toughness. The main applications are gears, shafts, camshafts, bearings, and other components requiring a hard, wear-resistant surface with a tough core.

Advantages include improved surface hardness, wear resistance, and fatigue life with relatively little sacrifice of core toughness. Disadvantages include distortion risk during processing, potential for surface defects if the atmosphere is not properly controlled, and the need for subsequent finishing operations such as polishing or grinding.

Carburizing has been widely used in the steel industry since the early 20th century and remains standard for producing high-performance gears and precision components.