Carburization

Carburization is a thermochemical heat-treatment process that diffuses carbon into the surface of low-carbon or alloy steel at elevated temperatures, producing a hard, wear-resistant case while retaining a tough, ductile core. It is typically followed by quenching and often tempering to lock in the hardened structure. This case-hardening technique is applied primarily to gears, shafts, splined components, and loaded wear surfaces.

On the shop floor, carburization is used for parts that must survive heavy rolling or sliding contact—gears, shafts, splined components, and wear surfaces. These parts are rough-machined soft, then carburized in a carbon-rich furnace atmosphere around 850–950°C and quenched, producing a hard case that can reach HRC 58–60 while the core stays tough. Because the cycle distorts the part and changes dimensions, extra stock must be left on critical features for finish grinding or corrective machining after heat treatment. Case depth is governed by time, temperature, and carbon potential, so the CNC operator has to plan for growth, warpage, and hardness gradients. The practical sequence is: remove most material first, carburize and quench, then finish grind the hardened case. This leaves a wear-resistant surface and a tough core, which is why carburized components resist pitting and surface fatigue under repeated contact loads.

• ⚠️Distortion after quench: Thin sections, long shafts, and asymmetric geometries move during heating and quenching, pushing bores, faces, and journals out of round or bowed. This forces heavy post-grinding and can scrap parts when stock allowance is insufficient.
• ⚠️Insufficient case depth: If cycle time, temperature, or carbon potential is too low, the carbon-enriched layer is too shallow to carry the service load. The surface may look fine but fails early by pitting, spalling, or wear-through.
• ⚠️Brittle over-carburized surface: Excessive carbon creates an overly hard, brittle case with retained austenite or carbide-rich layers. Parts grind poorly, chip at sharp corners, or crack at fillets after quench because the heat-treat cycle was pushed too aggressively.