Karburieren

Karburieren, or carburizing, is a heat-treatment process used to enrich the surface of steel with carbon. The resulting surface layer, known as the case, becomes hard and wear resistant, while the core remains comparatively softer and tougher. The process is commonly applied to low- and medium-carbon steels to achieve a durable exterior without sacrificing core toughness.

Carburizing is typically performed by heating parts to austenitizing temperatures in a carbon-rich environment. Common variants include gas carburizing, pack carburizing, and vacuum carburizing. In gas carburizing, a hydrocarbon-containing atmosphere (such as endothermic gas, methane, or propane) diffuses carbon into the surface. In pack carburizing, parts are enclosed with a carbonaceous pack and heated. Vacuum carburizing uses hydrocarbon gas in a vacuum furnace to improve control and reduce distortion. The carbon potential and temperature are carefully controlled to achieve the desired case depth and carbon content.

Typical temperatures range around 875 to 950 degrees Celsius, with process times varying according to the required case depth. After diffusion, the parts are quenched to transform the carbon-enriched surface to martensite, producing high surface hardness. A subsequent tempering step adjusts hardness and relieves stresses to balance hardness with toughness.

Applications include gears, camshafts, crankshafts, shafts, and fasteners—components where a hard, wear-resistant surface is beneficial while the core remains impact resistant. Advantages of karburieren are high surface hardness and improved fatigue life; drawbacks include equipment costs, sensitivity to decarburization and distortion if not properly controlled, and the need for additional finishing steps.