gaskarburisering

Gaskarburisering, commonly referred to as gas carburizing in English, is a thermo-chemical surface hardening process used to increase the hardness and wear resistance of the outer layer of steel by diffusing carbon from a hydrocarbon-containing gas into the surface at elevated temperature.

The process takes place in a furnace with a controlled gas atmosphere. Typical carburizing temperatures are about 880–980°C (1600–1790°F). The gas mixture may include methane, propane, natural gas, and other hydrocarbons, often with hydrogen or nitrogen as diluents. A controlled carbon potential is maintained to regulate carbon uptake and diffusion, creating a surface layer with elevated carbon content. Case depths vary with temperature, time, and steel chemistry, ranging from a few tenths of a millimeter to over a millimeter. After carburizing, the part is usually cooled and prepared for hardening, often by quenching.

Post-processing commonly involves quenching from the carburizing temperature to form martensite in the case, followed by tempering to achieve the desired hardness and toughness. Some cycles include diffusion annealing or subsequent surface treatments such as nitriding to improve wear resistance or fatigue life.

Materials typically carburized include medium- and high-carbon steels and certain alloy steels designed for carburizing. The presence of alloying elements like chromium, nickel, and molybdenum influences diffusion, carbide formation, and the final surface properties.

Advantages of gas carburizing include a relatively uniform and controllable surface hardening and suitability for complex geometries and larger parts. It can be more energy-efficient than some other carburizing methods and allows precise control of the surface carbon content. Limitations include longer cycle times, equipment and process costs, and the need for careful control to avoid excessive case depth or distortion. Gas carburizing is often followed by other surface engineering steps, such as nitriding or carbonitriding, to tailor surface properties.