Carburieren

Carburieren, or carburizing, is a heat treatment process used to harden the surface of steel by introducing carbon while the metal is heated in a carbon-rich environment. This creates a hard, wear-resistant outer layer while preserving a tougher, more ductile core, a combination valued for surface fatigue resistance and longevity of gears, bearings, and other components.

The process typically heats steel to austenitizing temperatures, roughly 900 to 980°C, in a carbon-containing atmosphere or medium. Carbon diffuses into the surface, increasing its carbon content. After a specified diffusion time, the part is quenched to transform the high-carbon surface into martensite, and then tempered to achieve the desired balance of hardness and toughness.

Variants of carburizing include gas carburizing, pack (solid) carburizing, vacuum carburizing, and plasma carburizing. Gas carburizing uses a controlled carbon potential in a gaseous mixture (often containing methane or other hydrocarbons). Pack carburizing employs a solid carbon source in a sealed medium. Vacuum and plasma carburizing offer tighter control and cleaner processing, with similar diffusion aims.

Typical case depths range from about 0.25 to 3 millimeters, depending on alloy composition, temperature, and time. Surface hardness after quenching and tempering commonly reaches around 60–65 HRC, while the core remains softer and more tough, often in the 30–40 HRC range. Materials are usually low to medium carbon steels (approximately 0.15–0.4% C), sometimes alloyed to tailor case properties.

Quality is evaluated by hardness profiling and microstructural assessment to verify case depth and uniformity. Carburizing has a long history in manufacturing and remains a standard method to improve wear resistance in critical steel parts.