karburoinnin

Karburoinnin, or carburization, is a heat-treating process used to increase the surface hardness and wear resistance of steel by introducing carbon into its surface layer. The carbon diffuses from a carbon-rich atmosphere or from solid carbon sources into the iron-carbon matrix at elevated temperatures, forming a carburized case atop a comparatively tougher core.

Common methods include gas carburizing, pack carburizing, liquid (salt-bath) carburizing, and plasma carburizing. Gas carburizing controls the process with a carbon-rich atmosphere and a defined carbon potential; pack carburizing encloses the parts in a carbonaceous pack that releases carbon during heating; liquid carburizing uses molten salt baths; plasma carburizing employs low-pressure plasma to deliver carbon. Typical temperatures range from about 850 to 980°C for steel, with process times from minutes to many hours depending on desired case depth. After carburizing, parts are usually quenched and tempered to achieve a balance of surface hardness, core toughness, and residual stress.

The resulting case hardness can greatly exceed the core hardness, and case depths commonly range from fractions of a millimeter to several millimeters. Carburized components include gears, camshafts, bearings, and cutting tools. Process control focuses on temperature, time, atmosphere or carbon potential, and cooling rate. Potential drawbacks include distortion, decarburization near the surface if exposure conditions are excessive, and the need for subsequent finishing operations to achieve final geometry and dimensional accuracy.