Karbonitridoinnin

Karbonitridoinnin is a surface-hardening heat treatment used to improve the wear resistance and fatigue life of steel by creating a hard, diffusion-dominated case on the surface while keeping the core relatively tough. The process combines carbon uptake with nitrogen diffusion, producing a hardened layer that enhances surface properties without significantly altering overall dimensions.

Typical implementation involves heating steel to high temperatures in a carbon- and nitrogen-rich environment. Gas carbonitriding, often conducted around 870–950°C, uses a mixture that may include ammonia and carbon-bearing gases. Salt-bath variants and plasma-assisted methods are also used. Diffusion times range from short cycles to several hours, after which the part is cooled and often tempered to balance hardness and toughness.

The treated steels are usually low- to medium-carbon steels or alloy steels. The resulting surface hardness commonly reaches high values (often around 550–700 HV or about 60 HRC), with a case depth typically in the range of 0.2–0.8 mm, depending on material, time, and temperature. The core retains ductility, contributing to overall toughness and resistance to shock.

Compared with pure nitriding (nitrogen only) and carburizing (carbon only), carbonitriding offers a compromise: greater case depth than nitriding and lower process temperatures than carburizing, with efficient improvements in wear resistance and fatigue strength.

After-treatment steps may include finishing grinding to remove any brittle surface layer, tempering to relieve stresses, and sometimes additional polishing. Environmental and safety considerations include the use of ammonia gas or hazardous salt baths in some variants.

Applications span gears, cams, shafts, rollers, bearings, and cutting tools where a hard surface and a tough core are beneficial.