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Carbonitriding is one of the heat-treating processes under various gas atmospheres and temperatures mainly to improve hardness, wear-resistance, and fatigue or tensile strength properties of industrial parts in order to prolong their lifespan and improve their properties to suit specific usability.

Carbonitriding is a process in which carbon and nitrogen are simultaneously infiltrated into the surface of steel at a temperature of about 800°C to 880°C, lower than ordinary gas carburizing, and then quenched and hardened. In gas carbonitriding, NH3 gas is added to a normal gas carburizing atmosphere, and nitriding and carburizing are performed simultaneously by

the N component decomposed from NH3. Since the hardenability is improved by nitriding, it is possible to treat non-alloy steel such as SPCC and low carbon steel which cannot be applied by gas carburizing, and the reduction of material cost is also a great advantage. Since it can be quenched at a lower temperature than gas carburizing, deformation, and distortion due to heat treatment can be reduced. Characteristics of gas carbonitriding are including

1. Applicable steel type: Low carbon steel (low carbon steel such as SP material, SS material, S10C), case hardening steel (low carbon alloy steel such as SCM / SCr / SNCM)
2. Quenching is possible at low temperatures, reducing quench deformation (Excluding case-hardened steel)
3. Since the hardenability is improved by the influence of nitrogen, quenching becomes easy even with carbon steel, which is advantageous in terms of quenching cracking.
4. Compared to gas carburization, the abnormal hardening layer on the outermost surface is suppressed, and a uniform hardened layer can be generated.
5. Improved temper softening resistance compared to gas carburizing.

This process is important because it can improve the mechanical properties of the metal, such as its hardness and toughness. In addition, carbonitriding can also help to protect the metal from corrosion.

The carbonitriding process usually applies with power units parts such as engines, transmissions, and differentials parts (connecting rod, crankshaft, transmission gear/shafts, CVT pulley shaft, driveshaft, constant velocity joint parts, final gear, differential side gear, etc.)