Carbonitriding is the absorption andĀ diffusionĀ ofĀ carbonĀ andĀ nitrogenĀ into the surface of steel to give a hard surface and softerĀ coreĀ afterĀ hardeningĀ byĀ quenching. Carbonitriding is a surface heat treatment, a form ofĀ case hardening, for plain low carbon andĀ low alloy steelsĀ and castĀ irons, which provides wear resistance and moderate load bearing capability.s
It is found withĀ plain carbon steels, that the use ofĀ gas carburisingĀ is restricted to small section sizes if theĀ caseĀ is to be fully hardened by oil quenching. The addition of nitrogen (provided by addingĀ ammoniaĀ as well as propane to the furnaceĀ atmosphereĀ in aĀ sealed quenchĀ furnace), increases surfaceĀ hardenabilityĀ by allowing both carbon and nitrogen diffusion to occur. Carbonitriding can therefore be considered as a gaseous equivalent to cyanideĀ salt bath hardening. The normal range of temperature employed is 820/910°C, with 870°C being the optimum temperature for best case hardening conditions with the majority of suitable steels. Single quench treatments are generally employed and the process is mainly used for case depths up to 0.75mm (0.030″). For deeper cases in plain carbon steels it is useful to carburise only at 930/950°C and then reduce the furnace temperature to 870°C and complete the process by carbonitriding followed by oil quenching.
Fluid bedĀ furnaces may also be employed to provide carbonitriding heat treatment. This method is particularly suited to the treatment of small components and those whose geometry would be prone to masking and attendant uneven hardening, were the sealed quench method to be used. Cyanide salt bath treatments have now largely been superseded by fluid bed treatments which do not have the health and safety and environmental risks associated with the operational and disposal aspects of cyanide salt baths.
As with all hardening processes, it is good practice to finish with a tempering treatment to reduce brittleness and impart optimum strength. Irrespective of which carbonitriding method is used, a tempering temperature of 150°C is generally suitable.
Carbonitriding should not be confused with its lower temperature partner,Ā nitrocarburising.
Carbonitriding is the absorption andĀ diffusionĀ ofĀ carbonĀ andĀ nitrogenĀ into the surface of steel to give a hard surface and softerĀ coreĀ afterĀ hardeningĀ byĀ quenching. Carbonitriding is a surface heat treatment, a form ofĀ case hardening, for plain low carbon andĀ low alloy steelsĀ and castĀ irons, which provides wear resistance and moderate load bearing capability.s
It is found withĀ plain carbon steels, that the use ofĀ gas carburisingĀ is restricted to small section sizes if theĀ caseĀ is to be fully hardened by oil quenching. The addition of nitrogen (provided by addingĀ ammoniaĀ as well as propane to the furnaceĀ atmosphereĀ in aĀ sealed quenchĀ furnace), increases surfaceĀ hardenabilityĀ by allowing both carbon and nitrogen diffusion to occur. Carbonitriding can therefore be considered as a gaseous equivalent to cyanideĀ salt bath hardening. The normal range of temperature employed is 820/910°C, with 870°C being the optimum temperature for best case hardening conditions with the majority of suitable steels. Single quench treatments are generally employed and the process is mainly used for case depths up to 0.75mm (0.030″). For deeper cases in plain carbon steels it is useful to carburise only at 930/950°C and then reduce the furnace temperature to 870°C and complete the process by carbonitriding followed by oil quenching.
Fluid bedĀ furnaces may also be employed to provide carbonitriding heat treatment. This method is particularly suited to the treatment of small components and those whose geometry would be prone to masking and attendant uneven hardening, were the sealed quench method to be used. Cyanide salt bath treatments have now largely been superseded by fluid bed treatments which do not have the health and safety and environmental risks associated with the operational and disposal aspects of cyanide salt baths.
As with all hardening processes, it is good practice to finish with a tempering treatment to reduce brittleness and impart optimum strength. Irrespective of which carbonitriding method is used, a tempering temperature of 150°C is generally suitable.
Carbonitriding should not be confused with its lower temperature partner,Ā nitrocarburising.
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