Two stage gas-nitriding processes can be used to prevent the formation of white layer. White layer thickness may vary between 0.0003 and 0.002 in. which depends on nitriding time. The most commonly nitrided steels are chromium-molybdenum alloy steels and Nitralloys. Surface hardnesses of 55 HRC to 70 HRC can be achieved with case depths varying from 0.005 in to 0.020 in. Nitrided steels are very hard and grinding operations should not be performed after nitriding.
White layer is removed by lapping.
Methane or paropane serve as the source of carbon, the ammonia serves as the source of nitrogen. Quenching is done in a gas which is not as severe as water quench. As a result of les severe quench, there is less distortion on the material to be treated. A typical carbonitriding system is shown in the following slide. Case hardnesses of HRC 60 to 65 are achieved at the surface.