Numerous trademarked, standardized or proprietary nitriding and ferritic nitrocarburizing recipes and control methods are used in industrial furnaces. Surface Combustion has developed a new tool to predict the in-process composition of nitriding and ferritic nitrocarburizing atmospheres from these different processes. In addition, the activities and potentials of carbon, nitrogen and oxygen can be found, leading to prediction of the associated equilibrium phase on the part surface. The theory behind the tool and the application of the tool to control nitriding and ferritic nitrocarburizing atmospheres will be discussed. An overview of different equipment designs that can use the tool will also be presented.

Because of its qualities such as surface uniformity and high load density, controlled gas nitriding is recognized as one of the best nitriding techniques available. It guarantees greater dimensional and surface morphology stability and, therefore, is applied to a variety of stainless steels components. Classical depassivation methods often contribute to a decreased corrosion resistance. In certain applications, alternative methods may be used to achieve the same extent of surface uniformity and similar results, without the use of classical halogen activation methods.

Dilatometry and transmission electron microscopy were used to characterize the effects of V content, Si content, tempering temperature and starting microstructure on the hardness and microstructural evolution of a 0.4 wt pct carbon steel after a simulated nitriding thermal cycle. When tempered at 500 °C, significant amounts of V are left in solution leading to precipitation during the nitride thermal cycle increasing the hardness and dilation strain. Increases in Si content also lead to higher core hardness after nitriding, but Si does not significantly increase dilation strain during nitriding. Bainite starting microstructures produced less dilation strain during nitriding compared to martensite starting microstructures when tempered at 500 °C.