Change in Dimensions and Surface Roughness of 42CrMo4 Steel after Nitridation in Plasma and Gas

Abstract

The influence of plasma nitriding and gas nitriding processes on the change of surface roughness and dimensional accuracy of 42CrMo4 steel was investigated in this paper. Both processes almost always led to changes in the surface texture. After plasma nitriding, clusters of nitride ions were formed on the surface of steel, while gas nitriding very often led to the new creation of a formation of a “plate-like” surface texture. In both cases of these processes, a compound layer in specific thickness was formed, although the parameters of the processes were chosen with the aim of suppressing it. After the optimizing of nitriding parameters during nitriding processes, it was found that there were no changes in the surface roughness evaluated using the Ra parameter. However, it turned out that when using a multi-parameter evaluation of roughness (the parameters Rz, Rsk and Rku were used), there were presented some changes in roughness due to nitriding processes, which affect the functional behavior of the components. Roughness changes were also detected by evaluating surface roughness profiles, where nitriding led to changes in peak heights and valley depths. Nitriding processes further led to changes in dimensions in the form of an increase of 0.032 mm on average. However, the magnitude of the change has some context on chemical composition of material. A larger increase in dimensions was found with gas nitriding. The change in the degree of IT accuracy is closely related to the change in dimension. For both processes, there was a change of one degree of IT accuracy compared to the ground part (from IT8 to IT9). On the basis of the achieved dimensional accuracy results, a coefficient of change in the degree of accuracy IT was created, which can be used to predict changes in the dimensional accuracy of ground surfaces after nitriding processes in degrees of accuracy IT3–IT10. In this study, a tool for predicting changes in degrees of accuracy of ground parts after nitriding processes is presented.

Influence of Surface Roughness on the Properties of Nitrided Layer on 42CrMo4 Steel

“…42CrMo4 steel was selected for the present experiment due to its popularity in nitriding processes [ 7 , 19 , 20 , 21 , 26 , 27 ]. Its chemical composition is shown in Table 1 .…”

“…The material is applied in components such as gear wheels, crankshafts and barrel and breechblock mechanisms due to the high strength and high toughness properties of the steel grade. However, the steel has characteristics of unfavorable tribological properties due to its low abrasive resistance [ 19 , 21 , 22 ]. Surface properties of 42CrMo4 steel can be improved by thermochemical treatment—nitriding [ 23 , 24 , 25 ].…”

“…A significant factor is the grade of the applied material [15,16]. Dobrocky et al [19] investigated changes of surface roughness of 42CrMo4 steel after nitriding in plasma and gas. The results showed no changes in the Ra parameter after the nitriding process and small decrease in other roughness parameters such as Rz.…”

Diffusion Nitride Coatings for Heat-Resistant Steels

“…However, the authors proved that using hard nitriding for tool steels shows the highest wear resistance values compared to gas and plasma nitriding. Dobrocky et al [23] compared the effects of gas and plasma nitriding for 42CrMo4 alloy steel on its surface roughness and dimensional accuracy. The analysis of the results of the experiments confirmed the expected increase in surface hardness of the material, reduction in the coefficient of friction, and increase in wear resistance.…”