The current development of chemical-heat treatment technologies is aimed at increasing the utility properties of components and improving the quality of the produced surface. A prerequisite for a quality produced surface is the selection of a suitable method of surface machining before the application of chemical-heat treatment technology. Due to the requirements for functional areas of special technology, grinding is chosen in most cases. The present paper deals with the effect of nitriding in plasma and gas on the geometric accuracy of parts made of 42CrMo4 steel. This steel is widely used in special technology for the production of barrels, breech-block cases, ball screws and gears. On the ground steel samples, the 3D measurement on the coordinate measuring machine analyzed the change of dimensions after the application of nitriding in plasma and gas. Furthermore, the surface texture change was evaluated using 2D surface roughness parameters and 3D parameters of area. After nitriding in both plasma and gas, the dimensions increased by 0.034 mm in diameter. After the nitriding processes, the values of 2D and 3D surface roughness parameters decreased. A change in surface texture was observed when evaluating 3D parameters in both chemical-heat treatment processes. Increasing the dimensions and changing the texture of the surface affects the subsequent function of the components.

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Nitriding is a technology that leads to an increase in the utility value of the product. It's most important benefits include increased corrosion resistance, abrasion resistance, wear resistance, increased resistance to fatigue failure under cyclic loading, and many others. The design of a suitable nitriding technology not only on the basis of empirics requires a closer study of the relationship between the structure of the nitriding layer, its properties and the course of a particular degradation process. Because the life of most components is related to abrasion on the surface, the occurrence of fatigue cracks and corrosion effects, it is crucial to influence the mechanical and other properties in this surface area. High functional requirements are placed on the functional surfaces of steels for weapons production, which lead to a long service life, reliability and dependability of the components of the weapon system and its safe use. The paper discuss the influence of selected nitriding technologies on the mechanical properties of steel 42CrMo4 and 34CrNiMo6, especially on the hard and microhardness of surface layers, change of its structure and next to change the surface texture and dimension of component. The steels were nitrided in plasma and gas. Nitriding in gas led to more significant structural changes in the surface layer of both steels compared to plasma nitriding.

Carburizing is used in applications where there is a high demand for surface hardness and abrasion resistance along with core toughness requirements. Carburizing is mainly used for parts which are subjected to abrasion, such as shafts, pins, gears, cams, etc. At the same time as the hardness of the surface layer increases, the fatigue limit of the steel increases after carburizing. The article deals with the evaluation of surface quality of carburized steels 16MnCr5 and 14NiCr14 in terms of surface texture change and dimension change after application of carburizing. The analysed steels are used mainly in the production of gear wheels for gearboxes of wheeled, tracked and artillery. Furthermore, the coefficients of friction and wear were evaluated on these steels. The functional surfaces of heat-treated steels were analysed after grinding and after gas carburizing. The evaluation of the surface quality results in a deterioration of the surface roughness and an increase in dimensions after carburizing. The coefficient of friction after carburizing reaches a higher value compared to ground surfaces, while the coefficient of wear decreases.

Stainless steels, particularly the austenitic stainless grades are widely used in many industries due to good corrosion resistance, but very poor mechanical properties as surface hardness and wear resistance limit its possible use. Plasma nitriding is one of the few ways to increase the surface hardness of these steels, even though this will affect its corrosion resistance. This paper focuses on the description of the mechanical properties of nitrided layers in the two most widespread austenitic stainless steels AISI 304 and AISI 316L. The microstructure and properties of nitrided layers were evaluated by metallography and microhardness measurement. Surface properties of nitrided steels were characterized by Martens hardness. The results show that plasma nitriding created very hard nitrided layers with thickness about 40 μm and microhardness about 1300 HV0.05. Surface hardness measurements have shown that the maximum values for both steels are about 8.5 GPa, but have different behaviour under higher loads, when the AISI 316L nitrided layer began to crack on the surface and sink.