UDC 621.162 © Jan Senatorski, Jan Tacikowski, Ewa Kasprzycka, Bogdan Bogdanski APPLICATION OF NITRIDING TO IMPROVE TRIBOLOGICAL PROPERTIES OF CONSTRUCTIONAL STEEL The study presents results from investigation of tribological properties demonstrated by nitrided layers developed on 18HGT and 38HMJ constructional steels with use of the controlled gas nitriding. <...> It was revealed that application of the gas nitriding process to samples of 18HGT and 38HMJ constructional steel grades significantly improved their resistance to friction wear. <...> INTRODUCTION Gas (ammonia) nitriding of steel that consists in introduction of nitrogen atoms into the surface layer of the metal by means of the diffusion process is used to improve the fatigue life of steel, its resistance to friction wear and jamming of mating components [1 – 6]. <...> The nitriding process represents a low-temperature (450 – 650°C) thermal and chemical treatment technology that is widely applied in industry to various products, mainly made of steel, both to single units and to mass or serial production and its popularity is permanently growing. <...> It is a cost-effective alternative to widespread high temperature technologies (800 – 950°C) thermal and chemical treatment methods, such as carburizing or carbonitriding. <...> The gas nitriding technology leads to development of a diffusive case on the metal surface, where the layer thickness is up to 0.6mm and its hardness reaches as much as 1300 HV, which makes the parts more resistant to wear due to friction, seizure and fatigue impacts [10 – 13]. <...> This study focused on determination of friction wear resistance demonstrated by the 18HGT steel grade that used to be surface hardened by gas carburizing as well as the 38HMJ steel grade that is typically treated by nitriding. 2. <...> DEVELOPMENT OF PROTECTIVE CASES Nitrided cases were developed on samples made of cases with the desired surface concentration of nitrogen. <...> INVESTIGATION METHODOLOGY Nitrided cases were developed on samples with the dimensions of 8 x 35 mm. The mating conical samthe 18HGT and 38HMJ steel grades. <...> The technology assumed short-term treatment in the controlled atmosphere of the NH3 type that enables formation of ples with the dimensions 23/12x13 mm were made of the 45 steel grade with thermal treatment <...>