The work is concerned with the improvement of the technological process of chemical-thermal and thermal treatment of piston fingers made of 12ХH3A steel in order to improve the structure and to increase their fatigue strength. The microstructure of piston fingers made of 12ХH3A steel, which are subjected to cementation, hardening and low tempering to give them operational properties, and the structure of the fingers after the proposed technology—thermocycling, which is chosen to increase the fatigue strength of these parts, are studied. The piston pin is a responsible part of the crank mechanism. It is designed to convert the reciprocating stroke of the piston into the rotational movement of the crankshaft and is responsible for the reliable connection of the piston with the connecting rod. The piston pin works in difficult conditions; all the loads, to which the piston of the crank mechanism is subjected due to the combustion of the fuel-air mixture in the cylinders of the internal combustion engine, are transferred to the piston pin. These loads contribute to the appearance of such harmful defects of the piston pin as ovality, which is the cause of further destruction of the piston. The causes of premature failure of the piston pin include design and technological defects, among which we can highlight: non-compliance of the pin in terms of the dimensions of the seat size, the presence of backlash at the junction of the piston and pin, insufficient strength and hardness. Such conditions of operation of the parts of the crank-connecting mechanism require the materials of which the parts are made to have sufficient strength, rigidity, and resistance to operation. The material of the piston pin must provide high hardness and wear resistance of the surface, fatigue strength in combination with a viscous core. Piston fingers are made of low-carbon and low-alloy steels of grades 15, 15X, 20ХH. High-nickel steels 12ХН3A, 12Х2Н4A are used for the production of loaded piston fingers. The piston fingers must have a high surface hardness and a thick core under the working conditions. The surface hardness should be within $HRC$ 58–62 that will ensure high wear resistance of these parts. To achieve such hardness, the fingers are subjected to cementation at a temperature of 950°C with a holding time of 8–10 hours. Further quenching and low tempering should ensure the formation of the tempered martensite structure and the specified operational properties. However, after processing according to the technology adopted at the factory, the fingers do not have the specified characteristics of fatigue strength. As it turned out, the reason for this is the imperfection of the structure of the fingers after the final treatment: the increased size of the grains of the core, the presence of coarse cementite inclusions along the width of the saturated cemented layer. It is proposed to introduce technological processes for processing piston fingers that would contribute to the grinding of steel grain and, as a result, increase the fatigue strength of the material. The research task is set as follows: without changing the grade of steel, to improve the technology of thermal and chemical-thermal treatment of piston fingers made of 12ХH3A steel to increase their fatigue strength. It is proposed to use thermocycling treatment to eliminate the identified deficiencies. Thermocycling is based on the accumulation of changes in the structure that occur during one cycle of heating$\rightarrow$cooling. During thermocycling, positive changes in the structure of the metal occur from cycle to cycle, and short exposures at the temperatures of phase transformations contribute to the grinding of structural components. Because of these changes, the material acquires structure and phase compositions, which are unattainable during normal heat-treatment operations. As a result of thermocycling, defects in the atomic-crystalline structure accumulate that increases the strength of the material. After thermocycling according to the regime, the cementite mesh is crushed and practically eliminated. Significant grinding of the grain occurs after the last three cycles. The size of the grain almost did not change after the first of them. After the next two cycles, the grain score increases from 4 in the original structure to 5, and after the third cycle, it is possible to reduce the grain in the surface layer to 0.016 µm that corresponds to a score of 8. After thermocycling, the dispersity of the structure is increased; the structural components are more uniformly distributed. Temperature fluctuations during thermocycling cycles have a positive effect on the spheroidization of cementite inclusions. Fatigue strength of piston fingers is increased by 20%. Thermal cyclic processing is carried out to improve the structure and properties of piston fingers made of 12ХH3A steel.