Strengthening of engine valves by gas nitriding
Students Name: Korovainyk Nazar Orestovych
Qualification Level: magister
Speciality: Motor Vehicle Transport
Institute: Institute of Mechanical Engineering and Transport
Mode of Study: full
Academic Year: 2023-2024 н.р.
Language of Defence: ukrainian
Abstract: Valves of the gas distribution mechanism of internal combustion engines work under conditions of maximum temperature and mechanical loads. Engine valves are heated due to the combustion of the fuel-air mixture in the car’s cylinders. This especially affects the thin edges of the valve plates, which are subject to sharp heating. Valves are subjected to mechanical stress at the point of contact between the valve plate and its seat in the block head. At high engine speeds, the valves quickly descend into the seats, which creates a shock at the edges of the part. The exhaust valve, which opens the hole, in diesel engines heats up to 700?С, and in gasoline analogues - up to 900? above zero. The situation is complicated by the fact that with such strong heating, the open valve does not cool down. As for the intake valves, they are cooled due to contact with the seat of the block head and the intake portion of the air-fuel mixture. However, their temperature is also high - about 300 degrees, so it is not allowed that these parts deform when heated [1]. With such large fluctuations in temperature and loads, there is also an urgent need to treat the valve stem in order to resist abrasion in the valve guide sleeve, under conditions of limited lubrication, or other types of wear. To increase the wear resistance of highly loaded interacting surfaces of car parts made of steel, chromium plating of a significant thickness (0.07 0.08 mm) or the process of cementation followed by hardening is most often used. An alternative to these processes is surface hardening by nitriding. At the same time, we are talking about a thermochemical process of diffusion to enrich the surface layer of parts with nitrogen. At the same time, nitrogen interacts with the base metal and alloying elements, forming chemical compounds. As a result of nitriding, a nitrided layer with an outer region (the so-called connecting layer SS) and an inner diffusion region (the so-called ZD diffusion zone) appears in the surface area of the part. Due to the hardness of the nitrided layer and the stresses arising in it, wear resistance, corrosion resistance and resistance to long-term loads increase, regardless of the strength characteristics of the part. At the same time, a significant advantage of nitriding in comparison with carburizing is that temperatures equivalent to tempering temperatures for tempering and tool steels are required for diffusion of nitrogen into the steel. Structural transformations and related warping, changes in size and strength during nitriding are significantly lower. In addition, after nitriding, as a rule, no additional processing is required [2]. The object of research is the process of diffusion nitriding of the valve surface of an automobile engine. The subject of the research is the metal intake and exhaust valves of the gas distribution mechanism of the automobile engine, which have undergone the process of diffusion nitriding. The purpose and tasks of the research. To develop a method of diffusion nitriding of low-alloy structural steel 40X. For this purpose, the following tasks should be solved: 1. Select the method and main parameters of the nitriding process of parts such as valves: temperature, gas pressure, prolongation. 2. To determine the methods of controlling the parameters of the properties of nitrided surfaces. 3. Investigate the influence of the chemical composition of the product material and parameters of the nitriding process on the properties. 4. Investigate the effect of finishing on the structure and phase composition of nitrided steel layers. Main results. - Combined processing of low-alloy structural steel 40X, which includes ultrasonic finishing and high-intensity, low-energy implantation with nitrogen ions, effectively affects the structure and phase composition of nitrided steel layers. - In the process of high-intensity low-energy implantation of nitrogen ions on the surface of 40X steel, a nitrided layer with a thickness of up to 200 microns is formed, which represents the zone of internal nitriding of the following phase composition: a solid solution of nitrogen in ferrite, cementite, iron nitrides - ?- Fe3N... - When the implantation temperature increases from 350 to 500 ?С, the proportion of low-nitrogen nitride Fe4N increases, which is associated with an increase in nitriding depth. - Preliminary ultrasonic finishing treatment intensifies the implantation process, increasing the depth of the strengthened layer due to the accelerated diffusion of nitrogen ions through additional defects of the crystal structure and increasing the microhardness of the nitrided layer, due to the increase in the proportion of nitride phases. 1. https://uk.avtotachki.com/klapan-dvigatelya-naznachenie-ustrojstvo- konstrukcziya/ https://www. Mehanika.ru/informatory/puplications/ kolonka-mastera/ iznos-shtoka / Special coatings of valve stems in internal combustion engines as a means of reducing wear.