Determining the Influence of Electro-Spark Alloying on the Strength Indicators of Machine Parts

Abstract

Problems The strengthening of the case and striker was carried out by electric spark alloying in order to protect against corrosion, wear, sticking to the surface of contacting materials. The results of testing parts strengthened by electric spark alloying show that the wear resistance of parts increased by 1.3 times compared to the initial state of parts. Regression equations are obtained, which can be interpreted as a knowledge base for controlling the strength indicators of the striker body, allowing to control its residual resource during operation. It was established that the strength indicators increase when the fractal dimension of the sorbite component increases, since it has better strength indicators compared to the original ferrite-pearlite structure. Goal. In order to increase the wear resistance and fatigue strength of the material of hydraulic hammer parts, it is not always advisable to change the traditional technology of manufacturing the part and, in particular, the methods of its heat treatment. Different types of finishing are applied only specifically to the given product. In some cases, it is worth applying surface strengthening of the product. Currently, there are a number of surface strengthening technologies, each of which has its own advantages and disadvantages. Methodology. All parts were strengthened by electric spark alloying with tungsten. The power of the processing current was 1 kW. The peak, in addition to strengthening with tungsten, was additionally processed by electric spark alloying with chromium at a current of 1.5 kW. Surfaces processed by electric spark alloying were polished to obtain the roughness of the hardened surfaces of parts R and 04-08. Results. During the micro-examination of areas strengthened by electric spark alloying, which are outside the load zone during the test, it was established that the areas strengthened by electric spark alloying on the body and sleeve have a thickness of 10–40 μm and a hardness of Н V 600–650. On the strikers, the initial thickness of the strengthened layer is 20 μm with a hardness of НV 600-650. The strengthened zones in the section have the appearance of arc-shaped, embedded surface layers of metal parts, phases. There are no structural changes under this zone in the main metal. Originality. The microstructure of the base metal consists of sorbitol. The mechanical properties of the material of the device parts were determined at a temperature of 20 °C on samples cut in the axial and tangential directions. Since the obtained structure of sorbite was difficult to quantify by traditional methods of quantitative metallography, it was studied using the theory of fractals. The obtained results make it possible to forecast the strength indicators of the body of the hydraulic hammer striker based on the fractal dimension of photographs of the microstructure at a magnification of 100. Practical value. The structural changes that occur during the tests in the surface layers of the parts are characteristic of the phenomena of secondary hardening with a lower level of hardness than on the parts of the previous options. The relationship between the fractal dimension of the sorbite structure and the strength characteristics was established, which allows us to use the obtained results as a non-destructive method of controlling the strength of parts after electric spark alloying.