Changes in the Structural-Phase State of Ferrite-Perlite Steel Under the Action of Electrolyte-Plasma Surface Quenching: Electrolytic-Plasma Surface Quenching of Steel Grade Two

Introduction

The development of modern mechanical engineering is associated with the development of new materials, the introduction of new technologies and equipment, the invention of new ways to improve the performance of machine parts and mechanisms. The wear resistance, strength and corrosion resistance of machine parts are significantly affected by the condition of their surface layer, which is dictated by the manufacturing technology. Because the destruction of the surface during wear leads to the failure of 60-80 percent of mechanical engineering products (Makarov, 2009). Wear of working surfaces and fatigue of joints are key factors limiting the strength and reliability of various components of railway transport, construction, road and agricultural machinery, metallurgical and pressing equipment. Wear leads to a change in the shape, size and condition of the surface of the parts, which leads to a loss of functional qualities and operability of technical means of production, as well as to an increase in the probability of failure. Most mechanical engineering products are still made of steel or cast iron. Therefore, increasing the wear resistance of iron alloys is one of the most important and urgent tasks of technical physics.

There are several technical solutions to improve the quality of component surfaces. The most common electroplating and chemical methods of coating, surfacing, spraying, chemical and thermal treatment, surface hardening with high frequency currents, surface hardening with concentrated energy flows (plasma, electron beam, laser), etc. (Vyacheslav, 2018). Surface hardening by focused energy flows is the most promising method of surface hardening of iron alloys. However, the widespread introduction of some methods of surface hardening with a concentrated flow of energy, such as laser and electron beam, is hindered by the high cost and complexity of the equipment, its insufficient reliability and performance, the need for vacuum, special rooms with special requirements, the need for qualified maintenance and high operating costs (Lahtin & Arzamasov, 1985). As a consequence, according to its technical and economic indicators, as well as the results of a comparative study, a method of plasma surface hardening, devoid of the listed disadvantages, is proposed for widespread use (Troyannikov, 2021). Plasma surface hardening has been successfully developing in recent years and is currently widely used in various industries, primarily for the heat treatment of railway transport parts (the сenter plates of the freight wagons, the spring beam and the side frame of the trolley, the bandage, etc.) (Dyachenko, 1981).

Being one of the varieties of plasma quenching – electrolyte-plasma surface quenching (EPSQ) has recently been developing and intensively studied. This method is characterized by lower energy consumption, simplicity of technological equipment and large size of the hardened zone (Zaides, 2020). This method has several advantages, including a sufficiently high performance and the possibility of quenching parts of a larger and more complex profile, and the degree of hardening is equivalent to plasma quenching. It is well known (Tyurin, 1999) that the resource of steel parts is determined by the indicators of their operational characteristics (starting from the chemical composition of the material and ending with the conditions in which one or more parts should be operated), most of which are directly dependent on the structural and phase state of the material. There are very few publications devoted to the study of structural-phase transitions in wheel steel during plasma surface quenching, and they do not sufficiently cover the problems of structure formation. At the same time, there is no data in the literature on the treatment of wheel steels by the method of electrolytic-plasma hardening, which requires additional experimental work to assess the prospects for the applicability of the method for strengthening wheelset bands.

In connection with the above, this work focuses on the development of a method for hardening wheel steel, as well as the study of the formation of the structure, phase composition and tribological properties of the hardened surface layer of grade two steel by quenching during electrolytic plasma surface treatment.