Search for a command to run...
Purpose. To consider and summarize the research results that show the influence of metastable austenite on the surface layer of steels in order to increase abrasive wear resistance. To demonstrate that in a number of cases, to enhance the specified characteristics in the structure of the surface layer of alloys, it is necessary to obtain metastable residual austenite alongside other components through various treatments. To present data showing that a self-hardening effect can be achieved under load, resulting in the formation of a renewable martensitic high-strength layer that provides protection against destruction. To present new data on the advantages of a differentiated approach to selecting the structure considering specific testing conditions or operational properties. Regarding these, it is necessary to optimize the quantity and stability of austenite in relation to the deformation martensitic transformation (DMT). Research methods. Cemented steels 20Х, 18ХГ, 12Х13, 12XН3A, and 12Х2Н4A, У8, ШХ15 were tested for abrasive wear resistance on the X4B installation. Abrasive wear tests were conducted on a setup designed according to the Brinell-Haworth scheme. The microstructure was studied on microsections prepared according to the generally accepted polishing and etching methodology. Metallographic and durometric studies were conducted. Cementation was carried out in a solid carburizer with additives that prevented surface oxidation. Results. It has been established that to enhance the operational properties of cemented steels, it is necessary to utilize the self-hardening effect under load. It has been determined that the ambiguous assessments of the influence of residual austenite on the properties of cemented steels are due to the fact that the loading conditions, the amount, and the stability of austenite, which must be optimal for each specific case, are often not taken into account. It has been shown that in some cases it is advisable to ensure the formation of a large amount of metastable austenite after high-temperature treatment, and then, through deformation or (and) heat treatments, as well as other influences, to induce its partial transformation into martensite. Scientific novelty. The work presents an alternative viewpoint, according to which, under dynamic loads, diffusion-alloyed steels should create a metastable austenite sublayer by means of the diffusion layer's absorption. To obtain wear-resistant thermodiffusion layers of significant thickness, it is advisable to create a structure of white chromium-manganese cast irons with metastable austenite. The effective use of concentrated energy sources for strengthening cemented steels ensures high surface hardness and the necessary amount of metastable austenite in the structure. Furthermore, this allows the creation of a discrete structure that alternates in a specified sequence between hard and soft components, significantly enhancing wear resistance. Practical value. Increasing the mechanical properties of steels allows for greater operational stability of machine parts, which is an important task in materials science. One of the directions for solving this issue is to obtain a multiphase structure in steels, one component of which is metastable austenite, where dynamic deformation martensitic transformation (DDMT) occurs under load, resulting in the self-hardening effect under load (SHE). Methods for obtaining a surface layer structure of iron-based alloys, along with other components of metastable residual austenite, to enhance wear resistance under abrasive impact are easily implementable in production conditions. A differentiated approach to selecting the structure, taking into account specific testing or operational conditions, is necessary.
Published in: New Materials and Technologies in Metallurgy and Mechanical Engineering