A Comparison of the Effects of Ultrasonic Cavitation on the Surfaces of 45 and 40Kh Steels

The ultrasonic treatment of metal products in liquid is used mainly to remove various kinds of contaminants from surfaces. The effects of ultrasound not only separate and remove contaminants, they also significantly impact the physical–mechanical and geometric properties of the surfaces of products if there is enough time for treatment. The aim of this study was to compare the dynamics of ultrasonic cavitation effects on the surface properties of 45 (ASTM M1044; DIN C45; GB 45) and 40Kh (AISI 5140; DIN 41Cr4; GB 40Cr) structural steels. During the study, changes in the structure, roughness, sub-roughness, and microhardness values of these materials were observed. The results showed significant changes in the considered characteristics. It was found that the process of cavitation erosion involves at least 3 stages. In the first stage, the geometric properties of the surface slightly change with the accumulation of internal stresses and an increase in microhardness. The second stage is characterized by structure refinement, increased roughness and sub-microroughness, and the development of surface erosion. In the third stage, when a certain limiting state is reached, there are no noticeable changes in the surface properties. The lengths of these stages and the quantitative characteristics of erosion for the considered materials differ significantly. It was found that the time required to reach the limiting state was longer for carbon steel than for alloy steel. The results can be used to improve the cleaning process, as well as to form the required surface properties of structural steels.

Methodology for the Study of Residual Temperature Stresses in the Butt Contour of a Welded Joint Made of Carbon and High-Alloy Structural Steels during Multi-Pass Welding

The method of investigation of residual temperature stresses in the butt contour of the welded joint "shell – plate" made of carbon and high-alloy structural steels during multi-pass welding is described. The temperature problem was solved on the basis of the obtained experimental data of temperature measurement at the reference points of the structure during the application of the rollers. A solution is proposed that takes into account several stages, each of which corresponds to a specific intermediate temperature field due to the peculiarities of welding technology. The evaluation of residual stresses was carried out on the basis of the energy theory of plasticity, taking into account the dependences of the yield strength and elastic modulus of welded metals on temperature.

Methods for obtaining a dispersed structure and increasing the strength of silicon-manganese steels

For high-strength structural steels, the problem of grinding grain and increasing strength is solved by the use of highly efficient technologies, the development of new steel compositions and the development of rational thermomechanical processing. Goal. The aim of the work is to transform the structure, study the methods of grain grinding and increase the strength properties of structural steels 09Г2, 09Г2С as a result of modification by nanodisperse compositions, heat treatment and intense plastic deformation. Methodology. The research material was structural low-carbon steels 09G2, 09G2S. The process of modifying the steel parameters of the geometric shape of the melts was carried out by smelting steels 09G2 and 09G2C in an induction furnace. The modified workpieces were subjected to intensive plastic deformation and heat-treating treatment according to the mode: heating temperature 1050 °C, exposure 5 min; cooled medium: water and 20 % solution of NaCl in water. Then – a rest at temperatures of 500 °C; 600 °C, exposure time – 30 minutes. Metallographic studies of the structure of steels before and after modification and mechanical testing of standard samples were performed. Results. The study of the structure grains of steels 09Г2 and 09Г2С in the initial state showed the presence of large grains up to 30 μm, reduced microhardness and yield strength. Originality. The substantiation of the choice of type and fraction of nanodisperse modifier was carried out. The use of plasma-chemical synthesis to obtain nanopowders based on titanium was substantiated. Nanopowders of titanium carbonitride Ti (CN) fraction 50 ... 100 nm were obtained by the method of plasma chemical synthesis. Practical value. The following methods were proposed for grinding grain and increasing the strength properties of steels: nanomodification, intensive plastic deformation in combination with heat-strengthening treatment.

Assessment of the effect of the steels structure dispersion on its magnetic and mechanical properties

Introduction: The control of the mechanical properties of structural steels is one of the main processes that regulate the service life of equipment. In most technical processes (pressure treatment, welding, rolling, thermal exposure), structure changes both in local areas and in the entire volume. Changes in the steel structure entail changes in its properties and as a result in local areas, at various stages of operation, the likelihood of the occurrence and development of critical defects increases. Its presence significantly affects the performance of the equipment, and leads to premature aging of the material and its failure. Precisely because the control of the mechanical properties of steel remains one of the urgent problems, new control methods are being developed. It is known that all properties of steel depend on the structure of the substance, however, studies on the effect of the dispersion of the structure under consideration on the mechanical properties are presented in an insignificant amount. Purpose: to analyze from a mathematical point of view the influence of the factor of different grain size, as a parameter reflecting the dispersity of the system, on the mechanical properties of structural steel. The paper studies a heat-treated planar samples of steels 15KhSND, 09G2S and St3. Methods of research: scanning electron and optical microscopes are used to study the grain structure and grain boundaries; SIAMS 700 software package is used for finding the boundaries and average data of the grain structure; portable X-ray fluorescence analyzer of metals and alloys X-MET 7000 is used to determine the chemical composition of the test samples in percentage; tensile testing machine IR-50 is used for measuring the tensile strength of samples; Vickers hardness tester is used to determine the hardness of samples. Results and discussion: it is found that there is a satisfactory correlation for the mechanical properties of structural steels (hardness and ultimate strength) and the grain size factor, which can be used to predict the hazardous states of structures and the operating time. The analysis of variance and regression of the detected dependencies is carried out. It is noted that the dropout of some values from the general regression dependence can most likely be associated with a decrease in the value of internal stresses as a result of a decrease in the distortions of the crystal lattice of steel occurring during heat treatment. It should be noted that the processes occurring and the degree of its influence on the properties of the structural steels under consideration can be different due to the presence of different amounts of alloying elements in the composition of the studied steels.