OBRABOTKAMETALLOV technology Vol. 24 No. 4 2022 technologies for modifying the surface layers of die steels is multicomponent CTT, such as boroaluminizing, which allows increasing significantly the wear resistance, as well as heat resistance, corrosion resistance and a number of other properties of the surface layers of machine parts and tools [13–16]. The service life of products after hardening largely depends on the distribution of technological residual stresses (TRS) in the diffusion layer and adjacent layers of the base material and on the general nature of the microstructure of the entire section changed during the CTT process [8,17–20]. Control and management of TRS is one of the most important tasks of mechanical engineering [21, 22]. Therefore, when developing Fe-Me-B coatings by diffusion alloying methods on the surface of steel products, efforts should be directed to finding TRS distributions that improve the operational properties of products. It is known that the study of the stress-strain state (SSS) of borated layers can be carried out by the methods of destructive and non-destructive testing [23–26]. In our work [27], the first data on the assessment of the stress state of boride layers were presented. In this paper, we review the methods for determining the TRS that can be used after hardening CTT, in particular, in Fe-Me-B coatings in the surface layer of carbon and alloy steels, and also consider the problems of measuring residual stresses by mechanical method and its solution. The results of experimental studies on the detection of the TRS distribution in the diffusion layers of 3Cr2W8V and 5CrNiMo tool steels after hightemperature boroaluminizing (HBA) are presented. Research methodology CTT was carried out in saturating pastes containing powders of boron carbide, aluminum and sodium fluoride as an activator of the following composition: 80 % B4C + 16% Al + 4% NaF [15]. Samples with overall dimensions of 1.8×80×60 mm (Fig. 1, a) were made of 3Cr2W8V and 5CrNiMo tool steels (see Tables 1, 2). After tamping, the molds were removed, and the resulting briquettes were dried at a temperature of 50–100 °C for two hours in a drying chamber. After that, the briquettes were loaded into a furnace preheated to the process temperature. The treatment duration was 2 hours, the temperature was 950 and 1,050 °C. The samples were cooled outside the furnace in calm air at room temperature. The sample after CTT is shown in Fig. 1, b. a b Fig. 1. Flat samples Ta b l e 1 Chemical composition of 5CrNiMo steel, wt. % С Si Mn Cr Mo Ni P S Cu 0.50–0.60 0.10–0.40 0.50–0.80 0.50–0.60 0.15–0.30 1.40–1.80 ≤ 0.03 ≤ 0.03 ≤ 0.30
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