OBRABOTKAMETALLOV technology Vol. 24 No. 4 2022 under study as a function of the thickness of the removed layer. Removal of stressed layers from the surface under study in this installation is realized by the means of chemical etching – gradual dissolution of the material in electrolyte solutions. Basically, the compositions of electrolytes used in chemical etching are a combination of solutions of inorganic acids with water. At the same time, in order to ensure accuracy and minimize measurement error, it is necessary to ensure the following surface quality parameters during the etching process: low roughness, absence of pitting, undercuts under the protective coating, pits, nonscratches, and, if possible, to achieve a constant etching rate throughout the process. For a stable flow of the process and the establishment of the optimal duration of the experiment, the recommended etching rate should be 0.005–0.01 mm/min. When processing products by CTT methods [1, 13–16], the surface layer of the metal acquires the following properties: – decrease in magnetic permeability; – increase in electrical resistance; – increase in torsional stiffness; – increase in hardness; – increase in wear resistance; – increase in corrosion resistance, in particular acid resistance. The latter property makes it difficult to study the TRS in products subjected to the types of CTT under consideration, at least during chemical etching in acid solutions. To confirm this, we conducted a number of studies on the chemical etching of test samples made of 3Cr2W8V steel after boroaluminizing in various compositions of acid electrolytes (Table 3). The test samples were made in the form of strips with overall dimensions of 1.7×8×60 mm. An area of 80 mm2 was etched, rubber enamel was used to protect the rest of the sample. Etching was carried out in a small volume of electrolyte, not exceeding 200 ml, in a thermostatic bath of the UDION2 installation with a control of the average rate of removal of layers (etching), calculated by the formula [29]: ∆ = ρτ etching 1000 m V S , mm/min (1) where Δm – weight of the removed material, g; S – the surface area from which the material was removed, mm2; ρ – material density, g/sm3; τ – test time (etching), min. Ta b l e 3 Electrolyte compositions, parameters, and results of chemical etching of samples after CTT Composition No. Electrolyte composition t, oC etching V , mm/min Comments 1 (g/l): HF – 30; Н2SO4 – 150; Н2O – rest 23 – There are practically no signs of poisoning 2 (g/l): HF – 120; Н2SO4 – 590; Н2O – rest 35 0.0014 The surface is dark gray with large amounts of non-etched areas (Fig. 4, a) 3 (% vol.): HF – 10; Н2SO4 – 8; HNO3 – 9; H2O – rest 35 0.0076 Black relief surface with numerous small bumps and depressions (Fig. 4, b) 4 (% vol.): HCl – 565; HNO3 – 237; NaF – 30; H2O – rest 37 0.0063 Gray wavy surface with a non-etched area in the middle (Fig. 4, c)
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