OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 2 2023 Fig. 5. Microstructure of the 2nd specimen after plasma-jet hard-facing: a, b, c – the upper part of coating; d – the lower part of the coating near the boundary with the base metal а b с d be seen from the resulting diagram that the boron content in the hard-faced layer decreases from the coating surface to the base metal. At the same time, in the hard-faced layer of the first specimen, the boron content is higher by 1.5–2 % compared to the second specimen, and higher by 7–8 % compared to the third specimen, depending on the depth of the hard-faced layer. Figure 10 shows the distribution of microhardness over the depth of the boronized layer at various current after plasma boronizing. With an increase in current from 120 A to 160 A, the hardened depth increased from 0.625 mm to 1.95 mm. The maximum hardness of 1,547 HV for Steel 20 was observed at a depth of 0.075 mm from the layer surface, which is typical for boronizing due to the formation of solid iron borides. Iron boride particles are a high-strength phase, which determines the degree of hardening in the alloyed layer. These higher hardness values are associated with a higher boron content, which led to the formation of a large amount of primary FeB and Fe2B borides. An increase in current to 140 A leads to an increase in the thickness of the coating to 1.125 mm and the maximum hardness drops to 1,293 HV. This is explained by the fact that the higher the current, the greater
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