OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Results of the research Carbon content analysis The surface layer of the low-alloy steel initially had a relatively low carbon content of approximately α = (0.21 ± 0.06) wt. %. before carburization, which corresponded to the initial carbon amount of low alloy steels, as shown in Table. Effect of carburization period on carbon content in Steel 20 Chemical elements, % C Si Mn S P Ni Cr GOST 1050-2013 0.17–0.24 0.17–0.37 0.35–0.65 up to 0.035 up to 0.030 up to 0.30 up to 0.25 Fact 0.21 0.27 0.36 up to 0.035 up to 0.030 up to 0.30 up to 0.25 Cementation period: 4 hours 0.53 0.27 0.36 up to 0.035 up to 0.030 up to 0.30 up to 0.25 Cementation period: 6 hours 0.68 0.27 0.36 up to 0.035 up to 0.030 up to 0.30 up to 0.25 However, after carburization of varying duration, the carbon content in the surface layer gradually increased. Specifically, after 4 hours of carburization, the carbon content reached α = (0.53 ± 0.016) wt. %, after 6 hours, it reached α = (0.68 ± 0.012) wt. %. Experiments with longer saturation duration were also carried out. The results of the experiments are shown in Fig. 1–3. It was found that increasing the saturation period of the samples with carbon to 8 hours increases the carbon content in the surface layer of steel. Moreover, with saturation of 8 hours or more, the samples completely have a pearlite structure with a carbon content of 0.8 %. Based on these experiments, it was subsequently decided to reduce the saturation time to 2 hours in order to minimize the experiments. Microstructural analysis After carburizing, a significant increase in the surface layer thickness by more than 41 % was observed as the equalizing period increased (Figs. 1 and 2). The thickness increased from approximately 1,100 μm to more than 1,500 μm, as shown in Fig. 3. As the equalizing period in the furnace increases, a decarburized layer appears during heating for hardening. This can be seen from the results of microhardness measurements in Fig. 4 and the metallographic analysis of the surface in Fig. 5. The effect of heating temperature on hardening is shown in Fig. 6. In our experiments, it was found that temperature played an important role in decarburization. At 700 °C, no decarburization phenomenon was observed, indicating that the decarburization reaction did not occur in the samples below 700 °C. When the temperature exceeds 750 °C, the sample exhibits obvious Fig. 1. The microstructure of the cemented layer of Steel 20 after equalizing for 4 hours at 900 °C: a – surface layer; b – at a depth of 100 μm; c – transition layer to the base metal; d – reverse side of the sample a b c d
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