OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 To prevent decarburization, considerable efforts have been made to develop anti-decarburization coatings [6–10]. Decarburization of steel is influenced by many factors, including heating temperature and heating period [1, 2], atmosphere [12, 13], alloying elements [2, 7, 9], scale layer characteristics [1], electric field [2], etc. Among these, heating temperature and heating period have been proposed as the two most important control variables according to practical experience [1, 2, 15, 16–22]. The purpose of this work is to evaluate the effects of heating temperature during carburizing and quenching, as well as equalizing period, on the depth of the decarburized layer formed during quenching. Materials and methods The chemical composition of the steel in the delivered condition was determined using an optical emission spectrometer, model LAVFA18B Spectrolab. For this study, non-alloyed hypoeutectoid Steel 20, compliant with GOST 1050-2013, with an initial ferrite-pearlite microstructure, was selected. Rectangular samples measuring approximately 50 mm × 10 mm × 10 mm were cut from a rolled sheet of Steel 20. Mechanical cleaning and grinding of the samples were performed; the surfaces were free of oxide traces. The carburizer used as the cementing mixture consisted of charcoal grains sized 3.6–10 mm, coated with a barium carbonate film according to GOST 2407–83. Carbon saturation was carried out on one side (the side in contact with the poured carburizer), while the reverse surface of the samples was protected by a layer of clay. The samples were placed in a metal container and covered with a 25–30 mm layer of carburizer. The container was sealed with a lid. The operating temperature for carbon saturation of the sample surfaces was set at 900 °C, with a saturation period of 4–8 hours [1, 2]. After saturation, the container with samples was removed from the furnace and cooled in air. Samples were cleaned of scale using a grinding machine. The influence of surface oxides on decarburization kinetics was eliminated by grinding the samples before quenching, as surface oxides increase the apparent decarburization [1, 2]. Quenching was performed in a furnace in air (humidity was not measured) at furnace temperatures of 780 °C, 850 °C, and 950 °C, with equalizing periods of 4 and 6 hours, using a laboratory electric resistance furnace with a chamber volume of V = 22 dm³. Each sample was placed at the same position in the preheated furnace on a refractory brick in the chamber’s center. This ensured identical conditions and the fastest possible heating of each sample to the quenching temperature. Heating temperatures were monitored using a certified contact thermocouple, which was in contact with the side surface of the sample during heating (introduced into the furnace through a small hole in the furnace door). Heating period was counted from the moment the control thermometer inside the furnace reached the target temperature. Temperature fluctuations during heating were within the range of Ta − 1 °C ≤ T ≤ Ta + 3 °C , where Та is the ambient temperature. After equalizing, quenching was carried out in water. The depth of decarburization [1, 2, 14] was investigated using optical microscopy by two methods: the traditional method using an optical microscope equipped with a grid, and computer-assisted measurement based on the image displayed on the screen. Metallographic samples were prepared by wet grinding with SiC paper up to 4,000 grit, polishing with ¼ μm diamond paste, and etching with 3% HNO3 in ethanol. Decarburization varies on different surfaces (top and side surfaces exposed to atmosphere, and the bottom surface in contact with the refractory brick, including edges and corners) due to differences in oxidation states. Typically, decarburization is more pronounced on surfaces with lower oxidation capacity; therefore, the bottom surfaces usually exhibit stronger decarburization [13, 15]. This study focused exclusively on flat surfaces exposed to the atmosphere. Decarburization was measured on three sections perpendicular to the long side of the sample on the top and both side surfaces.
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