PSI - Issue 68

Aleksandar Todić et al. / Procedia Structural Integrity 68 (2025) 534 – 539 Aleksandar Todić et al./ Structural Integrity Procedia 00 (2025) 000–000

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1. Introduction To achieve optimal mechanical characteristics of a particular type of steel, various elements are alloyed into the metal. During crystallization, these chemical elements form compounds—carbides—at the grain boundaries and within the metallic matrix, Lin, Y., et al. (2010). Similar materials can also be used to hard weld parts exposed to intense wear for operation in non-lubricated conditions, Arsić, D., et al. (2016). The tested material is steel X180CrMo12-1, which contains 1.8% carbon, 12% chromium, 1% molybdenum, 0.5% manganese, and a variable vanadium content ranging from 0.5% to 3% (Tab. 1). This steel belongs to the group of quenchable steels, Todić, A. et al. (2011). The objective of the research is to determine the chemical composition of the carbides and to investigate the influence of vanadium and its carbides on changes in the microstructure, wear resistance, and friction resistance of the tested material, Hu, J., et al. (2016), Tlili, B., et al. (2016), Todić, A., et al. (2022), Harouz, R., et al. (2022). 2. Experiment plan The samples for metallographic examinations were prepared using standard procedures, cast by the CO 2 casting method in sand molds. Melting was performed in a medium-frequency induction furnace, ASEA Brown Boveri – ABB, type ITMK-500, Todić, A., et al. (2012). The samples measured 10 ´ 10 ´ 10 mm, intended for electron microscopy with a planned chemical composition. The samples contained 0.5% V and other alloying elements as specified in Table 1. After casting, the samples were improved (quenched and tempered) at a temperature of 250°C. Post heat treatment, slight deviations in geometric shape and dimensional changes were observed in the samples. Therefore, mechanical processing was applied using lubricants and cooling agents at room temperature. The mechanical processing was performed on a surface grinding machine. Grinding removed irregularities and impurities, with constant heat removal. The defective layer was removed with minimal cutting depth in multiple passes, down to the desired dimensions of 10 ´ 10 mm. Given the small machining allowances, the total grinding depth did not exceed 0.5 mm, thus preventing any potential change in surface structure. For determining the chemical composition and microstructure, electron microscopy (SEM-EDS) was used. The scanning electron microscope used was a JEOL model JSM-6610LV. SEM-EDS was utilized to determine the chemical composition at specific points of the phases present on the sample surface. Additionally, a mapping of the influential chemical elements was performed to understand and detect the phases present on the tested sample. Further investigations were conducted using X-ray diffractometry. Identification and calculation of lattice parameters were performed. This analysis was carried out on a D8 ADVANCE device from Bruker. The device is equipped with a dynamic scintillation detector and a ceramic X-ray Cu tube (KFL-Cu-2K) with a scanning angle range from 10 to 150°. Samples for this analysis were ground and converted into fine powder. Working parameters included a step size of 0.02 and a step time of 20 seconds. Detection was conducted using the Topas 4.2 software package with data from the ICCD database PDF-2 Release 2013. For testing the wear resistance of the aforementioned steel, a CSM Nanotribometer, "Ball-on-plate" linear reciprocating type, was used. The ball material used for the friction and wear process was hard metal with a diameter of 1.5 mm. The testing conditions were as follows: normal load 1N, sliding speed 10 mm/s, amplitude 0.5 mm, 5000 cycles/10 m, without lubrication. Wear and friction testing was conducted on 4 series of samples with different vanadium percentages. Each sample was tested 5 times, documented with comparative diagrams of friction coefficients and ball penetration depth over time, cycle count, and sliding path. Additionally, photographs of the wear traces on the material and the ball were provided. For analyzing the surfaces of prepared samples and the wear traces, computer aided optical microscopes from "MEIJI Techno" were used, each equipped with its own illuminator and high resolution camera. Table 1. Chemical composition of the sample C Cr Mo S Si P Mn Al Ni V 1.753 11.754 1.125 0.035 0.514 0.034 0.533 0.02 0.16 0.502