PSI - Issue 43

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Miroslav Polášek et al. / Procedia Structural Integrity 43 (2023) 306–311 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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Fig. 2. Principle of measurement by the ball-on-disc method

2.3. Roughness of Counterpart Balls and Tool Steel The surface roughness of the balls and the tool steels tested was evaluated by AFM microscopy. Measurements were performed in five different areas each and average roughness values were calculated. The arithmetic mean height (Sa) was used as the main roughness parameter. This parameter three-dimensionally expands the parameter Ra of the profile (line roughness). Represents the arithmetic mean of the absolute coordinate Z (x, y) within the evaluation area.

Fig. 3. 3D topography of the quenching ball, measured by AFM

It provides stable results because the parameter is not significantly affected by scratches and measurement contamination. In FIG. 3 shows a 3D topography of the surface of the pressure ball. The resulting roughness value for the G40 ball was Sa = 37.6 nm. The roughness of the experimental materials was different due to their final technological processing. Since both experimental materials were equally technologically processed, they also achieved the same surface roughness values. Samples that were machined with a face cutter roughly reached a roughness of Sa = 12.5 µm, the second set of samples was machined to a roughness of Sa = 6.3 µm, the last set of samples was finely machined with a lathe and their roughness reached Sa = 3.6 µ m.

3. Result and Discussions 3.1. Coefficient of friction

A comparison of the values of friction coefficients (COF) of experimental materials 30CrNiMo8 and 42CrMo4 is in Tab. 3. The individual comparison pairs of both materials are compared with respect to the surface roughness of the experimental materials. The results indicate that the experimental material 30CrNiMo8 shows higher values of the