PSI - Issue 43

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

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coefficient of friction compared to the material 42CrMo4. The average COF value of the material 30CrNiMo8 from all measured values, with respect to the turning radius, was 0.87. For comparison, 42CrMo4 had an average COF value of 0.75 under the same measurement conditions. So, the decrease in COF in favor of 42CrMo4 was 24%. Higher COF values for 30CrNiMo8 materials are associated with the microstructure of experimental steel as well as its chemical matrix composition. This steel contains a higher percentage of Cr and is supplemented with Ni, which increases corrosion resistance as well as wear resistance, depending on the sample’s roughness. Here, the results for the material 30CrNiMo8 show approximately the same values, which differ slightly. In the second experimental material 42CrMo4, we observe that as the roughness of the material decreased, the COF value increased at all friction rates. Table 3. Resulting values of the coefficient of friction for different types of surface roughness experimental materials.

⌀ Rotation [mm]

COF 30CrNiMo8

COF 42CrMo4

Sa 12.5

Sa 6.3 0.847 0.867 0.893 0.944 0.906

Sa 3.6 0.897 0.866 0.903 0.906 0.867

Sa 12.5

Sa 6.3 0.778 0.790 0.722 0.745 0.675

Sa 3.6 0.838 0.862 0.894 0.893 0.832

22 26 30 34 38

0.921 0.876 0.886 0.873 0.890

0.644 0.650 0.644 0.628 0.644

3.2. Wear mechanisms

By a detailed examination of the worn surface using LOM, we identify one type of wear in selected observations, namely adhesive wear. This type occurred in all measurements depending on the surface roughness of the experimental samples. By the action of forces, the peaks of the protrusions on the surface are plastically deformed and the atoms of both surfaces are in close contact and form so-called micro-joints. All these micro-gaps later break in places above the material contact of one of the friction bodies due to the formation of the surface. This area is reinforced by plastic deformation and its strength is higher than the strength of subsurface areas. After breaking the micro-joints, the microparticles transferred from the surface of one body to another. These subsequently remained attached to the surface of the second body.

a)

b)

c)

d)

e)

f)

Fig. 5. Worn surfaces of tribological pair at friction speed 0. 39 m/s (ø30 mm): a) Sa 12 .5 - 30CrNiMo8, (b) Sa 6.3 - 30CrNiMo8, (c) Sa 3.6 - 30CrNiMo8, d) Sa 12.5 - 42CrMo4, e) Sa 6.3 - 42CrMo4, f) Sa 3.6 - 42CrMo4