# The Influence of Grain Size on the Abrasive Wear Resistance of Hardox 500 Steel
## 3 Results and Discussion
### Abrasive Wear Resistance
Figure 11: 3D images of sample surfaces subjected to wear testing along the longitudinal direction of abrasive movement: (**a**) as-delivered state; (**b**) \(\rm T_{A}\) = 850 \({}^{\circ}\)C; (**c**) \(\rm T_{A}\) = 900 \({}^{\circ}\)C; (**d**) \(\rm T_{A}\) = 1000 \({}^{\circ}\)C; (**e**) \(\rm T_{A}\) = 1100 \({}^{\circ}\)C; and (**f**) \(\rm T_{A}\) = 1200 \({}^{\circ}\)C. SEM. Surface roughness analysis after the abrasive wear test revealed notable differences depending on the material state and applied heat treatment (Figure 14a,b). The as-delivered state exhibits relatively high roughness parameters: _Ra_, _Rq_, _Rp_, _Rv_, and _Rz_ values of 0.41 \(\upmu\)m, 0.51 \(\upmu\)m, 1.38 \(\upmu\)m, 1.62 \(\upmu\)m, and 3.00 \(\upmu\)m, respectively, indicating pronounced peaks and deep valleys. High isolated peaks and valleys contribute to the elevated _Rq_ (root mean square deviation of the profile). After austenitizing at 850 \({}^{\circ}\)C, all roughness parameters decrease, with _Ra_ reducing to 0.31 \(\upmu\)m and _Rq_ to 0.40 \(\upmu\)m, suggesting a smoother surface. Maximum peaks average 1.30 \(\upmu\)m (a 6% reduction from the as-delivered state), while the deepest valleys reach 1.54 \(\upmu\)m (a 5% reduction), reflected in the _Rz_ value of 2.85 \(\upmu\)m. This indicates reduced plastic deformation at shallower groove edges. Further austenitizing at 900 \({}^{\circ}\)C improves the abrasion surface quality compared to the as-delivered state. _Ra_ (0.37 \(\upmu\)m) and _Rq_ (0.45 \(\upmu\)m) are slightly higher than those of samples treated at 850 \({}^{\circ}\)C but do not approach the baseline state. _Rv_ and _Rp_ values are similar to those after austenitizing at 850 \({}^{\circ}\)C (_Rv_ is 3% higher and _Rp_ 2% lower), reflecting shallower grooves but increased plastic deformation at their edges. After austenitizing at 1000 \({}^{\circ}\)C, _Ra_ and _Rq_ values rise to 0.42 \(\upmu\)m and 0.52 \(\upmu\)m, respectively, exceeding those of the as-delivered state, indicating increased surface roughness. This trend is also evidenced by the _Rz_ value of 3.14 \(\upmu\)m, 10% higher than in samples austenitized at 850 \({}^{\circ}\)C and 900 \({}^{\circ}\)C. Thus, austenitizing at 1000 \({}^{\circ}\)C may worsen  
Figure 12: Microstructure of sample cross-sections subjected to wear testing surfaces subjected to wear testing along the perpendicular direction of abrasive movement: (**a**) as-delivered state; (**b**) T\({}_{\text{A}}\) = 850 \({}^{\circ}\)C; (**c**) T\({}_{\text{A}}\) = 900 \({}^{\circ}\)C; (**d**) T\({}_{\text{A}}\) = 1000 \({}^{\circ}\)C; (**e**) T\({}_{\text{A}}\) = 1100 \({}^{\circ}\)C; and (**f**) T\({}_{\text{A}}\) = 1200 \({}^{\circ}\)C. SEM. surface quality compared to lower austenitizing temperatures and the as-delivered state, correlating with the observed reduction in abrasion resistance at this treatment level. At 1100 \({}^{\circ}\)C, _Rv_ and _Rp_ values decrease even relative to the lowest austenitizing temperatures, directly impacting _Ra_ and _Rq_, which measure 0.36 \(\upmu\)m and 0.45 \(\upmu\)m, respectively. These values suggest a more homogeneous surface post-heat treatment. The _Rz_ (2.73 \(\upmu\)m) and _Rp_ (1.11 \(\upmu\)m) values are the lowest among all samples, indicating minimal plastic deformation around formed grooves. The highest austenitizing temperature (1200 \({}^{\circ}\)C) leads to increased surface roughness, as reflected in parameters such as _Rz_ (3.38 \(\upmu\)m), _Rv_ (1.82 \(\upmu\)m), and _Rp_ (1.57 \(\upmu\)m), the highest among all heat-treated samples. _Ra_ and _Rq_ values of 0.39 \(\upmu\)m and 0.51 \(\upmu\)m, respectively, further reflect this increased roughness. The mean groove width across profile elements is shown in Figure 14c.