# The Influence of Grain Size on the Abrasive Wear Resistance of Hardox 500 Steel
## 3 Results and Discussion
### Abrasive Wear Resistance
Microcutting is also observed, though its contribution to the overall wear mechanisms is limited. Long and narrow grooves predominate, running parallel to the direction of loose abrasive movement on the sample surface. There are few scratches oriented at different angles, and these are shallow and short. These steel surfaces also show traces of chips breaking off from the edges of grooves and pits. The similarity of surface conditions between these two states, despite significant hardness differences, suggests that hardness does not influence the abrasive wear mechanisms or their intensity in martensitic microstructures. For the steel quenched from 1200 \({}^{\circ}\)C, significantly more intense wear is observed due to the increased grain size (Figure 10e,f). Deformations, primarily in the form of numerous pits, are deeper and cover a larger surface area. These pits lead to the detachment of substantial material fragments. Grooves dominate the surface, with signs of plastic deformation around them and chips breaking off from their edges. The grooves are relatively deep, increasing the amount of material displaced to their edges. Numerous fine scratches oriented at various angles to the direction of abrasive movement on the sample surface also appear, suggesting that the material could not effectively resist the multidirectional movement of abrasive particles. This may indicate a lower tendency for edge strengthening through plastic deformation. Abrasive particles move where it is easiest, indicating that the wear mechanism in this heat treatment condition also relies heavily on intensive microplowing. Thus, the greater mass wear is primarily influenced by the increased number of deep pits. It can be inferred that grain growth resulting in a coarse-grained microstructure increases susceptibility to mechanical surface damage, leading to a more intense abrasive wear process. The microstructural analysis of subsurface layer changes was performed on both transverse (Figure 12a-f) and longitudinal sections (Figure 13a-f) relative to the abrasive movement direction. Plastic deformation in the martensitic microstructure is observed in all heat-treated states, indicating retained material ductility despite high hardness. These deformations are especially evident in the thin subsurface layer directly exposed to abrasives, as well as within abrasive grooves where martensite grains deformed under intense contact with hard abrasive particles. Additionally, sample surfaces exhibit pits, with characteristics depending on the heat treatment state. Material ridges can be observed along pit edges, resulting from plastic buildup during wear. The deepest pits were recorded in samples heat-treated at the highest temperatures, 1100 \({}^{\circ}\)C and 1200 \({}^{\circ}\)C (Figure 12e,f), where  
Figure 9: Influence of hardness on abrasion resistance. extensive grain growth contributes to increased susceptibility to deeper surface damage. In finer-grained microstructures, achieved at lower heat treatment temperatures, pits are noticeably shallower, with smoother edges. Smaller grains promote an even stress distribution and higher resistance to localized mechanical damage, offering enhanced stability against abrasive wear, resulting in less deformation and shallower subsurface damage. Figure 10: Surface images of Hardox 500 steel samples after abrasive wear testing: (**a**) as-delivered state, magnification 2000\(\times\); (**b**) as-delivered state, magnification 10,000\(\times\); (**c**) T\({}_{\rm A}\) = 850 \({}^{\circ}\)C, magnification 2000\(\times\); (**d**) T\({}_{\rm A}\) = 850 \({}^{\circ}\)C, magnification 10,000\(\times\); (**e**) T\({}_{\rm A}\) = 1200 \({}^{\circ}\)C, magnification 2000\(\times\); and (**f**) T\({}_{\rm A}\) = 1200 \({}^{\circ}\)C, magnification 10,000\(\times\). Unetched, SEM.