# The Influence of Grain Size on the Abrasive Wear Resistance of Hardox 500 Steel
## 3 Results and Discussion
### Abrasive Wear Resistance
After austenitizing at 850 \({}^{\circ}\)C, hardness differs significantly compared to samples heat-treated at 1100 \({}^{\circ}\)C (\(p\) = 0.000140) and 1200 \({}^{\circ}\)C (\(p\) = 0.000138). Similarly, for the 900 \({}^{\circ}\)C condition, comparisons with higher austenitizing temperatures (1000 \({}^{\circ}\)C, 1100 \({}^{\circ}\)C, and 1200 \({}^{\circ}\)C) indicate statistically significant differences. For samples austenitized at 1000 \({}^{\circ}\)C, further significant differences were noted compared to samples treated at 1100 \({}^{\circ}\)C (\(p\) = 0.030820) and 1200 \({}^{\circ}\)C (\(p\) = 0.000162). The highest austenitizing temperatures showed statistically significant differences from other states, as well as between each other. These findings align with limited data available in the literature. For example, studies on commercially available 500 HBW hardness steel show that material quenched from 860 \({}^{\circ}\)C and 960 \({}^{\circ}\)C exhibited grain sizes of 14 \(\upmu\)m and 34 \(\upmu\)m, respectively, which partially coincides with the results of this study. In high-stress abrasive dry-pot tests [15], the best abrasive wear indices were obtained for the first of these heat treatment variants. Additionally, microhardness tests showed that steel quenched from 860 \({}^{\circ}\)C achieved the highest surface hardness after wear tests (793 \(\pm\) 63 HV), indicating superior hardening capability compared to the as-delivered and 960 \({}^{\circ}\)C-quenched conditions, where hardness was 589 \(\pm\) 22 HV and 602 \(\pm\) 38 HV, respectively. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & **SS Effect** & **df Effect** & **MS Effect** & **SS Error** & **df Error** & **MS Error** & **F** & \(p\) \\ \hline Mass wear per 1 m & 0.247804 & 5 & 0.049561 & 0.037302 & 30 & 0.001243 & 39.85862 & 0.000000 \\ \hline Hardness & 28,525.43 & 5 & 5705.086 & 1987.426 & 54 & 36.80419 & 155.0119 & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of ANOVA. Figure 7: Relative abrasion resistance coefficient \(K_{b}\) and mass wear per meter of sliding distance (**a**), and hardness (**b**) of Hardox 500 steel at various austenitizing temperatures. DS, as-delivered state. Analysis of the results shows that prior austenite grain size significantly affects the abrasive wear resistance of Hardox 500 steel. Grain growth, especially the appearance of abnormal grains, leads to a noticeable increase in mass loss. This relationship between grain size and wear intensity is illustrated in Figure 8a, where the data is approximated by a quadratic function with an \(R^{2}\) of 0.82, indicating a strong correlation. Given the uncertainty regarding the treatment conducted by the steel manufacturer in the as-delivered state (with hardness suggesting possible tempering), this material state was excluded from further analysis. The results for Hardox 500 steel can be compared with findings from similar studies on lower-grade steel, such as Hardox 450 [1]. In Hardox 450, as prior austenite grain size increased, the weight-based wear rate and abrasion resistance changed linearly. However, the differences in \(K_{b}\) values were less pronounced than for Hardox 500 steel, and no correlation was found between the relative abrasion resistance and hardness of Hardox 450. In contrast, for Hardox 500, both the correlation between average grain size and hardness and the relationship between hardness and abrasion resistance were well-represented by quadratic functions with high R\({}^{2}\) values of 0.97 and 0.87, respectively (Figures 8b and 9). This parameter has long been recognized as a key indicator of steel wear resistance, especially when comparing steels with similar microstructures but differing hardness levels. Examples include martensitic steels, where higher hardness, often due to varied carbon content, correlates with improved wear resistance [45; 46; 47]. Although widely used for assessing tribological resistance in similar microstructures, some studies have reported no such correlation [45; 48].