# The Influence of Grain Size on the Abrasive Wear Resistance of Hardox 500 Steel
## 3 Results and Discussion
### Abrasive Wear Resistance  
Figure 7a displays the parameters of Hardox 500 steel obtained during abrasive wear testing in the presence of loose abrasive. Alongside the relative abrasion resistance indices \(K_{b}\), mass wear per meter of sliding distance is shown to illustrate the standard deviation of the results and to facilitate statistical analysis. However, the \(K_{b}\) index offers greater comparative value and will be the primary focus of further discussion. All results are referenced to the as-delivered state, with a baseline \(K_{b}\) value of 1.00. After austenitizing at 850 \({}^{\circ}\)C and 900 \({}^{\circ}\)C, the \(K_{b}\) index remains unchanged at 1.01 and 1.00, respectively, indicating that the highest abrasion resistance is exhibited by the fine-grained microstructures in the as-delivered state and after austenitizing at the two lowest temperatures. A slight reduction in \(K_{b}\) (0.96) is observed after austenitizing at 1000 \({}^{\circ}\)C. Starting at 1100 \({}^{\circ}\)C, this trend becomes more pronounced, resulting in a clear reduction in abrasive wear resistance, represented by a \(K_{b}\) value of 0.87. The lowest abrasion resistance is observed in material quenched from the highest austenitizing temperature (1200 \({}^{\circ}\)C) with a \(K_{b}\) of 0.78. Examining these results in relation to the microstructures showing prior austenite grain size reveals that, from the onset of abnormal grain growth, Hardox 500 steel exhibits a successive reduction in tribological resistance. The results were analyzed statistically. ANOVA results are presented in Table 4, and [PERSON]'s post hoc test results are shown in Table 5. The Tukey test identified statistically significant differences between various heat treatment conditions. The results indicate that the abrasion resistance after austenitizing at 850 \({}^{\circ}\)C, 900 \({}^{\circ}\)C, and 1000 \({}^{\circ}\)C does not differ significantly from the as-delivered state (\(p\) > 0.05), suggesting that heat treatment within this temperature range does not lead to significant changes in this material property. However, beginning with austenitizing at 1100 \({}^{\circ}\)C, a statistically significant reduction in abrasive wear resistance is observed compared to lower temperatures and the as-delivered state. The \(p\)-values for comparisons between the 1100 \({}^{\circ}\)C condition and the as-delivered state and between the 850 \({}^{\circ}\)C and 900 \({}^{\circ}\)C conditions are 0.000195, 0.000169, and 0.000187, respectively (\(p\) < 0.05). The largest differences are observed in samples austenitized at 1200 \({}^{\circ}\)C, where the \(p\)-values were the lowest relative to other states, emphasizing the significant impact of high austenitizing temperature on reducing abrasion resistance. Changes in hardness with heat treatment state were also considered (Figure 7b). The lowest hardness for the steel was recorded in the as-delivered state (445 HBW), lower than the manufacturer's specification. Austenitizing at 850 \({}^{\circ}\)C and 900 \({}^{\circ}\)C increased hardness to 503 HBW and 508 HBW, respectively. Differences in hardness between these three conditions suggest that the steel manufacturer may have applied tempering processes that reduced hardness relative to heat-treated states at 850 \({}^{\circ}\)C and 900 \({}^{\circ}\)C, which have similar grain sizes. Further increases in austenitizing temperature result in gradual hardness reductions; however, even after heat treatment at the highest temperature, hardness (482 HBW) remains above that of the as-delivered state. Notably, after austenitizing at 1200 \({}^{\circ}\)C, hardness is over 8% higher than in the reference state. The results were statistically analyzed. [PERSON]'s test \(p\)-values (Table 6) indicate that heat treatment at each temperature significantly influences the increase in hardness compared to the as-delivered state.