# The Influence of Grain Size on the Abrasive Wear Resistance of Hardox 500 Steel
## 2 Materials and Methods
### Microstructural Analysis  
The microstructural examination was conducted using a Nikon Eclipse MA200 light microscope (LM) to assess the steel's microstructure. The specimens were etched using reagent No. 3 according to ASTM E407 standards [37]. To reveal prior austenite grain boundaries, reagent No. 8 (5 mL picric acid, 0.5% sodium alkyl sulfonate, 100 mL H\({}_{2}\)O) at approximately 55 \({}^{\circ}\)C, as specified in ASTM E407 [37], was utilized. These analyses were performed on both as-delivered and heat-treated samples.  
Surface observations after laboratory abrasion resistance testing were conducted on unetched specimens using a Phenom XL scanning electron microscope (SEM) equipped with a secondary electron (SE) detector at an accelerating voltage of 15 kV. The samples were examined in their as-delivered state and post-heat treatment.  
Quantitative assessment of the prior austenite grain size in representative sample areas was conducted using Image J software, version 1.54g. Through planimetric methods, cross-sectional areas (a) of 100 randomly selected grains were measured, and the flat grain diameter (d) was calculated as \(\sqrt{\text{a}}\). The results were analyzed using Statistica software version 13, which was used to generate grain diameter distribution patterns. A constant class count of 10 was maintained. The empirical distributions obtained were analyzed for conformity with theoretical distributions (log-normal, exponential, and gamma). [PERSON]'s chi-squared (\(\chi^{2}\)) test was used to evaluate the fit of experimental distributions to theoretical models.  
\begin{table}
\begin{tabular}{c c} \hline
**Designation** & **Heat Treatment Parameters** \\ \hline H500-DS & As-delivered state \\ \hline H500-A (850–1200 \({}^{\circ}\)C) & Normalizing: 890 \({}^{\circ}\)C, 30 min \\ Abrasion and hardness measurements & Austenitizing: 850 \({}^{\circ}\)C, 900 \({}^{\circ}\)C, 1000 \({}^{\circ}\)C, 1100 \({}^{\circ}\)C, \\  & 1200 \({}^{\circ}\)C, 120 min, water \\ \hline \multirow{4}{*}{H500, H500-A (850–1200 \({}^{\circ}\)C) Prior austenite grain size testing} & Normalizing: 890 \({}^{\circ}\)C, 30 min \\  & Austenitizing: 850 \({}^{\circ}\)C, 900 \({}^{\circ}\)C, 1000 \({}^{\circ}\)C, 1100 \({}^{\circ}\)C, \\ \cline{1-1}  & 1200 \({}^{\circ}\)C, 120 min, water \\ \cline{1-1}  & Tempering: 550 \({}^{\circ}\)C, 30 min, furnace cooling \\ \hline \end{tabular}
\end{table}
Table 2: Detailed parameters of heat treatment procedures applied to Hardox 500 steel; H500, Hardox 500.  
For surface reconstruction, a HITACHI TM-3000 SEM and dedicated graphic-analytical software 3D Image Viewer Version 2.1.0 were employed. Prior to surface roughness assessment, the samples were cleaned with dry compressed air, checked for mechanical damage, and marked at three points, P1, P2, and P3 (Figure 1), where the surface reconstruction procedures would be conducted. All surface reconstructions were performed at a uniform magnification, allowing the elementary segment length _lr_ = 198.03 \(\upmu\)m or its tenfold (1980.26 \(\upmu\)m), and consistent electron beam settings at 15 kV, ensuring detailed observation and recording of the steel sample surface features. Before examining the steel samples, a working distance (WD) calibration was conducted using a standard with a notched roughness profile.  
The following roughness parameters were analyzed:  
_Ra_, the arithmetic mean deviation of the profile,  
_Rq_, the root mean square deviation of the profile,  
_Rz_, the maximum height of the roughness profile based on 10 points,  
_Rp_, the height of the highest peak in the profile,  
_Rv_, the depth of the deepest valley in the profile, and  
_RSm_, the mean spacing of the roughness profile.