## 3 Test Results and Discussion  
Table 2 gives parameters of the heat treatment carried out on the tested samples and on the reference sample. The results of hardness measurements are also included. Solution heat treatment with water quenching of the tested alloys from the temperature of 1050 \({}^{\circ}\)C has only a minor effect on the hardness values compared to as-cast samples. The measured hardness of the tested samples as cast and after solution heat treatment is about 260-290 HV and is about 30-60 HV higher than the hardness of traditional Hadfield cast steel, which is 230 HV. \begin{table}
\begin{tabular}{c c c} \hline
**Alloy Designation** & **Heat Treatment** & **Hardness [HV]** \\ \hline \multirow{3}{*}{MnNb\_3} & \multirow{3}{*}{As cast} & 291, 295, 289, 289, 295, 294, \\  & & 290, 290, 293, 294 \\ \cline{2-3}  & & 276, 283, 289, 276, 289, 285, \\  & & 282, 287, 280, 277 \\ \hline \multirow{3}{*}{MnNb\_4} & \multirow{3}{*}{As cast} & 295, 291, 293, 291, 295, 294, \\  & & 295, 293, 291, 293 \\ \cline{1-1} \cline{2-3}  & 1050 \({}^{\circ}\)C/40 min/water quenching & 262, 257, 262, 281, 265, 268, \\ \cline{1-1} \cline{2-3}  & & 275, 277, 271, 269, \\ \hline \multirow{2}{*}{GX120 Mn13} & \multirow{2}{*}{1050 \({}^{\circ}\)C/water quenching} & 230, 227, 229, 230, 227, 228, \\  & & 227, 229, 230, 230 \\ \hline \end{tabular}
\end{table} 
Table 2: Heat treatment of the tested samples and their hardness. Based on the results obtained by light microscopy (Figure 8) and scanning electron microscopy (Figure 9), analysis of the chemical composition of carbides (Figure 10 and Table 3), surface distribution of elements such as Nb, Fe and Mn in the area of visible carbides (Figure 11), and X-ray phase examinations (Figure 12), it was found that the microstructure of the examined alloys after solution heat treatment consists of an austenitic matrix and primary niobium carbides. Carbides visible on the cross-sections of the metallographic specimens are evenly distributed in the austenitic matrix and partially also occur in the form of small clusters (Figures 8 and 9). Figure 11: Surface distribution of Nb, Fe, and Mn in the area of niobium carbides. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Place of Analysis**} & \multicolumn{6}{c}{**[wt\%]**} \\ \cline{2-9}  & **Si** & **Ti** & **Cr** & **Mn** & **Fe** & **Nb** & **Other** \\ \hline \multirow{3}{*}{carbide} & – & 0.6 & – & – & 2.6 & 94.9 & rest \\ \cline{2-9}  & – & 0.8 & – & – & 1.7 & 91.2 & rest \\ \cline{2-9}  & – & – & – & – & 1.4 & 92.8 & rest \\ \hline \multirow{3}{*}{matrix} & 1.1 & – & 0.7 & 13.5 & 84.7 & – & rest \\ \cline{2-9}  & 1.2 & – & 1.0 & 16.4 & 8.4 & – & rest \\ \cline{2-9}  & 1.3 & – & 0.5 & 15.4 & 81.4 & – & rest \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical composition in microregions of the alloy matrix and carbides. Based on the results of Miller test, a diagram was drawn up in Figure 13 showing total weight loss of the tested samples as a function of abrasion time. From this diagram it follows that the abrasive wear resistance of the tested high-manganese cast steel is at least 3 times higher than the abrasive wear resistance of Hadfield cast steel. The addition of 3.5% Nb to the alloy reduces the wear rate from 1.4 g/16h to 0.461 g/16h. With the niobium content of 4.5%, the wear rate is even lower and amounts to 0.366 g/16h, which gives a nearly four times higher value of the abrasive wear resistance. Some differences were also observed in the surface topography of samples subjected to abrasion test. The results are shown in Figure 14. The surface of Hadfield cast steel shows deep scratches and grooves with embedded abrasive particles (Figure 14a). The addition of niobium makes the wear of the samples more uniform (Figure 14b,c). The surface of the samples is even, the grooves and scratches disappear, and niobium carbides formed in the structure are protruding from the alloy matrix. Figure 12: X-ray diffraction pattern of alloy with the addition of 4.5% Nb.