## 6 The Structure of Cast Iron after Introducing Tungsten and Its Resistance to Abrasive Wear  
In the case of tungsten as an alloying additive to high-aluminum cast iron, the complete substitutability of the Al\({}_{4}\)C\({}_{3}\) carbide by WC carbide is uncertain. The reason is the value of the free energy \(\Delta\)G\({}^{0}\) of the WC carbide formation reaction, which is about \(-34\) kJ (for W\({}_{2}\)C carbide, similarly \(\Delta\)G\({}^{0}=-35\) kJ). Therefore, it can be assumed that the degree of replacement of aluminum carbides with tungsten carbides does not have to depend on the content of tungsten introduced (according to Equation (4)), as it was in the case with the introduction of titanium (Equation (3)). \[\text{W}+\text{C}\rightarrow\text{WC}, \tag{4}\]  
Equation (4) shows that 1 g of tungsten binds 0.065 g of carbon, which gives 1.065 g of WC carbide. It is four times less than titanium. Therefore, a much larger addition of tungsten was assumed in the research. The melted alloy with the chemical composition presented in Table 3 was superheated to a temperature of 1510 \({}^{\circ}\)C, and then samples were poured for metallographic tests at a temperature of 1420 \({}^{\circ}\)C. Tungsten in the form of ferroalloy was then introduced into the thus prepared melted cast iron. The samples were cast into dried molds made of bentonite mass, from which metallographic specimens were later made. In order to obtain information on the influence of tungsten on the structure of high-aluminum cast iron, the microstructure of the samples was examined. The analysis of the metallographic specimens shows, that after the addition of tungsten, with its content of approx. 16 mass %, The Al\({}_{4}\)C\({}_{3}\) aluminum carbide was completely replaced by WC tungsten carbides. No aluminum carbide was found in the tungsten sample either, which shows the effect of the complete replacement of the aluminum carbide with tungsten carbide. Figure 7 presents the morphology of WC carbide precipitates in the alloy and their chemical composition. Moreover, graphite is present in the structure of the obtained high-aluminum cast iron. According to [PERSON]. [PERSON]'s rule, this type of formed carbide can be determined, when it depends on the ratio of the radius of the carbon atom r\({}_{\text{w}}\) to the radius of the metal atom r\({}_{\text{m}}\). Thus, according to this rule, carbides can be divided into two types:  
* when r\({}_{\text{w}}\)/r\({}_{\text{m}}\) < 0.59--straight carbides are formed; this group includes carbides of the MC type, i.e., TiC, NbC, WC, VC, ZrC, and the M\({}_{2}\)C type, i.e., Mo\({}_{2}\)C, W\({}_{2}\)C, Nb\({}_{2}\)C. If various transition metals appear in the thermodynamic system, the formation of complex carbides can be predicted with high probability. Moreover, in some carbides, not all interstitial spaces are filled with \"non-metal\" atoms. Then the average chemical composition of these phases' changes and, for example: instead of the MC carbide, the M\({}_{4}\)C\({}_{3}\) phase, with a deficiency of non-metal atoms may appear in the structure;
* when r\({}_{\text{w}}\)/r\({}_{\text{m}}\) > 0.59--complex structure iron, chromium, and manganese carbides are formed. The M\({}_{3}\)C type carbide crystallizes in the orthorhombic pattern. On the other hand, the M\({}_{23}\)C\({}_{6}\) and M\({}_{6}\)C carbides are characterized by a complex cubic lattice, and the M\({}_{7}\)C\({}_{3}\) carbide crystal lattice is a complex hexagonal lattice (possibly orthogonal and rhombohedral). Good examples of these carbides are: Fe\({}_{21}\)W\({}_{2}\)C\({}_{6}\) ternary carbides, for the M\({}_{6}\)C type--W\({}_{6}\)C, Fe\({}_{3}\)W\({}_{3}\)C, Fe\({}_{4}\)W\({}_{2}\)C ternary carbides, visible from the EDS tests presented in Figures 8-11. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Element** & **Al** & **C** & **Si** & **Mn** & **W** & **S** & **Fe** \\ \hline \% mass & 31.30 & 1.35 & 1.05 & 0.37 & 16.08 & 0.01 & remain \\ \hline \hline \end{tabular}
\end{table}