## 3 Results and Discussion
A chemical analysis conducted at EDS spot 2 confirmed that the chemical composition of this area corresponds to (Ti,Al)N, as indicated in Table 1. In some sections of the tool's flank face, the abrasion wear has been so severe that the workpiece material adhered to the tool surface, resulting in the removal of the upper and middle layers of the tool coatings. This revealed the tool's bulk material, which is tungsten carbide (bare WC), as depicted in Figure 4d. The chemical composition of point EDS Spot 3 in this region in Figure 4a (Table 1) confirms the existence of the element tungsten in this area. It is clearly illustrated in Figure 3a-d that with increasing workpiece preheating temperature in hot machining, the cutting tool resulting in abrasion and adhesion mechanisms have been reduced [18]. Figure 3: Comparison of flank wear in (**a**) conventional turning, (**b**) hot turning at 200 \({}^{\circ}\)C, (**c**) at 300 \({}^{\circ}\)C, (**d**) at 400 \({}^{\circ}\)C; for f = 0.102 mm/rev and V\({}_{\text{c}}\) = 123 m/min (magnification = 200\(\times\)). SEM micrographs of cutting tool flank wear and crater wear are shown in Figure 5. It is indicated from Figure 5 that the flank wear width during conventional turning is 114 um (Figure 5a) while applying hot turning reduces the flank wear width to 76 um (Figure 5b), however, increasing the workpiece preheating temperature to 400 \({}^{\circ}\)C results in increasing flank wear to 84 um (Figure 5c). Therefore, improved machining performance concerning the cutting tool wear can be obtained under a hot turning process with a workpiece preheated temperature of 300 \({}^{\circ}\)C. Figure 5d shows a magnified illustration of the black box marked on the tool flank face. As a result, it has been found by the chemical analysis of point Spot 4 that the chemical composition of this part is like that of the workpiece material \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**EDS Spot** & **Fe** & **Cr** & **Ni** & **Co** & **Cu** & **W** & **Ti** & **Al** & **N** & **O** & **C** \\ \hline EDS spot 1 & 76 & 16.3 & 3.5 &... & 3.2 &... & 0.2 &... &... & 0.6 & 0.2 \\ \hline EDS spot 2 &... &... &... &... &... &... & 43.6 & 21.8 & 32.4 & 0.2 & 1.9 \\ \hline EDS spot 3 & 1.1 & 0.3 &... & 5.6 &... & 87.1 &... &... & 0.2 & 5.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of wear surfaces on cutting tools (wt. %). Figure 4: (**a**) Magnified worn area shown in Figure 3a. (**b**) EDS map of the Fe-rich region where workpiece material adhered to the tool surface. (**c**) Chromium-free region, where the coating layer on the tool’s top surface was worn. (**d**) EDS map of the W-rich region, where both the top and base coating layers of the tool have worn away (cutting tool: PVD-(Ti,Al)N/(Al,Cr)\({}_{2}\)O\({}_{3}\) coated carbide). adhered to the tool face as Built of Edge (BUE). Moreover, the chemical composition of point Spot 5 also includes the elements Ti, Al, and N; indicating that the upper coating of the cutting tool has been removed under abrasion while the tool's middle coating still exists on the tool bulk material (sublayer; tungsten carbide-bare WC). Cutting tool flank wear and crater wear for different machining processes are shown in Figure 6. As it is indicated in this figure, during conventional turning, the tool cutting edge has been broken in the nose radius section (Edge Fracture) on the rake face, and consequently, the tungsten carbide is visible. However, this area where the carbide is trapped is visible and has been reduced significantly by performing hot turning at 400 \({}^{\circ}\)C. In addition, hot turning has been shown to reduce flank wear as well (Figure 6). Figure 5: \(Cont.\)  
Cutting force and tool tip temperature values during turning processes have been calculated by applying a verified FEM analysis using Power Viscosity Law [13].