## 3 Results and Discussion
The maximum tool tip temperature (T\({}_{\text{P}}\)) and cutting force (F\({}_{\text{C}}\)) for different workpiece preheating temperatures are plotted in Figure 7. As Figure 7 shows, with increasing the workpiece initial temperature from 25 \({}^{\circ}\)C to 400 \({}^{\circ}\)C, the maximum tool tip temperature increases from 760 \({}^{\circ}\)C to 920 \({}^{\circ}\)C, while the cutting force value has decreased from 327N to 220N (33% force reduction). Therefore, although hot turning increases the tool temperature, it significantly reduces the cutting force and applied stresses on the cutting tool edge. As a result, hot turning process reduces cutting tool wear. This fact has also been confirmed by the experimental results shown in Figure 3.  
Figure 5: Comparison of flank wear in (**a**) conventional turning, (**b**) hot turning at 300 \({}^{\circ}\)C and (**c**) at 400 \({}^{\circ}\)C; for V\({}_{\text{c}}\) = 62 m/min and f = 0.175 mm/rev (magnified illustration of the black box in (**d**). Figure 6: Comparison of flank wear in conventional turning **(a)** and hot turning at 400 \({}^{\circ}\)C (**b**) for V\({}_{\rm c}\) = 96 m/min and f = 0.175 mm/rev. Figure 7: Predicted cutting force and maximum tool’s tip temperature at a cutting speed of 123 m/min and a feed of 0.102 mm/rev. An Increase In the Initial temperature of the workpiece, and consequently, the elevation of the cutting zone temperature, results in a decrease in the hardness of the carbides present in the workpiece material. This decrease in hardness brings the carbides closer to the tool elements' hot hardness, which is another factor contributing to the reduced wear of the tool observed in preheating machining in contrast to conventional machining. It's worth noting that the martensitic matrix of the material used in the experiments (hardened AISI630 steel) holds Niobium Carbide and Iron-Chromium Carbide. These carbides exhibit varying hardness values, as depicted in Figure 8a, with respect to temperature changes. Furthermore, Figure 8b illustrates the changes in the hardness of the tool's components with temperature variations. This includes the (Ti,Al)N coating, (Al,Cr)O3, and the WC-Co substrate. The interplay between these hardness values is an important factor in understanding the differences in wear behavior between hot machining and conventional machining. Since the mechanical properties and hardness values of both (Al,Cr)O3 and Al2O3 coating layers are similar [18], Figure 8 incorporates the hardness data available presented in the previous studies for (Al,Cr)2O3, along with the hardness data for Al2O3. The literature review provided hardness values, as depicted in Figure 8a,b. It's important to highlight that, minor variations in hardness values could be due to differences in hardness measurement methods and various manufacturing parameters, like porosity, the size of the grains, and the chemical elements. For instance, as an illustration, two dissimilar hardness values have been presented for the two elements (Fe0,64, Cr0.36)C3 and (Fe0,415, Cr0.585)C3 [16]. It is obvious that during turning operation the cutting tool reaches a stable temperature, which is called the tool/chip interface temperature or cutting temperature. As the martensitic phase of the workpiece material passes through the primary shear (deformation) zone, it undergoes severe plastic deformation and consequently its temperature increases. But the existing hard carbide phase in the bulk of the workpiece material undergoes a slight plastic deformation compared to the martensitic phase, so its temperature rise due to the plastic deformation is negligible. Further, because of the high thermal resistance of the available carbides in the workpiece background [15] as well as their very short passage time through the secondary shear zone (tool/chip friction interface), their temperature in direct contact with the cutting tool face is much lower than the temperature of the cutting tool, and is approximately about the workpiece first temperature [16].