## 3 Results and Discussion
Making the assumption that the carbide hardness ratio remains consistent, the calculations for the proportion of hardness of the carbide at the workpiece's beginning temperature to the hardness of the tool constituents at the cutting temperature have been presented in Figure 9. The results indicate that as the workpiece's starting temperature increases from 25 \({}^{\circ}\)C to 300 \({}^{\circ}\)C, the ratio of carbide hardness to the hardness of the tool constituents decreases. This decrease, together with a notable decrease of cutting force during preheated turning (25%), contributes to a general decrease in abrasive wear in preheated turning in contrast to turning at room temperature. However, when the component's beginning temperature is raised from 300 \({}^{\circ}\)C to 400 \({}^{\circ}\)C, there is a slight increase in the ratio of carbide hardness to the tool elements' hardness. Consequently, the tool flank wear at 400 \({}^{\circ}\)C has slightly increased compared to that at 300 \({}^{\circ}\)C. The effects of initial temperature and cutting parameters on workpiece surface roughness are depicted in Figure 10, illustrating a decrease in machined surface roughness during hot turning at 400 \({}^{\circ}\)C, with reductions of about 27% and 36% in contrast to traditional turning at feed rates of 0.102 and 0.175 mm/rev, respectively. Figure 11 underscores the marked differences in the morphology of machined surfaces at different initial temperatures, indicating a significant influence of preheating techniques on chip-formation mechanisms. Figure 4:0 The ratio of carbide hardness at the workpiece initial temperature to the hardness of the tool constituents (at the cutting temperature) for V\({}_{c}\) = 123 m/min and f = 0.102 mm/rev. The application of a thermally enhanced cutting technique results in machined surfaces with minimal side flows and defects. Conversely, surfaces produced under dry conditions at ambient temperatures exhibit side flow and more surface damage. Furthermore, an increase in cutting speed at each feed rate leads to a reduction in workpiece surface roughness (Figure 10). Additionally, elevating the workpiece's initial temperature in hot turning reduces workpiece surface roughness compared to conventional turning. This increase in initial temperature results in reduced hardness and strength of the uncut chip, subsequently leading to decreased cutting forces (Figures 12 and 13a). Consequently, workpiece surface roughness is diminished, enhancing the overall efficiency of the cutting process. Figure 12 provides insight into the predicted cutting forces and their fluctuations at a cutting speed of 96 m/min and a feed rate of 0.175 mm/rev. The data in Figure 12 demonstrates that the amplitude of the cutting force oscillation decreases with higher preheating temperatures. Figure 13b illustrates the amplitude of the cutting force oscillation (peak to peak) for different cutting speeds. Figure 4:1 SEM micrographs of machined specimens under V\({}_{\rm c}\) = 96 m/min and f = 0.175 mm/rev. Figure 4:2 Effects of initial temperature of the workpiece and cutting parameters on the surface roughness. Reducing cutting force oscillation (\(\Delta\)F\({}_{\text{C}}\)) in hot turning can be another cause of decreasing surface roughness in comparison to the achieved surface roughness in conventional turning operation. It has been observed in [17] that the cutting tool will be under cyclic deflection when the saw-tooth chips are formed. The frequency of the cyclic deflection of cutting tool is close to the fluctuation frequency of the cutting force. In these conditions, as a result of tool cyclic deflection, cutting speed and tool's rake angle are changed locally, and accordingly, the machined surface roughness of the workpiece increases. However, it has been found that preheating process applied in hot machining reduces the average cutting force (Figure 13a), and at the same time it decreases the cutting forces' fluctuation amplitude in comparison to conventional turning process (Figure 13b).