## 2 Materials and Methods  
This research focused on conducting a turning operation on AISI630 hardened stainless steel bars, characterized by a composition of 17% Cr, 4% Ni, and 4% Cu. These bars exhibited a diameter of 35 mm, a length of 240 mm, and a hardness rating of 47 HRC. The chosen cutting tool inserts belonged to the SANDVIK DNMG150608 (SANDVIK, Stockholm, Sweden) type with a grade of 1115, and a tool holder of PDJNR2525M1506 (SANDVIK, Stockholm, Sweden) type was utilized. The primary cutting-edge angle was configured at 93\({}^{\circ}\), and the cutting depth was maintained at 0.9 mm, as depicted in Figure 1. Notably, the rake angle was set at \(-6^{\circ}\), while the clearance angle was \(6^{\circ}\). The cutting-edge radius and nose radius were measured at 0.02 mm and 0.8 mm, respectively. The turning process encompassed two distinct conditions: conventional dry machining conducted at ambient temperature and hot turning, incorporating workpiece preheating at temperatures of 200 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, and 400 \({}^{\circ}\)C. Additionally, the cutting tool feed rates were applied at values of 0.175 mm/rev and 0.102 mm/rev.  
For the hot turning process, the workpiece specimens underwent preheating within a furnace to achieve a temperature 40-60 \({}^{\circ}\)C above the desired level. This preheating phase lasted for 45 min. For example, to perform hot machining at a temperature of 200 \({}^{\circ}\)C, the samples were pre-heated inside the furnace at a temperature of 240 \({}^{\circ}\)C (Figure 1b). Subsequently, the preheated samples were promptly mounted on the lathe machine chuck and centered in less than a minute. The actual turning operation then took place, spanning a duration of 3 min. To ensure that the workpiece's temperature did not experience a significant drop during the entire 4-min process, continuous temperature monitoring was carried out. This monitoring involved the use of a contact thermocouple to measure the workpiece surface temperature at 15-s intervals. Measuring the temperature of the workpiece showed that after 60 s (to clamp the workpiece to the machine), the surface temperature of the workpiece drops to 230 \({}^{\circ}\)C. The simulation of temperature drop was performed using Fluent software (Version 2023 R2), and it was found that the surface temperature drops at the end of 3 min is almost 40 \({}^{\circ}\)C. As depicted in Figure 1b, the surface temperature exhibited a decrease of approximately 50 \({}^{\circ}\)C by the conclusion of the 4-min machining process. Cutting tool wear mechanisms and tool failure modes were scrutinized using a scanning electron microscope (SEM) model FEI Quanta 450 (FEI Europe B.V., Eindhoven, The Netherlands). Furthermore, the surface m  
Figure 1: **(a)** Tool, holder and workpiece used for hot turning, **(b)** workpiece surface temperature versus time.  
workpieces was assessed through an SEM microscope model FEI NOVA NanoSEM450 (FEI Europe B.V., Eindhoven, The Netherlands). To complete the evaluation, surface roughness measurements were conducted using a HOMMEL-WERKE Turbo Roughness V3.34 instrument (Hommelwerke GmbH, Hamburg, Germany) after the machining process.