## 3 Experimental Results and Analysis
In the second case, seen in Figure 9b, the identical sample was examined for its core, leading to an average value of 279 HV 0.5, with a minimum measured value of 258 HV 0.5 and a maximum of 307 HV 0.5. Based on the evaluation of the results, it can be concluded that the average microhardness value of the AISI 304 sample in the initial state is 280 HV at a load of 0.5 kg. The differences in microhardness depending on the measurement location are caused by several factors. The cold-rolled rod to prepare the samples led to plastic deformation, which modified the microhardness. Consequently, the core of the sample reached the lowest values, while the highest hardness was found at both ends of the sample. Additionally, microhardness values decrease as the indentation distance approaches the center due to the deformation's impact, leading to the formation of deformation martensite with higher microhardness levels than the austenite grain itself. If the measuring diamond pyramid is in contact with the deformation martensite during the measurement, the microhardness reaches higher values. We made five measurements in each sample using a manual hardness tester and calculated the average hardness value. The results of these measurements at different annealing temperatures are displayed in Figure 10. The fluctuation of the obtained waveform can be caused by several factors (if we neglect the variability of the indenter and the measuring instrument). Possible causes include the following: the inhomogeneity of the microstructure, the presence of residual stresses and, of course, the history of the sample's heat treatment. Surface roughness and sample preparation can also affect the obtained results, but in our case, the defined procedures were revised, and based on this, influence can be excluded. Figure 9: Experimental results: microhardness of AISI 304 in the initial condition; (**a**) measurement from the proximal to the distal part; (**b**) measurement to the core of the sample. Thanks to selecting different areas for measurements, implementing multiple measurements has eliminated measurement errors. Based on the results, the average hardness value of AISI 304 austenitic steel depends on the processing temperature. The hardness of the samples remains relatively consistent up to a temperature of 640 \({}^{\circ}\)C. Beyond this temperature, a gradual decrease in the hardness of the samples begins to be observed. The material's hardness decreases significantly within the temperature range of 760 \({}^{\circ}\)C to 860 \({}^{\circ}\)C. This decrease is likely caused by the material's recrystallization, resulting in reduced intrinsic stress and strain hardening. The gradual transformation of \(\alpha^{\prime}\) martensite (deformation martensite) into austenite leads to changes in the material's properties [25; 26; 27; 28; 29; 30]. The material gradually softens and the structure reaches a state of equilibrium. The studied material acquires a constant value of hardness at approximately 860 \({}^{\circ}\)C. At this point, the process represents the annealing dissolution, and the samples attain a homogenized structure. In this range, several hardness values are the lowest within the entire hardness range. Compared to the sample in its initial state, the average value after surpassing the annealing dissolution temperature decreased by approximately 100 HV 10. In comparing the hardness of the samples at the initial state and the sensitized findings, there was an increase in hardness. This increase in hardness in the sensitization temperature range, as shown in Figure 10, can be attributed to the precipitation of chromium carbide precipitates at the grain boundaries. These formed precipitates inhibit the movement of dislocations, which are the primary carriers of ductility and plastic deformation of the material. Chromium carbides also reduce defects in the crystal lattice of sensitized steels.