## 3 Experimental Results and Analysis  
This section summarizes the measurement results and compares them with the available theoretical knowledge. We used a light microscope to analyze the microstructure of the initial state samples of AISI 304. The material structure consists of polyhedral austenite grains of various sizes, as shown in Figure 6.  
In the microstructure, there are numerous oval-shaped non-metallic intrusions of manganese sulfide (MnS), as shown in Figure 7. The presence of sulfur in steel can be attributed to its occurrence in ores. Sulfur has a detrimental effect on austenitic steels, weakening their cohesion and leading to increased brittleness and decreased fatigue limit. However, the negative impact of sulfur can be mitigated by the presence of manganese, which binds to sulfur to form MnS. This binding process not only limits the degradative effects of sulfur but also increases the strength of the material. Figure 5: Magnetic field mapping experimental arrangement: (**a**) an example of the scanning procedure; (**b**) comb scanning procedure. Figure 6: Experimental results: microstructure of AISI 304 in the initial state, induced by G + HF + HNO\({}_{3}\) etchant: (**a**) general microstructure; (**b**) microstructure detail. At the same time, a relatively large number of typical annealing twins and deformation martensite with various orientations can be observed. These are formed due to plastic deformation, which involves cold rolling the bar in one direction to achieve the required square cross-section. It is important to note that heat treatment significantly alters the amount of deformation martensite. This leads to changes in the mechanical and magnetic properties of the material. This understanding is critical for assessing the behavior of austenitic steel at both microscopic and macroscopic levels. For better visualization, refer to Figure 7b, which shows a sample annealed at 1100 \({}^{\circ}\)C. The sample was then cut, manually sanded using P100 and P600 sanding wheels, and polished with diamond paste. After inducing the austenitic structure with an etchant, the resulting microstructure was observed using a microscope, as shown in Figure 7b. By comparing images in Figures 6a,b and 7a,b, there is a difference in the microstructure of the samples before and after annealing, specifically a decrease in the content of deformation martensite. The presence of sulfur in the composition was also confirmed through EDX analysis (Energy-Dispersive X-ray spectroscopy), shown in Figure 8, using a Scanning Electron Microscope (SEM). The non-metallic intrusion of manganese sulfide MnS is highlighted with blue, representing areas with sulfur and turquoise, indicating the presence of manganese. Figure 8: EDX mapping and analysis: detail of non-metallic manganese sulfide intrusions: (**a**) native SEM image; (**b**) SEM image with highlighted presence of sulfur and manganese; (**c**) SEM image with highlighted sulfur K-alpha emission line; (**d**) SEM image with highlighted manganese K-alpha emission line. Figure 7: Microstructure of the inspected material: (**a**) AISI 304 at initial state indicating important features; (**b**) AISI 304 after annealing at 1100 \({}^{\circ}\)C at 400\(\times\) magnification. The initial state samples were measured for microhardness using a Zwick/Roell ZH\(\mu\) microhardness meter on metallographically prepared samples. This method offers increased measurement accuracy due to the flat and polished surface and better visibility of impressions in the examined samples. The measurement results in Figure 9a show the microhardness from the proximal part to the distal part of the sample. The figure illustrates that the course is relatively axisymmetric regarding the sample's core. The arithmetic mean of microhardness in the longitudinal section was 281 HV 0.5, with a maximum value of 318 HV 0.5 and a minimum of 254 HV 0.5.