## 3 Results
### Microhardness  
In general, surface hardness is directly proportional to wear resistance. The key principle in improving wear resistance through nitriding treatment is the increase in surface hardness [11]. The hardness of the substrate and the nitrided samples, both before and after deformation, was measured, and the findings are depicted in Figure 3. The average surface hardness values of the 316L stainless steel substrates at various deformation levels were measured multiple times, yielding values of 272 HV, 313 HV, 327 HV, 342 HV, 354 HV, and 376 HV, respectively. In a similar manner, the average surface values of the nitrided samples at different deformation levels were 992 HV, 1054 HV, 1146 HV, 1278 HV, 1369 HV, and 1470 HV, respectively. The nitrided specimens were significantly harder than the non-nitrided specimens [12]. As presented in Figure 3, the hardness of the substrate of 316L stainless steel significantly increased after deformation. This is attributable to the persistent increase in dislocation density within the sample during the deformation process. The increase in dislocations results in the creation of dislocation pile-ups, which hinder the movement of dislocations and enhance the material's resistance to deformation [13]. This effect retains the work-hardened microstructure, resulting in the elevation of the sample's surface hardness. On the other hand, the surface hardness of the nitrided samples at different deformation levels also increased significantly with the increase in deformation. Among them, the nitrided sample with a 50% deformation level had the highest surface hardness, reaching 1470 HV, which is about five times the hardness of the substrate. This is because the density of dislocations and other defects in the 316L stainless steel significantly increased after deformation. Figure 2 illustrates that as deformation increases, the size of the grains significantly decreases, while the number of grain boundaries increases markedly. Additionally, the clarity of the grain boundaries diminishes with an increase in the volume of deformation, resulting in a progressively blurred appearance. This observation suggests that 316L austenitic stainless steel undergoes a process of homogenization and refinement of grains following low-temperature compression deformation, accompanied by a substantial increase in both the number of grain boundaries and sub-grain boundaries. During low-temperature compression deformation, slip mechanisms contribute to an elevated density of dislocations within the original grains, facilitating the formation of sub-grain boundaries. The further development of these sub-grain boundaries leads to the emergence of new grain boundaries, thereby promoting grain refinement. Furthermore, the presence of dislocations, laminations, grain boundaries, and other microstructural features significantly influences the hardness of the stainless steel. During nitriding, nitrogen atoms can fully utilize these defects for diffusion, thus increasing the diffusion rate and accelerating the growth of the nitriding layer, leading to a corresponding increase in hardness.  
Figure 3: The surface microhardness of different deformations of the plasma-nitrided samples.