Investigation of the effects of different sandblasting processes and addition of molybdenum on the mechanical properties of 51CrV4 and 52CrMoV4 steels

51CrV4 and 52CrMoV4 grade spring steels are materials particularly preferred for applications requiring high mechanical strength and extended service life. The performance of these steels can be significantly enhanced through various surface treatment techniques. Shot peening is an effective surface treatment method that considerably alters the surface characteristics, residual stres state, and overall mechanical strength of steels. In conventional (free) shot peening, small steel shots are blasted onto the surface, while in stres peening, a bending pre-stres is applied to the steel surface after peening, thereby inducing additional stres in the material. These two types of peening can have different effects on the mechanical properties of the steels, particularly in terms of fatigue strength. Additionally, the presence of molybdenum (Mo) in 52CrMoV4 steel is known to induce significant changes in both the microstructure and mechanical properties of the steel. The objective of this thesis is to conduct a comprehensive investigation into the effects of shot peening on the mechanical properties of 51CrV4 and 52CrMoV4 grade spring steels that have undergone quenching and tempering heat treatment. The study will be carried out with two main objectives. The first objective is to examine the effects of different shot peening methods. In this context, the effects of both free (conventional) peening and stres peening on 51CrV4 and 52CrMoV4 steels will be compared. This comparison aims to determine the influence of peening type on surface properties, hardness, tensile strength, and fatigue strength of the steels. The second objective is to investigate the impact of the molybdenum (Mo) element in 52CrMoV4 steel on its mechanical properties. Accordingly, the effects of different peening processes and the Mo content on the microstructural and mechanical properties, with a particular emphasis on fatigue resistance, will be analyzed. This research aims to provide valuable insights into the optimization of peening processes and alloying elements for enhancing the performance of spring steels.