Analysis of shot peening influence on short crack fatigue threshold of nitrided steels

Great advance in technology requires each time better materials with better mechanical properties, able to resist high stresses, fatigue, wear. For getting this objective surface treatments are very useful. In terms of fatigue, nitriding and shot peening are known as two of the most effective methods to increase components' strength. In this paper the effect of nitriding plus shot peening on fatigue threshold of a low-alloy steel is investigated by means of experimental rotating bending tests carried out on sandglass specimens containing a micro-hole acting as a pre-crack. Different sizes of micro-hole obtained with different processes were considered to assess the influence of crack dimension on fatigue strength in the field of short cracks. After that a critical discussion of the results in terms of residual stress, micro-hardness trend and fatigue strength is done, bearing out the influence of the defects dimension on the fatigue threshold of nitrided and shot peened low alloy steels.