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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 precrack.
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.