Effects of stress- and/or warm peening of AISI 4140 on fatigue life

Using a new system shot peening and/or stress peening in an air blast machi ne at elevated temperatures is feasible. The effects of conventional shot p eening, stress peening, warm peening and stress peening at elevated tempera tures on the characteristics of regions close to the surface, on the stabil ity of residual stresses and on the fatigue strength of a quenched and temp ered AISI 4140 steel (German grade 42 CrMo 4) are presented. The alternatin g bending strength is increased by stress peening, warm peening and especia lly the combination of both compared to conventional shot peening. These ef fects are due to the residual stresses induced and the stability of the dis location structure, which is highly affected by strain ageing effects.