Influence of residual stresses due to mechanical surface treatments on the fatigue strength capacity of welded high strength steels

The fatigue strength of welded steels can be significantly increased compared to conventional manufacturing by the application of post-weld treatment processes to improve the properties at critical weld details. In particular, mechanical surface treatment processes like high frequency hammer peening or shot peening can be used to induce beneficial compressive residual stresses in conjunction with work hardening, which have a beneficial effect on fatigue strength. Various examples of steels with yield strengths up to 1100 N/mm² reveal that the improvement of the fatigue strength results from the interaction of near-surface residual stresses and work hardening. It is also taken into account that the initial residual stresses can be partially released depending on the load history, and these changes must be considered in fatigue life assessments. It is shown that well adjusted shot peening, especially in welded joints of high-strength fine-grained structural steels, can raise the fatigue strength to the level of the respective base material which is not possible with help of alternative procedures. This opens up a significantly expanded application potential for high-strength steels in welded structures and extends the application limits currently defined in applicable design guidelines.