Influence of surface condition due to laser beam cutting on the fatigue behavior of metastable austenitic stainless steel AISI 304

Austenitic steels are among the stainless steels the most common used type of material to produce sheet metal parts which can be manufactured by laser beam cutting in a useful manner. However, the use of this technique to manufacture structural thick parts is restricted due to the creation of macroscopic defects and the lack of reliable fatigue strength data. In this context, the fatigue behavior of sheet-like samples made of metastable austenitic stainless steel AISI 304 cut by laser beam is discussed in this paper. The analyses showed that laser beam cutting creates three kinds of macroscopic defects, which are a pronounced relief-like structure along the cut surface, burr in the underside of the cut edge and pores in the interface between the recast layer and base material or inside the recast layer. As a consequence, the fatigue strength of parts cut by laser beam is 40% lower in comparison to specimens in a macroscopically quasi defect-free state. An evaluation of the fatigue results based on comprehensive fractographic analyses allows to explain the reasons for distinct differences between the aforementioned influence factors. The most significant reduction of fatigue life is attributed to the notch effect of the burr, followed by the notch effect created by pores, while the influence of the surface relief is of minor significance.