Cutting edge and its influence on the fatigue life of high strength CrMn-austenitic stainless steel

In the field of product design the fatigue behavior is one of the most challenging issues, especially in the case of high strength steels. It is well known that surface quality has significant influence on a steel component fatigue properties. Different cutting methods have dissimilar effects on cutting edge's surface properties and quality. Thus different cutting methods have distinct influence on fatigue life of steels. For example, while thermal cutting is often fast and effective, it induces heat to work piece and thereby influences on microstructure. Unlike thermal cutting methods, waterjet cutting does not create any heat in the material, but it impairs the surface quality. In this work, the influence of laser-, high-definition plasma- and waterjet cutting on fatigue life has been studied. The results obtained by these cutting methods were compared to ones reached with machined specimens. The test material was 2.27 mm thick sheet of a temper rolled CrMn-austenitic stainless steel grade AISI 201 LN TR with the yield strength of 666 MPa and tensile strength of 814 MPa. Load-controlled low-cycle fatigue tests were performed using the R ratio (R=sigma(min)/sigma(max)) of -1 to flat type specimens. Specimens were stressed on transverse orientation at the stress amplitude of 70%, 80% and 90% of the yield strength. The qualities of cutting edge surfaces were evaluated by measuring surface roughness (R-a-value and R-z-value). Length of heat affected zone was measured from thermally cut edges and also hardness of cut edges was measured.