Effect of Surface Roughness on Fatigue Strength in Martensitic Stainless Steel

This research was performed to study the effect of surface roughness on the fatigue limit in martensitic stainless steel (STS 410). After heat treatment of STS 410 steel, mechanical property tests and rotary bending fatigue tests were performed by varying the surface roughness conditions of A-polishing, A-grinding, and A-#60 of STS 410 steel, respectively. The fatigue fracture surface was observed and analyzed using SEM and EDS. The fatigue limit of STS 410 steel decreased by 0.98% from 509 to 504 MPa when the surface roughness increased about 3 times from 0.226 to 0.664 mu m. However, when it increased about 9 times from 0.226 to 2.053 mu m, it showed a significant decrease of 7.66% from 509 to 470 MPa. The ratio of fatigue limit to tensile strength (fatigue ratio) of STS 410 steel decreased from 54.9 to 50.5% as the surface roughness increased from 0.226 to 2.053 mu m. Beach marks, a typical shape of a fatigue fracture surface, were observed on the fracture surface near the start point of fatigue failure, and brittle (Fe, Cr, Mn, Si) based non-metallic inclusions that promote crack propagation and reduce fatigue limit existed.