1 ORAL/POSTER REFERENCE: FT432 ANALYSES OF THE EFFECTS OF SURFACE FINISH ON FATIGUE LIMIT IN AUSTENITIC STAINLESS STEELS BY MECHANISTIC MODELING 1 Masatoshi Kuroda* and T. James Marrow Materials Performance Centre, School of Materials, University of Manchester, Grosvenor Street, Manchester M1 7HS, UK ABSTRACT The effect of surface finish on fatigue limit of Type 304 austenitic stainless steels has been studied in terms of mechanistic modelling and experimental observations. A mechanistic model originally proposed by Navarro and Rios (N-R model) was selected as the most suitable generic model for short fatigue crack behaviour, and was assessed in a study of the effect of surface and microstructure effects on the fatigue endurance limit. Two types of Type 304 stainless steels with different grain size were employed; fatigue specimens having two different surface conditions were produced by changing the final cutting conditions of lathe; annealing was performed to separate the residual stress effects from surface roughness. The surface/material properties required to implement the N-R model were fully characterised by electron backscatter diffraction (EBSD), surface profilometry, hardness testing and X-ray diffraction residual stress measurement. The fatigue limits were determined using a rotating-bending machine by means of the staircase method. The predictions of the N-R fatigue model disagreed with the observed fatigue limit significantly. A modification of the model is required for proper prediction of surface effects on fatigue in stainless steels. KEYWORDS Mechanistic modelling, Short fatigue cracks, Surface roughness, Residual stress, Closure stress, Fatigue limit, Austenitic stainless steel, Grain orientation factor INTRODUCTION Austenitic stainless steels are key materials in light water reactors (LWRs) due to their high performance with respect to strength and corrosion resistance [1]. The fatigue limit is one of the most important fatigue properties, and it is known to be sensitive to surface roughness, work hardening, microstructure and residual stress induced by surface working [2, 3]. However, the fatigue limit obtained by experiments is complicated by the interactions of these factors, which results in difficulty in obtaining a fundamental understanding of the mechanism. Therefore, a well-established fatigue model which can elucidate the contribution of each surface effect to the fatigue limit is required. 1 Notice: this is the author’s copy of a paper presented at FATIGUE 2006 9th International Fatigue Congress May 14-19, 2006 - Atlanta, USA