EFFECT OF SURFACE FINISH ON FATIGUE OFAUSTENITIC STAINLESS STEELS

Abstract

The effect of surface finish on fatigue limit of two types of austenitic stainless steels(AISI 304L and AISI 316L) has been investigated. Fatigue specimens having twodifferent surface conditions were obtained by changing the final cutting condition;annealing was performed to separate the residual stress effects from surface roughness.Electropolished samples were tested as a reference for each material.A generic mechanistic model for short fatigue crack propagation proposed by Navarroand Rios (N-R model) was implemented to assess its suitability for predicting thefatigue behaviour of specimens with various controlled surface conditions, obtained bymachining. The surface/material properties required to implement this model wereobtained by electron backscatter diffraction (EBSD), surface profilometry, hardnesstesting and X-ray diffraction residual stress measurement. The fatigue limits weredetermined using rotating-bending by means of the staircase method.The fatigue limits predicted by the N-R fatigue model were compared with the results ofthe fatigue tests. There was no agreement between the prediction and observations,indicating that the original form of the N-R model is not appropriate for austeniticstainless steels.In AISI 304L, the surface residual stresses are the dominant parameter, allowingprediction of the effects of machining on fatigue resistance while, the surface roughnessdeveloped by machining has no significant effect. In AISI 316L, the effect of surfaceroughness is found to be negligible, with a weaker effect of surface residual stress thanhas been observed for AISI 304L.Crack nuclei in run-out (>107 cycles) fatigue tests were observed to arrest at twins andmartensite packets, developed by fatigue in AISI 316L and AISI 304L, respectively.Good agreement with experiments was achieved by using a modification to the fatiguemodel, which takes account of the observed effect of the plastic deformation on themicrostructure.

Date of Award	31 Dec 2010
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Thomas Marrow (Supervisor)