Abstract
The present work deals with the influence of deformation induced martensite formation and grain size on plain fatigue (PF) (without fretting) and fretting fatigue (FF) behaviour of AISI 304 austenitic stainless steel at room temperature. Two grain sizes, namely 43 and 277 μm, were developed via suitable solution annealing treatments. The martensitic transformation was studied using a ferrite scope, X-ray diffractometry, optical and transmission electron microscopy. More martensite formed in coarse grained (CG) material and at higher cyclic stress levels. Owing to the additional influence of contact stress, more martensite formed in the fretting scar region of FF tested samples compared with that in the PF tested specimens. In PF tests conventional behaviour was observed at higher cyclic stress levels, i.e. fine grained material showed superior fatigue lives. But at lower cyclic stress levels CG material exhibited superior fatigue lives. This was explained in terms of amount and time of martensite formation and whether crack initiation or propagation controlled the fatigue life at a given stress level. Fretting fatigue test results indicated a tendency for cross-over in the stress life plots corresponding to two grain sizes.
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