LAUSR

Abstract This work shows in details how the γ→α′(e) (austenite (γ), martensite (α′, e)) strain-induced martensitic transformation affects the cavitation erosion behavior of the solution-treated AISI 304 austenitic stainless steel. For this purpose, mirror-polished surface samples initially presenting ~93 vol% γ + ~7 vol% α′ were subjected to cavitation erosion testing according to ASTM G32-10 , being carefully characterized by X-ray diffraction and hardness measurements at the tested surfaces. Under cavitation, the studied steel surface showed total γ→α′ transformation fraction of ~89 vol% (which supposedly is directly related to the needed ~4 vol% expansion for the transformation), with no effective mass loss for 180 min testing time, clearly defining the transition from the incubation period (IP) to the acceleration stage of the cavitation testing. For this transformation condition, initially presenting remaining ~11 vol% γ fraction, successive material removal steps and XRD analysis were carried out aiming at determining the actual depth at which this cavitation-related transformation takes place into the steel austenitic matrix. In this case, ~57 μm depth was found when XRD patterns before testing (leading to ~93 vol% γ results) were obtained. Finally, the variation of the average γ→α′ transformation rate along all IP presented a maximum level of ~0.60% min−1 between 60-120 min, which is attributed to the great difference on the mechanical properties of the γ and α′ phases, whose volume fractions continuously change at the surface under cavitation, thus affecting the evolution of the referred surface transformation.