Friction stir processing of dual certified 304/304L austenitic stainless steel for improved cavitation erosion resistance

Abstract

Cavitation erosion is known to be prevalent in equipment in hydraulic environments. Understanding cavitation erosion and improving the erosion resistance of commonly used materials is of interest for both scientific and economic reasons. In this study, friction stir processing was employed to modify commercial dual certified AISI 304/304L austenitic stainless steel plates. The cavitation erosion behavior of the processed plates was evaluated and compared to that of the unprocessed steel. A temperature control algorithm was employed to maintain a target tool temperature during the processing. The cross sections of the processed nuggets were evaluated using optical microscopy, scanning electron microscopy and Vickers hardness testing. Erosion testing by cavitation liquid jet was performed conforming to ASTM G134 on specimens cut out of the nuggets of the commercially unprocessed and the processed 304/304L steel. The tool temperature was found to affect the microstructure and the cavitation erosion behavior. Friction stir processed steel showed greater than 3× improvement in cavitation erosion resistance (defined as the reciprocal of the mass loss of a given material) than the unprocessed 304/304L. Surface erosion patterns and erosion rates were characterized and the mechanisms of material removal were discussed.