Cavitation erosion behavior of ion-nitrided 34 CrAlNi 7 steel with different microstructures

In the design of hydraulic machines, the selection of the correct materials and the application of surface treatments are essential to improve the cavitation resistance of components. In this investigation, the cavitation erosion behavior of the compound and of the diffusion layer of ion-nitrided 34 CrAlNi 7 steel was studied. Before nitriding, the 34 CrAlNi 7 steel was heat treated by quenching and tempering and by annealing, generating microstructures that are used or could be used in the production of parts. The cavitation tests were carried out according to the ASTM G32-98 standard method. The nitriding microstructure and the wear mechanisms were analyzed using scanning electron microscopy, X-ray diffraction and laser interferometry. The results showed that the compound layer had a deleterious effect. It led to a reduction in the incubation time and to a high wear rate at the beginning of the test. Afterwards, the wear rate stabilized, but it was higher than that measured on the nitride samples without the compound layer. The main wear mechanism in the compound layer was microcracking. The initial steel microstructure had no effect on the cavitation erosion performance.