Effect of hard second phase on cavitation erosion of Fe-Cr-Ni-C alloys

This work presents an analysis on the effect of carbides on the cavitation erosion resistance of cast Fe-Cr-Ni-C alloys. Two main groups of alloys were tested: one with chromium content of 25% and another with chromium content of 35%. Several compositions were tested in each group, varying the amounts of carbon and nickel. The cast microstructure obtained for all alloys was an austenitic matrix with carbides (M7C3 for the 25% Cr alloys and M23C6 for the 35% Cr alloys) formed during the solidification. The cavitation tests were conducted with ultrasonic equipment using distilled water. The results showed that alloys with M23C6 carbide have a better cavitation resistance when compared with those with M7C3. During cavitation, the M7C3 carbide (with a coarse morphology) was preferentially worn, increasing the mass loss of the specimens due to a notch effect. On the other hand, the matrix was preferentially worn in alloys with M23C6 carbide. To better understand the role of carbide morphology, the stress distribution over the matrix and the carbide was calculated through finite element modelling (FEM). The meshes used in the simulations were generated through the software OOF, based on sample microstructures, and analyses were conducted in the software ABAQUS. The FEM results showed that the carbides are always subjected to higher stresses, independently of their morphology, but the stress distribution over the phases is altered with the change in morphology.