Cavitation erosion of martensitic and austenitic stainless steel welded coatings

The cavitation erosion resistance of four alloys used to repair worn turbines by welding was tested in laboratory. AWS E309 alloy (3 layers) and a High-Cobalt stainless steel (2 and 3 layers) were applied by manual process (SMAW) onto ASTM A743 grade CA6NM stainless steel (commonly known as 13-4 steel) and their cavitation resistance was compared to that of conventional alloys E410NiMo (applied by SMAW) and a ER410NiMo (applied by semiautomatic process GMAW). The microstructure of the weld deposits was studied by Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), while the chemical composition was analyzed by Optical Emission (OES) and Energy Dispersive X-Ray Spectrometry (EDXS). Cavitation erosion tests were performed in an ultrasonic tester according to ASTM G32 standard and the worn surfaces were analyzed by SEM and XRD. The best cavitation erosion resistance of all the materials tested was shown by the High-Cobalt stainless steel coating applied in 3 layers, while the AWS E309 presented the highest value of maximum erosion rate. Conventional E410NiMo and ER410NiMo alloys showed an intermediate behavior. Incubation periods were 10.9 h and 21.5 h for High-Cobalt stainless steel in 2 and 3 layers, respectively, and 1.4 h for the 13-4 steel. In High-Cobalt stainless steel samples, occurrence of austenite-to-martensite phase transformation and profuse formation of twins and slip lines at the worn surfaces were observed.