Cavitation erosion deteriorates components like metallic parts of water pumps, valves and blades of hydraulic turbines, in this last case being responsible for high economical losses, associated to direct maintenance costs, but above all due to the interruption of the electric power generation. Among the materials usually applied in the welding repair of cavitation erosion are included the common stainless steels AISI 308 and 309, special Co-alloyed stainless steels and Co-base alloys (stellites), whereby these have as handicap a higher susceptibility to cracking, the difficult in finishing by grinding and the higher cost. In this context this work had the purpose to design, develop and evaluate CrMnSiN austenitic stainless steels, as deposited by the PTA process. The cavitation erosion resistance was evaluated using the vibratory ultrasonic test according ASTM G32-92. The microstructure was analyzed by means of optical and scanning electronical microscopy and the nature of phases present in the coatings - the cavitation induced formation of martensites α' and ε - was estimated by x-rays diffraction. Besides that the surface quality as examined by NDT, the hardness and the feasibility of finishing by grinding, where all evaluation criteria of the welded deposits. It was verified that the coatings applied by PTA were free from solidification cracks, had low porosity, good wetability and adequate surface finishment. The best austenitic stainless steel developed (0,03%C; 0,35% N; 13,2%Cr; 11,8% Mn; 2,8%Si; bal %Fe) showed a cavitation erosion resistance quite near the most resistant commercial alloys.
Cavitation; PTA process; hardfacing; austenitic stainless steels
