EROSION BEHAVIOUR OF 21-4-N AUSTENITIC NITRONIC STEEL

Abstract

The erosion effect of silt-laden water in hydroelectric power project is very severe, especially in the Himalayan region. The (13/4) martensitic steel is being used presently for underwater parts. The erosion of these leads to temporary closer of generating unit. Furthermore, as the martensitic steel has poor weldability, the welded parts fail prematurely. This increases the cost of production as the replacement of the assembly by a new one is very expensive. This creates the need for the development of erosion resistant steel. The present work is a step in this direction with keeping in mind the weldability factor. Here 21-4N austenitic nitronic steel was analyzed for its erosion resistance characteristics after different heat treatments. Erosion is a complex phenomenon. It is not affected by any single mechanical property. All the mechanical properties come into picture in the erosion mechanism. To obtain good erosion resistance, the microstructure should be such that it gives an optimum combination of hardness and toughness. As hardness and toughness are inversely related to each other, the best way to achieve this is to devise a heat treatment to obtain a suitable microstructure and consequently good erosion resistance. In the present study, 21-4N austenitic nitronic steel was analyzed at different heat treatments. It was observed that erosion rate varies in the same profile as that of hardness after aging i.e. erosion rate is minimum at peak hardness after aging. But if we compare between quenched and aged specimens, the erosion rate is higher in case of aged specimen even if the hardness of the as quenched sample is higher than that of the aged sample.