EFFECT OF HEAT TREATMENT ON SLURRY EROSION BEHAVIOUR OF 13/4 MARTENSITIC STAINLESS STEEL

Abstract

Here in the project ,the studies and heat treatment are being done on the 13/4 martensitic stainless steel that is CA-6NM which has a Nominal composition in weight% as: C-0.020 Mn-0.18 Si-0.14 Cr-13.75 Ni- 3.45 P-0.018 S-0.009 In case of hydroelectric power projects, this steel is greatly used for the fabrication of underwater parts in such project. A thorough investigation should have been conducted in order to develop resistance of high erosion by giving several heat treatments to the cast steel. Various heat treatments were given to the as received bars of the 13/4 martensitic stainless steel. Austenitization of cast steel at the temperatures ranging 940°C, 990°C and 1040°C along with the holding time of 3 hours respectively are given under heat treatments then this process is followed by oil quenching and then tempering occur at 600ºC for 0.5 hr, 1 hr and 2 hr respectively. The treated steel specimens should have been tested for Tensile strength (UTS), Toughness (Impect Strength), Hardness, and Ductility (% Elongation) and their effect on erosion behaviour. Optical microscope is used for identifying carbides, lath martensite or the similar other distinct micro constituents in the as received or the steel being heat treated steel. It should be studied by using the optical microscope. The micro constituents precipitates during the heat treatment along the boundaries of grains. Scanning electron microscope (SEM) is used for investigating the mechanisms of failure of material in tensile test, impact test and erosion test. From the impact of particles of silt, the plastic deformation occurs at the target surface during the first stage of erosion. Ploughs and material lips are formed due to this. Due to the shear, the lips are produced that later on becomes brittle. This brittleness causes the removal of material from the surface. Subsequently, a rough pattern is caused on the target surface as the material gets eroded frequently. Cutting mechanism is also vulnerable during erosion. Further for identifying the mechanism of erosion, the eroded surface is scanned under SEM. The erosion behaviour is also affected by the microstructural aspects. For the resistance from high erosion, tempered martensite is the best option. The decrement in erosion resistance is result of the coarsening of carbides. The studies done on SEM by researchers reveal that the erosion occurs by cutting and ploughing trailed by the formation of lip. Several mechanical properties and the microstructure affects the erosion behaviour. It is also observed from the studies that the erosion is also likely to get affected due to the inclination of the material with respect to particles of silt present in the slurry. The resistance of erosion is improved with the increase in the toughness and ductility. UTS as well hardness also impacts the behaviour of erosion in the way such that the weight loss increases with the increase in UTS. The same goes with the hardness. By using heat treatment on the as received bar, we had try to find the steel with the minimum weight loss but due to corona virus outburst we were unable to find out how much reduction in the weight loss is possible in the as received material.