EFFECT OF HEAT TREATMENT ON STRUCTURE AND EROSION OF NITRONIC STEEL

Abstract

Heavy damages of under water parts in. hydroelectric projects due to hard silt particles are responsible for serious erosion problem. Solid particle erosion is a major problem in hydro and steam turbines. Various grades of austenitic stainless steels strengthened with nitrogen are used under water parts of hydroelectric power plants. In this work 21-4 N Nitronic steel samples having the composition 21 %Cr, 4%Ni, 0.08%C, 0.4%N, 8-10%Mn, 1%Si, 0.065%S, 0.06%P were quenched in water from five different solutionizing temperature (i.e. 900°C, 950°C, 1000°C, 1050°C and 1100°C). Various mechanical test (i.e. Tensile test, Impact test and Hardness test) and Erosion test were conducted at room temperature on As Received and As Quenched samples. The effects of heat treatment on mechanical properties were studied with help of suitable graphs. Various microstructural changes were studied by using optical microscope. A qualitative relationship was established between the microstructure and mechanical properties of material, which were effected by heat treatment. The fractured surfaces of Tensile test and Impact test samples were examined by Scanning Electron Microscope (SEM). Erosion test for As Received and Heat treated at 1100°C sample is carried out using Air jet erosion tester with Aluminum oxide erodent at 20° impact angle. From the experimental results it observed that heat treated sample shows improved erosion resistance. Rate of erosion is correlated with the mechanical properties and microstructural changes. The Scanning Electron Microstructural details of eroded sample have been carried out to ascertain the mechanisms of erosion..