DEVELOPMENT OF WEAR RESISTANT HYDRO TURBINE STEEL THROUGH PHASE TRANSFORMATION INVOLVING MICRO- AND NANO-SIZED SECOND PHASE DISPERSED IN THE METALLIC MATRIX

Abstract

The aim of this research is to enhance the sliding wear and slurry erosion resistance of 13-4 MSS which is chiefly used to fabricate the hydroturbine blades and other components so as to improve the sustainability level of the hydropower generation (station) which would have decline due to the wear of material by sliding and slurry erosion. The erosion behaviour of 13-4 MSS mainly governed by its microstructural features e.g. matrix and second phase particles, and concerned mechanical properties. A new technique (which has not been addressed for this purpose previously), i.e. cyclic heat treatment (CHT), was employed in this research for strengthening the 13-4 MSS as consequences of phase transformation and grain refinement. Various CHT schedules were conducted using thermomechanical simulator (Gleeble® 3800) and detailed microstructural characterization of as-received and the cyclic heat-treated (CHTed) 13-4 MSS was carried out. Mechanical properties including microhardness of matrix and second phase (delta ferrite), bulk hardness, tensile properties (yield and ultimate tensile strength, ductility, and tensile toughness) were experimented to characterize the various schedules of the CHT. Structure-property relations for the as-received and CHTed 13-4 MSS were studied by investigating the influence of microstructure on mechanical properties. The influence of microstructure, second phase, and mechanical properties on sliding wear behavior of 13-4 MSS was then studied. Then, slurry erosion behavior using slurry pot erosion tester was carried out along with the detailed microstructural characterization and structure-property correlations. The effects of micro-sized (delta ferrite) and nano-sized (carbides) second phase particles were assessed on mechanical properties and slurry erosion performance. Finally, the wear (sliding wear and slurry erosion) mechanisms were analyzed through scanning electron microscopy and atomic force microscopy.