SOME STUDIES ON WELDABILITY AND EROSION BEHAVIOUR OF NITRONIC STEELS

Abstract

Erosive wear commonly occurs whenever hard particles entrained in gas or liquid medium impinge/slide on a surface with high velocity. This continuous interaction between hard particles and the surface starts damaging the target surface, which increases with time, and after a specific time period, the component fails. One of the severely affected applications by this phenomenon is the hydroelectric power plants located in the Himalayan regions, where slurry containing silt particles damages the underwater parts of hydro turbines. CA6NM (13/4 Cr-Ni or ASTM A743) martensitic stainless steel has wide application in hydro turbine manufacturing due to its higher erosion resistance, high impact, and fracture toughness. In spite of having good mechanical properties, CA6NM is not capable of overcoming the problem effectively due to surface damage after prolonged time and its limited weldability. Therefore, the hydropower industry is looking for alternative materials having high erosion resistance and easy maintenance than the existing CA6NM or 13/4 Cr-Ni martensitic stainless steel. In view of the above, the main aim of this research is to study the weldability and erosion aspects of nitrogen-containing austenitic stainless steels (NC-ASS) as a potential alternative for martensitic stainless steels in the fabrication of underwater parts of hydroelectric projects. Two grades of Nitronic steels (NC-ASS), i.e., 21-4-N (nominal composition: 21% Cr, 4% Ni, 0.53%C and 0.39%N) and 23-8-N (nominal composition: 23% Cr, 8% Ni, 0.32%C and 0.29%N), were welded in two formats, V-groove and bead-on-plate (BOP) using gas metal arc welding (GMAW) process with nitrogen-containing filler wire (ER2209). The slurry erosion testing of NC-ASS base metals and BOP welds was carried out on a jet-type erosion tester and cumulative weight loss (g/mm2) was compared with that of CA6NM martensitic steel.