Effect of mechanical alloying of Ti and B in pre alloyed gas atomized powder on carbide dispersed austenitic matrix of Iron based hardfacing alloy

Abstract

In fast breeder reactors Austenitic Stainless steel structural components like grid plates, sleeves, etc. are in contact under stress in a flowing liquid sodium environment at temperatures up to 823 K. To tackle self-welding characteristics, hardfacing alloys are required. In the present work, Thermocalc software was used to arrive at suitable composition of alloy consisting of Fe-20Cr-2C-18Ni-2Mn-4Si-2Ti-1B. This proposed alloy was atomized in argon atmosphere. Due to loss of Ti and B in atomization, additional alloying in the form of pure elements and ferro alloys were made by mechanical alloying in attritor ball milling setup with BPR of 10:1 (by wt.) in ultra-high purity (UHP) argon atmosphere. Mechanical alloyed powder exhibits sphericity of 0.908, apparent density of 4.3 g/cc and flow rate of 17 s per 50 g of powder. Laser cladding of 1-3 mm thick overlay layer was made on 10 mm thick SS 316 plate and its characterization was made by optical microscopy, SEM, XRD and micro-hardness. Weld overlay showed moderate distribution of complex carbides in the austenitic matrix and resultant improved hardness in the range of 445–474 HV by mechanical alloying as compared to prealloyed atomized powder.