Evaluation of microstructural and mechanical properties of Fe-16Cr-1Ni-9Mn-0.12N austenitic stainless steel welded joints

This study has been aimed to find out the proper welding procedure/conditions for a newly developed Fe-16Cr-1Ni-9Mn-0.12N austenitic stainless steel (ASS), which is uniquely modified from 200 series alloy, in order to control the microstructural metastability of the weld metals. The welded joints of 4 mm thick sheet were prepared in a square butt configuration by using three modes of metal transfer, i.e., short-circuit (SC), spray (S), and pulse (P) mode of metal transfer and three austenitic filler metals (304L, 308L and 316L) under two shielding gas environments using gas metal arc welding (GMAW) process. It is observed that the variation in modes of metal transfer and filler metals can effectively manipulate the metastability of gamma-phase, formation of delta-phase and grain size of the weld metals. Among the modes of metal transfer, pulse mode of metal transfer produces more metastable gamma-phase and higher delta-phase fraction responsible for finer grain structure in weld metals irrespective of filler metals used. Again, higher microstructural metastability was obtained with the 304L filler metal irrespective of modes of metal transfer used. It is evident that the weld metals having higher microstructural metastability also improved mechanical properties (i.e. hardness, strength and toughness). However, weak fusion boundary (FB) region of welded joint limits the beneficial effect of metastability and creates a weakest link in the joint. On the other hand, high temperature heat affected zone (HTHAZ) having a coarse austenite grain surrounded by grain boundary precipitates is governed only by the modes of metal transfer.