ESSC & DUPLEX 2019

Summary: Increased interest in light-weight solutions for exhaust systems drives the need for application of thin-walled elements, and in consequence using more and more advanced materials. However, welding of thin-wall parts made of highly alloyed austenitic steels can result in hot cracking in heat affected zone. The paper discusses weldability of highly alloyed 1.4539 grade with the respect to this particular issue. Metal Inert Gas (MIG) method was used to perform welding trials on flat and plastic deformed samples. Welded samples were prepared using varying torch position and varying heat input in order to reveal relation between process parameters and susceptibility to hot cracking. Macro and micro-structure were investigated using optical microscopy, particularly focusing on weld seam geometry and size of heat affected zone. Solidus temperature was determined by means of differential thermal analysis (DTA) both in initial and equilibrium condition. Microstructure changes in heat affected zone were studied using scanning electron microscope (SEM) and energy dispersive x-ray spectrometry (EDS). Presence of relatively large partially melted zone was revealed in samples made using pushed torch, even at relatively low heat input. Mo-rich precipitates were detected at grain boundaries, which suggest grain boundary liquation as primary mechanism leading to hot crack formation.