Physical simulations of heat-affected zone microstructures to compare weldability characteristics of additively manufactured and wrought 17-4 stainless steel

Abstract

Microstructure and behavior of parts fabricated via additive manufacturing (AM) usually differ from their conventionally manufactured counterparts. In an effort to further study such differences, this paper is concerned with comparing weldability characteristics of AM and wrought materials, for integration of replacement AM parts into legacy systems. A Gleeble 1500 was used to simulate the heat affected zone (HAZ) generated during fusion welding. Weldability of the as-built AM samples of 17-4 stainless steel (SS) was compared with that of wrought (Condition A) 17-4 SS samples. Furthermore, the AM samples were manufactured from 17-4 SS powders atomized in nitrogen gas and argon gas to evaluate whether differences in the initial powder feedstock would affect weldability. X-ray diffraction, optical microscopy, and electron backscattered diffraction (EBSD) were employed to characterize microstructures. Results show that both the wrought and the AM samples made with argon atomized powder after HAZ simulations contain large concentrations of undesirable delta-ferrite phase, which is known to deteriorate the toughness of the material. In contrast, the AM samples made with nitrogen atomized powder contain no delta-ferrite. The absence of delta-ferrite is a consequence of the additional nitrogen picked up during the atomization process. Nitrogen promotes the growth of austenite and suppresses delta-ferrite at high temperatures. These findings reveal that the nitrogen atomized 17-4 SS powder may be a better choice than the argon atomized 17–4 SS powder if the part is intended to be installed or repaired via welding.