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Effect of oxygen on the gas tungsten arc weldability of laser-powder bed fusion fabricated 304L stainless steel, The
Gonzales, Devon Scott
Gonzales, Devon Scott
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2019
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2019-11-24
Abstract
Through the development of advanced manufacturing techniques, including additive manufacturing, material and component design has evolved to integrate structures previously unachievable through conventional methods. In addition, production via additive manufacturing can reduce material costs and production time for high value materials. Currently, there is a push in industry to exploit the benefits realized in different manufacturing techniques and incorporate a spectrum of such techniques into desired components or assemblies. However, the trade-off in part resolution and limitation of size of the build, as in powder bed processes leads to questions in joining small additively manufactured parts to build larger assemblies. The objective of this research was to develop fundamental understanding of how the inherent microstructural and compositional characteristics of 304L stainless steel produced via laser-powder bed fusion would affect the cracking response during gas tungsten arc welding. Weldability and solidification studies were performed on 304L stainless steel material produced via the laser-powder bed fusion process and compared with the behavior of wrought material. It was determined that the major difference between the two base materials was the oxygen concentration, which was significantly higher in materials produced using powder feedstock. The high oxygen levels was attributed to the large surface area inherent to the powders and caused distinguishable differences in fluid flow and solidification behavior in the L-PBF material during welding. Increased oxygen levels contributed to the formation of high temperature iron and chromium-rich spinels and low melting temperature silicates during welding. The presence of these oxides did not significantly affect the solidification cracking susceptibility of L-PBF 304L relative to wrought 304L stainless steel. In addition, there were no significant changes in solidification cracking susceptibility in either weld direction of the L-PBF samples relative to the build direction. However, ductility dip cracking susceptibility was higher in L-PBF fabricated 304L stainless steel compared to wrought. This increase in sub-solidus cracking was caused by the presence of the low melting temperature silicates, broadening the ductility dip temperature range.
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