Abstract
Dissimilar welds between austenitic and ferritic steels suffer from premature failure driven by interfacial stresses and material degradation, brought about by mismatch in the co-efficient of thermal expansion and carbon migration from ferritic steels to the interface, respectively. Tri-metallic transition joints using graded composition between ferritic and austenitic alloys are considered as a viable pathway to address this issue. However, hot cracking may occur during welding nickel alloys to stainless steel. This research attempts to reduce the hot cracking susceptibility of Inconel-82 alloys by functionally grading them with 316L. Optical and Electron microscopy showed extensive cracking in the graded regions. Calculations using Scheil-Gulliver techniques attributed the cracking to the expansion in the solidification range of Inconel-82. To circumvent solidification cracking another transition joint between SA 508 Gr 22 and SS-316L has been designed and fabricated with co-axial powder blown additive manufacturing using a SS 410-SS 316L grading. After fabrication, the joint was characterized using optical and scanning electron microscopy, wavelength dispersive spectroscopy, and electron back scattered and x-ray diffraction techniques. Characterization showed a successful transition joint with minor porosity. The measured composition gradients agree with the designed composition gradients. This study shows that 12-Cr steels could potentially be used to fabricate transition joints without any hot cracking.
