Source: Welding Journal. August 2017
ABSTRACT Dissimilar welds between austenitic and ferritic steels suffer from premature failure driven by interfacial stresses and material degradation brought about by a mismatch in the coefficient of thermal expansion and carbon migration from ferritic steels to the interface, respectively. Trimetallic transition joints using graded composition between ferritic and austenitic alloys are considered a viable pathway to address this issue. However, hot cracking may occur when welding nickel alloys to stainless steel. This research attempts to reduce the hot cracking susceptibility of Inconel82 alloys by functionally grading them with 316L. Optical and electron microscopy showed extensive cracking in the graded regions. Calculations using ScheilGulliver techniques attributed the cracking to the expansion in the solidification range of Inconel82. To circumvent solidification cracking, another transition joint between SA 508 Grade 22 and SS 316L was designed and fabricated with coaxial powderblown additive manufacturing using an SS 410SS 316L grading. After fabrication, the joint was characterized using optical and scanning electron microscopy, wavelength dispersive spectroscopy, as well as electron backscattered and xray diffraction techniques. Characterization showed a successful transition joint with minor porosity. The measured composition gradients agreed with the designed composition gradients. This study showed that 12Cr steels could potentially be used to fabricate transition joints without any hot cracking.