| Abstract Scope |
Tubular components from gravity cast Fe-Ni-Cr alloys in olefin furnaces have experienced premature failures in service by creep fracture, thermal fatigue, and/or thermal shock due to a combination of outer diameter (OD) oxidation from furnace flue gases, inner diameter (ID) carburization from hydrocarbon-rich process fluids, and rapid cyclic heating to temperatures reaching 1,100◦C. To improve service life, a functionally graded material (FGM) is being produced with wire arc additive manufacturing (WAAM) to enhance OD oxidation resistance, ID carburization resistance, and creep/thermal fatigue properties in the bulk cross-section (Core). Three welding wires have been selected and designed to produce an FGM based on a Fe-35Cr-45Ni-0.4C-0.7Nb (Core) composition with OD and ID wires containing Si and Al additions, respectively. The present study is evaluating the AM printability of each welding wire to determine their suitability for producing an FGM with WAAM. First, cast pin tear testing (CPTT) is being conducted to rank the solidification cracking susceptibility of each welding wire. CPTT samples without full separation are being tensile loaded to failure to further evaluate cracking trends. Cross-sections of cracked samples and samples with visible crack healing are being characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). Straight cast samples are also being produced to perform Gleeble thermal simulations that mimic the reheats experienced during WAAM to characterize any microstructural evolution. CPTT and Gleeble results will be compared to behaviors witnessed in WAAM builds from each of the welding wires. Finally, CPTT and Gleeble results are being compared to CALPHAD-based solidification crack susceptibility and precipitation models to develop alloy design criteria for future iterations of the FGM welding wires that improve AM printability. |