Microstructure and Hot Oxidation Resistance of Wrought and Wire Arc Additive Manufactured Austenitic Stainless Steel 347

Boiler steels in gas turbines and waste-to-energy recovery units undergo severe damage due to oxidation. The hot oxidation behavior of wire arc additive manufactured austenitic stainless steel 347 (WAAM 347) and wrought alloy AISI 347 are examined at 700 degrees C for 50 cycles in a hot still environment. The microstructural characteristics and oxidation species are evaluated. In comparison with the wrought AISI 347, the WAAM 347 wall with equiaxed and large columnar dendrites along with lower residual ferrite and niobium carbide aids in better oxidation resistance despite having an identical oxide layer comprising of an inner oxidation zone rich in Cr and Fe, and an exterior oxide layer rich in Fe. The overall weight gain in WAAM 347 specimens ranges between 0.83 and 0.90 mg cm-2 with a lower oxidation rate and is less than that in AISI 347 (3.29 mg cm-2). X-ray diffraction analysis reveals the presence of Fe2O3, FeCr2O4, NiO, and Cr2O3 along with NiCr2O4 spinel phases. The higher wt% of Cr and the formation of oxidation species such as NiO, NiCr2O4, and Cr2O3 are attributed to the reduced oxidation rate in WAAM 347. The research findings indicate that WAAM can fabricate customized components with comparable hot oxidation performance.