Microstructure and Properties of FeCrAl Overlay Welds at High Temperature Service

Abstract Recently developed FeCrAl alloys could be an economical alternative to nickel-based alloys in overlay welds for the power generation industry. However, more investigation on their microstructure and properties is needed at temperatures for boiler applications. This work compared the performance of three FeCrAl alloys (EF100, EF101, and APMT) as overlay welds, in as-deposited condition and after being exposed for 6 months in a CFB boiler’s evaporator tube bank. Bending, high temperature tensile test, restraint-cooling test, hardness, fractography, microscopy, microanalysis, and atom probe tomography (APT) were used. The results showed a ranking for ductility, being EF100 > EF101 > APMT. A high ductile-to-brittle transition temperature, below 100 °C, confirmed the low ductility and high cold cracking susceptibility. The microstructural analysis was in line with the previous grading. For APMT, APT showed that the exposure of the alloy at 400 °C for 11 days resulted in higher Cr concentration around carbides than in the matrix. This suggests that carbides could be initiation sites pushing toward the α -phase separation (Fe-rich vs Cr-rich), explaining the hardening and resulting in a drastic reduction in the ductility of APMT overlay welds.