Effect of short-term aging on microstructural evolution and mechanical properties of Fe-Ni-Cr-W-Al alloy for ethylene pyrolysis furnace tubes

Short-term aging tests were conducted on a novel Fe-Ni-Cr-W-Al aluminum-containing heat-resistant alloy for ethylene pyrolysis furnace tubes at its typical service temperatures of 870 °C and 1100 °C to investigate the effects of short-term aging on microstructural evolution and mechanical properties of the alloy. The results indicate that the as-cast microstructure primarily consists of nanoscale γ′ phase, blocky γ′ phase, and M 23 C 6 carbides. After aging at 870 °C, the nanoscale γ′ phase dissolved, while M 23 C 6 carbides coarsened. Notably, B2-NiAl and α-Cr phases were observed to co-precipitate in a coupled manner for the first time in this alloy system. The precipitation of the α-Cr phase was promoted by Ti and exhibited a cube-on-cube orientation relationship with the B2-NiAl phase. Following aging at 1100 °C, the microstructure retained only coarsened M 23 C 6 carbides and blocky γ′ phase. Mechanical tests revealed that strength decreased with increasing aging temperature, while elongation and impact energy showed a “decrease first then increase” trend: deterioration at 870 °C due to the precipitation of brittle phases, and recovery at 1100 °C due to the suppression of these precipitates. This work clarifies the competitive precipitation behavior among multiple phases during high-temperature short-term aging and provides a theoretical basis for understanding secondary phase precipitation and optimizing the performance of this alloy in high-temperature environments such as ethylene pyrolysis furnaces.