Microstructure evolution and high-temperature oxidation behavior of FeCrAlNbNi alloyed zone prepared by laser surface alloying on 304 stainless steel

To improve the high-temperature oxidation performance of 304 stainless steel and increase its service life, a FeCrAlNbNi alloyed zone (AZ) was prepared on the surface of 304 stainless steel through laser surface alloying, and the microstructure of the AZ was studied. The micromorphology of the AZ was mainly equiaxed dendrites, and the Nb element segregated in the interdendritic region. In addition, the AZ and substrate were subjected to isothermal oxidation experiments for 100 h at 900 °C. The AZ showed less weight gain and a lower oxidation rate, and it had better oxidation resistance than the substrate. In the early stage of oxidation, a less dense Al2O3 oxide layer was formed on the surface of the AZ. As oxidation progressed, Al passed through the oxide layer to form aggregated Al2O3 on the surface. In the middle of oxidation, the Al2O3 oxide layer gradually became dense, and aggregated Al2O3 began to scatter. In the late stage of oxidation, a stable, dense and continuous Al2O3 layer was formed on the surface of the AZ with a thickness of approximately 1.2 µm. At the same time, energy dispersive spectroscopy showed that the Al under the oxide layer was not depleted, which indicates that the FeCrAINbNi AZ has excellent high-temperature protection performance.