The influence of annealing on the oxide scale characteristics of hot rolled samples of 2507 super duplex stainless steel have been investigated using well controlled lab scale annealing experiments. High resolution scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the oxide scales with respect microstructure and chemical composition.
SEM and EDS-analysis of the oxide scales after annealing show an outer Fe-rich oxide layer and an inner Cr-rich oxide layer close to the interface. While the hot rolled oxide scale displays a relatively porous oxide composed of oxide particles, the hot rolled plus annealed oxide scale displays a more dense, “sintered”, microstructure.
The annealing peak temperature was found to have a strong impact on the oxide scale microstructure. The higher peak temperature, 1150 °C, resulted in a significantly denser microstructure with more pronounce, larger grains, as compared with the lower peak temperature, 1100 °C, which resulted in a less dense microstructure. In contrast, the influence of annealing atmosphere, was found to be relatively small.