Dynamics of tempering processes in stainless steel

In this study, we focused on the dynamics of the continuously changing microstructure at an elevated temperature upon tempering of stainless steel. We used a Scanning Electron Microscope (SEM) with an Electron Backscatter Diffraction (EBSD) setup in combination with a High Temperature specimen stage to perform in-situ orientation imaging microscopy experiments. This experimental setup allowed us to observe in-situ the microstructural changes like grain growth, grain-boundary movement and modification in crystal orientations. By subsequent imaging of the outer surface area, the evolution of the microstructure can be examined leading to a better understanding of the dynamics of the tempering process of stainless steel. In particular, we discussed the results obtained of the microstructural changes at a fixed temperature of 500°C. A loss of the EBSD signal started at the triple junctions and at high angle grain boundaries over time and is attributed to oxidation. We concluded that preferred oxidation occurs during treatment and that dynamic in situ observations are possible.