In this bachelor thesis, research is done on the microstructure of 316L stainless steel and its weld after it has been exposed to liquid LBE (lead-bismuth eutectic). The aim of the thesis is to investigate the corrosion on the steel in order to better understand it. The samples were exposed to LBE for 2000 hours, with a temperature of 400 °C and a dissolved oxygen concentration of 3·10-8 wt.%. After exposure, the samples were mechanically and chemically cleaned. To gain insight into how the LBE corroded the samples, cross sections were made of the samples. The cross sections were embedded, polished and examined with a digital microscope. The depth, the affected area and the average corrosion depth were determined using various techniques. To investigate the microstructure of the samples, an SEM (Scanning Electron Microscope) was used. The SEM made it possible to take detailed images of the corroded samples, and also offered the possibility to determine the chemical composition with EDX (Energy Dispersive X-Ray) as well the possibility to view the crystal structure with EBSD (Electron Backscatter Diffraction). From the results it is concluded that the samples are affected for a major part by the LBE for both the base and the weld material. The measurements showed that there is no difference between the base and the weld material regarding the corrosion depth and the affected area. The SEM gave a better insight of the base and weld microstructure. From this it was concluded that the LBE penetrates the material more quickly along the grain boundaries. It also seemed that some grains were more affected than others. After using EBSD it appears that this is due to the crystal orientation. Certain orientations are more vulnerable to corrosion depending on the area the LBE penetrates into the grain. EDX has shown that the parts that were not affected by corrosion had an oxide layer on the surface, which protected the steel.
|Date of Award||25 Jun 2021|
|State||Published - 8 Jun 2021|