Effect of deformation twinning on the early oxidation behaviour of 316L steel exposed to liquid lead-bismuth eutectic

Twins were introduced into 316L austenitic stainless steel by shot peening treatments. The twinned 316L was then exposed along with pristine 316L to oxygen-saturated liquid lead-bismuth eutectic at 550 degrees C for 120 h. We observed that the inner oxide layer on the pristine 316L consisted of Fe -Cr spinel and reticulated nickel-rich phases, whereas that on the twinned 316L consisted of Fe -Cr spinel and Cr 2 O 3 without the nickel-rich phases. The factor contributing to the different microstructure and composition of the oxide layer on pristine and twinned 316L is that the twin boundaries provide additional channels for Cr diffusion into the oxide front, allowing the formation of Cr 2 O 3 and high Cr dense Fe -Cr spinel. As a result, the Ni rich phases do not have sufficient space to exist and are pushed back into the Cr poor steel matrix.