Characterisation of surface grain boundary precipitates formed during annealing of low carbon steel sheets

Grain boundary precipitates formed on the surface of batch annealed low carbon steels under atmospheres that are reducing relative to iron have been characterised by the use of transmission electron microscopy combined with energy dispersive spectroscopy. These surface precipitates were determined to be MnCr2O4 spinel and it is concluded that they form by selective oxidation of manganese and chromium.