Application of Nomarski differential interference contrast microscopy to highlight the prior austenite grain boundaries revealed by thermal etching

Revealing prior austenite grain boundaries by thermal etching has been demonstrated to be a reliable and fast method compared to chemical etching for microalloyed carbon steels. However, sometimes visualization of the thermally etched prior austenite grain boundaries is hindered by the presence of grain boundaries of other phases (e.g. ferrite and/or pearlite) which are thermally etched during slow cooling from high temperature. This work shows that, under these conditions, the use of Nomarski differential interference contrast microscopy under bright field illumination helps to highlight the thermally etched prior austenite grain boundaries.