Revealing austenite grain boundaries by thermal etching: advantages and disadvantages

This article reviews the method of thermal etching for revealing the prior-austenite grain boundaries in steels. This method involves preferential transfer of material away from grain boundaries when the steel is exposed to a high temperature in an inert atmosphere. Thus, during austenitization of a prepolished sample, grooves are formed at the intersections of the austenite grain boundaries with the polished surface. These grooves remain intact after cooling and are clearly visible at room temperature outlining the austenite grain boundaries. However, at very high austenitization temperatures, those grooves might interfere with the advance of the austenite grain boundaries on the surface. In that case, this technique could lead to a wrong measurement of the austenite grain size. The aim of this work is to study the advantages and disadvantages of the technique to reveal the austenite grain boundaries in microalloyed steels.