Development of an Oxidation Method for Prior Austenite Grain Boundary Revelation

The prior austenite grain size is a very important quantitative parameter which has a great influence on steel final microstructure and properties. Therefore, its measurement is a useful metallographic tool. To measure the austenitic grain size, it is necessary to reveal the prior austenitic grain boundaries by applying contrast methods. The technical literature reports many limitations to achieve satisfactory results using known methods that are, generally, susceptible to steel chemical composition and processing routes. In this context, this study proposed an oxidation method to reveal the prior austenite grain boundaries in different steel grades. This method was evaluated in the samples of AISI 4340 and AISI 1030 steels. Aiming to confirm the proposed technique efficiency, a parallel and classical method, based on picric acid etching, was applied to same steels. In the suggested oxidation method, the samples were mechanically ground, polished, and then austenitized in an argon atmosphere with low oxygen partial pressure. The obtained results confirm the success of the proposed method for both studied steels.