Presentation and Verification of an Electrolytic Etching Technique for the Determination of prior Austenite Grain Boundaries in the Steel PH15-5

In the field of hot working, modelling of austenite grain size makes a significant contribution to the prediction of future material properties. One of the difficulties when it comes to modelling is the detection of grain sizes at different recrystallization stages by means of etching methods. Especially with high-purity steels with a martensitic structure, imaging of prior austenite grain boundaries without simultaneous highlighting of lath martensite boundaries, is, in many cases, only possible to some extent when using etching technology. Due to small electrochemical potential differences, increased purity of the alloy causes a more uniform etching attack on grain and lath boundaries and thus leads to a poorer discrimination. An alternative technique for grain size determination is Electron Backscatter Diffraction (EBSD). However, this technique maps only a relatively small area of the sample and is also significantly more expensive than the combination of electrolytic etching and light microscopic analysis. Therefore, this work will present a novel electrolytic etching technique for light microscopic imaging of prior austenite grain boundaries in high-purity and corrosion-resistant grades of precipitation hardening steels. For this purpose, a series of tests was carried out on the alloy PH15-5 and the results were verified by correlative EBSD measurements.