Optimized Preparation of Deep Cryogenic Treated Steel and Al-alloy Samples for Optimal Microstructure Imaging Results

Abstract The research investigates the varying effect of commonly used etchants for revealing the microstructure of steels and aluminum alloys. Selected representatives of different types of tool steels and aluminum alloys were chosen to indicate the general effects of etching on different phases with different elemental contents and enrichments. The representatives were also investigated under two different preparation states. One state of the materials was selected based on the heat and forming processing determined by the producer of the selected materials. Whereas the other state is developed by a modified heat treatment procedure with included deep cryogenic treatment processing step. The purpose of this study is to provide a systematic overview for the evaluation of microstructure of selected materials with various etching reagents based on their different processing history. The intent of this research is also to deliver clear guidelines to the growing community involved in cryogenic processing of metals for the most in-depth microstructural observation with etching of the metallographically prepared sample surface. It was determined, that the optimal etching reagents are different for the same materials under different processing conditions. For the cryogenically treated tool steels, the optimal reagents for both examples was determined to be nital and Groessbeck’s reagent. Whereas for the aluminum alloy the combination of Weck’s and modified Keller’s reagent was determined as the most optimal etching reagents.