Development of an efficient evaluation concept for the validation of cryotreatment of tool steels based on instrumented cyclic indentation tests

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To improve the mechanical properties of tool steels and thus, the lifetime of tools, a cryogenic treatment can be used, which contains an austenitizing and quenching, a cryogenic cooling process at temperatures down to -180 °C as well as a tempering. However, to optimize the process parameters with respect to the material used as well as the application considered, a high effort is required, as the influence of the cryogenic treatment can only be rated within the application. As an alternative, the mechanical properties of the cryogenically treated steel can be thoroughly characterized, which however, requires a high experimental effort. Consequently, the evaluation of a change of the process parameters is very time consuming. The objective of this research work is the development of a concept for an efficient rating of the properties of cryogenically treated tools using the short-time procedure PhyBaLCHT, which is based on instrumented cyclic indentation tests (CIT). As shown in preliminary work, the material parameters determined by this method are useful for rating the mechanical proper-ties of cryogenically treated tool steels. To obtain a sufficient data base, CIT will be performed at differently cryogenically treated specimens made of the tool steel Vanadis 4E, whereby different process sequences and tempering temperatures will be considered. In addition to that, a special focus will be put on the influence of a cyclic cryogenic process on the mechanical properties, in relation to the effects achieved by a single step cryogenic process or a conventional quenching and tempering. Based on these investigations, the lifetime as well as the damage mechanisms of different variants of cryogenically treated Vanadis 4E with sufficiently different properties will be analyzed in fatigue tests as well as conventional and adiabatic blanking tests, whereby the different loading conditions applied will be considered. These results will be correlated to the material parameters determined by PhyBaLCHT, which enables the elaboration of the rating concept and thus, reaching the main objective of this project. To ensure the transferability of this concept to other materials and tools, the microstructures in the initial states as well as their evolution during the cryogenic treatment will be characterized thoroughly. Moreover, this will be complemented by analyses of the microstructural changes caused by the different loadings applied in the fatigue and blanking tests. This concept aims at an efficient rating of the influence of a cryogenic treatment on the mechanical properties of tools and hence, a significant acceleration of the development of cryogenic treatments. Consequently, the objective of this research project is of great scientific and industrial interest for the field of cryogenic treatments of tool steels.