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

为了改善工具钢的机械性能，从而提高工具的寿命，可以使用深冷处理，包括奥氏体化和淬火、温度低至-180°C的深冷工艺以及回火。然而，要根据所使用的材料和所考虑的应用来优化工艺参数，需要付出很大的努力，因为深冷处理的影响只能在应用范围内进行评定。作为另一种选择，深冷处理的钢的机械性能可以得到彻底的表征，但这需要很高的实验工作。因此，工艺参数变化的评估非常耗时。这项研究工作的目的是开发一种概念，使用基于仪表化循环压痕试验(CIT)的短时间程序PhyBaLCHT对深冷处理工具的性能进行有效评级。初步工作表明，用该方法确定的材料参数对评定深冷处理工具钢的力学性能是有用的。为了获得足够的数据库，将在由工具钢VANADIS 4E制成的不同深冷处理的试件上进行CIT，由此将考虑不同的工艺顺序和回火温度。此外，还将特别关注循环深冷工艺对力学性能的影响，这与单步深冷工艺或常规调质工艺所达到的效果有关。在这些研究的基础上，将在疲劳试验以及常规和绝热冲裁试验中分析具有足够不同性能的不同变种深冷处理的VANADIS 4E的寿命和损伤机理，其中将考虑应用不同的加载条件。这些结果将与PhyBaLCHT确定的材料参数相关联，从而能够详细阐述评级概念，从而达到本项目的主要目标。为了确保这一概念可移植到其他材料和工具上，将彻底表征深冷处理过程中初始状态的微观结构及其演变。此外，还将通过分析疲劳和冲裁试验中应用的不同载荷引起的组织变化来补充这一点。这一概念旨在有效地评定深冷处理对工具机械性能的影响，从而显著加速深冷处理的发展。因此，本课题的研究对工具钢的深冷处理具有重要的科学意义和工业意义。

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.