Development of a methodology for the assessment of the fatigue life of hot forging dies based on advanced material models

• Applicants: Professor Dr.-Ing. Bernd-Arno Behrens; Professor Dr.-Ing. Thomas Seifert
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 244928365

For hot forming tools, martensitic tool steels are often used which are heat-treated according to specified processes in order to achieve a high strength. The hot forming tools are subjected to complex thermal and mechanical loading conditions during operation. In mass production, this leads to cyclic plastic deformation and damage of the material due to thermo-mechanical fatigue (TMF), so that the service life of the hot forming tools is limited. As a result of the thermal load, microstructural changes, such as the coarsening of strength-increasing carbides, lead to the softening of the material, which can significantly influence the course of damage. Finite element calculations (FEM) are increasingly used to design the tools. However, so far no computational concept that describes the damage mechanisms by means of advanced material models is available. On the one hand, a plasticity model is required that takes into account the thermal softening of the material, while on the other hand, damage models based on time- and temperature-dependent thermomechanical fatigue crack growth are necessary.The proposal of this research project represents the continuation of the first proposal with the same name. The first application focused on the characterization of the hot-work steel X38CrMoV5-3 with a quenched and tempered hardness of 54 HRC and the development of plasticity models with thermal softening and their numerical FEM implementation.The aim of the planned project is to develop a model for TMF life prediction that accounts for the actual damage mechanisms and for thermal softening of the material. The material properties of the mechanismbased models are determined for the considered steel based on experimental results. The models developed in the first proposal and in this proposal are to be validated using application-oriented forging processes.The in-depth understanding of the deformation and damage behaviour of the examined tool steel and as well as the life cycle prediction models based on this behaviour makes an important contribution to the mathematical design of hot forming tools. Based on the calculation concept to be developed, design measures can be taken in advance during the design phase to increase the tool life of forging dies. A further advantage is that mass production readiness for a forged product can be achieved more quickly as cost-intensive and time-consuming testing cycles can be avoided.

• DFG Programme: Research Grants