Anforderungsgerechtes Werkstoffdesign am Beispiel von Quenching und Partitioning Stählen für den Einsatz in sicherheitsrelevanten Karosseriebauteilen

Sparrer, Yannik; Münstermann, Sebastian (Thesis advisor); Springer, Hauke Joachim (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

The engineering sciences are called upon to provide rapid and sustainable solutions to the issues society is currently facing. However, to be able to provide these solutions, particularly in the field of e-mobility, a stronger interlinking of the various engineering disciplines is required. In contrast to past practice, this linkage enables the realization of additional lightweight design potential by means of integrative materials and component development, taking the requirements derived from the component into greater consideration from the very beginning of the development of new types of materials. Therefore, the generic and extendable method of component-oriented material design was developed in this work. The conventional material design method is based on a specific improvement of standardized properties (e.g.: A20mm) by varying the microstructure and process parameters. However, the properties required on the component level (e.g.: local plastic equivalent strain in the critical stress state) are insufficiently addressed. The approach of component-oriented material design can be understood as an extension of the conventional material development method. As a result, not only the standardized material properties are considered in the development process, but rather the material properties tailored to the application (e.g.: stress-state-dependent strain variable) and the component performance (e.g.: energy absorption capacity) are formulated as target variables. In this way, the conventional view of the correlation of process-microstructure-properties is extended by the element of performance. On the one hand, material requirements and test methods are considered and, on the other hand, the success of the development process is assessed on the basis of component performance and not only on the basis of the material properties.The developed method’s potential was demonstrated for quenching and partitioning (Q&P) steels on the example of a B-pillar subjected to quasi-static loading in a side impact. As a reference material for the B-pillar, the conventionally used manganese-boron steel 22MnB5 in the hardened state was used. In order to design the material according to the relevant properties for the component, the component-oriented material design process first used numerical and analytical approaches to convert load-case-specific requirements of the component into material-specific target values. In the following material design process, the correlation between process-microstructure-properties was identified on the Q&P steel 0.2C-4.5Mn-1.7Si (QP1). This involved transformation kinetic measurements, high-resolution microstructure investigations, tensile as well as bending tests. Through specific adjustment of the microstructure and adaption of the alloy design (0.3C-2.5Mn-1.7Si, QP2) while taking processing-related boundary conditions into account, the material concept could comprehensively be adapted to the specific application. The results show that both in the uniaxial stress state and in the plane strain state, the developed steel QP2 exhibits significantly better ductility properties (A20mm = +400%, α = +250%) than the reference material 22MnB5. The strength (Rp0.2 = 1049 MPa, Rm = 1404 MPa) is at a similar level to that of the reference material. Only the material hardening behavior is lower, resulting in pre-dominantly ductile material failure. From the concluding numerical evaluation of the component performance, it is evident that the energy absorption potential of the B-pillar consisting of the developed Q&P steel could be significantly increased compared to the conventional material concept. Future research will need to extend this methodological approach to consider elements such as manufacturability or sustainability. In addition, the numerical approach needs to be stressed to a greater extent.

Institutions

• Division of Materials Science and Engineering [520000]
• Integrity of Materials and Structures Teaching and Research Area [522520]