Microstructure modeling guided design of high-strength steels

Liu, Wenqi; Münstermann, Sebastian (Thesis advisor); Bleck, Wolfgang (Thesis advisor); Lian, Junhe (Thesis advisor)

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

Dissertation, RWTH Aachen University, 2022


The microstructure of steels determines their mechanical property profiles. Consequently, microstructure design has been understood to be the key factor for the development of modern steels, in particular, the advanced high strength steels. However, for the improvement of the mechanical property and competitiveness of newly developed steels, well-established unitary strategies like grain size refinement have been more or less fully exploited, and the conventional understanding of the microstructure and property relationship might be not reliable anymore due to the more and more complex microstructure. Besides, the combination and balance between varying property profiles might be necessary to optimize the end-user structural performance. Therefore, new, reliable, and efficient material design approaches are demanded based on the top-bottom approaches. A computer-assisted simulation toolkit for the performance-oriented microstructure-based high-strength damage-tolerant material design is developed in this study in the integrated computational materials engineering (ICME) framework. The general concept of the design toolkit is that with macromechanics models, the targeted component performance can be transformed to the required mechanical property profiles, then with micromechanics models, the tailored microstructure can be identified for the desired mechanical property profiles. The generation of the design toolkit includes the selection and development of individual mechanics models as well as the communication between different models. A demonstrative example of microstructure design of dual-phase (DP) steel for crash boxes in the automotive industry is chosen to build up the simulation toolkit. Individually experimental and numerical approaches are developed and validated correspondingly to this specific application with a DP1000 steel grade. The characterization of microstructure, mechanical properties including damage mechanisms, and component performance of the reference steel DP1000 have been investigated to support the selection, development, and parameter calibration of individual models. The extended modified Bai-Wierzbicki damage mechanics model involving temperature, strain rate, and stress state has been employed to bridge the mechanical property and component performance. The fine-resolution statistically representative volume elements based on the proposed microstructure representativeness assessment criterion have been generated as artificial materials. Both crystal plasticity and dislocation-based plasticity models have been utilized to connect the microstructure with mechanical properties. Detailed parameter calibration procedures have been developed for each modeling approach. With the constructed virtual laboratory on both macro and microscales, parametric studies have been carried out to evaluate the influence of input factors on output performance and properties based on a quantitative sensitivity parameter, and further identify the required property profiles and derive the desired microstructure. The delivered microstructural features can only be partially achieved in the followed production validation due to the restrictions in realistic process procedures. Although, the performance mainly in terms of the dissipated energy during crash testing of the tailored-DP material has reached the pre-defined target. Besides, based on the microstructure and property characterization, several main conclusions from the simulation toolkit have been supported by the production validation. The concept of the toolkit for the computer-assisted microstructure-guide material design approach is promising and could be extended to other application cases with certain modifications on individual models. The outlooks on challenges and possible solutions in future model development within the ICME framework have been discussed as well.


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