Experimental and numerical determination of relationships between process variables of thermo-mechanical material treatment and mechanical properties in graded mixed microstructures with bimodal grain size distribution

为了在运输部门负责任地使用资源和减少二氧化碳排放，组件专门适应各自的负载情况。对于钢，这可以通过分级组织和晶粒尺寸来实现。热-机械工艺链使得设置不同的混合微观结构和不均匀晶粒尺寸成为可能，即所谓的双峰晶粒尺寸分布。后者可以提高延展性、疲劳强度和腐蚀性能。该研究项目的总体目标是基于模拟确定热机械材料加工过程变量与由此产生的具有双峰晶粒尺寸分布的梯度混合微观结构之间的关系。对于Robusal900®钢，这是通过初步的临界间退火和冷成形，然后再结晶退火来实现的。通过扩展在第一个资助期开发的光学测量方法，将进行临界间退火过程中奥氏体含量的定量测定。在数值研究领域，相场法旨在建立模拟微观组织转变的材料模型。为此，应用了一个已经用于相变的概念。实验结果与数值结果的比较应采用积分法。通过模拟，将根据双峰微观结构的定量组成确定强度和塑性的载荷适应组合。

For responsible use of resources and reduction of CO2 emissions in the transport sector, components are specifically adapted to the respective load case. For steels, this can be achieved by grading the microstructure and grain sizes. A thermo-mechanical process chain makes it possible to set different mixed microstructures and heterogeneous grain sizes, so-called bimodal grain size distributions. The latter can improve ductility, fatigue strength and corrosion properties.The overall objective of the research project is the simulation-based determination of the relationships between the process variables of thermo-mechanical material processing and the resulting graded mixed microstructure with bimodal grain size distribution. This is to be achieved for Robusal900® steel by a preliminary intercritical annealing and cold forming followed by recrystallization annealing. By extending the optical measuring method developed in the first funding period, a quantitative determination of the austenite content during intercritical annealing is to be carried out. In the field of numerical investigations, the phase field method is intended to be used to develop a material model for simulating the microstructural transformations. For this purpose, a concept is applied which has already been used for phase transformations. The comparison between experimental and numerical results shall be done by integral quantities. Through the simulation, load-adapted combinations of strength and ductility will be determined based on the quantitative compositions of the bimodal microstructure.