Experimental and numerical investigations on the morphological evolution of non-metallic inclusions in the steel matrix during hot forging

由于材料的优异性能，热锻部件通常是力和扭矩传递的关键部件。在这种情况下，含硫的现代锻钢提供了巨大的强度潜力，这在轻量化和资源节约型结构设计方面尤为重要。由于特殊的材料，钢锻件在模具分割平面的区域中具有薄弱点。这是由具有制造相关几何形状的变形非金属夹杂物引起的，即硫化锰（MnS）。MnS在该区域中被压平为“片状”，因此减少了与锻造飞边区域正交的钢基体的承载面积，并且由于它们的形状，充当内部凹口。取决于主要的工艺条件，非金属夹杂物可以在奥氏体钢基体中的锻造阶段期间不同地变形，从而决定性地影响锻件的局部宏观性能。MnS变形的精确映射严重受损的各种变形状态的发生，以及缺乏知识的温度和应变速率依赖的MnS流变性能。为了通过数值模拟预测这种影响的程度，本研究项目的主要重点是开发一种基于模拟的方法，用于沿着热锻工艺链的硫化锰形态发展的真实映射。硫化锰和奥氏体钢基体的实际流变性能，将在温度和应变条件下通过实验确定与模锻相关的速率范围。样品材料由MnS粉末通过在自己的初步工作中所示的方法制备。为了提高后续的多尺度模拟的质量，逆向工程方法的数值识别的流动特性是在这个项目中使用。此外，控制模型转换试验进行了特定的挑衅MnS变形。从实验中，相应的边界条件，为随后的多尺度模拟的基础上，RVE方法。随后，微观调查的结果将被转移到宏观层面的增量建模方法的形式，并在商业FE系统中的用户子程序的形式实现。为了验证所提出的方法，锻件具有复杂的几何形状将进行实验和数值研究。基于这些基本的调查，一个基于有限元模型预测的MnS形状演变的钢基体的基础上，当地的工艺条件将被开发。

Due to the outstanding material properties, hot forged components are frequently the key compo-nents for the force and torque transmission. In this context, modern forging steels with sulfur content offer an enormous strength potential, which is especially important in terms of lightweight and a resource-conserving construction design. Due to specific material, the steel forgings have a weak point in the region of the die dividing plane. This is caused by deformed non-metallic inclusions with manu-facturing-related geometry, i.a. Manganese sulfides (MnS). The MnS are flattened in this area as 'sheet-like' and thus reduce the load bearing area of the steel matrix orthogonally to the forging flash region and, due to their shape, act as inner notches. Depending on the prevailing process conditions, the nonmetallic inclusions can deform differently during the forging phase in the austenitic steel matrix, thereby decisively influencing the local macroscopic properties of the forgings. An exact mapping of the MnS deformation is severely impaired by the variety of deformation states occurring as well as by the lack of knowledge about the temperature and strain rate-dependent rheologic properties of MnS. In order to predict the extent of this effect by means of numerical simulation, the primary focus of this research project is to develop a simulation-based methodology for the realistic mapping of the morphological development of manganese sulfides along the hot forging process chain.For this purpose, the realistic rheologic properties of manganese sulfides and of the austenitic steel matrix are to be determined experimentally in the temperature and strain rate ranges relevant for die forging. The sample material is prepared from MnS powder by means of the methodology shown in the own preliminary work. In order to improve the quality of subsequent multiscale simulations, reverse engineering methods for numerical identification of flow properties are to be used in this project. Furthermore, controlled model transformation tests are carried out for the specific provocation of MnS deformation. From the experiments, corresponding boundary conditions for the subsequent multiscale simulations have to be derived on the basis of the RVE method. Subsequently, the results of the microscopic investigations will be transferred to the macro level in the form of an incremental modeling approach and implemented in a commercial FE system in the form of a user subroutine. In order to validate the presented approach, forgings with a complex geometry will be investigated experimentally and numerically. Based on these fundamental investigations, an FE-based model for the prediction of the MnS shape evolution in the steel matrix based on the local process conditions will be developed.