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

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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.