Experimental and numerical analysis of morphological changes regarding nonmetallic inclusions in the steel matrix during hot forming

Due to their outstanding material properties, bulk formed components are often the key elements for power and torque transmission in many areas of application. Due to the manufacturing process, all die forged steel components have a weak spot in the area of the die parting line. This is caused by deformed non-metallic manganese sulphide (MnS) inclusions that form in manganese-containing steels. The geometry of the inclusions is influenced by the preceding forming processes. In the area parallel to the die parting line, extremely flattened MnS inclusions form, which act as internal notches due to their shape and have a negative effect, especially under cyclic loading. This research focuses on gaining a fundamental understanding of the forming behaviour of MnS. At first, extensive characterisation tests on the forming behaviour of MnS and the steel matrix are performed. Through model experiments, the MnS inclusions are deliberately plastically deformed and numerically modelled using the obtained material data. For the simulation, representative volume elements (RVE) will be used at the micro level. The results of the MnS deformation will be transferred to the macro level by linking the RVE. The final step is to develop a user subroutine for the macro simulation that takes into account the morphology of MnS without linking the RVE. This model will then be validated with experiments, where demonstrator components are forged. The numerical results will be compared to metallographic examinations and SEM images. In order to analyse to what extent the flattening of the MnS inclusions can be influenced by varying the process parameters forming temperature and tool kinematics, numerical sensitivity studies will be carried out.