The present paper deals with the influence of the duration of isothermal spheroidization annealing on the evolution of pearlite bands in various initial states. In this study, two initial conditions of the steel 16MnCrS5 are considered: a) industrially hot-rolled pearlite structures in their ferritic matrix and b) a specifically adjusted microstructure in the lab condition. Based on the experimental investigations and quantitative microstructural analyses, an empirical model for the prediction of pearlite banding within a broad range of annealing durations could be derived. Both, experiment and model, agree that pronounced pearlite bands in the initial state almost disappear after 25 h of spheroidization annealing. On the other hand, a marginal degree of pearlite banding in the initial state increases slightly during annealing. This fact could be explained by inhomogeneous cementite formation inside and outside the primary segregation regions of manganese.

In the present paper a practically relevant extension of the known modelling methods with regard to the description of forming limits of steels typically used in the cold bulk forming is developed and implemented in a commercial finite element code Abaqus. The modeling approach is based on the so-called micromechanical damage concepts which represent the microstructure evolution more detailed than phenomenological models and, therefore, provide better prediction of damage and failure during the forming process. Particularly, the well-known damage models of Gurson as well as Gologanu-Leblond are considered. It is shown that in combination with fracture criteria such models are able to describe failure in bulk forming

In this study, two initial conditions of the steel 16MnCrS5 are considered: the industrially hot-rolled pearlite structures in their ferritic matrix and a specifically adjusted microstructure in the lab condition. Based on the experimental investigations and quantitative microstructural analyses, an empirical model for the prediction of pearlite banding within a broad range of annealing durations could be derived. Both, experiment and model, agree that pronounced pearlite bands in the initial state almost disappear after 25 h of spheroidization annealing. On the other hand, a marginal degree of pearlite banding in the initial state increases slightly during annealing. This fact could be explained by inhomogeneous cementite formation inside and outside the primary segregation regions of manganese.

Die Herstellung komplexer Bauteilformen für die Automobil- und Maschinenbaubranche erfordert mehrstufige Massivumformprozesse, bei denen die Werkstoffe häufig an die Grenze ihrer Verformbarkeit gebracht werden. Ein anwendungsorientiertes, schädigungsarmes Prozess- und Bauteildesign wird darum immer wichtiger. Dem steht entgegen, dass die üblichen Versagenskriterien meist nicht in der Lage sind, die Schädigungsentwicklung präzise genug vorherzusagen. Das Fraunhofer-Institut für Werkstoffmechanik IWM hat darum in einem Forschungsprojekt ein Modell entwickelt, das die tatsächlichen Schädigungs- und Versagensmechanismen im metallischen Werkstoff abbildet und so eine bessere Vorhersage von Schadensort und Versagenszeitpunkt bei Kaltmassivumformprozessen ermöglicht (Bild 1). Damit ist das Fraunhofer IWM-Team Massivumformung seinem Ziel einen großen Schritt näher, den Umformprozess bereits im Vorfeld so auszulegen, dass die angestrebte Bauteilqualität kosteneffizient und ressourcenschonend erreicht wird und dass der Anlauf der Produktion bei Herstellern von massivumgeformten Bauteilen ohne zusätzlichen Zeit- und Kostenaufwand realisierbar ist. Die erzielten Projektergebnisse können branchenübergreifend für verwandte Problemstellungen wie der Blechumformung oder im Bereich der Bauteilsicherheit eingesetzt werden.