In this paper the influence of core segregations on the formability of workpieces made of bearing steel is analysed and discussed on the basis of compression tests. First the necessary material properties and flow curves, taken at different regions of the bar stock material, were investigated. The core segregation material shows significantly higher flow stress at higher strain rates than the surrounding segregation‐free material. Further a strong influence of the forming temperature on the flow stress was found. On basis of these findings an FEM‐model was developed, that considers the core segregation properties, its shape and position. The results of the compression simulation with this model show a clear impact of the inhomogeneous material properties on the stress distribution.

Kurzfassung Verzug ist eine Systemeigenschaft und alle an der Prozesskette beteiligten Fertigungsschritte können dem entstehenden Bauteil von außen nicht sichtbare Veränderungen mit auf den Weg geben, sein Verzugspotenzial beeinflussen. Diese Aussage hat sich in den letzten 10 Jahren immer weiter manifestiert. Beginnend mit vielen Einzeluntersuchungen in verschiedenen Unternehmen und Instituten, Diskussionen im Fachausschuss „Maß- und Formänderungen infolge Wärmebehandlung“ der AWT, entsprechenden Vorträgen (bspw. [1]), der Erstellung einer Verzugsmonographie durch den genannten Fachausschuss 1 , der Einrichtung des Sonderforschungsbereiches „Distortion Engineering“ 2001 in Bremen und der im Jahr 2005 erstmals durchgeführten Internationalen Tagung Distortion Engineering, IDE, zu diesem Thema wurde diese Erkenntnis konsequent weiterverfolgt. In der vorliegenden Arbeit werden entsprechende Untersuchungen, die sich konsequent an diesen Ansatz gehalten haben, für den Fall einer vereinfachten Fertigungskette „Zylinderring aus 100Cr6“ vorgestellt.

Distortion is a system property. All process steps of the manufacturing chain can cause invisible changes of the construction unit, which influence the, distortion potential". This statement was manifested in the last 10 years. It was thoroughly pursued in many individual investigations in different companies and institutes, discussions in the AWT's research committee, Changes in size and shape due to thermal treatment", appropriate lectures (e.g. [1]), the creation of the monograph(1) (''Changes in size and shape due to heat treatment") by the mentioned research committee, the establishment of the Collaborative Research Centre, Distortion Engineering" (SFB 570) in Bremen in 2001, and the organization of the First International Conference on Distortion Engineering (IDE) in 2005. This paper presents appropriate investigations for the case of a simplified manufacturing chain, SAE 52100 cylinder ring", which follows strictly the idea of the system property of distortion.

The influence and significance of several process parameters in a manufacturing chain of cylindrical bearing rings made of steel SAE 52100 (100Cr6) on the quench hardening distortion were identified using the method of Design of Experiments (DoE) and a statistical analysis of the results. The change in out-of-roundness can be explained by the used clamping technique during turning, which led to characteristic residual stress distributions in circumferential direction. Size alterations were smaller and depended also on clamping (height) resp. on clamping and an interaction of clamping and feed (radius). Other investigated factors like stirring during continuous casting, deformation ratio during forging and cooling after forging did not significantly influence shape or size changes. Density measurement was found to be a simple and effective method, to check size changes. The results confirm the necessity of concerning the whole manufacturing chain, to understand and influence heat treatment distortion. DoE has been proven to be a useful tool in this way.