Microstructural Adjustment of the Degenerated Graphite Layer in Ductile Iron for Targeted Evaluation on the Fatigue Prop
- PDF / 3,812,461 Bytes
- 12 Pages / 595.276 x 790.866 pts Page_size
- 95 Downloads / 173 Views
Copyright 2020 The Author(s) https://doi.org/10.1007/s40962-020-00455-w
Abstract Graphite degeneration is the most prominent microstructural defect in the casting skin of ductile iron. Induced by either sulfur or oxygen contained in the molding material, its occurrence can be observed in a large range of iron castings, having substantial negative influences on the mechanical properties, especially fatigue resistance. Previous investigations predominately focused on the influence of the degenerated graphite layer, while accompanying changes of the iron matrix were neglected. The superposition of these effects hinders the evaluation of casting skin defects in state-of-the-art design of ductile iron components. The presented solution utilizes an experimental procedure, which enables the production of specimens with specific, individual microstructural configurations in the
casting skin. This approach is based on the application of a modified sand core coating. By adding sulfurizing additives to the coating and adjusting its binder content and viscosity, a predominately homogeneous degenerated layer of 0.5 mm thickness was obtained. Using specific heat treatment steps assured a fully ferritic or pearlitic iron matrix, isolating the degenerated layer as the main microstructural defect. Fatigue testing of these specimens will further enable the numerical evaluation of the fatigue resistance in dependence of the casting skin microstructure.
Introduction
This general term includes not only surface roughness and near-surface nonmetallic inclusions but also irregularities in the microstructure at the edge of the casting.
Design engineers are facing special challenges in the component layout of castings. In particular, the wall thickness dependence of the microstructure and thus the locally existing mechanical properties considerably complicate a reliable workpiece design and can lead to significant deviations between the simulation and the actually achieved properties of the component. Especially for ductile iron, this situation is even more complex. In addition to the wall thickness dependence of the nodule count, the nodularity or the pearlite fraction, which all have a direct influence on the mechanical properties of the material, interactions between the melt and the molding material lead to the formation of a casting skin.
This paper is an invited submission to IJMC selected from presentations at the 6th Keith Millis on Ductile Iron held October 23–26, 2018, at the Sonesta Resort, Hilton Head Island, SC. It is published in the IJMC by permission of the DIS (Ductile Iron Society).
International Journal of Metalcasting
Keywords: cast iron, SGI, graphite degeneration, molding material, casting skin
The most prominent example of these microstructural defects is the degenerated graphite layer (DGL), also known as the degraded graphite layer. This defect is caused by the absorption of sulfur or oxygen during solidification and leads to the formation of a layer of lamellar graphite at the interface between the moldin
Data Loading...
