Thermo-mechanisch hergestelltes, mehrphasiges Kugelgraphitgusseisen
Zusammenfassung der Projektergebnisse
This work highlights the transformation kinetics, microstructure evolution, mechanical behaviour of thermo-mechanically processed ductile irons. In the framework of this study, ductile irons (DIs) with different aluminum content, varying from 0.0 to 1.7 wt% at four levels are investigated. The effect of increasing the silicon, manganese and copper is also examined. The DIs are subjected to different total values of true strain of 0, 0.3 and 0.5. Additionally, four types of matrices were produced, namely martensitic, martensitic-ferritic, ausferritic, ausferritic-ferritic matrices. The introduction of ferrite to the matrix to produce dual matrix (DM) DI is accomplished by three different methods, which are: the controlled cooling in the intercritical region, the isothermal holding in it after austenitization and finally, the direct heating to this temperature range. It is observed that increasing the aluminum widened the intercritical region and shifted it to a higher temperature range. The former effect rendered the intercritical annealing more controllable. The latter effect is also observed as a consequence of increasing the silicon level. Thus, increasing the aluminum- and silicon-levels in DI resulted in increasing the intercritical annealing temperature and consequently increasing in the carbon saturating the intercritical austenite. This carbon increase substantially enhanced the strength and hardness of DI with dual matrix structure, especially the martensitic-ferritic one. The microstructure evolution and mechanical properties of the DI with DM are mainly governed by the chemistry of the intercritical austenite. On the other hand, the manganese increase yielded a reduced rate of ausferrite transformation simultaneously; significant higher volume percentage of untransformed austenite was retained on the expense of the strong ausferrite which lowered the strength and ductility. Thus, manganese is not beneficial for the ausferritic and ausferritic-ferritic DI. However, increasing its level increased the strength and hardness of the martensitic and martensitic-ferritic DI. The copper addition to the DI in a level of 0.8 enhanced both of the graphite nodularity and the nodule count and resulted in improving the strength and ductility of the all produced DI. The generated ferrite by controlled cooling in the intercritical region, the isothermal holding after austenitization in it is clustered around the graphite nodules, whereas that produced by heating and holding in the intercritical region is well distributed in the matrix. The latter microstructure showed superior strength, ductility and impact toughness to the former one. It is also shown that the kinetics of transformation is accelerated by both increasing the deformation and introducing ferrite to the matrix. The strength and hardness are significantly increased by the former- and decreased by the latter factor. The fracture strain has not shown a continual increase by increasing the ferrite content. Mechanical deformation of austenite prior to the ausferrite transformation (ausforming) is also investigated. The ausforming resulted in a pronounced increase in transformation rate and also caused refinement and uniformity of the microstructure. This refinement is not accompanied by a significant increase in the retained austenite. These microstructural effects of ausforming resulted in remarkable increase in hardness, strength and ductility of the ausformed ductile DI.
Projektbezogene Publikationen (Auswahl)
- Effect of aluminum content on phase transformation and mechanical properties of dual matrix, thermo-mechanically processed austempered ductile iron, 70th World Foundry Congress, April 2012, Monterrey, Mexico
Soliman, M., Palkowski, H., Nofal A.
- Effect of Intercritical Annealing on Phase Transformation and Mechanical Properties of Thermo-mechanically Processed Dual Matrix Ductile, TMS2014
Soliman, M., Ibrahim, H., Nofal A., Palkowski H.
(Siehe online unter https://doi.org/10.1007/978-3-319-48237-8_113) - Effect of Thermo-mechanical Processing Parameters on Phase Transformation and Hardness of Dual Matrix Ductile Iron, SPCI10, Mar del Plata, Argentina, 10-13 November 2014
Soliman, M., Ibrahim, H., Nofal, A. and Palkowski, H.
