Investigation on the correlation between process, microstructure and properties in high silicon ductile iron with special focus on graphite degenerationWednesday (28.09.2016) 14:45 - 15:00 Part of:
Caused by the increasing demand for high-strength ductile iron, the high silicon solution strengthened ductile irons GJS 450-18, GJS 500-14 and GJS 600-10 have been developed and introduced in the DIN EN 1563 . With their advantageous machinability, a higher resistance to carbide precipitation and minimal content of pearlite, these cast irons serve as perfect structural materials for the automotive industry as well as for the wind-energy sector. Never-theless, due to the higher silicon content, this material is inclined to degeneration of graphite spheroides which can lower the mechanical properties. Depending on type and amount of micro-alloyed elements as well as temperature conditions, different graphite degenerations are possible like vermicular graphite or the more severe ‘chunky graphite’. In order to pro-duce reliable ductile iron parts, the influences of the logical chain “process – microstructure – properties” needs to be well understood. This includes the quality and chemical compositions of the charge make-up as well as the alloying with carbon, silicion and additional elements. Furthermore the execution of melt treatments like the reaction with a magnesium master alloy as well as the inoculation are also critical process steps which determine whether the demanded properties of the customer can be fulfilled or not. In a series of experiments, indi-vidual aspects are investigated. Since minor trace elements like lead (Pb), antimony (Sb), bismuth (Bi), cerium (Ce) and lanthanide can be harmful already at content as low as 0,001 % to 0,02 %  to the graphite precipitacion, their single influence and interdependency are critical factors. While cerium favors chunky graphite, elements like antimony lead to a more lamellar degeneration. At a certain Ce:Sb ratio, nearly no graphite degeneration is observed. Scanning electron microscopy with energy dispersive spectroscopy revealed the formation of small Ce-Sb-composite particles. Since cerium and antimony atoms are conjuncted they can’t interfere with the graphite growth. Additional work includes the determination of the correla-tion between the graphite morphology and the static and dynamic properties.
 DIN EN 1563; Gießereiwesen – Gusseisen mit Kugelgraphit, 2012
 L. Magnusson Åberg, C. Hartung, J. Lacaze: Trace elements and the control limits in ductile iron, 10th International Symposium on the Science and Processing of Cast Iron, Mar del Plata, Argentinien, 2014