MSE 2016 - Full Program

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Investigation on the correlation between process, microstructure and properties in high silicon ductile iron with special focus on graphite degeneration

Wednesday (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 [1]. 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 % [2] 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.

[1] DIN EN 1563; Gießereiwesen – Gusseisen mit Kugelgraphit, 2012

[2] 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


Jessica Frieß
RWTH Aachen University
Additional Authors:
  • Prof. Dr. Andreas Bührig-Polaczek
    Gießerei-Institut, RWTH Aachen University