SOLUTION STRENGTHENED FERRITIC DUCTILE CAST IRON PROPERTIES, PRODUCTION AND APPLICATION
Wolfram Stets and Herbert Löblich Institut für Gießereitechnik, Düsseldorf, Germany
Gert Gassner and Peter Schumacher Österreichisches Gießereiinstitut, Leoben, Austria
Copyright © 2014 American Foundry Society
A version of this paper was previously published in the 2013 Keith Millis Symposium Proceedings Abstract
The ductile cast iron standard in Europe also considers new ductile cast iron grades with a unique combination of ten- sile strength with high elongation (e.g. Rm 72520 psi with A5
14%) achieved by the solution strengthening of the fer- ritic matrix by silicon with contents between 3% and 4.3%. The new grades tolerate a higher amount of pearlite and carbide stabilizing elements without the generation of em- brittling pearlite or carbides in the microstructure. The presence of Cr, Mn, and V do not influence the elongation significantly. An advantage of the new cast irons is the cost efficient machining due to lower tool wear. The tool life with the machining of the fully ferritic grades GJS-500-14 and GJS-600-10 is about 50–60% longer in comparison to the ferritic-pearlitic grades. The investigated grades show very
Introduction
EN-GJS (European Standard for ductile cast iron) is used in many areas of mechanical engineering, automotive and en- gine construction as well as energy, environmental and nucle- ar technology. In all these applications, the EN-GJS grades must be in line with the applicable standards. When the DIN standard EN 1563 established in March 2012 was revised,1 the ferritic, solution strengthened grades EN-GJS-450-18, EN-GJS-500-14 and EN-GJS-600-10 with higher Si con- tents were newly added to the standard. (DIN = Deutsches Institut fΰr Normung, German Institute for Standardization) The values listed in Table 1 are valid for a nominal thickness ≤ 1.18 in. The conventional ferritic/pearlitic grades continue to be in the standard without any modifications. Due to the
good cyclic mechanical properties but lower dynamic prop- erties. The pre-condition to achieve optimized properties by well-shaped graphite nodules, achievable with special inoc- ulation techniques, adjusted to the high silicon content and the solidification rate, otherwise threaten graphite degen- erations. There is no increased danger of dross generation or of a worsening flowability (investigated with special test equipment). Also the supposed inclination to the generation of porosities with the higher Si content was not confirmed.
Keywords: new silicon-alloyed ductile cast iron grades, ferrite, solution strengthened, tensile strength, elongation, hardness, machinability, DIN EN 1563, GJS, Germany, con- tinuously cast products, rollers and pinion cages.
benefits associated with the new ferritic grades—namely higher yield strength and greater elongation, the number of applications is expected to increase quickly.
The mechanical properties of the ferritic/pearlitic EN-GJS grades under EN 1563 are set by adjusting the ferritic/pearl- itic ratio through the addition of pearlite forming agents. These cast iron grades usually contain between 2.0% and 2.5% Si. Strongly varying wall thicknesses in EN-GJS-500 and EN-GJS-600 castings with pearlite contents of ap- proximately 30%-70% may lead to strongly varying pearlite fractions and as a result significant differences in hardness. This makes it difficult to comply with close hardness toler- ances. The unique combination of yield strength and tensile strength with high elongation in the new material grades
Table 1. New Material Grades in Standard DIN EN 1536 (Values in brackets are conventional ferritic/pearlitic grade properties)
International Journal of Metalcasting/Volume 8, Issue 2, 2014
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