Battling Graphite Degeneration


in Heavy Section Ductile Iron


Glidewell Specialties developed an approach to controlling chunky graphite in heavy section ductile iron castings using late inoculation with bismuth and cerium. MARK BEERS, ASK CHEMICALS, DUBLIN, OHIO


iron castings have forced metalcast- ing facilities to meet increasingly demanding specifications. Design engineers are specifying that heavy section ductile iron castings exhibit mechanical properties previously confined to thinner castings, thanks largely to standards set in the wind energy industry. If a metalcaster wants to participate in these markets, its castings must be able to meet demanding mechanical properties such as as-cast elonga- tion of 18% at room temperature and impact properties of 9 joules at -20C (-4F). Heavy section ductile iron (cast-


R


ings more than 2 in., or 51 mm, thick) presents a unique metallurgi- cal challenge, one that can affect a casting’s microstructure and signifi- cantly reduce its physical properties. Chunky graphite—the formation of large branches instead of evenly dis- tributed nodules—can be caused by slow cooling rates, high carbon levels


ecent technical developments in heavy section ductile


This ductile iron torque arm casting has a 7,800-lb. pour weight.


Table 1. Effects of Chunky Graphite on Mechanical Properties of Ductile Iron Elongation, %


Tensile Strength, Mpa


Without Chunky Graphite


25% 20% 22%


With Chunky Graphite


5% 3%


4, 5%


Without Chunky Graphite


500 440 405


With Chunky Graphite


440 345 315


August 2013 MODERN CASTING | 31


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