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The success of this investigation will rely on the completion of extensive experimental work that will provide critical data required in the understanding of casting skin formation and elimination. The developed correlations between process variables, casting skin quality and mechanical properties will provide the impetus to further expand the applications of CGI. During Phase I, the mechanism for skin formation and test specimens design was validated. During Phase II, fatigue specimens will be cast and the influence of skin formation on fatigue will be determined. Also, potential actions to re- duce or eliminate skin formation will be investigated.


Status Update: Papers resulting from Phase I were present- ed at the 2011 Metalcasting Congress. Phase II has begun with test specimens for fatigue testing cast at OSU’s new metalcasting lab. Those wishing further information on the project should contact Prof. Doru Stefanescu, The Ohio State University, at stefanescu.1@osu.edu.


Ductile Iron Structure/Property Optimization & Enhancement—Phase II (10-11#02) Phase I (09-10#02)—Complete


Coordinator: Element Materials Technology, AFS Cast Iron Division (5), Ductile Iron Society and Consortium


ASTM A536 contains examples of the yield strength, ten- sile strength and percent elongation relationships expected in ductile cast iron. Frequently, both castings and test bars will exhibit mechanical properties that are significantly bet- ter than the minimums expected as indicated in the ASTM specification. One example is the information generated by the researchers from testing a pearlitic ductile iron expected to have mechanical strength properties that would be con- sistent with the pearlitic 80-55-06 grade but exhibiting high ductility of almost 15% elongation.


To our knowledge, research has not been conducted to de- termine what is required to consistently achieve such proper- ties with this extent of ferrite. It is known that strengthening mechanisms in metal include solid solution strengthening with both substitutional and interstitial elements. Work hard- ening is another means to strengthen metals. Phase trans- formation, precipitation hardening and grain refinement are still other mechanisms utilized to strengthen metals.


This study will characterize the graphite and other factors that control the matrix mechanical properties that are inde- pendent of nodule count, size and morphology. The char- acterization will include tensile and compression testing of sections from example casting and test bars, as well as im- pact testing. The impact test temperature will be at room temperature and -30C (-20F), as required in GGG 40.3, for example. The ductile to brittle transitions temperature determination could also be made for select samples. The microstructure of the test bars will be evaluated using quan- titative metallography. Optical microscopy will be used to determine ferrite grain size. Chemical analysis will also be required. It will be essential to procure castings in this first


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task that exhibit those properties which both meet as well as exceed the ASTM A536 minimum expectations. The second task will characterize all of the data generated from Task 1 using multiple regression analysis to determine how the dif- ferent factors interact with the mechanical properties with the intent to isolate those factors that contribute to the high tensile strengths and yield strengths (and other properties) when the structure is predominantly ferrite. From these re- sults a determination will be made to go to Phase II, which includes DOE tests to reproduce these results.


Status Update: Phase II is underway and starting with DOE heats and validation of improved properties. The project re- sults continue to be reviewed during updates given to con- sortium members and the steering committee. Information on the project is limited to the consortium members and will be released at a later date to AFS corporate members. Those wishing to participate should contact John Tartaglia, Ele- ment Materials Technology, at John.Tartaglia@element.com.


Phase II—Development of Core Gas Venting Guidelines (11-12#02a/b)


Coordinator: Andrei Starobin, Alchemcast, and AFS Engi- neering Division (1)


Venting of chemically bonded sand cores and molds is neces- sary to prevent excessive binder gas blow into a poured casting. All major organic binders currently in use in foundry core mak- ing practice outgas significantly and the problem of core/mold venting remains an engineering foundry challenge.


Some of the venting techniques practiced today involve form- ing vent channels in molds drilled to core prints, forming vent channels in cores during core blowing, forming blind core vents in multi-core assemblies, coarsening sand for better permeabil- ity, reducing binder content and coating cores. In some cases re-gating, core re-orientation and slowing of metal pour also leads to better core performance.


The available means of control of core gas pressure generate a large engineering design space where one would like to make quick and balanced choices. This project delivers to the found- ryman a simple Core Venting Design Calculator that should in- dicate if a given core requires venting and if so would report approximate impact of various venting techniques and process parameters on core gas pressure.


Status Update: Experimental Phase II work so far focused on the measurement of peak gas pressure at different core immer- sion rates. Faster core immersion in iron castings leads to higher peak gas pressure. Programming of the first full version of the Core Venting Design Calculator has been completed. PUNB, Shell and PUCB Isocure binders are covered in the calculation framework. The calculator is currently being validated for a num- ber of cored Al and Iron castings. The project is looking for sam- ple cores for which the calculator can be tested. Please contact Andrei Starobin (starobin@cybermesa.com), or members of the 1F steering committee: John Grabel at irongrabel@yahoo.com, or Krishnan Venkatesank at venkatesank@stahlspecialty.com


International Journal of Metalcasting/Spring 2012


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