Ductile & CG Iron Casting Skin—Evalua- tion, Effect on Fatigue Strength & Elimination Phase II (09-10#01)
Coordinator: Ohio State University and AFS Cast Iron Division (5)
The elimination of the flake skin is one of the key elements of unlocking the full design potential of Compacted Graph- ite Iron (CGI). Capitalizing on the results of a previously AFS sponsored effort 04-05#02, “Study of the Effect of the Casting Skin on the Tensile Properties of Light Weight Ductile Iron Castings,” the Department of Materials Science and Engineering at The Ohio State University (OSU) pro- poses to conduct research with the goal of understanding the mechanism of formation of casting skin in CGI, evaluating its effect on selected mechanical properties, and developing the methodology for its complete elimination. The results of this research will be of immediate applicability to the industry without major capital investment.
The research strategy is designed to develop the knowledge required to improve and ultimately eliminate skin quality of CGI castings and to generate data on its impact on the static mechanical and fatigue properties of CGI, as well as on the efficiency of shot blasting in improving these properties. Ad- ditionally, the study may help in the definition of the minimum thickness of the layer that must be removed by machining to avoid negative skin quality effects. The research will capitalize on the experience in the characterization of casting skin ac- cumulated in the Virtual Solidification and Casting Laboratory (VisionCast) at OSU.
The success of this investigation will rely on the comple- tion of extensive experimental work that will provide critical data required in the understanding of casting skin formation and elimination. The developed correlations be- tween process variables, casting skin quality and mechani- cal 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 influ- ence of skin formation of fatigue will be determined. Also, potential actions to reduce or eliminate skin formation will be investigated.
Status Update: The final report was presented at CastExpo’10 & Congress. Phase II has begun. Those wishing further infor- mation on the project should contact Prof. Doru Stefanescu, The Ohio State University, at
stefanescu.1@osu.edu.
Ductile Iron Structure/Property Optimization & Enhancement Phase I (09-10#02)
Coordinator: Stork CRS and AFS Cast Iron Division (5), Ductile Iron Society and Consortium
ASTM A536 contains examples of the yield strength, tensile strength and percent elongation relationships expected in
80
ductile cast iron. Frequently, both castings and test bars will exhibit mechanical properties that are significantly better than the minimums expected as indicated in the ASTM specifica- tion. One example is the information generated by the re- searchers from testing a pearlitic ductile iron expected to have mechanical strength properties that would be consistent with the pearlitic 80-55-06 grade, but exhibiting high ductility of almost 15% elongation.
To our knowledge, research work has not been conducted to determine what is required to consistently achieve such prop- erties with this extent of ferrite. It is known that strengthen- ing mechanisms in metal include solid solution strengthening with both substitutional and interstitial elements. Work hard- ening is another means to strengthen metals. Phase transfor- mation, 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 independent of nodule count, size and morphology. The characterization will include tensile and compression testing of sections from example casting and test bars as well as impact testing. The im- pact test temperature will be at room temperature as well as -30C (-20F) as required in GGG 40.3 for example. Ductile to brittle transitions temperature determination could also be de- termined for select samples. The microstructure of the test bars will be evaluated using quantitative metallography. Optical mi- croscopy will be used to determine ferrite grain size. Chemical analysis will also be required. It will be essential to procure cast- ings in this first 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 different 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 results a determination will be made to go to Phase II, which included DOE tests to reproduce these results.
Status Update: The project has begun and initial updates have been given to consortium members and the steering commit- tee. Since information on the project is limited at first to the consortium members and then at a later date to AFS Corporate Members, those wishing to participate should contact George Goodrich, Stork CRS, at
george.goodrich@us.stork.com.
Effects of Varying SiC Purity on Cupola Perfor- mance (09-10#03)
Coordinator: Grede, S. Katz Associates and AFS Melting Methods & Materials Division (8)
Nearly eight million tons of cast iron products were produced in the United States in 2007. This required the production of about sixteen million tons of liquid iron. About 60% of the liq- uid iron was generated in cupola furnaces. The major materials charged to the cupola are cast iron and steel. On average, about
International Journal of Metalcasting/Fall 10
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