Fig. 10. This ASTM A743 grade CF8 stainless steel as-cast microstruc- ture is shown with Oxalic acid etchant at 200X.
As a final example, a casting was successfully produced in
ASTM A743 grade CF8 stainless steel (304 SS). Te use of this component is confidential. Figure 9 shows the surface finish after shot blasting to remove the refractory coating. Te roughness matched the foam pattern, as this component was a prototype and cast from machined foam. Figures 10 and 11 show the as-cast microstructure at 200X and 400X. Table 3 shows the chemistry of the casting, which is within normal ranges. Again, the microstructure was uniform throughout with no evidence of carbon variation or pickup. Te microstructure also is the same as standard ASTM A743 grade CF8 stainless (304 SS) cast by other metalcast- ing techniques. Seven stainless steel heats were analyzed for carbon before
pouring and in the solidified castings. Tis allowed a deter- mination of carbon pick-up from the process. Te average carbon pickup in the process was 0.053% with a standard deviation of 0.0275%. Heats 6 and 7 had the lowest amounts of carbon at 0.032% and 0.034%.
Future Potential Steel in lost foam is just beginning commercialization, but it
has a strong potential for widespread adoption as a technology due to the cost saving benefits that the technology allows. Lost foam casting has advanced to the point that the casting of plain carbon and stainless steel is currently possible. It is used at three companies in the U.S. so far, and research reports indicate its use in a variety of other countries. Te majority of it is used in captive applications. For low carbon steels (less than 0.03%), more work needs
to be performed to better predict the carbon pick-up in the castings. Te grains of the stainless steel parts need to be smaller and refined to reduce the grain boundary inclusions. Tere needs to be more research performed to understand the minimum thickness steel castings can be cast in the lost foam process and if this thickness is alloy dependent. Chemistry analysis and metallography of the steel cast- ings via lost foam reveals little carbon pick up or degradation
October 2016 MODERN CASTING | 41
Fig. 11. This ASTM A743 grade CF8 stainless steel casting as-cast microstructure is shown with Oxalic acid etchant at 400X.
of microstructural properties. Based on the microstructural examination, it is expected that the mechanical and other material properties are the same as steel castings produced via other metalcasting techniques. However, additional test- ing is necessary to confirm this.
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