cast via lost foam because most other metalcasting processes would not be able to obtain the necessary part geometry at the price required. In addition, the elimination of most machining is important as CF8M stainless (316 SS) is somewhat difficult to machine. Figure 5 shows the foam
Fig. 9. The surface finish of the ASTM A743 grade CF8M stainless steel casting matched the roughness of the foam pattern.
pattern and Fig. 6 shows the as-cast component after shot blasting. In this case, the foam was “blown” in a process similar to injection molding. Again, the surface finish matches that of the foam and depends on the quality of the foam beading. Figures 7 and 8 show the result-
ing microstructure of the ASTM A743 grade CF8M (316 SS) com- ponent at 200X and 400X. Again, this as-cast microstructure appears consistent throughout and typical of this grade of steel. Table 2 lists the chemistry results that are also in the standard range for CF8M stain- less steel (316 SS). 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 met- alcasting techniques. Seven stainless steel heats were an-
alyzed for carbon before pouring and in the solidified castings. Tis allowed a determination 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 begin-
ning commercialization, but it has
a strong potential for wide- spread adoption as a technol- ogy 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. The majority of it is used in captive applications. For low carbon steels (less than
0.03%), more work needs to be per- formed 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. More research is needed 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 metal-
lography of the steel castings via lost foam reveals little carbon pick up or degradation of microstructural properties. Based on the microstruc- tural examination, it is expected that the mechanical and other material properties are the same as steel cast- ings produced via other metalcasting techniques. However, additional test- ing is necessary to confirm this.
44 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2016 Fig. 10. This ASTM A743 grade CF8 stainless steel as-cast micro-
structure is shown with Oxalic acid etchant at 200X.
Fig. 11. This ASTM A743 grade CF8 stainless steel casting as-cast microstructure is shown with Oxalic acid etchant at 400X.
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