Implementation of Metal Casting Best Practices - EERE - U.S. ...

1. Implemented Best Practices
Age Strengthening and Machinability of Iron
Researchers from the University of Missouri-Rolla (UMR) have worked to identify the agestrengthening
mechanism in cast iron, quantify the parameters that control the process, measure
properties, develop a predictive model, and quantify the relationship between aging and
machinability. The mechanism and control of this phenomenon has not been conclusively
determined. Yet initial research at UMR indicated that dissolved nitrogen may be the control
mechanism. There was also an indication that these aging phenomena may favorably affect the
machinability of gray cast iron. The ability to initiate and control this phenomenon could result
in a significant improvement in casting mold yield, casting weight reduction, and possibly
improved machining productivity. The reported 7-11% increase in strength would allow the
production of higher carbon equivalent irons and a corresponding improvement in mold yield.
The researchers found that aging not only improved tensile strength but that the machinability of
cast iron also improves dramatically, especially when compared to “young”, one-day old iron.
There is also the potential to reduce casting weight by producing higher-strength iron. This
research concluded that a foundry could hold a casting for a period to increase its strength and
lower its machining costs.
Iron Foundry-1 was skeptical of this research at first. Holding castings in inventory requires
space and lower inventory turnover initially as more and more castings are stored. However,
after running some tests, the foundry found that holding did in fact increase the strength and
improve the machinability of their castings. At present, Iron Foundry-1 experiences an increase
in tensile strength of approximately 10% because of allowing the castings to age. This has
resulted in less concern in situations where the carbon equivalent is on the high side, which could
jeopardize meeting minimum tensile requirements. Further evidence was provided to Iron
Foundry-1 when it received complaints from customers about the difficulty of machining
castings that were sent in as a rush order. At present, Iron Foundry-1 holds its castings for
several days before shipping, many times at the request of its customers due to the problems they
had experienced when machining “young castings.” This process has enabled Iron Foundry-1 to
deliver high-quality castings that save its customers money on machining costs. Similar analysis
can be made for gray iron and compacted graphite iron.
Thin Wall Iron Casting R&D
Today's foundries are confronted with a continuous demand to manufacture high-quality, cost-
effective cast products. Those specializing in automotive castings have the added pressure of
developing new processes and materials that reduce overall car weight to meet federally
mandated fuel economy standards without sacrificing performance. In order to meet these needs,
automakers have increasingly turned to lighter-weight materials, and castings continue to be a
prime target. This explains why some ferrous castings markets have been lost in the past 15
years, as aluminum displaced cast iron for parts such as cylinder heads, engine blocks, and
steering components. However, a closer examination actually reveals that ferrous castings are, in
many cases, superior to – or at least competitive with – aluminum-based alloys. For instance,
ductile iron is not only cheaper, but also superior to aluminum in many cases in terms of relative
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