Cast iron is generally thought of as a weak, dirty, cheap, brittle material that does not have a place in applications requiring high strength and defined engineering properties. While gray cast iron is relatively brittle by comparison with steel, ductile iron is not. In fact, ductile iron has strengths and toughness very similar to steel and the machinability advantages make an attractive opportunity for significant cost reductions. Gray and ductile iron bar stock is commercially available and can be used as a direct replacement in applications that are currently being made from carbon steel bar. Ductile iron bar stock conversions are very prevalent in many fluid power applications including glands and rod guides, cylinders, hydrostatic transmission barrels and in high-pressure manifolds. Automotive gears are being converted to ductile iron for its damping capacity and cost reductions. Both gray and ductile iron has been used for years in the machine tool industry because of their performance in sliding wear applications and vibration damping. Understanding the metallurgical concepts of ductile iron is the key to understanding its potential use as an engineered metal and allows the design engineer to determine its suitability in specific applications and to intelligently select the best grade. Recent developments in understanding the variables that influence the machinability of gray and ductile iron grades have allowed the process engineer to quantify the expected cost savings when converting from carbon steel bars to continuously cast gray and ductile iron. This paper will include a background on the development of continuous casting of gray and ductile iron, the definitions of ductile irons and the metallurgical characteristics of the engineered grades and some basic material properties. An update on recent studies in the machining characteristics of ductile iron will also be presented.
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