Effects of refrigeration and cryogenic treatments on austempered ductile iron

Low temperature treatment, as a method of improving mechanical properties of metals, has been studied and used for well over 60 years. Until recently these treatments have been limited to hardness and wear improvements of high alloy irons and steels. The purpose of this research is to determine the effects of refrigeration and cryogenic treatments on the mechanical properties, including hardness and tensile strength of austempered ductile iron.This research included the production of a high strength ductile iron of low alloy content capable of being used in either the as cast, conventionally heat treated or austempered condition. Refrigeration and cryogenic treatments were applied to the material at different points within the production cycles to determine the most effective order of treatment. After production of the base material at the university, representative specimens were treated by a series of sub-zero temperatures and austempering cycles at commercial treatment facilities. These specimens were then returned to the university and were subjected to a series of mechanical tests that included tensile and hardness property testing.After analysis of the data, it was determined that the greatest effects on the iron were in the increase in hardness and tensile strength of samples that had been cryogenically treated and after undergoing a commercial austempering cycle. Tensile and hardness properties of the material were increased approximately 16% over the nontreated samples. The study concluded that cryogenic treatment of austempered ductile iron is possible, and that it may have benefits over conventional hardening methods by preserving the surface _quality of machined components.