Effect of Liquid Environments on the Tensile Properties of Ductile Iron 2004-01-0793
The open literature suggests that high strength ductile irons (Q&T or ADI with hardnesses over 250 BHN) in contact with liquids, such as water or motor oil, may show a loss of ductility in the standard tensile test. This study determined the effect of water and various automotive fluids (mineral oil, motor oil, gear oil, brake fluid, power steering fluid and diesel fuel) on the tensile properties of various low and high strength grades of ductile iron (D-4512, N&T, Q&T, Grade 1 ADI and MADITM). The low strength grade of ductile iron (D-4512), the low strength grade of MADI™ and the high strength quenched & tempered ductile iron showed no loss of ductility when in contact with water or automotive liquids but the industry standard high strength grade of ductile iron (Grade 1 ADI) showed significant degradation. Further, high strength normalized & tempered ductile iron and MADITM, a new, machinable, high strength grade of ductile iron, showed no loss of ductility in contact with automotive fluids and significantly better performance compared to Grade 1 ADI when in contact with water. Shot blast cleaning, which produces beneficial surface compressive stresses, did not suppress this embrittlement phenomena in Grade 1 ADI. This program did not attempt to determine the mechanism responsible for the environmentally induced degradation observed in this study, however, the “liquid metal embrittlement” theories of chemisorption of embrittling atoms at the crack tip causing a reduction in bond strength or enhanced dislocation generation were supported.