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The influence of austenite content on the properties of austempered ductile iron (ADI) was investigated. The “reacted” austenite content in the ADI structure was controlled by varying austenitizing temperature and, thus, the carbon content of the austenite during austenitizing. Phase transformation studies revealed how to vary the carbon content during austenitizing. The investigation included “step-austenitizing”, where the material was first heated above the critical temperature and subsequently cooled and held below the upper critical temperature. Intercritical heat treatments were also performed to produce a mixed ferrite + ausferrite microstructure containing nominally 50% proeutectoid ferrite + 50% ausferrite. Cast plates containing 3.4C-2.7Si-0.3Mn-1.1Ni-0.16Mo were austempered at 725F (385C). The evaluated properties included tensile properties, machinability (in drilling) and thermal expansion coefficient.

Data on the low and high cycle fatigue response as well as monotonic (non-cyclic) and cyclic flow properties are required by design engineers for the proper design of many components. Currently, there are no readily available sources for such information on ductile/nodular cast iron. The purpose of this study was to determine property design data similar to those in SAE standard J1099 for SAE Grade D5506 ductile iron. In this study, the monotonic and cyclic strin hardening properties, and the variation of elastic modulus after repetitive cyclic testing were determined for eight ductile iron castings selected to represent the range of properties possible in Grade D5506 ductile iron. Strain-life testing was conducted on four of the eight materials to calculate the strain and stress versus fatigue life (reversal) constants.