Papers by Author: Florin Serban

Abstract: The constant reduction of production costs and the development of materials during recent years are favoured the development of Austempered Ductile Iron (ADI) because of favourable combination of technological and structural properties. The process of forging on ADI makes it possible to obtain final parts with good dimensions. Moreover, Austempered Ductile Iron has a remarkable workability. ADI has many advantages, including the possibility of modifying and of improving the mechanical characteristics by thermo mechanical treatments while preserving a relatively low production cost, thus competing with many categories of steels. The study presented relates to the influence of the parameters of the thermo mechanical treatments on the proportion of residual austenite allowing modification of the mechanical characteristics of the material and on the evaluation of the residual stresses.

Abstract: Recently, austempered ductile iron (ADI) has emerged as a new class of ferrous materials and represents a major achievement in cast iron technology [1]. The mechanical strength and impact toughness of nodular iron are provided by the precipitation of the graphite phase as spheroids surrounded by ferrite (bull’s-eye structure) in a continuous pearlite matrix. The quality of ductile iron increases with the number of the graphite spheroids. A high spheroids volume fraction, which is mainly controlled by the inoculation process, limits the chemical segregation during solidification and ensures the structural homogeneity of the component. In this work, a lower value of Young modulus was obtained when the graphite phase was taken into account in the self-consistent modelling. For 12% of graphite the theoretical Young modulus agrees with the measured one (mechanical tensile test). The volume fraction of graphite was confirmed independently by micrographic observation (14%). It can be concluded that the macroscopic behaviour of ADI steel can be modelled by the self-consistent approach in which the austeno-ferritic aggregate is represented by an effective matrix, while instead of the graphite spherical empty spaces are introduced. Using such an approach it was shown that in the elasto-plastic range of deformation, presence of graphite phase caused stress relaxation.