Papers by Author: I. Salvatori

Abstract: An up to date approach to material cold formability, based on a conventional J₂ theory for plasticity together an uncoupled linear plastic damage evolution theory, is applied to the study of steel bolt head cold forming. Specific laboratory tests to characterize the material formability have been used. Finite element simulations have been performed to characterize the strain and stress state both in the forming process and in experimental tests to determine the material ductile fracture locus. The influence of chemical composition and initial microstructure is discussed.

Abstract: In this paper the recrystallisation kinetics of cold rolled strips as a function of magnetic field intensity has been studied on a Fe-0.05C-1.5Mn alloy. The retarding effect on recrystallisation due to the application of a magnetic field on samples treated with magnetic field up to 10T, has been experimentally confirmed. The effect was more evident for high magnetic field and for long annealing times. In addition, a small retarding effect of magnetic field on grain growth has been noticed.

Abstract: Refinement of grain size is one of the biggest challenges to produce steels with improved combination of strength and toughness. Ultrafine structures are being produced world-wide on various materials, including low carbon steel, using different types of processes. However, the majority of these processes also exhibit severe limitations because they are generally restricted to small samples and are difficult to be implemented on an industrial scale. A promising technique for industrial implementation is the Accumulative Roll Bonding (ARB), a process able to supply large samples, even in the laboratory scale. In this paper, warm intense straining (ε = 4) by ARB was applied to a plain low-C steel in order to develop ultrafine grains, aiming at sizes around 1-2 μm, suitable to maintain an adequate combination of strength and ductility. The effect of annealing conditions on the evolution of the work-hardened microstructure and the bonding behaviour after each pass were investigated. Orientation Imaging Microscopy was used to investigate the microstructure and give a quantitative assessment of high angle and low angle boundaries. It is showed that the frequency of high angle grain boundaries increases with the strain but the misorientation distribution remained far from that typical of a recrystallised material.