Hot-upsetting tests on steel cylinders after solidification

A frequently occuring set of forming sequences involves deformation of the workpieces at a strain rate of less than 0.02 s −1 immediately after solidification. The determination of the stress-strain relationship in these circumstances requires new specific devices and related procedures for the achievement of upsetting. Cylinders to be upset are obtained by fusion of an adequate volume of steel in a silica container which is placed on the lower platen of a testing machine. The specimens are upset immediately after in-situ solidification. The influence of strain-rate hardening and of the occurence of a central shrinkage cavity are analysed using elasto-plastic and elasto-visco-plastic finite-element models for reference manganese-alloyed steels. Besides basic upsetting experiments on specimens after solidification, new experiments are performed on room-temperature specimens in which different cylindrical holes have been drilled in the centre zone to represent a well-defined cavity. It is shown that the occurrence of a central cavity, which appears more or less after complete solidification, does not change significantly the state-variable values in the specimens, nor the strain-rate hardening, so that at the present time elasto-plastic pore-free modelling remains relevant in most cases.