Behavior of the Flow Stress in Hot Upsetting in a Crank Press.

During the upsetting process in a crank press, deformation rate usually decreases toward the end of deformation and reaches phi equals 0/sec at the lower reversal point. In hot upsetting of steel it was noticed that the flow stress, k//f, also decreases at the end of deformation. However, at the lower reversal point, k//f behavior does not correspond to that of a deformation rate of phi equals 0/sec but reaches a value corresponding to phi greater than 0. This is attributed to recovery processes in the material. It is possible, therefore, that owing to a decrease of flow stress the maximum value of deformation force does not occur, as often assumed, at lower reversal point but somewhat earlier.