A Low Temperature Yield Instability in Iron

Abstract

Polycrystalline specimens of a 0·07% C steel were tested in tension at liquid air temperatures. Under particular conditions of temperature and strain rate, following the upper yield point, the recorded stress descended below the lower yield stress then returned to the lower yield stress quasi. elastically thus forming a serration on the stress-strain curve. The magnitude of the serration depended on the difference between the upper and lower yield stresses, on the rigidity of the testing machine employed, and on the applied strain rate.