Temperature, strain rate, stress state and the failure of HY-100 steel

The influence of temperature and strain rate on the deformation and failure behavior of HY-100 steel has been examined as a function of stress state using notched and un-notched axisymmetric tensile specimens. Behavior over the range of temperatures/strain rates from −85°C and 1 s−1 to 27°C and 10−3 s−1 shows an equivalence of decreasing test temperature or increasing strain rate on deformation behavior in a manner that can be predicted by the thermally activated flow theory. Over the entire range of temperatures/strain rates, the influence of stress state on failure is such that two void coalescence mechanisms control failure; at low stress triaxialities, relatively equiaxed voids grow to impingement, while at high triaxialities, a void-sheet process intervenes linking elongated MnS-initiated voids by a shear instability. The failure strains decrease rapidly with increasing stress triaxiality ratio in a similar manner for all temperatures and strain rates except for an intermediate stress triaxiality condition where the void-sheet mode of failure extends to lower stress triaxialities under cryogenic test conditions.