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 u sing notched and un-notched axisymmetric tensile specimens. Behavior over t he range of temperatures/ strain rates from - 85 degreesC and 1 s(-1) to 27 degreesC and 10(3) s(-1) shows an equivalence of decreasing test temperatu re or increasing strain rate on deformation behavior in a manner that can b e predicted by the thermally activated flow theory. Over the entire range o f temperatures/strain rates, the influence of stress state on failure is su ch that two void coalescence mechanisms control failure; at low stress tria xialities. relatively equiaxed voids grow to impingement, while at high tri axialities, a void-sheet process intervenes linking elongated MnS-initiated voids by a shear instability. The failure strains decrease rapidly with in creasing stress triaxiality ratio in a similar manner for all temperatures and strain rates except for an intermediate stress triaxiality condition wh ere the void-sheet mode of failure extends to lower stress triaxialities un der cryogenic test conditions. (C) 2001 Elsevier Science B.V. All rights re served.