Effect of Prestrain at Elevated Temperature on Ductile Fracture of High Strength Steel

The processes of ductile fracture of KD32 steel specimens subjected to prestrain at elevated temperature are observed. Although several large voids are observed at a relatively small strain level, they have no important role in fracture processes. As soon as micro-voids nucleate at some strain level, which is the stage just before final fracture, they rapidly grow and coalesce. It is proposed that ductile fracture of KD32 steel specimens occurs when the value of equivalent stress reaches a critical value. It seems that the most important reason for the decrease in fracture strain with prestraining at elevated temperature is the strain hardening according to amount of prestrain and prestraining temperature.