Study of Ductile Fracture of High Strength Steel Using Specimens Subjected to Prestrain at Elevated Temperature

Abstract

The processes of ductile fracture in KD32 steel specimens subjected to prestrain at elevated temperature are observed in detail by using fractographic and sectioning techniques. A criterion of ductile fracture and a mechanism of decrease in ductility with prestraining at elevated temperature are also investigated. The results are summarized as follows.
(1) The processes of ductile fracture in KD32 steel specimens are as follows: Although several large voids are observed at a relatively small strain level, they have no important role in fracture processes. As soon as microvoids nucleate at some strain level, which is the stage just before fracture, they rapidly grow and coalesce.
(2) Ductile fracture of KD 32 steel specimens occurs when the value of equivalent stress reaches to a critical one.
(3) It seems that the most important factor of decrease in ductility with prestraining at elevated temperature is the work hardening according to amount of prestrain and prestraining temperature.