Effect of microstructure and chemical composition on dynamic factor of high strength steels

The high strain rate properties of high strength steels with various microstructures and static strength levels were studied by means of split Hopkinson bar apparatus in shear punch mode. The as received cold rolled sheet steels were subjected to a variety of heat treatment conditions to produce several different microstructures, namely ferrite plus pearlite (F+P), ferrite plus bainite (F+B), ferrite plus martensite (F+M) and ferrite plus bainite and retained austenite (F+B+RA). According to the variation of dynamic factor (ratio of dynamic to static strength) with static strength, two groups of microstructures with two distinct behaviours were identified, i.e. classic dual phase (ferrite plus martensite) and multiphase (including ferrite-pearlite, ferrite-bainite, etc.). It was also observed that the general dependence of microstructure on the dynamic factor was strongly influenced by chemical composition in the case of ferrite plus martensite microstructures.