Shear band patterning and post-critical behavior in AISI 4340 steel with different microstructure

Abstract We explore the role of the microstructure of AISI 4340 steel with different values of microhardness (as-received and hardened) on shear band nucleation and post-critical behavior with a well-developed pattern of shear bands. Critical and post-critical behavior was investigated with the help of the explosively-driven Thick-Walled Cylinder technique, which allowed comparative study of the material deformation at similar strain rates and final strains. It was observed that the collapsed as-received AISI 4340 samples were resilient to shear localization and propagation and mainly preserved its cylindrical geometry at the investigated small and larger global strains. The hardened specimens at the similar final global strains exhibited a dramatically different behavior. At small strains, some well-developed shear bands were observed. Larger global strains were accommodated mostly by growth of the initially generated shear bands, resulting in the complete loss of cylindrical symmetry. Numerical simulations reproduced the main features observed in the experiments and the dramatic difference in behavior of as-received and hardened AISI 4340 steel. It is shown that the initial number of defects introduced in calculations as well as the material constants used for the material model have a direct effect on the pattern of shear bands.