Dynamical behaviour of very high strength nitrogen alloyed steels

The dynamical behaviour of some nitrogen alloyed steel are investigated. These steels with two different levels of high hardness were obtained by cold drawing. Static and dynamic compression tests are carried out as well as quasi dynamic tests at intermediate rate. Flow curves are analysed in terms of strain rate sensitivity, maximal strain before rupture and mechanical instability. Cylinder impact tests on a rigid boundary are performed at various velocities. The profile of the specimens shows a markedly difference in the plastic deformed zone. A constitutive law has been chosen, based on the Johnson-Cook model. Results of calculation are discussed in comparison to experimental data in the plastic zone. Microscopic observations shows the formation of strain and damage localization in the different test conditions. (orig.)