Macro- and microdamage behaviors of the 30CrMnSiA steel impacted by hypervelocity projectiles

Macro- and microdamage behaviors of a 30CrMnSiA steel under impacts of GCr15 steel projectiles have been studied. The results show that, in the impact velocities of 2.5∼7 km s−1, hemispherical craters are often formed in semi-infinite targets, and with decreasing the target thickness or increasing the projectile velocity, the form of craters changes to conical one, and obvious spall phenomenon occurs on the back face of targets. Depth and diameter of craters increase with the projectile velocity, and can be calculated by the formulas: Pc=0.47 v02/3 and Dc=0.85 v02/3. Microstructure analyses show that, there are three kinds of microdamages: microcracks, microvoids and adiabatic shear bands, in the region around the crater. The size of the microdamage zone is much larger than that of the macrodamage one for the medium thick targets, inferring that when studying the damage behaviors of materials under impacts of hypervelocity projectiles, attention should also be paid to microdamages besides macrodamages. Adiabatic transformed shear bands always form networks and shows white contrast in scanning electron microscope (SEM) micrographs. While, when these transformed shear bands are studied by a SEM attachment in transmission electron microscope (TEM), it is found that obvious melt has occurred in the head of bands. A lot of microcracks have been formed in the tail and many deformation shear bands are observed in junctures of transformed bands and the matrix. TEM results show that, dislocation cells are the predominant deformation structure in the region just near the crater, and with increasing the distance from the crater, the density of dislocation decreases, and dislocation tangling is the main feature. Deformation twins are also found in the region just near the crater, while only micro-twins in individual laths of martensite are observed in the region a little farther from the crater.