Microstructure evolution of 6252 armor steel under hypervelocity impact

6252 armor steel is an improved version of 685 armor steel, with a high tensile fracture strength 1700 MPa. In this study, 6252 armor steel was used as the impact target, and 10 gs of spherical 93 W and 30CrMnSiA were used as the projectile. The impact velocities were designed to be 1.0 km/s, 1.5 km/s, 2.0 km/s and 2.5 km/s. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD) were used to study microstructural changes in the armor steel. It was found that when the impact pressure was less than 27.75 GPa, no phase transition or twinning was observed in the target plate. When the impact pressure was greater than 27.75 GPa, phase transition occurred. The phase transition evolution was martensite -> austenite -> bainite +martensite/austenite islands +martensite. Twins also occurred when the impact pressure was greater than 27.75 GPa. Ledeburite was revealed in the projectile residue when the impact pressure was greater than 47.80 GPa. The grain orientation was more uniform than the original one, and more small-angle grain boundaries were observed.