Dynamic deformation influence on microstructure of Cr-4Ni-Mo steel has been studied by using an optical, scanning electron microscopy and X-ray analysis- The light gas gun in bore diameter 37 mm has been used in these experiments. The steel specimens-targets have been impacted within velocity range 200-400 m/s after different tempering regimes. Anomalous increase of the carbide particle size in steel alter shock aoading has beert established.