Investigation of the Effect of the Strain Rate on the Tendency of U8 Carbon Steel to Strain Aging

Abstract

The effects of the strain rate and degree on the scale of the strain aging effect in carbon steel U8 with lamellar pearlite microstructure, which is a eutectoid mixture of ferrite plates and brittle plates of secondary cementite Fe3C have been investigated. The microstructure and properties of Russian steel U8 after quasistatic compression, dynamic compression (shock processing), and explosion processing have been investigated. A low-temperature annealing (150–500 °C) of the non-deformed steel U8 has been shown to result in a monotonous reduction of hardness. The quasistatic compression and shock processing of the carbon steel were found to result in the strain aging manifested as an increasing hardness at annealing of the deformed steel U8. The increasing of the deformation degree and strain rate was accompanied by the increasing of hardness of the annealed steel. The explosion treatment was shown not to result in a notable improvement of the mechanical properties of carbon steel as well as in a change of the morphology of cementite plates. The deformation aging effect in steel U8 after the explosion loading was absent. The strain aging effect in U8 steel after quasistatic compression and dynamic loading was suggested to originate from an increasing of the lattice dislocation density, the long-range internal stress fields from which lead to the dissociation of the cementite Fe3C plates and to increasing of the concentration of carbon atoms in the ferrite crystal lattice. The absence of the strain aging effect in the carbon steel after the explosion loading is due to a small degree of the explosion deformation that doesn't allow providing an essential increasing of the lattice dislocation density in ferrite.