THE INFLUENCE OF INTENSIVE PLASTIC DEFORMATION ON THE STRUCTURE AND PHYSICAL AND MECHANICAL PROPERTIES OF HIGH-CARBON STEEL

The hydrostatic extrusion method as a type of intensive plastic deformation is an effective way to improve the mechanical properties of metals and alloys. The improvement of mechanical properties is generally a result of the structure dispersing and the increase of dislocation density. A large number of works consider the influence of deformation on the structure and mechanical properties of metals and alloys. However, literature pays far less attention to the study of physical characteristics of a material strengthened by means of intensive plastic deformation. Such investigations are necessary to develop nondestructive physical methods of diagnostics of such materials state. The authors carried out the study of high-carbon steel structure using the methods of scanning and transmission electron microscopy and performed mechanical tensile tests and a number of magnetic measurements. It is shown that the extruding causes the dispersing of U8A high-carbon steel structure. When extruding, the cellular, fragmented and submicrocrystalline structures are formed in ferrite constituent of steel perlitic structure in the conditions of dynamic recovery, continuous dynamic and post-dynamic recrystallization, causing the dislocation density reduction in a grain body under the true strain more than 1.62. With the growth of true strain, strength characteristics of U8A steel change monotonically: ultimate resistance increases twice, and conventional yield strength – by 3.6 times. It is established that the structure dispersion exerts the prevalent influence on strength characteristics, and the dislocation density plays the minor role. Unlike the mechanical characteristics, the coercive force, the maximum magnetic permeability, the residual induction and the elastic waves propagation speed are more sensitive to the dislocation density changes.