Effect of severe plastic deformation by hydrostatic extrusion on the physical-mechanical properties of the U8A steel

Abstract

One of the promising lines in the improvement of the properties of metal materials is the formation of ultra-fine grained structure, in particular, by means of severe plastic deformation. Note, however, that the effect of deformation by hydrostatic extrusion on the structure and properties of pure metals is described in considerable detail in the literature, whereas the peculiarities of hydrostatic extrusion of such widespread materials as steels are given much less attention. This paper presents the results of studying the mechanical and magnetic properties, as well as the rate of distribution, of other elastic waves of the U8A pearlite steel subjected to intensive plastic deformation by hydrostatic extrusion. It is revealed that, as the amount of strain increases, ultimate strength and yield strength increase monotonously, and unit elongation decreases. At the same time, the ratio of yield strength to ultimate strength increases, and this indicates the reduction of the hardening reserve of the material and the increasing danger of its brittle fracture. Meanwhile, the dependences of magnetic properties (coercive force, maximal magnetic permeability and residual induction) on the amount of accumulated strain from hydrostatic extrusion have extrema. This can be explained by the peculiarities of structure formation using this deformation plan. It is shown that, in case of estimating the strength properties in the items manufactured from the steel under study, after severe plastic deformation by hydrostatic extrusion, the most effective is a combined use of coercive force, maximal magnetic permeability, residual induction, elastic wave propagation rate prior to the amount of strain 1.62, and at higher amounts of strain it is the root-mean-square values of the voltage of Barkhausen magnetic noises.