Evolution of structure and physical-mechanical properties of iron under deformation

Abstract
The dependencies of true yield stresses s on true tensile strain values ε were experimentally determined on the specimens of technically pure iron after cold rolling and after annealing at different temperatures. The correlations between strain values ε and coercivity H_c which made a basis for nondestructive evaluation of residual deformations of structural elements and machine components were investigated. It has been shown that there is the unique relation between the yield strength and grain sizes in recrystallized iron and also the disoriented subgrain sizes in polygonized iron. The strain hardening curves of exponential type were reconstructed by a method of approximation for two structural states of iron - recrystallized and polygonized. Under low and medium deformations (before the formation of the neck) the growth of the yield stresses s is mainly caused by the strain hardening. Wthin the interval of large deformation, as ε grows, the contribution by tension-sheare deformation modes increases. As a result, the dislocation density is increasingly influenced by the formation of the fragmentary structure along the strain axis. The feedback equations ε(H_c) were dirived, that can be used for evaluation of the residual deformation by magnetic nondestructive testing methods.