Effect of high-pressure torsion on microstructure changes in microalloyed steel

Abstract

Тhe most common method of manufacturing parts is metal pressure treatment, as a result of which the entire reserve of strength and ductility of the material is not exhausted. Therefore, the issues of the influence of plastic deformation on the cyclic durability and endurance limits of steel rings are relevant. In this article experimental studies of the effect of high pressure torsion in a die of new design on the evolution of the microstructure and the change of mechanical properties have been carried out. As a result, the fundamental possibility and efficiency of using the proposed method for the formation of ultrafine grained structure and increasing the strength properties of steel rings has been proved. Strain was carried out at ambient temperature in six passes. The strain resulted in an ultrafine-grained structure with an average grain size of 0.5 μm and a great number of large-angle boundaries. The strength properties of microalloyed steel increased almost threefold compared to the initial state, the microhardness also increased threefold, i.e. increased from 760 MPa in the initial state to 1935 MPa after strain. The greatest increase in strength properties occurred in the first 3 cycles of strain.