Strain hardening of structural metals with metastable structure under complex loading

Abstract

We investigated distinctive features of strain hardening under complex loading for quenched and low-tempered steels of ferritic-pearlitic (40KhN), martensitic (30Kh3NSMV), and maraging (Kh16N5D3) types and an Al-4Cu age-hardening alloy whose matrix phase is characterized by the metastable structure corresponding to supersaturated interstitial and substitutional solid solutions susceptible to disintegration in the process of plastic deformation. We analyzed structural indicators of the depletion of the matrix phase of supersaturating alloying elements forming carbides and intermetallic compounds and the mechanisms of hardening and softening influence of preliminary deformation (within reasonable ranges of its variation) on the value of the yield limit when repeated loading changes its sign. It is shown that, for the investigated type of metastable materials, in the analyzed range of preliminary deformations governed by alloying, the application of repeated biaxial tension leads to a uniform extension of the limiting yield curves. As the degree of supersaturation decreases (in the process of thermal treatment) and we observe the formation of equilibrium solid solutions of the matrix phase, the character of strain hardening evidently changes from predominantly isotropic to kinematic.