Structure Factors That Influence the Stability of Plastic Strain of BCC Metals under Tensile Load

Abstract

The effect of the Peierls stress on the ultimate tensile stress and uniform strain prior to the formation of a neck during stretching of metals and alloys with bcc structure is theoretically analyzed. The analysis is based on the equation for the variation of the dislocation density with deformation; this equation determines the shape of the work-hardening curve for a bcc material and the effect of the Peierls stress on the parameters of this equation (the annihilation coefficient for screw dislocations). Using the Considere condition for plastic instability of the neck type, the ultimate tensile stress and the magnitude of uniform strain are found theoretically as a function of the Peierls stress at different temperatures below 0.15T m , where T m is the melting temperature of the bcc metal. Theoretical results are illustrated with experimental data on the temperature dependences of the annihilation coefficients for screw dislocations and of the magnitude of uniform strain in molybdenum and Armco iron.