ON DISLOCATION LINK LENGTH STATISTICS FOR STRAIN-HARDENING AND RECOVERY DURING ELEVATED-TEMPERATURE PLASTIC-DEFORMATION

Tensile tests are performed for an AISI 310 type stainless steel over a range of test temperatures and strain rates. The experimental results generally show that the strain hardening behaviour of the 310 stainless steel has two distinctive regions, namely: (i) a low-temperature region, in which strain hardening decreases linearly with strain and is almost independent of the strain rate; and (ii) a high-temperature region (where the temperature is higher than about half of the melting point), in which strain hardening is affected by strain rate, and the strain hardening coefficient increases with an increase in strain rate at a given temperature. For the 310 stainless steel, the low-temperature region is from 298 to about 873 K, and the high-temperature region is above 873 K. The dynamic effects of strain hardening and recovery processes during elevated temperature plastic deformation of the 310 stainless steel are then analyzed by means of dislocation link length statistics. The main findings are: (i) The strain hardening coefficient for an elevated temperature tensile test is given by theta = H - 2A(0)(-1)psi(t) R/epsilon, where H is strain hardening coefficient for low-temperature plastic deformation without recovery, A(0) a numerical constant about unity, psi(t) is dependent on dislocation structure during deformation, R recovery rate, and epsilon strain rate; (ii) for steady state deformation, the relationship between flow stress, sigma, and dislocation density, rho, namely sigma = alpha(1)M mu b rho(1/2), can be deduced from this analysis, where alpha(1) is a constant, M the Taylor factor, mu shear modulus, and b the Burgers vector; (iii) the dislocation annihilation rate, rho(a), has a stronger dependence on stress than recovery rate, R, and strain rate, epsilon(s). The dislocation annihilation rate, rho(a), is proportional to the dislocation density, rho, in the manner rho(a) proportional to rho(m), where m = 2 to 3 is a constant. Direct comparison of these new results from dislocation link length statistics is made with the experimental results for the 310 stainless steel. Agreement is good between the analysis and the experimental results.