  The microstructure and mechanical properties of materials saturate to steady
states after severe plastic deformation (SPD). Despite the well-known effect of
temperature on the steady-state microstructure, there is no general agreement
on the significance of strain rate and the applicability of the Zener-Hollomon
parameter in this regard. In this study, several pure metals (aluminum, copper,
titanium, and iron) and a Cu-30Zn (wt%) brass alloy have been processed by a
high-speed high-pressure torsion (HPT) equipment with controllable rotation
speeds in the range of 0.06 to 60 rpm. It is found that crystallite/grain size,
dislocation density, microhardness and shear stress at the steady state are
reasonably rate-independent for the von Mises strain rates in the range of
0.004 to 20 s-1. Because both rates of grain refinement and of dynamic
recrystallization are proportional to the strain rate, it is suggested that
their balance, which determines the steady state, is rate-independent.
