High-temperature deformation characteristics of free-machining steels

Abstract

The high-temperature deformation of three as-cast free-machining steels with different lead contents and Mn : S ratios has been studied by torsion testing at temperatures in the range 900°-1 150°C and at constant strain rates in the range 6·9 x 10₋₃–5·3 S_−l. The stress-strain curves obtained were characteristic of the occurrence of dynamic recrystallization over the entire range of testing conditions. Analysis of flow-stress data before the peak, at the peak, and during steady state gives a constant activation energy for deformation of 310 kJ mol₋₁, indicating that the activation energies for dynamic recovery and dynamic recrystallization are the same. Correlation of the strains to the peak flow stress and to steady state with the Zener-Hollomon parameter shows agreement with previously published work on mild steel, with minor variations between the experimental steels that are attributable to differences in grain size.