An extensive experimental investigation comprising tensile testing and high voltage electron microscopy studies of interstitial-free α-Fe was carried out. The temperature and strain rate were varied in the ranges 25 – 630°C and 10⁻² – 10⁻⁴ s⁻¹ respectively.

A previously presented dislocation model for the σ-ϵ behaviour of polycrystalline b.c.c. metals was computer fitted to the experimental σ-ϵ curves and the variation in the three main parameters of the model with temperature and strain rate was determined. The empirically derived Ludwik-Hollomon and Ludwik relationships for the σ-ϵ behaviour of metals was computer fitted to the same set of experimental data and the results were compared.

Based on the temperature and strain rate variations in the three main parameters of the dislocation model a new theory for the strain hardening of interstitial-free α-Fe at higher temperatures is proposed.