Grain size effect on the warm deformation behaviour of a Ti-IF steel

The effect of grain size on the warm deformation behaviour of a titanium stabilized interstitial free (IF) steel was investigated using hot torsion. The initial work hardening regime is followed by the development of a broad stress peak after which work softening occurs. The hypothetical saturation stress (Estrin-Mecking model) and the stress at final strain were relatively insensitive to grain size. However, the strain to the peak stress was strongly dependent on the grain size at low values of the Zener-Hollomon parameter. A simple phenomenological approach, using a combined Estrin-Mecking model and an Avrami type equation, was used to model the flow curves. The hypothetical saturation stress, the stress at final strain and the strain to peak stress were modelled using three different hyperbolic sine laws. A comparison with independent data from the literature shows that the apparent activation energy of deformation determined in this work (Q = 372 kJ/mol) can be used to rationalize the steady-state stress in compression data found in the literature. (C) 2003 Elsevier B.V. All rights reserved.