The 0.045% V HSLA and the C steel were deformed in torsion over the range 850–1150°C and 0.1–30 s−1. Flow stress, temperature and strain rate were related by the combination of the Arrhenius function with either the exponential or sinh functions. Based on peak stress from the sinh equation and a linear peak strain dependence, an equation is proposed for calculating flow curves. The constants in the exponential law were evaluated at strain intervals of 0.05 up toε= 0.5, so that flow curves and mean pass stresses could be estimated for any rolling condition. Calculated and measured roll separating forces were compared for a nine-pass schedule. Ferrite grain size increased linearly with risingTat constantεandε. In multistage, isothermal tests after pass strains of 0.3, the fractional softening for delay times of 1, 10 and 30 s were determined. In mill simulations of nine passes withTdeclining from 1270 to 750°C, the pass flow curves and the finishing grain sizes were determined. The behaviours of the steels are contrasted and also compared with those of other HSLA steels.