Behaviour of low-carbon and HSLA steels during torsion-simulated continuous and interrupted hotrolling practice

Abstract

Continuous and interrupted torsion tests have been conducted in the range of 900°−1000°C at surface strain rates of 0·1–10s⁻¹ on a low-carbon and a Nb-bearing steel. During continuous deformation, the strains for recrystallization and for fracture had dependencies on temperature and strain rate that were similar for both steels but were higher and lower, respectively, for the Nb-bearing steel. For both steels, the flow stress depended on temperature and on strain rate according to an Arrhenius and a power-law relationship, respectively, and was consistently higher for the Nb-bearing steel. The interrupted deformations were performed so that in a given test, interruptions were of equal duration being 10, 20, or 40 s at equal strain intervals of either 0·2 or 0·4. The difference in stress at the instant of un loading and upon reloading was measured to assess the amount of static recovery and recrystallization taking place during the interval. At 0·1 S⁻¹ recrystallization took place in the carbon steel while recovery operated in the Nb-bearing steel; at 1·0s⁻¹ recrystallization occurred in both steels. The progress of softening was augmented by increase in the strain rate, the temperature, and the interruption time.