CONSTITUTIVE RELATIONSHIPS FOR HOT DEFORMATION OF A CARBON-STEEL - A COMPARISON STUDY OF COMPRESSION TESTS AND TORSION TESTS

A 0.34% carbon steel was subjected to hot working (800-1100-degrees-C) by Gleeble compression to 0.7 strain at strain rates of 0.1-8 s-1, ca m plastometer compression to 0.4 strain at strain rates of 3.5-100 s-1 and torsion to fracture strains greater-than-or-equal-to 8 at strain rates of 0.05-4 s-1. The compressive flow curves exhibited continual h ardening towards saturation except at high temperatures or low strain rates where work softening finally occurred; in torsion, the curves ex hibited the peak, softening and steady state characteristics of dynami c recrystallization. The sinh-Arrhenius constitutive equation was foun d suitable for describing the compression tests at a series of strain levels. The constants are power functions of strain with negative expo nents; however, they differ for the two compression techniques as a re sult of anvil/specimen contact friction in the Gleeble tests and the p resence of a glass lubricant in the cam plastometer. Each set of const ants can be employed to predict the flow curves of the other compressi on test with errors of only 7% as well as the stresses at the peak str ains in torsion.