Continuous and interrupted hot torsion tests are extensively used to simulate thermo mechanical interactions that take place in rolling mill processes and radial forging. Any interpretation of the microstructure evolution depends on the accuracy of the methods used to convert the hot torsion test results into flow curves. The method of Fields and Backofen is widely used to convert data from the hot torsion test into flow curves. The method, however, is most suitable for materials with monotonic strain hardening behavior. Therefore, such methods do not enable accurate prediction of onset of recrystallisation. A new method for converting hot torsion data into a flow curve, by taking into account the variation of constitutive parameters during deformation, is presented. First torque-twist data is filtered using a linear least squares model. Hyperbolic coefficients are used as the parameters in the linear model. The mathematical representation of the data obtained in this way is employed then for flow stress determination using direct derivation of the mathematical model. Experimental data obtained by FHTTM, a flexible hot torsion test machine developed at IROST, for a C-Mn austenitic steel was used to demonstrate this method. The results compared with those obtained in the conventional approach using constant strain and strain rate hardening characteristics.