Comparative Study of Various Data Conversion Methods for Torsion Tests Applied to a HSLA Steel

Abstract

The influence of methods for converting torsion data (torque, number of turns and speed rotation) into equivalent variables (true stress, true strain and true strain rate) on the Garofalo equation parameters is studied. Torsion tests for a high strength low alloy steel at temperatures in the range 900 to 1150ºC and strain rates in the range 0.5 to 30 s-1 were conducted. The flow behavior of the material was analyzed by means of the Garofalo equation which is especially adequate for the correlation of torsion data in wide ranges of temperatures and strain rates. The Garofalo equation was fitted at different strains: from peak strain to a value of strain where a steady-state is assumed. The parameters of this equation, A, Q, n, , were determined by the RCR method which does not need initial values and provides coefficients indicating the quality of the fitting. Finally, the Garofalo equation parameters were related to creep mechanisms operating in this steel.