High temperature stress-strain curve fitting of a Nb-Ti microalloyed steel

Abstract

A series of hot plane strain compression tests have been conducted on a Nb-Ti microalloyed steel in a Servotest machine on samples of approx. 10 mm in thickness. Two sets of tests at strain rates of 5 s^-1 and 15 s^-1 were used and monitored the stress-strain behavior at deformation temperatures varying from 850 to 1,025 °C. The experimental data were corrected for friction, deviation from plane strain compression (PSC) conditions and adiabatic rise of temperature, to give the isothermal equivalent tensile stress-strain curves. Thereafter these curves have been modeled by two types of equations depending on the softening mechanism operating during the deformation process and calculated the value of the coefficients in the equation by the application of a Taylor series around an initial point close to the solution. Finally, by the application of the least squared method, the previous values are compared to the experimental ones in order to determine an optimized value of the coefficients in the equations which model the stress-strain behaviour of the steel.