General expression of the Zener-Hollomon parameter as a function of the chemical composition of low alloy and microalloyed steels

Using torsion tests the Zener-Hollomon parameter has been determined in a selection of 18 steels with compositions appropriate for the study of the influence of each alloying element (C,Mn,Si,Mo,Ti,V,Nb) on the Zener-Hollomon parameter (epsilon over dot exp(Q/RT) = A(sinh alpha sigma(p))(n)). It is demonstrated that all the alloying elements influence, to a greater or lesser extent, the activation energy (Q). A rise in the content of any alloy was found to increase the activation energy, except in the case of carbon which has the opposite effect. An expression is given for Q as a function of the content of each alloying element and the second side of the equation is completed by determining the optimum values of alpha and n for all the steels, giving 0.01187 MPa(-1) and 4.458, respectively. It is demonstrated that A is not a constant but is a function of the activation energy. In this way it is possible to calculate the peak stress (sigma(p)) at any temperature and strain rate for any low alloy or microalloyed steel in the austenite phase. This study brings a new dimension to the Zener-Hollomon parameter and potentially improves its applications, for example in the calculation of stress-strain curves.