activation energy and zener-hollomon mapping of hot-deformed api x80 steel using modified hyperbolic sine constitutive models

This study investigates the hot deformation behavior of api x80 pipeline steel using modified hyperbolic sine-based constitutive models. uniaxial compression tests were conducted at temperatures of 950 to 1100 °c and strain rates of 0.001 to 1 s⁻¹. five constitutive approaches were evaluated: linear-linear shi (lls), linear-polynomial shi (lps), polynomial-polynomial shi (pps), and polynomial-polynomial yang (ppy). results indicate that activation energy (q) varies significantly with deformation conditions. while the constant q (cae) model provides reasonable predictive accuracy and remains useful for simplified analysis, the ppy model demonstrates superior performance by capturing complex dependencies between stress, temperature, and strain rate. zener-hollomon (z) maps and q contours further illustrate the impact of model selection on process prediction. these findings establish a reliable computational framework for accurately modeling and optimizing hot deformation in high-strength steels.