Experimental study of hot deformation behavior in API X65 steel

The hot deformation behavior of API X65 steel was investigated by hot compression tests. A temperature range between 950 and 1150 °C was used for experiments with different strain rates of 0.01, 0.1 and 1 s−1. The obtained flow curves were used together with work hardening rate analyses to study the dynamic recrystallization (DRX) behavior of the tested steel. The retardation of DRX in higher Zener-Hollomon parameter (Z) values was observed. In lower Z values however, transition from single peak DRX to multiple peaks DRX occurred. Different constitutive equations, including the power law, the exponential law and the hyperbolic sine law were used to express the Z parameter as a function of the peak stress. A new procedure was proposed to determine the optimum value of stress multiplier (α) in the hyperbolic sine law equation. This equation with the proposed procedure had the best performance for modeling the DRX behavior of API X65 steel. Furthermore, the relationship between the Z parameter and the peak stress was investigated using the power law relation. This gave the Z exponent of 0.173 for peak stress and 0.153 for peak strain. The normalized critical stress and strain for initiation of DRX were found to be 0.89 and 0.6, respectively. The obtained results are in general consistent with the experimental results from similar works.