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In this research, the hot deformation behavior of API X70 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 work hardening rate versus stress curves were used to reveal if dynamic recrystallization (DRX) occurred. The application of constitutive equations to determine the hot working constants for the tested steel was discussed. Using regression analysis, the stress multiplier (α), the apparent stress exponent (n), and the activation energy (Qd) for DRX were calculated as 0.016 and 4.420, and 382 kJ/mol, respectively. Furthermore, the effect of Zener–Hollomon parameter (Z) on the characteristic points of flow curves was investigated using the obtained relations. The dynamic recrystallization (DRX) kinetics of API X70 steel was also studied and its governing equation was derived.

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In this study, the hot-working behavior of Mn-25Ni-5Cr alloy was studied using hot compression tests at the temperatures of 850 ˚C, 900 ˚C, 950 ˚C and 1000 ˚C and the strain rates of 0.001 s^-1, 0.01 s^-1, 0.1 s^-1 and 1 s^-1 to a true strain level of 0.7. The results of flow curves showed that the flow stress decreases with increasing temperature and decreasing strain rate. Regarding the shape of flow curves, peak appearance represents the dynamic recrystallization. The peak stress and strain of flow curves appeared in fewer strains at high temperatures and strain rates. The microstructural evolution is mainly controlled by dynamic recrystallization. The presence of evolving boundaries around the recrystallized grains also indicates the occurrence of continuous dynamic recrystallization during hot working. In closer scrutiny of microstructure and fasciology, using by SEM microscope equipped with EDS detector, in addition to the background phase, second phase consisting of manganese, nickel and chromium was identified. The constants of n, α and β were determined using constitutive, power and exponential equations at 0.3 strain. According to the constitutive equation of the hyperbolic sinus, the amount of activation energy in the strain of 0.3 is 394.6258 kJ/mol.

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The purpose of this research is to investigate the hot working behavior of the cobalt-nickel base superalloy with the chemical composition of Co-22.8Ni-3.4Al-8Cr-17.1W-1.5Ti-2.8Ta-1.5Nb-1.5Mo-0.06C-0.02B (%wt) by performing compression test, providing the constitutive equation and deformation procssing map and determining the safe and unsafe regions of deformation. In this regard, the hot compression test was performed in the temperature range of 1050-1200 degrees Celsius, with a step of 50 degrees Celsius and strain rates of 0.1, 0.01 and 0.001/s up to a strain of 0.7. The evaluation of the constitutive equations governing the hot deformation process of the superalloy showed that the presented model based on the hyperbolic sine equation predicts the experimental results with acceptable accuracy. Using the mentioned equation, the hot deformation activation energy of the investigated alloy in the present study was obtained as 497 kJ/mol. Based on the process in map drawn for the investigated alloy in the present study, at a strain of 0.4, an instability region was observed at a temperature of 1050 degrees Celsius and a strain rate of 0.01 1/s. the extent and intensity of instability region decreased with the increase in deformation temperature. According to the results of the processing map and the constitutive equations, the optimal conditions of deformation of the investigated alloy are in the temperature range of 1150  to 1200  and the strain rate of 0.1 1/s and the temperature range of 1100  to   1200 and the strain rate of 0.1 to 0.001 the peak efficiency of  45% energy consumption.