Description of flow behavior and changes in grain size and structure of API-5CT-L80 steel in hot deformation process

Knowing the behavior of hot deformation and microstructure changes of API-5CT-L80 alloy steel is of great importance in the production of oil and gas industry pipes. For this purpose, in this research, the thermomechanical behavior of this steel was investigated by isothermal hot compression test in the temperature range of 1173 to 1373 K and strain rates of 0.001 to 1 s-1 s. The experimental results showed that the hot deformation behavior of steel is a softening behavior caused by the dynamic recrystallization phenomenon that in some conditions, the material shows complex behavior in the form of multi-peaked curves. The results of the microstructural investigation showed that with the increase in the deformation temperature, the formed grains have a larger size compared to the low temperature state, and more martensite phases are formed, which are more elongated martensite blades compared to the phases formed at low temperatures. The effect of strain rate was also significant like the effect of temperature because the rate of deformation had an inverse effect on grain growth, so recrystallized grains have enough time to grow at low strain rates. At high strain rates, the pearlite phases appeared more polygonal, and very small nucleation were observed in the austenitic boundaries of the ferrite and Wiedmannstein phase, which did not have enough time to grow, and at high strain rates, the martensite blades also tend to thin.