Constitutive modeling, processing map optimization, and recrystallization kinetics of high-grade X80 pipeline steel

Abstract

Hot compression tests were used to examine the hot deformation behavior and of high-grade pipeline X80 steel at strain rates of 0.001–1 s−1 and temperatures of 950–1100 °C. Two approaches were used to model material flow curves. The first used the Zener-Hollomon parameter, Z, to show the impact of deformation temperature and strain rate on flow stress, using the Arrhenius constitutive equation. The second used a rule of mixture to represent the material's flow curve, considering work hardening and dynamic recrystallization flow stresses. The first method was accurate at low Z and low strains, while the second method accurately displayed peak stress, was suitable for large strains, and predicting flow curves at industrial strain rates. The microstructure of X80 steel exhibits strain rate dependence under hot deformation conditions, with finer and more equiaxed microstructures observed at higher strain rates. These findings align with processing map predictions for stable deformation behavior, suggesting potential for optimized hot working processes. The static recrystallization kinetics showed that the Avarmi exponent, n, ranges from 1 to 2 for strains of 0.2 and 0.35 at 950 °C, but higher values were observed under hot deformation conditions.

Keywords

• High-grade pipeline steel
• Hot deformation
• Flow stress
• Processing map
• Recrystallization
• Microstructure