Hot Deformation Behavior of an API X۷۰ Steel: A Processing Map Approach

This study investigates the hot deformation behavior of an API X۷۰ microalloyed steel using a processing map approach. Cylindrical specimens were subjected to compression tests at temperatures ranging from ۹۵۰ to ۱۱۰۰ °C and strain rates from ۰.۰۰۱ to ۱ s⁻¹. Flow curves revealed typical features of work hardening, dynamic recovery, and dynamic recrystallization. Power dissipation efficiency and instability criteria were calculated using a dynamic material model to construct processing maps at various strain levels. The maps identified three optimal hot deformation regions at higher strains, with the most favorable zone (efficiency of ۲۵–۳۳%) located at ۱۰۷۵–۱۱۰۰ °C and ۰.۰۰۱–۰.۰۰۵ s⁻¹. Microstructural validation confirmed these safe zones, while unstable regions were characterized by crack formation and deformation bands. A constitutive analysis yielded an apparent activation energy for hot deformation of ۵۷۲.۵ kJ/mol. The findings provide valuable guidance for optimizing hot working conditions of API X۷۰ steel.

Keywords:

API X۷۰ steel , Hot deformation , Processing map , Microstructure