Article ID: ISIJINT-2025-167
To better understand the recovery and recrystallization behavior of lamellar pearlite, the microstructural evolution of eutectoid steel during annealing was analyzed using electron backscattered diffraction (EBSD) with wide-area coverage and high precision. The results were compared with those for hypoeutectoid steel. After cold-drawing and annealing at 973 K, eutectoid steel with fully lamellar pearlite exhibited locally distinct annealed microstructures, which were categorized into three stages based on the characteristics of ferrite matrix: (1) deformed microstructure with a continuous orientation gradient (deformed region), (2) sub-grain microstructure with ultrafine grains with low-angle misorientations (sub-grain region), and (3) recrystallized microstructure comprising fine grains primarily surrounded by high-angle grain boundaries (recrystallized region). In the deformed and sub-grain regions, cementite particles too fine to be analyzed by EBSD were densely distributed, while relatively coarse cementite particles were observed in the recrystallized region. These particles tended to localize at the ferrite grain boundaries in the sub-grain and recrystallized regions. Detailed EBSD analysis revealed the misorientation of ferrite grain boundaries increased continuously with the coarsening of cementite particles, regardless of their regions, suggesting a continuous recrystallization process. In contrast, hypoeutectoid steel, consisting of proeutectoid ferrite and pearlite, exhibited a discontinuous recrystallization process, where fully recrystallized grains predominantly formed in the proeutectoid ferrite and expanded into deformed pearlite. This difference in recrystallization mechanism resulted in faster softening in hypoeutectoid than eutectoid steel. The transition between continuous and discontinuous recrystallization and the discontinuous recrystallization mechanism were further discussed using Zener's pinning model, focusing on the influence of cementite particles.
