Elucidating the warm deformation behavior of GCr15 bearing steel: Modeling and microstructure evolution

The warm compression behavior and microstructural evolution of GCr15 bearing steel were investigated by single-pass isothermal compression at 650-720 °C and strain rates of 0.01-10 s -1 . The flow curves showed strong temperature and strain-rate dependence: at 10 s -1 , the peak stress decreased from 370 MPa at 650 °C to 293 MPa at 720 °C, reflecting enhanced thermally activated softening. A peak-stress-based Arrhenius constitutive model was established with an apparent activation energy of 278.17 kJ mol -1 and a stress exponent of 6.34. The model accuracy was evaluated using AARE and RMSE, giving 7.53% and 18.13 MPa, respectively. A strain-compensated constitutive model was further developed by introducing strain-dependent material constants. Processing maps constructed at true strains of 0.1, 0.5, and 0.9 showed that the stable high-efficiency domain gradually evolved toward the intermediate-temperature and low-strain-rate region. SEM, EBSD, carbide morphology statistics, and hardness measurements revealed that low-temperature/high-strain-rate deformation produced elongated deformation bands, high local misorientation, and incomplete carbide spheroidization, whereas low-strain-rate deformation promoted dynamic recovery, recrystallization-like low-strain regions, and carbide spheroidization. The 680 °C/0.01 s -1 condition exhibited the highest spheroidization index and a relatively low aspect ratio while maintaining moderate hardness. Although 720 °C/0.01 s -1 showed the highest GOS < 2° area fraction, it caused carbide coarsening and significant hardness reduction. Unlike previous studies focusing mainly on constitutive behavior or microstructural observation alone, this work directly correlates strain-dependent constitutive response, processing-map stability, carbide spheroidization, EBSD-derived GOS/KAM indicators, and hardness. The optimum warm-compression window was identified as 665-685 °C and 0.01-0.02 s -1 .