Effect of Ultrasonic-Assisted Casting on Hot Deformation Mechanism and Microstructure of 35CrMo Steel Ingot

Hot compression tests were performed with strain rates (0.01-10 s(-1)) and temperatures (850-1150 degrees C). The power law relationship between the critical stress and critical strain and Zener-Hollomon parameters was determined by theta-sigma curves. Microstructure was investigated by electron backscattered diffraction. The results showed that the flow behavior and microstructure of 35CrMo steel was affected by ultrasonic-assisted casting. The activation energy of non-ultrasonic and ultrasonic-assisted 35CrMo steel were 410 +/- 9.9 and 386 +/- 9.4 kJ/mol, respectively, and the activation energy of ultrasonic-assisted specimens was reduced by 6%. In addition, the ultrasonic-assisted treatment refines the grains to some extent and makes the softening process of ultrasonic-assisted samples progress faster, which promoted the development of dynamic recrystallization and the production of sigma 3 boundaries. The discontinuous dynamic recrystallization was the main DRX nucleation mechanism of the 35CrMo steel.