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

Abstract

Hot compression tests were performed with strain rates (0.01–10 s−1) and temperatures (850–1150 °C). The power law relationship between the critical stress and critical strain and Zener–Hollomon parameters was determined by θ-σ 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 Σ3 boundaries. The discontinuous dynamic recrystallization was the main DRX nucleation mechanism of the 35CrMo steel.

Thermal Deformation Characteristics and Dynamic Recrystallization Mechanism of Incoloy 800H Alloy under Different Deformations

“…∑3 n ( n = 1, 2, 3) boundary, as a special grain boundary, can improve the mechanical properties of the alloy and has a significant effect on the microstructure of the material. [ 18 ] Furthermore, research has found that annealing twins can reduce the grain boundary energy and increase the grain boundary migration ability, playing a crucial role in the DRX process. In contrast, thermal processing promotes the interaction and regeneration between ∑3 and its variants (∑9 and ∑27).…”

“…[15,17] CDRX mainly occurs inside the grain, continuously absorbing dislocations through progressive rotation of subgrains to increase the misorientation at subgrain boundaries, thereby forming DRX grains. [18,19] In the study of DRX, Zhang et al [20] studied the thermal deformation behavior of HIPed FGH96 superalloy and found that DDRX is the main nucleation mechanism and CDRX is the auxiliary mechanism in the DRX process. Wang et al [21] investigated the DRX mechanism of Inconel 740 superalloy and noted that DDRX and CDRX occur simultaneously during thermal deformation, while CDRX behavior is not active.…”