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.
Highlights
35CrMo alloy steel is extensively used in the manufacture of important structural components, such as main bearing rotating shafts, vehicle and engine transmission parts and heavy load transmission shafts that work in load environments, because of the excellent impact toughness, high static strength, good hardenability and high fatigue limit [1,2,3,4].many casting defects such as blowholes, inclusions, composition segregation and coarse grains often occur in the process of non-ultrasonic casting, which seriously affect the subsequent forging and properties
Some thick columnar and equi-axed grains were found in the central region of the ingot, owing to the dendritic branches of columnar grains being broken and drifting to the center to become the nucleus of the remaining metal liquid, which formed coarse equi-axed grains at the center
Small equiaxed grains were found in the central region, which indicates that introducing ultrasonic waves can effectively improve the grain uniformity of 35CrMo steel ingot
Summary
Shi et al [8,9] showed that the introduction of ultrasonic wave in the casting process of 35CrMo steel makes the microstructure change from coarse dendrites to fine dendrites or equi-axed grains and more pronounced grain refinement observed with increasing ultrasonic power. Introduced ultrasonic waves into the casting process of AZ91 magnesium alloy and found that fine and uniform non-dendritic structure was obtained under the action of ultrasonic cavitation and flow, and the material exhibited strong yield strength. Shi et al [11] revealed that the uniform and fine with weakened texture and well-distributed precipitates microstructure obtained by introducing an ultrasonic energy field into the two-roll casting process of 8011 aluminum alloy effectively improves the tensile and yield strength. The influences of microstructures introduced after ultrasonicassisted casting on high temperature deformation behavior of alloy steels, especially the work hardening properties and microstructure evolution, have not been reported. EBSD was used to analyze the evolution of deformed microstructure, the characteristics of grain boundary and misorientation angle and the characterization of DRX in detail
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