Microstructure Evolution Mechanism of Ultrafine Grained Bar of 45 Steel Rolled by Severe Torsional Compression
ZHAO Jiahao1,2, PANG Yuhua1,2,*, SUN Qi1,2, NIU Ben1,2, LIU Dong3, ZHANG Zhe3
1 School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China 2 Metallurgical Engineering Technology Research Center of Shaanxi Province, Xi'an 710055, China 3 School of Materials, Northwestern Polytechnical University, Xi'an 710072, China
Abstract: Based on the self-developed severe torsional compression rolling method, taking 45 steel as the research object, the ultrafine-grained bar with a diameter of 25 mm was obtained by single pass rolling at 750 ℃ with a diameter reduction rate of 48%. The microstructure evolution and grain refinement mechanism were analyzed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and the mechanical properties were measured and analyzed. The results show thatthe degree of torsional compression in the center of the bar was slightly weaker than that of the edge, the grains were oriented along the axial direction and the grain size was refined to 2.3 μm. In contrast, the edge region experienced intense torsional compression, resulting in a uniform distribution of grain orientation and significant grain size refinement to 1.7 μm. The main refinement mechanism of grain:the transformation from austenite to ferrite induced by severe torsional compression deformation, as well as the occurrence of a sufficient continuous dynamic recovery and dynamic recrystallization process. After rolling, the yield strength, tensile strength and elongation of the steel bar were 402.5 MPa, 643.5 MPa and 25.7%, respectively, representing a 24%, 5.6%, and 14.7% increase compared to the pre-rolling values.
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2023, Vol. 37 
