Evaluation of Mechanical Properties and Microstructures of Ultrafine Grain Low-Carbon Steel Processed by Cryorolling and Annealing
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In the present study, low-carbon steel was first evenly cryorolled by 50% reduction at liquid nitrogen temperature (LNT) and then annealed at 400–550 °C for 1800 s. A transmission electron microscope was employed to analyze the microstructures and the tangled dislocations in the processed steel. The presence of Fe3C particles in the steel was confirmed by X-ray diffraction method, and the mechanical properties were measured by an electronic universal tensile machine. It was found that cryorolling at LNT significantly improved the potentials of refined ferrite grains. Grain refinement at LNT occurred due to the suppression of dynamic recovery during cryorolling, thus resulting in high defect density and abundant nucleation sites for ferrite grains. An average ferrite grain size of 133 nm was observed in the specimen annealed at 450 °C for 1800 s, and its strength increased to 970.2 MPa with a reasonable ductility of 12.34%. The work extended the cryorolling from alloys and austenitic stainless steels to the low-carbon steels and provided a technical support for the fabrication of ultrafine grained low-carbon steel.
KeywordsUltrafine grain Cryorolling Annealing Martensite Mechanical property
The authors gratefully acknowledge the financial supports from The Major Projects of Technology Innovation of Hubei Province (2017AAA116), the National Natural Science Foundation of China (NSFC) (Nos. 51874216 and 51704217), and Hebei Joint Research Fund for Iron and Steel (E2018318013).
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