In order to reveal the change and reason of microstructure and hardness of antimony micro-alloyed ferrite cryogenic steel during continuous cooling transformation, hot compression tests were conducted on a Gleeble 3800 thermal simulator and the dynamic continuous cooling transformation (CCT) curves of the experiment steel were determined based on the experiments. The microstructure and the Vickers hardness at different cooling rates was characterized by optical microscope and microhardness tester, respectively.The results show that when the cooling speed remains at 0.1 ℃ / s, the microscopic organization of experimental steel is composed of polygonal ferrite and beads; when the cooling speed is within 0.3 ℃-1 ℃ / s, the microstructure appears as polygonal ferrite, pearlosite and granular bainite; When the cooling speed is increased to 3 ℃/ s,-40 ℃/ s, the microstructure appears as polygonal ferrite and plated bainite. Due to fine grain and granular bainite strengthening, the hardness increases rapidly from 172.1HV to 207.7HV when the cooling rate is 0.1 ℃/s-1 ℃/s. Due to the refinement of the microstructure and the increase of the proportion of plated bainite, when the cooling rate is 3 ℃/s-40 ℃/s, the hardness increases linearly from 214.9 HV to 261.8 HV with the cooling rate. The suitable controlled cooling interval of Sb-alloyed ferritic cryogenic steel is 3 ℃/s-40 ℃/s.
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