Abstract: Dilations of S34MnV steel during continuous cooling at different cooling rates were measured utilizing DIL-805ADT dynamic dilatometer. The transformation points of S34MnV steel, which are the austenitizing critical points Ac1 and Ac3, bainite transformation points Bs and Bf, martensitic transformation points Ms and Mf, were obtained under different heating and cooling speeds by the tangent method that fits the expansion curves before and after the transformation inflection point. The microstructure and phase of continuous cooling transformation of S34MnV steel were observed and analyzed by optical microscope(OM), scanning electron microscope(SEM), energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).The CCT curve of S34MnV steel was drawn according to the transformation time corresponding to these transformation points and the microstructure analysis. Meanwhile, a more accurate and practical Li model for low alloy steel is adopted in this paper to describe the diffusion transformation in the continuous cooling process. The ferrite, pearlite and bainite transformation described by the Li model, which was used to calculate the complex austenite decomposition reaction in the cooling process of heat treatment was modified by the CCT curve and the Koistinen-Marburger (K-M) equation of the martensitic transformation was fitted. The dynamic models of ferrite transformation, pearlite transformation, bainite transformation and martensite transformation in the continuous cooling transformation process of S34MnV steel were established comprehensively. The results of the experimental observation are consistent with the transformation calculated by the model, which could provide an accurate mathematical model for the numerical simulation of large marine crankshaft, and could be used to predict the phase transformation of S34MNV steel during the cooling process of heat treatment.
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2021, Vol. 35 
