Modelling of Phase Transformations in Solid State and Dilatometric Curves Using Interpolation Methods to Determine CCT Diagrams

M. Kubiaka, W. Piekarskab, T. Domańskia, Z. Saternusa aDepartment of Mechanical Engineering and Computer Science, Czestochowa University of Technology, Dąbrowskiego 73, 42-201 Częstochowa, Poland bFaculty of Architecture, Civil Engineering and Applied Arts, University of Technology, Rolna 43, 40-555 Katowice, Poland

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This paper presents mathematical models for the determination of the kinetics of phase transformations in a solid state, volumetric fractions of structural constituents, as well as thermal and structural strain occurring during the cooling process of elements made of carbon steel. The kinetics of phase transformations in a solid state is determined using Johnson-Mehl-Avrami equations for diffusive transformations like ferrite, pearlite, and bainite, and Koistinen-Marburger for martensite transformation. The continuous cooling transformation diagram is determined using interpolation functions and experimental research. Experimental dilatometric analysis for chosen cooling rates is performed in order to define the start and final temperatures as well as start and final times of phase transformations. The increase model for thermal and structural strain is used for the cooling process. Methods of model tuning are used to define thermal expansion coefficients varying in temperature for each analysed phase.

DOI:10.12693/APhysPolA.142.184 topics: phase transformations, Johnson-Mehl-Avrami (JMA) model, Koistinen-Marburger (KM) model, continuous cooling transformation (CCT) diagram