from the conferences organized by TANGER Ltd. provisional website
The heat treatment process of ductile iron involves two stages: austenitising at temperatures in the range of 850-950oC with the following austempering of alloy in the temperature range of 250-380oC. The resulting microstructure contains ferrite saturated with carbon in a matrix of reacted high-carbon austenite with spheroidal graphite typical of ductile iron. This microstructure confers high mechanical properties to the alloy. The microstructure and mechanical properties of ADI depend on the kinetics of phase transformations during austempering.The kinetic model of phase transformations occurring during austempering of undercooled austenite in ADI was developed. The model is based on Fick’s diffusion laws. The differential equations were solved by the Finite Difference Method (explicit scheme) under the boundary conditions adequate for the austempering temperature. In calculations, the effect of carbon content in austenite on its diffusion coefficient was considered. The developed model and computer program enabled tracing the process of ausferrite growth. Using the developed computer program, the effect of isothermal annealing temperature on the growth rate of ferritic phase was investigated.Keywords: Austempering, ADI, modelling of phase transformations
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