This paper analyses solid-state decarburisation kinetics with the aim to clarify the transition rule of restrictive links in the process of decarburisation, providing a theoretical basis for regulating the solid-state-decarburisation rate. Experimental calculation of the Fe–Mn–C ternary alloy phase diagram using FactSage thermodynamic software, with medium manganese cast steel as the research object, experiments conducted at
and a total gas flow rate of 1500 mL·min−1.The results show that the increase in manganese content has little effect on the carbon equivalent of solid solution in the γ-phase. This is because the proportion of γ-phase in the manganese cast steel decreases as the manganese mass fraction increases, but the increase in the γ-phase-carbon mass fraction makes the change in the carbon equivalent of solid solution in the small manganese cast steel plate. At 950°C, the internal diffusion of carbon in a 1 mm manganese cast steel plate has an obvious limiting effect on the decarbonisation process. When the decarburisation temperature rises to 1090°C, the effect of carbon diffusion on the whole decarburisation process decreases. The limiting factors inhibiting the whole decarbonisation process are the surface chemical reaction, that is, the temporary surface chemical reaction, as well as the internal diffusion limit of solid carbon, which leads to cementite decomposition. In the entire process of solid decarbonisation, a higher manganese content is beneficial for improving the reaction rate because, at the temperature of this experiment, manganese carbide dissolved into solid carbon, thus reducing the restrictive effect of the cementite decomposition on the decarbonisation process.
