Abstract: The martensite transform amounts during the quenching process of the medium and low carbon steel plates were predicted using extend volume method. Based on modified thermoelastic altering temperature martensite transformation kinetics， blockage function was introduced to describe the phase interfacial resistance of thermal hysteresis and martensitic transformation dynamic function was established to describe the relationship to its ideal free energy and blockage functions. On this basis， blockage enthalpy which defined in blockage function was introduced to characterize the enthalpy existed on blockage interface. Through the calculation of reversible elastic energy and irreversible work， the latent heat of the phase transformation was finally obtained according to the change of the Gibbs function and the model of the latent heat of phase transformation was established. The simulated results according to the model were in good agreement with the experimental results， which indicated that this model was suitable to use to simulate martensitic transformation during quenching process of medium and low carbon steel plates of moderate thickness.

Key words: medium and low carbon steel plate of moderate thickness, roll quenching machine, thermoelastic martensite, blockage function, latent heat of phase transformation