Improved Model of Kinetics of Strain Induced Precipitation and Microstructure Evolution of Nb Microalloyed Steels during Multipass Rolling

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One of the main problems of empirical and semi-empirical models that are used to predict austenite microstructure evolution during hot rolling is their limited range of applicability regarding chemical compositions. This paper aims to improve a previous microstructural model paying special attention to the development of a more general equation for the prediction of the onset of strain induced precipitation in Nb microalloyed steels. This has been done with the help of new expressions describing the kinetics of strain induced precipitation as a function of the chemical composition. Moreover, the evolution of strain induced Nb precipitation was also modeled in order to determine the amount of Nb precipitated after each strain pass. The predictions obtained with the new model have been compared to results obtained in multipass laboratory tests using several Nb microalloyed steels. The model allows us to better understand the complex interactions occurring between Nb and microstructural softening depending on composition and process parameters.