Multipreci model

The recurrence of nitrogen in solid solution in steels implies that the precipitation kinetics of the carbonitrides that form from the metallic elements in solid solution be understood and modelled. One of the main difficulties of this task is the accounting of tri-atomic particles having a variable C7N ratio. This paper proposes a simple and fost computer model that treats the precipitation of the vanadium carbonitride V(C,N). This case is chosen here to exemplify the principles a new version of the Multipreci model which is designed to be valid for M(C,N)-type precipitates, M=V, Nb orTi. 

The generic case of vanadium precipitation in a model Fe-V-C-N steel is used here to exemplify the approach used in the Multipreci model. The steel has the following composition (Table 1) ... 

In the Multipreci model, we treat the nucleation stage at each time step as follows a new class is introduced in flie histogram of size of radius / and composition according to Equations (9) and (12). The number of precipitates N of size R" is given by the classical non stationary nucleation rate equation ... 

The Multipreci model is applied here to isothermal treatments of the model alloy presented above. The entry data of the model are summarised in Tableau 3 ... 

In order to monitor the mechanical properties in relation to the microstructure, the knowledge of the precipitation state at the end of a thermo-mechanical treatment is of prime importance. In this purpose, Arcelor develops models that allow for the prediction of the influence of the process parameters on the state of precipitation. The model Multipreci, developed at IRSID is one of them. It (Hedicts the precipitation kinetics of mono- and di-atomic particles in ferrite and austenite as a function of the time-temperature history. It is based on the classical theories for diffusive phase transformation and treats simultaneously the nucleation, growth and ripening phenomena. The state of precipitation that is predicted includes the particle size distribution, their number and volume fraction. From these values, the effect of the precipitates on the mechanical properties can be calculated. 

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