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A model to simulate the kinetics of formation of strain-induced martensite ( α ′ ) in austenitic stainless steel (SS) 304 is derived. The model predicts sigmoidal behaviour of the γ → α ′ transformation. The model was successfully applied to various levels of α ′ obtained after cold-rolling of type 304 SS and to many previously reported experimental data set with the volume fraction of α ′ as high as 1.0. This model was compared with two other sigmoidal models and it was shown that the fitting parameters for the proposed model can be correlated to physical parameters associated with γ → α ′ transformation. The fitting parameters of the model consist of the saturated level of α ′ for a given condition, the strain value associated with the maximum rate of γ → α ′ transformation, and a parameter that characterises the rate of γ → α ′ transformation. [ABSTRACT FROM AUTHOR]

The article presents the study which presents a mathematical model to predict the kinetics of austenite decomposition in Nb-microalloyed steel once it undergoes hot strip rolling. The modelling includes the use of Avrami type equation, wherein the time constant b was expressed as a function of parameters A and B. Prediction of B was derived from an artificial neural network (ANN). It concludes that early site saturation, with diffusion as the operating mechanism, governs the transformation.

The influence of hydrogen pressure on the kinetics of hydrogen-induced direct and reversed diffusive phase transformations in a Nd15Fe77B8 alloy has been investigated. It was shown that increase (decrease) of hydrogen pressure provokes a marked acceleration of both the direct and reversed-phase transformations. [Copyright &y& Elsevier]

The transformation rate of the chains in amorphous sulphur doped with 0.43, 0.86 and 1.28% at. P was examined by calorimetric method at 298 K. The samples were remelted at Tf=443 K. For description of the results the equation X=1−exp[−( kt)z] was used ( X — transformation degree, t — time, k and z — constants). The admixtures of phosphorus inhibit the transformation strongly. The constants k and z are less smaller for the samples S+P than for pure sulphur. Samples S+1.28% at. P were examined in the range of the temperatures from 203 to 308 K. The activation energy is equal to E=86.6 kJ mol−1 with standard error SE=12.0 kJ −1. The effect of the admixture of phosphorus on the kinetics of the nucleation and the growth of the nuclei was discussed. [ABSTRACT FROM AUTHOR]

In this paper, we present a kinetic investigation of the polymorphic transformation γ → α of sorbitol under milling in the objective to identify the microscopic mechanisms that govern this type of solid-state transformation. The milling was performed with a high energy planetary mill and the milled material was analysed by DSC, PXRD and Raman spectrometry. The transformation kinetics was found to be sigmoidal with a noticeable incubation time. Moreover, this incubation time was shown to shorten rapidly when seeding the initial form γ with the final form α. The origin of the incubation period and its evolution upon seeding are puzzling as polymorphic transformations induced by milling are not expected to occur through a nucleation and growth process. To explain these puzzling kinetic features, we propose a two-step transformation mechanism involving local amorphisations due to the mechanical impacts, immediately followed by rapid recrystallizations of the amorphized fractions. The key point of the mechanism is that recrystallizations are oriented towards the forms γ or α, depending on the crystalline form of neighbouring crystallites. This mechanism has been validated by numerical simulations which were able to reproduce all the experimental kinetic features of the polymorphic transformation (kinetic law and effects of seeding) upon milling. [ABSTRACT FROM AUTHOR]