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Model for Strain-Induced Precipitation Kinetics in Microalloyed Steels
SEBASTIAN F. MEDINA, ALBERTO QUISPE, and MANUEL GOMEZ
Based on Dutta and Sellarss expression for the start of strain-induced precipitation in micro-alloyed steels, a new model has been constructed which takes into account the inuence of variables such as microalloying element percentages, strain, temperature, strain rate, and grain size. Although the equation given by these authors reproduces the typical C shape of the precipitation start time (Ps) curve well, the expression is not reliable for all cases. Recrystallizationprecipitationtimetemperature diagrams have been plotted thanks to a new experimental study carried out by means of hot torsion tests on approximately twenty microalloyed steels with dierent Nb, V, and Ti contents. Mathematical analysis of the results recommends the modication of some parameters such as the supersaturation ratio (Ks) and constant B, which is no longer a constant, but a function of Ks when the latter is calculated at the nose temperature (TN) of the Ps curve. The value of parameter B is deduced from the minimum point or nose of the Ps curve, where t0.05/T is equal to zero, and it can be demonstrated that B cannot be a constant. The new expressions for these parameters are derived from the latest studies undertaken by the authors and this work represents an attempt to improve the model. The expressions are now more consistent and predict the precipitationtimetemperature curves with remarkable accuracy. The model for strain-induced precipitation kinetics is completed by means of Avramis equation.
DOI: 10.1007/s11661-013-2068-1 The Minerals, Metals & Materials Society and ASM International 2013
I. INTRODUCTION
WHEN strain-induced precipitation starts in micro-alloyed steels, static recrystallization is inhibited for a certain time, normally until the end of precipitation, before proceeding until recrystallization is complete. It is well known that the static recrystallization of microalloyed steels is dierent before and after strain-induced precipitation. Before the precipitation, all the elements are in solution and recrystallization kinetics occurs in the same way as in low alloy steels, whereby the various alloying elements contribute to delaying recrystallization to a greater or lesser degree.[13] As the temperature drops, a critical temperature is reached, after which static recrystallization is momentarily inhibited by the eect of strain-induced precipitates. This momentary inhibition of recrystallization appears as a plateau...