Analysis of precipitation mechanisms in tempering of low-alloy steels using the kinetic theory of the overlapping transformations

Abstract

The kinetic theory of overlapping phase transformations is a valuable tool in the characterization of diffusion-controlled precipitation reactions. Using this approach, one can obtain the kinetic parameters (n, k) for simultaneous diffusion-controlled precipitation reactions, based on the knowledge of a specific macroscopic parameter, P(t), chosen to study the ongoing reaction. Both large and small process overlaps are considered. This methodology calculates the kinetic parameters for defined intervals of the fraction-transformed curve rather than for the entire curve. The approach used in this study permits an evaluation of which are the best protocols for the precipitate nucleation and growth rates during tempering reactions in low-alloy steel, whereas an analysis of the total combined transformations data set could lead to erroneous conclusions.

Keywords:

• diffusion-controlled precipitation
• low-alloy steel
• isothermal heat treatments
• phase transformation kinetics

Acknowledgements

The authors thank Dr M. Llanes for reading through the manuscript. They also thank the Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES) in Brazil for the financial support offered by the project CAPES-MES/Cuba No. 046/08.