Oomputer Model for Prediction of Carbonitride Precipitation during Hot Working in Nb-Ti Bearing HSLA Steels

Abstract

Acomputer model which predicts complex precipitation behavior quantitatively in Nb-Ti bearing steel has been developed on a theoretical basis. Thesolubility and composition of the complex precipitates, and the chemical driving force of the precipitates from supersaturated austenite are estimated by meansof thermodynamicanalysis of regular solution composedof four-binary compounds.Thechangein dislocation density which acts as a nucleation site during hot working is calculated by using dislocation theory. And the time dependenceof volume fraction and the particle radius of strain induced precipitation are also predicted on the basis of classical nulceation theory. In order to estimate the effect of deformation on nucleation, the change in elastic energy of dislocation with nucleation is calculated. Experimental results showedthat combination of Nb and Ti addition, decreased the solubility of carbonitrides and accelerated the precipitation rate from supersaturated austenite becauseof the formation of complex precipitates. Suchexperimental results are in goodagreementwith the prediction by the present model. And both the acceleration of precipitation rate and the refinement of precipitates particles due to hot deformation are a]so quantitatively explained. © 1992, The Iron and Steel Institute of Japan. All rights reserved.