Influence of Deformation on Stability of TiC Precipitates in .ALPHA.-Fe.

Abstract

To investigate the influence of deformation on the stability of TiC precipitates in the α-Fe region, the temperature of precipitation treatment and the strain rate of deformation prior to final soaking at 773 K were changed with an Fe-0.05mass%Ti-0.002mass%C alloy. Precipitation treatment at 973 K for a short time generated very fine TiC particles (average radius: 2 nm) which were presumed to be coherent or semi-coherent because of a strong strain contrast in TEM images. Deformation with a high strain rate (1226 s-1) just after precipitation treatment of 973 K for a short time resulted in a distinct increase in the solute C content, suggesting that some of the coherent TiC precipitates had dissolved. The elastic interaction between the coherent TiC particles and a high density of dislocation induced by the high strain rate deformation is considered to be the most conceivable explanation of several mechanisms including the temperature increase due to deformation and binding between dislocations and C at grain boundaries. Based on the micromechanics of an anisotropic and inhomogeneous system, the interaction energy was calculated from a simple case consisting of an isolated coherent TiC particle and a straight-edge dislocation. The calculation of the change in total free energy supported the possibility of TiC dissolution due to the elastic interaction between coherent TiC precipitates and a high density of dislocations induced by the high strain rate deformation.