Modelling coarsening behaviour of TiC precipitates in high strength, low alloy steels

Abstract

Some of the most modern automotive sheet steels rely on a dispersion of fine precipitates based on TiC, generated during the major phase changes that occur as the rolled material is cooled to the coiling temperature. The coils themselves cool extremely slowly, thus leading to the coarsening of the precipitates and a loss of strength. Beginning with a calculation of the interfacial energy, the precipitate coarsening kinetics are modelled as a function of the stoichiometry of titanium and carbon. The purpose was to assess the influences of interface energy and Ti/C stoichiometry which limit the rate at which the dispersion coarsens by the diffusion of solute from the small to the larger particles. It is found that Ti/C ratio plays a critical role; a titanium concentration which is slightly less than required to combine with carbon leads to a dramatic reduction in the coarsening rate.

Keywords:

• HSLA steel
• TiC
• Ferrite
• Coarsening
• Multicomponent diffusion

We acknowledge Professor Chong Soo Lee for the provision of laboratory facilities at GIFT. This work was supported by the Steel Innovation Programme by POSCO and the World Class University programme (project no. R32-2008-000-10147-0) by the National Research Foundation of Korea.

Notes

* BCC and FCC stand for body centred cubic and face centred cubic respectively.