2004 Volume 44 Issue 4 Pages 710-716
It is necessary that the yield ratio (YR) of fire-resistant steel for construction is below 0.8. However, during the industrial production of fire-resistant steel, the rapid cooling rate of the laminar cooling configuration makes the ferrite grain become fine and increases the yield ratio (YR>0.8). In order to reduce the YR, by using Gleeble 1500 thermomechanical simulator the experiment of the effect of delay time after hot deformation on the grain size of ferrite was carried out. The results indicate that the hot deformation can increase the system free energy and the “ledges” generate at the grain boundary of deformed austenite, which leads to the increase of the ferrite nucleation rate and the refinement of ferrite grain. However, with the increase of delayed time, that the release of deformation energy and the reduction of “ledges” would decrease ferrite nucleation rate and increase the grain size of ferrite. Based on the experimental results, the technology to prolong the delay time after hot rolling is adopted in the industry production. The tested results indicate that the technology is effective to reduce the YR of fire-resistant steel and the YR decreases to 0.79 from initial 0.84.