MEASUREMENT AND MODELING OF THE EFFECTS OF PRECIPITATION ON RECRYSTALLIZATION UNDER MULTIPASS DEFORMATION CONDITIONS

The effects of precipitation on austenite recrystallization during the multipass deformation of Nb-containing HSLA steels were investigated under continuous cooling conditions. For this purpose, the processing temperature at which recrystallization is no longer complete (the T(nr)) was first determined from rolling simulations. The changes in the size distributions of the freshly precipitated particles were then followed by transmission electron microscopy. Models were also developed for predicting the precipitation start and finish temperatures, T(Ps), and T(Pf), during continuous cooling. The present results indicate that the recrystallization behavior of steels can be divided into three distinct regions: (i) when the interpass time t(I) is short and the cooling rate PSI is rapid, the rate of recrystallization is solute-controlled and the T(nr) decreases when t(I) is increased or PSI decreased; (ii) when t(I) and PSI adopt intermediate values, precipitation is rate-limiting and the T(nr) increases with increasing t(I) or decreasing PSI; (iii) finally, when t(I) is relatively long and PSI relatively slow, particle coarsening weakens the effect of the precipitates so that the T(nr) tends to decrease again.