Modelling Grain Size Distributions during TMCR of Nb-microalloyed Steels

Models for recrystallisation and precipitat ion during hot deformation of HSLA steels, based on the original Dutta-Sellars approach, show good agreement with experimental data for co mpositions around 0.04 wt% Nb, strains around 0.3 and p rior austenite grain sizes up to 600 µm. The experimentally determined recrystallisation start and finish temperatures have been compared with predictions made with the original and a modified Dutta -Sellars model for ho mogenised and segregated samples. These modificat ions include the use of Thermo-Calc to predict the solute Nb content and prior austenite grain size d istributions, rather than an average prior austenite grain size, which have been shown to give consistently bette r predictions using literature data. The application of a Clyne-Kurz model has accounted for the amounts of solute-rich and solute-depleted material for steels with co mpositions solidify ing through the peritectic transformation.