DISSOLUTION BEHAVIOR OF NB-RICH PRECIPITATES DURING REHEATING OF MICROALLOYED STEEL HEAVY PLATES

Abstract

The effect of reheating temperature of slabs on the dissolution of precipitates and mechanical properties of Ti-Nb

microalloyed steel was investigated in pilot scale. Transmission electron microscopy indicated a significant decrease in the

presence of precipitates formed during the solidification of the steel as the reheating temperature increased from 1100°C to

1200°C. With further temperature increase up to 1280°C no significant changes in size and shape of the precipitates were

observed. Together with the precipitates dissolution behavior, an increase in strength was observed with the elevation of

the reheating temperature up to 1200°C, due in part to the reprecipitation of fine Nb-rich precipitates during hot rolling.

When reheating at 1200°C the presence of deformed ferrite on the microstructure contributed to the additional increase

in strength. After reheating above 1200°C up to 1280°C, a decrease in strength of the rolled plates was observed. This

effect has been credited to the absence of deformed ferrite grains and to a small increase in the low angle grain boundaries

size. The results were in agreement with Thermo-Calc and Dictra simulations.