Effect of Boron and Titanium Addition on the Hot Ductility of Low-Carbon Nb-Containing Steel

The effect of boron and titanium addition on the hot ductility of Nb-containing steel was investigated using hot tensile tests. The fracture surface and the quenched longitudinal microstructure were examined by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that both steel samples had the similar change from 1,100 degrees C to 700 degrees C. The hot ductility of Nb-containing steel with boron and titanium addition was higher than the steel without boron and titanium in the temperature range of 900-750 degrees C. Because the formation of intergranular ferrite was inhibited by solute boron segregating on the grain boundary, the formation of TiN changed the distribution of Nb- and boron-containing precipitates and improved the amount of intragranular ferrite.