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

Abstract

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°C to 700°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°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.

Comparison of Hot Ductility Behavior of microAlloyed Steels with Different B-, Cr-, Ni- and Ti-content

“…These results indicate an improved hot ductility behavior with the addition of the alloying elements mentioned, especially B and Ti, and the lower S content. Boron can move the ductility trough to lower temperatures by delaying austenite/ferrite transformation during cooling and improve ductility when it segregates to grain boundaries, repelling S and occupying vacancies [3,14,15]. However, the formation of BN at austenite grain boundaries can be a reason for crack initiation.…”

“…However, the formation of BN at austenite grain boundaries can be a reason for crack initiation. The titanium addition is thus also beneficial, since it can build TiN, which precipitate earlier and dispersively, leaving less N available for the formation of BN [3,14]. TiN can also be nucleation sites for other precipitates, reducing the pinning effect of precipitates at grain boundaries, thus improving ductility [14].…”

“…The titanium addition is thus also beneficial, since it can build TiN, which precipitate earlier and dispersively, leaving less N available for the formation of BN [3,14]. TiN can also be nucleation sites for other precipitates, reducing the pinning effect of precipitates at grain boundaries, thus improving ductility [14]. Furthermore, when the Ti/N ratio is high enough, as it is for the second steel, the ductility has been seen to be improved [16,17].…”

Hot Ductility, Homogeneity of the Composition, Structure, and Properties of High-Strength Microalloyed Steels: A Critical Review

“…More recent works have focused on studying the effect of co-microalloying with boron and titanium [91][92][93][94][95][96]. In the experiments, a cooling rate of 3 • C/s was used.…”

“…This was due to the inhibition of the formation of intergranular ferrite by the segregation of dissolved boron at the grain boundary, since titanium prevented the binding of boron to nitride due to the formation of TiN. Moreover, the addition of Ti reduces the amount of AlN and NbN [95,96]. It should be noted that, with an increase in the strain rate from 10 -4 to 10 -2 s -1 , a decrease in the amount of BN and TiN precipitates and an increase in their size was observed, which was accompanied by an improvement in hot ductility [96].…”