Due to their low ratio of cost versus performances, quenched and tempered (Q&T) high strength low
alloyed steels are widely used as tubular goods. For several decades, steel suppliers and academics
are investigating the mechanisms of sour corrosion of these materials. Several publications highlighted
the different parameters influencing the KISSC of Q&T high strength low alloyed steels like the prior
austenitic grain size, the dislocation density or the precipitation state. Niobium is known to have an
impact on these 3 parameters, but authors often looked at its impact separately. Additionally, complete
data relating the Niobium content and the KISSC are extremely rare in the open literature.
The present study focuses on the impact of Nb on the Prior Austenite Grain Size (PAGS) refinement for
several quenching and tempering cycles and additionally on the role of Nb on the critical stress intensity
factor for sulfide stress cracking (KISSC). A common Cr-Mo high strength OCTG steel alloyed with three
different Nb contents ranging from 300 to 1000 ppm is used. It was found that Nb addition allows the
use of higher strength material without compromising the resistance to crack propagation (KISSC). The
results are discussed in terms of microstructure, hydrogen pick-up and precipitation state.