A Microstructural Study of the Sulfide Stress Cracking Resistance of a Cr-Mo-V-B Steel

A study was conducted to determine the effect of microstructure and strength level on the sulfide stress cracking (SSC) performance of a Cr-Mo-V-B steel. The steel was heat treated by quenching and tempering in a temperature range of 1100 to 1325 F (593 to 718 C). Crack initiation and propagation behaviors were examined using three-point bending tests. The experimental results showed that an increase in tempering temperature was associated with an increase in crack initiation time, indicating an increase in SSC resistance. The increased tempering temperature also changed the crack propagation path from a mixture of transgranular and intergranular to primarily transgranular cracking. Crack initiation and propagation were shown to be associated with decohesion and/or microvoid formation at car-bide/matrix and inclusion/matrix interfaces. Differences in the SSC resistance were correlated with the morphology of carbide particles.