An Investigation of Microstructure Characteristic and Sulfide Stress Cracking Behavior of 110 ksi Cr-Mo Grade Casing Steel

Abstract

The sulfide stress cracking (SSC) behavior of three micro-alloying 110 ksi grade Cr-Mo casing steels were evaluated according to the A-Method tensile test specified in the NACE TM0177 standard (NACE A-method). The fractures of SSC specimens and the micro-structures of the casing steels were characterized by scanning electron microscopy (SEM) with electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM) in the BF and STEM mode. The results show that on the premise of 110 ksi, the yield strength of Co-Mo steel was satisfactory, finer spherical carbides increased the number of irreversible traps; widened polygonised martensitic laths, lowered dislocation density, and lowered the proportion of high-angle grain boundaries and the Σ3 boundaries decreased hydrogen permeability and diffusivity. The SSC resistance of Co-Mo steel with above micro structure characteristics was enhanced.

Simultaneous Enhancement of Strength and Sulfide Stress Cracking Resistance of Hot-Rolled Pressure Vessel Steel Q345 via a Quenching and Tempering Treatment

“…The usual viewpoint on the SSC of steel is that hydrogen penetration can happen under the condition of the release of hydrogen. It is well known that the SSC mechanism is attributed to the susceptibility of the hydrogen embrittlement (HE) [24][25][26][27][28][29], which could also be substantiated by the evidence revealed in the present work shown in Figure 4, where Figure 4a shows blisters of hydrogen on the outside surface in the cracked specimen, Figure 4b shows secondary cracks on the fracture surface in a cracked specimen, and Figure 4c shows the predominant quasi-cleavage characteristic on the fracture surface in a cracked specimen. Therefore, the SSC failure of the present experimental steel agreed with the hypothesis on the embrittling contribution by hydrogen, i.e., decided by the hydrogen permeation-controlled mechanism [24][25][26][27][28][29].…”