Abstract
A medium-carbon Cr–Mo–V martensitic steel was thermally processed by quenching (Q) at 890 °C and tempering (T) at increasing temperatures from 650 °C to 720 °C and the effect of tempering temperature, Tt, on sulfide stress cracking (SSC) behaviors was estimated mainly via double cantilever beam (DCB) and electrochemical hydrogen permeation (EHP) tests and microstructure characterization. The results indicate that the threshold stress intensity factor for SSC, KISSC, increased with increasing Tt. The overall and local H concentration around the inclusions decreased with increasing Tt, due to reductions in the amounts of solute atoms, grain boundaries and dislocations, which effectively prevented SSC initiation. Also, increasing Tt caused an increased fraction of high-angle boundaries, which evidently lowered the SSC propagation rate by more frequently diverting the propagating direction and accordingly restricted SSC propagation. The overall SSC resistance of this Q&T–treated steel was therefore significantly enhanced.
Highlights
Quenching and tempering (Q&T)–treated martensitic steels have long been widely used for important oil country tubular goods production, such as C90–C110 or higher grades for sour oil/gas well service [1,2], T125 and V150 grades for ultra-deep oil/gas well service [3,4,5] and 155 ksi or higher grades for perforation and drill services [6]
The mechanical properties of each Q&T–treated sample are summarized in Table 1, indicating that the yield strength (YS), tensile strength (TS) and hardness (HRC) decreased, while the elongation (EL)
The 28CrMo48VTiB martensitic steel used for this work was melted in an electric furnace, 177.8 × 10.36 mm
Summary
Quenching and tempering (Q&T)–treated martensitic steels have long been widely used for important oil country tubular goods production, such as C90–C110 or higher grades for sour oil/gas well service [1,2], T125 and V150 grades for ultra-deep oil/gas well service [3,4,5] and 155 ksi or higher grades for perforation and drill services [6]. SSC/HIC behaviors and to achieve the desired combination of high strength, high toughness and superior SSC/HIC resistance in these steels by optimizing the alloying design, metallurgical quality and Q&T parameters Among these efforts, the correlations between various metallurgical factors and the susceptibility to SSC/HIC have recently received increasing attention [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. After the H atoms enter the material, these metallurgical factors might have their respective impacts on H mobility or diffusion [10], by acting as reversible (solute atoms, dislocations, grain boundaries, etc.) or irreversible (nonmetallic inclusions, precipitated particles, voids, etc.) traps for H atoms, depending on their binding enthalpies with H [12]
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