Effects of the Primary NbC Elimination on the SSCC Resistance of a HSLA Steel for Oil Country Tubular Goods

Abstract

Sulfide stress corrosion cracking (SSCC) has been of particular concern in high strength low alloyed (HSLA) steels used in the oil industry, and the non-metallic inclusions are usually considered as a detrimental factor to the SSCC resistance. In the present work, continuous casting (CC) and electroslag remelting (ESR) were adopted to fabricate a 125 ksi grade steel in order to evaluate the effect of microstructure with and without primary NbC carbides (inclusions) on the SSCC resistance in the steel. It was found that ESR could remove the primary NbC carbides, and hence, slightly increase the strength without deteriorating the SSCC resistance. The elimination of primary NbC carbides caused two opposite effects on the SSCC resistance in the studied steel. On the one hand, the elimination of primary NbC carbides increased the dislocation density and the proportion of high angle boundaries (HABs), which was not good to the SSCC resistance. On the other hand, the elimination of primary NbC carbides also induced more uniform nanosized secondary NbC carbides formed during tempering, providing many irreversible hydrogen traps. These two opposite effects on SSCC resistance due to the elimination of primary NbC carbides were assumed to be offset, and thus, the SSCC resistance was not greatly improved using ESR.

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

“…The hardness indents were conducted ten times to obtain an average value. An SSC test was performed using the uniaxial constant load test with CORTEST (0-200,000 psi) proof-ring devices according to the NACE TM 0177-2005: Method A-uniaxial constant load test [19]. The specimens had a gauge length of 25.4 mm and a gauge diameter of 6.35 mm, which were carefully machined and ground in the gauge section to avoid overheating and cold working.…”

Effect of Cooling Rate on Sulfide Stress Cracking Resistance of a Q345 Pressure Vessel Steel Subject to Hydrogen Sulfide

“…The SSC resistance was evaluated using the uniaxial constant load test with CORTEST (0–200 000 psi) proof‐ring devices according to the NACE TM 0177‐2005 Method A. [ 16 ] All test specimens were cut from the center of hot‐rolled plates. The test specimen, with a 6.35 mm gauge diameter and a 25.4 mm gauge length, was machined and then ground carefully to avoid overheating and cold working in the gauge section.…”

Sulfide stress cracking (SSC) of a commercial Q345 pressure vessel steel in a wet H2S environment

“…The evolution of these microstructure characteristics affected by alloy compositions has a significant influence on the SSC behavior of the steel. 13,14 The Q345 steel currently used and studied had been usually optimised for its chemical compositions during steel production to improve the SSC resistance, but practical service experience has indicated that the Q345 pressure vessel steel in the wet H 2 S environments might experience SSC failure. To the best of our knowledge, no prior work has specifically studied the SSC of the Q345, and the details of the factors and mechanism influencing its SSC are not yet clarified.…”