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Owing to their excellent properties, duplex stainless steels (DSSs) may be selected for the H2S environment. Operational limits are not defined and depend on fabrication processes. In this work, the susceptibilities of two DSSs 2205 to sulfide stress corrosion (SSC) in saline solutions with three pH levels were investigated. The difference between materials is the fabrication route: hot rolled (HR) tubes and powder metallurgy with compacting and sintering final operations by hot isostatic pressing (PM‐HIP). The susceptibility parameters were evaluated by slow strain rate tensile tests (SSRT). Both materials suffered embrittlement in solutions with pH 3.5 and 4.5, but the susceptibility was slightly better in the HR. In the solution with pH 5.5, the HR fractured with ductile behavior, while the PM‐HIP was brittle. The better resistance of HR to SSC can be explained by microstructural features, such as the lower grain size and austenite island interspace. [ABSTRACT FROM AUTHOR]

The 9%Ni low-carbon steel is applied to utilities and processes at temperatures as low as − 196 °C. However, the microstructural features play an important role on the mechanical properties. Notably, the cryogenic toughness and mechanical strength are strongly dependent on the final heat treatment. In this paper, the microstructure of a 9%Ni low-carbon steel was modified by different heat treatments. The hardness and cryogenic toughness were measured and correlated to microstructural features. The material shows a temper embrittlement with intergranular cracking and minimum cryogenic toughness after tempering around 400 °C. Austempering at 480 °C also produced very low toughness results. On the other hand, excellent cryogenic toughness was obtained with single tempering at 600 °C after quenching or normalizing. Even higher toughness was obtained with the double tempering at 670 °C/2 h plus 600 °C/2 h. The amount of reversed austenite and its morphology in the specimen quenched and tempered at 600 °C were shown in the paper. [ABSTRACT FROM AUTHOR]

Alloy 904L (UNS N08904) is a superaustenitc stainless steel with high Cr and Mo additions. The steel also contains high nickel content, which is important to maintain the austenitic structure. Because of its high corrosion resistance, Type 904L alloy is being used in much equipment in chemical and petrochemical plants. Some of this equipment may experience high temperatures in service or during fabrication. The microstructural changes associated with exposures in the range of 650°C to 850°C or as a consequence of melting were analyzed in this paper. The microstructure / corrosion resistance relationships were studied by means of electrochemical pitting corrosion tests and microstructural analysis. Critical pitting temperatures (CPT) of annealed and cast specimens were determined and compared. The results show that the corrosion resistance can vary significantly with fabrication processes and/or service at high temperatures. [ABSTRACT FROM AUTHOR]

Some precipitation reactions of superduplex stainless steels (SDSS) can improve hardness, yield, and ultimate strength, but with substantial decrease of corrosion resistance. One of these reactions is the spinodal decomposition of ferrite into Cr-rich fine precipitates (α′) and Cr-depleted matrix during low temperature aging. In this work, the effect of the α′ precipitation on the pitting corrosion resistance was investigated. The results showed that short duration heat treatments at 475 °C do not decrease the pitting corrosion resistance, but increase the hardness of UNS S32750 and S32760 SDSS. The limits of heat treatment duration for both steels were determined. [ABSTRACT FROM AUTHOR]

The usage of superduplex stainless steels in offshore petroleum production has increased considerably in the last years. Particularly, the use as flowline pipes for oil production needs careful research on the effect of critical environmental conditions on the stress corrosion resistance of welded joints. In this work, welded joints of UNS $32750 were produced by automatic gas tungsten arc welding (GTAW-orbital) using a J-groove weld geometry. The welded joints were evaluated using slow strain rate tensile tests in acid solutions containing hydrogen sulfide (H2S) and chloride. H2S partial pressure and pH were varied to determine safe operating conditions. Specimens tested at pH = 3.5 and p(H2S) = 3.75 and 6. 75 showed brittle behavior. The specimens tested with lower p(H2S) or higher pH exhibited ductile behavior. [ABSTRACT FROM AUTHOR]