Evaluation of sulfide stress corrosion cracking resistance of supermartensitic stainless steel UNS S41426: comparison between forged and hot rolled tube
Ilson Palmieri Baptista, André Rocha Pimenta, Javier Alejandro Carreno Velasco, Maria Vittoria Moraschini Reis, Rejane Therencio Batista, Sérgio Souto Maior TavaresPurpose
This research aims to evaluate how manufacturing processes influence stress-corrosion cracking in two supermartensitic stainless steels (SMSSs) classified as UNS S41426. The samples were manufactured by forging and hot rolling process.
Design/methodology/approach
The microstructures of both materials were investigated by light optical microscopy, scanning electron microscopy, electron backscattered scanning diffraction, X-ray diffraction and magnetic measurements. Stress corrosion cracking was investigated using slow strain rate testing (SSRT). In the SSRT tests, two solutions were employed, both containing 200 g/L of NaCl at ppH2S 0.5 psi and a total pressure of 14.5 psi, at room temperature. The solutions were distinguished by the carbonate concentration and the pH level, 5.0 and 5.5.
Findings
The grain size of the forged sample is coarser than that of the hot rolled (HR). The microstructure of the 1'forged had more reverse austenite than the hot-rolled one, and this austenite forms fresh martensite during deformations of SSRT. In solution at pH 5.0, the more aggressive one, both materials exhibit brittle behavior with quasi-cleavage features and intergranular cracks near the exposed surface, and small dimples in the central part of the specimen. However, for the solution at pH 5.5, the less aggressive one, the forged piece presents a similar fracture, while the HR piece shows a ductile fracture.
Originality/value
Such a comparison of the behavior of forged and HR SMSSs with respect to the susceptibility to sulfide stress corrosion cracking, supported by microstructural analysis, has never been published. The value of this study lies in the fact that not only the UNS designation number, but also the processing route, must be taken into account to select the material for harsh environmental conditions found in deep-water oil reservoirs.