Estudo de Corrosão do Aço Maraging 300 em Meio de Cloreto contendo H2S e CO2

CO2 corrosion and H2S corrosion are two ofthe biggest problem in oil field extraction, since carbon steel has low corrosion resistance to both chemicals[1,2]. So, achallenger is to find alloys materials that can replace carbon steel in such corrosive environment. Maraging steels can be this alternative, because they present better corrosion resistance than carbon steel. Thus, the corrosion behaviour of 18Ni 300-grade maraging steel in a 0.6 mol L-1NaCl solution containing H2S 1 mmol L-1and saturated CO2 was investigated by open circuit potential monitoring, potentiodynamic polarization and electrochemical impedance techniques. For comparison purpose, a sample of 1020 carbon steel was submitted to the same corrosion tests. Two maraging steel samples were assayed: one solution-treated at 840 °C for 1 h and the other aged at 650 for 3h. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) allowed to observe the corroded surface morphology, to identify the corrosion products deposited on steel surfaceand to characterize formation of the austenite phase in theaged sample, respectively. The corrosion electrochemical tests proved that the austenite phaseformed during the aging thermal treatment was deleterious to corrosion resistance of the maraging steel. In addition, both investigated maraging steel samples presented higher corrosion resistance than carbonsteel. XPS spectraand allowed to identify FeCO3, Fe2O3, Fe(SO4) and Fe(SO4)3, NiO, Ni(OH)2, NiS, NiSO4, MoO2, MoO3 and MoS2 as the corrosion products deposited on maraging steel surface after the electrochemical corrosion tests. Lastly, the electrochemical results proved that the margin steel, even when submitted to a thermal treatment, has potential be an alternative to replace the carbon steel.