Corrosion investigation of the 18Ni 300 grade maraging steel in aqueous chloride medium containing H2S and CO2

The corrosion behavior of the 18Ni 300-grade maraging steel in 0.6 mol L⁻¹ NaCl solution, containing 1 mmol L⁻¹ H₂S, and saturated with CO₂, was investigated by measurement of the open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The maraging steel was solution-treated at 840 °C for 1 h and aged at 650 °C for 3 h. All corrosion electrochemical tests proved that the austenitic phase formed during the aging thermal treatment was detrimental to corrosion resistance of the 18Ni 300-grade maraging steel. The analysis of the XPS spectra suggested that FeCO₃, Fe₂O₃, FeS₂, FeSO₄, NiO, Ni(OH)₂, NiS, NiSO₄, MoO₂, MoO₃ and MoS₂ were the corrosion products deposited on the surface of both maraging steel samples after 29 days of immersion in the testing solution. Lastly, for industrial application requiring the corrosion resistance property of the 18Ni 300 grade maraging steel, it is recommended that it be thermal solution-treated before its use.