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CORROSION RESISTANCE OF CEMENTING STEEL X19NiCrMo4 IN MEDIUM OF 5 % NaOH AND 5 % H2SO4

This paper presents the results of testing the corrosion behavior of X19NiCrMo4 cementing steel in 5 % NaOH and 5 % H2SO4 solution. Electrochemical measurements were performed by measuring the open circuit potential, determining the corrosion parameters using electrochemical impedance spectroscopy (EIS) and Tafel extrapolation. The corrosion rate, which was determined by Tafel extrapolation method, was lower in 5 % NaOH solution than that in 5 % H2SO4 solution. The obtained results were confirmed by the method of electrochemical impedance spectroscopy, which showed a higher value of charge transfer resistance of the tested steel in an alkaline medium, which proves higher corrosion resistance. Metallographic analysis were performed on a sample previously etched in nital and on a sample after polarization measurements. Images of the electrode surface after polarization measurements in 5 % H2SO4 medium showed a completely corroded steel surface indicating dissolution of the oxide layer due to acid exposure. No changes were observed on the sample surface in the alkaline medium.

cementing steel, corrosion rate, impedance, charge transfer resistance, microstructure

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