Electrochemical and Corrosion Properties of Hydrogenated 45 and 12KH18N10T Steels

We study the influence of the conditions of electrolytic hydrogenation of steels on their electrochemical and corrosion properties in a hydrogen galvanic couple (HGC) formed by the hydrogenated and nonhydrogenated metals depending on their structure and the pH value of the medium. On the basis of the polarization characteristics and corrosion mass losses of the hydrogenated 45 steel, we estimate the correlation between the parallel reactions of oxidation of hydrogen and iron in the HGC. Immediately after hydrogenation, the current of the HGC is limited by a flow of diffusion-mobile hydrogen desorbed from steel, and the fraction of the reaction of oxidation of iron constitutes about 20% of the total current. Under these conditions, the corrosion rate of the hydrogenated steel is 20–30 times higher than for the nonhydrogenated steel. In the course of time, both the total current and the current of oxidation of iron become weaker but the role of the latter increases. As compared with the HGC of pearlitic steel, the HGC of martensitic 45 steel absorbs smaller amounts of hydrogen and, therefore, is characterized by lower currents but longer periods of functioning. The decrease in the pH value of the medium decreases the electromotive force and the initial current of the HGC of 45 steel, which leads to the deterioration of the protective properties of surface oxide films. Hydrogen absorbed by 12Kh18N10T stainless steel intensifies its general corrosion in the HGC and makes it susceptible to pitting corrosion. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 4, pp. 66–76, July–August, 2005.