2007 Volume 56 Issue 6 Pages 272-279
We examined the effects of temperature and Cr content on the active dissolution behavior of Fe-Cr alloys in a 500 mol·m−3(0.5 kmol·m−3) H2SO4 solution through immersion test and measurement of polarization curves. While the effect of temperature on the corrosion rates of Fe, Cr and Fe-Cr alloys can be approximated using the Arrhenius equation, the values of the apparent frequency factor A of Fe-Cr alloys in different temperature ranges were found to fall between the corresponding values of Fe and Cr, and the apparent activation energy E of the alloys, likewise, between the corresponding values of Fe and Cr. Roughly speaking, both A and E of the Fe-Cr alloys tended to decrease as Cr content or temperature increased. On the other hand, the effect of Cr content on the corrosion rates of Fe-Cr alloys was found to vary as Cr content changed, and the corrosion rates of the alloys drew closer to that of 100% Cr as the Cr content of the alloy increased. For example, the corrosion rate of the alloy increased exponentially as its Cr content increased from 10 to 50%, but the gradient of the curves, which represents the effects of Cr content on the corrosion rate, decreased as temperature increased. To enhance the efficiency of the pickling process in steel manufacturing, it is industrially very important to express the corrosion rate of Fe-Cr alloys in the form of a function of Cr content and temperature. We worked out such an experimental equation of the corrosion rate, and it proved to be effective in accurately estimating the corrosion rate of Fe-Cr alloys containing 10 to 50% Cr in an Ar-deaerated environment of a 500 mol·m−3(0.5 kmol·m−3) H2SO4 solution and in a temperature range of 298 to 353 K. We presume that the reason why the corrosion rate of Fe-Cr alloys increased as Cr content increased and Ecorr of the alloys became less noble is that, whereas the reaction rate of the active dissolution of a Fe-Cr alloy increases as the Cr content increases, the reaction rate of the reduction of H+ into H2 does not change significantly depending on Cr content.