Abstract
In this paper, the DL EPR method (electrochemical potentiokinetic reactivation with double loop) was modified and used to study the susceptibility to intergranular corrosion and stress corrosion cracking of a stainless steel type X5CrNi18-10. The tests were performed in a special electrochemical cell, with the electrolyte in the gel form. Modified DL EPR method is characterized by simple and high accuracy measurements as well as repeatability of the test results. The indicator of susceptibility to intergranular corrosion (Qr/Qp)GBA obtained by modified DL EPR method is in a very good agreement with the same indicator obtained by standard DL EPR method. The modified DL EPR method is quantitative and highly selective method. Small differences in the susceptibility of the stainless steel type CrNi18-10 to intergranular corrosion and stress corrosion cracking can be determined. Test results can be obtained in a short time. The cost of tests performed by modified DL EPR method is much lower than the cost of tests by conventional chemical methods. Modified DL EPR method can be applied in the field on the stainless steels constructions.
Highlights
During cooling or heating of stainless steels type CrNi18-10 in the temperature range from 420 °C to 820 °C, chromium rich carbides, mainly M23C6 can be precipitated on grain boundaries [1,2,3]
If the chromium content in these regions is less than the content that is necessary for maintaining the protective passive film in a given corrosive environment, the regions nearly to the grain boundaries become prone to intergranular corrosion [4,5,6,7,8,9]
Very low value of (Qr/Qp)GBA for the non-sensitized sample indicates that the stainless steel X5CrNi18-10, which was not heat-treated, is not susceptible to intergranular corrosion
Summary
During cooling or heating of stainless steels type CrNi18-10 in the temperature range from 420 °C to 820 °C, chromium rich carbides, mainly M23C6 can be precipitated on grain boundaries [1,2,3]. If the chromium content in these regions is less than the content that is necessary for maintaining the protective passive film in a given corrosive environment, the regions nearly to the grain boundaries become prone to intergranular corrosion [4,5,6,7,8,9] This is a result of slow diffusion of chromium in the austenite in the specified temperature. Susceptibility to intergranular corrosion is most common in welded joints of stainless steels, in the heataffected zone, which is parallel to the weld, or during annealing to reduce residual stresses [4,5,6]
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