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1 Zeszyty Naukowe. Mechanika / Politechnika Opolska

1 2005

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The EPR-test to characterize the senzitization behaviour of 02Cr21Ni33TiAl

Mikel P., Číhal V.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2005

z. 86

165-168

The Electrochemical potenciokinetic reactivation EPR (EPR) is nondestructive. No special sample preparation is required. It can be adapted to control various components during start-off or those already in service, especially the welded joints and surfaced components. The method is faster, more sensitive and more objective than the standard method, it can reliably determine the susceptibility to intergranular corrosion in heat-affected material and, as an added benefit, provide information on the overall corrosion resistance, and/or signal the danger of a selective, attack.. Criteria to assess the degree of susceptibility to intergranular corrosion using this method have not been unambiguously defined, and depend on the level of instrumentation. Measuring, of the current density peaks. - the critical passivating Jp and the reactivating Jr - and the values of the respective charges - the passivating Qp and the reactivating Qr. - is recommendable in addition to graphical plotting and observations of polarization curves at both the rising and decreasing potential. The influences of chemical analysis and sensitising are presented in terms of percent values expressing the reactivating/passivating charge ratio, or the so-called normalized reactivating charge. This method was used to measurement susceptibility to intergranular attack of the steel 02Cr21Ni33TiAl, probes from industrial oven working at 450 °C (probe A) to 650 °C (probe B) for 30.000 h. Referring to the Qr/Qp ratio, probe A exposed to a lower temperature, is highly sensitive, but probe B, exposed to higher temperature., is only slightly sensitive or insensitive, considering the fact that it is probably very heterogeneous due to considerable quantities of chromium carbides precipitated at the grain boundaries. Depletion in chromium at the grain boundaries at low temperatures, and equalisation of chromium content at the boundaries in the vicinity of carbides at higher temperature, were documented by the EPR test; these phenomena are also used to explain why probe A exhibited intergranular stress corrosion cracks.