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Characterization of a duplex stainless steel type saf 2205 heat treated at 475 °c using ultrasonic and electrochemical techniques

Abstract:

The present study aims to microstructurally characterize and evaluate the behavior of the longitudinal velocity acoustic variables and attenuation coefficient of samples from SAF 2205 duplex steel bars, after aging treatments at 475 °C. The corrosion resistance of the heat treated samples was evaluated and compared with the resistance of the steel without heat treatment. The study contemplated the microstructural analysis by optical and scanning electron microscopy and the ultrasonic evaluation at 3.5, 5, and 10 MHz frequencies. Finally, they were subjected to corrosion tests and evaluated again by conventional ultrasound using the pulse echo contact technique. The results of the ultrasonic evaluation show an increase in the longitudinal wave velocity as the treatment time increases. On the other hand, measurements of the attenuation coefficient are reported for each one of the evaluated samples, observing the effect of the microstructural changes that take place as a consequence of the thermal treatments. Regarding the accelerated corrosion tests, it was observed in the immersion tests that these generated damages in the microstructure of the samples, by causing pitting at the grain edges. The polarization curves obtained for all the samples under study, did not present a stable passivation zone. Presenting instability and noise range in the pseudo-passive area of the polarization curve, possibly due to selective corrosion in the microstructure of the material.