Abstract
This paper describes the feasibility of using direct current electrical resistivity measurements to evaluate AISI 304 austenitic stainless steel sensitization. ASTM A262 – Practice A and double loop electrochemical potentiodynamic reactivation (DL-EPR) tests were performed to assess the degree of sensitization (DoS) qualitatively and quantitatively, and electrical resistivity (ER) was measured by the four-point direct-current potential drop method. The results indicate that the DoS increases rapidly while the ER decreases gradually in response to increasing sensitization. Thereafter, the two parameters tend to remain approximately constant. This behavior may be due to the rapid increase in the volume fraction of M23C6 precipitates over a sensitization time of 4 to 6 hours, thereafter remaining relatively constant. The ER results, which were corroborated by other techniques used in this study, confirm the promising potential of this property to monitor the sensitization phenomenon in AISI 304 steel.
Highlights
Austenitic stainless steels (ASS) are well known for their high corrosion resistance in various aggressive environments and for their good mechanical properties at high temperatures
Tests to check the structure according toASTMA262 – PracticeA were applied to classify the degree of sensitization (DoS) qualitatively, and the results of these tests were correlated with the values of the double loop electrochemical potentiodynamic reactivation (DL-EPR) and electrical resistivity (ER) parameters
The DoS increased in response to decreasing sensitization temperature, while the ER decreased in the range of 600 to 900 °C, probably due to the increase in the volume fraction of M23C6 precipitates
Summary
Austenitic stainless steels (ASS) are well known for their high corrosion resistance in various aggressive environments and for their good mechanical properties at high temperatures. These characteristics have led to their widespread industrial use, by the chemical and petrochemical industries, often under severe operating conditions. Electrical resistivity measurements can be used to assess ASS sensitization, since this property varies as a function of microstructural factors such as solute atoms, size and volume fraction of precipitates and dislocations, making it potentially interesting for monitoring components during service and/or machine downtime. This work involved an investigation of the sensitization of a commercial AISI 304 steel treated at various temperatures and for different times, based on electrical resistivity measurements. Chemical and electrochemical techniques were applied to obtain experimental measurements independent of the sensitization process, in order to validate the resistivity measurements
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