Accelerated electrochemical methods of testing austenitic corrosion resistant steels for resistance to intercrystallite corrosion

The purpose of research is to study and clarify accelerated electrochemical methods of testing austenitic corrosion-resistant steels for resistance to intergranular corrosion (IGC) and provide recommendations for their wide use. Methods. Comparative tests for resistance to IGC by long-time and accelerated methods were performed on samples of 03Cr18Ni11, 08Cr18Ni10Ti, 03Cr17Ni14Mo3 and 02Cr25Ni22Mo3 steels not susceptible to IGC and specimens with varying degrees of susceptibility to IGC. AMU and DU methods according to GOST 6032 were used as long-term methods and electrochemical methods according to GOST 9.914 and methods of electrolytic etching metallographic sections in a 10 % solution of oxalic acid (EOA) at anode current density of 1 A/cm2 for 1,5 minutes were used as accelerated methods. Additionally, electrochemical studies of steels were performed by constructing anode potentiodynamic curves (APC) and potentiostatic etching (PE) samples in a solution of perchloric acid and sodium chloride. The mechanism of corrosion at grain boundaries was studied by chemical analysis of test solutions for the content of ions of main alloying elements of steels and determination of dissolution rates of steels and artificial carbides in transient and transpassive regions of potentials. Microstructure of steels was studied by light microscopy after testing. Results. Results of comprehensive comparative tests of austenitic corrosion-resistant steels for resistance to IGC by long-term and accelerated electrochemical methods were obtained. Mechanisms of corrosion occurring at the boundaries of steel grains have been determined during testing by accelerated electrochemical methods and corresponding long-term methods according to GOST 6032. Scientific novelty. New quantitative criteria of satisfactory resistance of steels to ICC in testing by PE method were proposed. Practical relevance. It was recommended to use accelerated electrochemical PE and EOA methods in acceptance tests of steels for resistance to IGC in order to shorten the technological cycle and improve production efficiency.