Study on the corrosion behavior of steel Q315NS heat-affected zone in a HCl solution using electrochemical noise

The microstructure and corrosion behavior of a base metal (BM) and heat-affected zone (HAZ) of Q315NS steel in 0.1 mol L−1 HCl solution at 60 °C were investigated with a thermal simulation technique, surface observation and electrochemical measurements. The transient characteristics, as well as the power spectral density (PSD) and wavelet transform, had been employed to analyze the electrochemical noise (EN) data. It was revealed that the microstructure of BM, the fine grained region (FGHAZ) and the inter critical region (ICHAZ) mainly consisted of ferrite and pearlite, while the coarse grained region (CGHAZ) mainly consisted of granular bainite. The corrosion processes of BM, FGHAZ and ICHAZ were similar and characterized by two stages. The first stage involved the metastable pitting process and the second stage corresponded to the pitting corrosion. On the CGHAZ electrode, metastable pitting occurred in the initial corrosion stage and then the corrosion process turned into uniform corrosion. With increasing corrosion time, the corrosion strength of all electrodes decreased significantly at first and then remained constant. The corrosion rate of CGHAZ was slightly lower than the other electrodes in the second corrosion stage, and there was no obvious difference in corrosion rate among BM, FGHAZ and ICHAZ.