Studying the Effect of Ttempering Heat Treatment on the Corrosion Susceptibility of Carbon Steel Weld Zone

Due to the observation of numerous cases of coating failure in weld areas in some refineries in the country, the effect of heat treatment as one of the weld preparation processes before coating application was considered in this study. To investigate the effect of the type of preparation process, the samples were first subjected to five conditions: no preparation, sandblasting, sandblasting + Tempering heat treatment, Tempering heat treatment + sandblasting, and Tempering heat treatment in a ۱۰۰% humidity test for ۲۴ hours, and no significant difference was observed in the appearance of the samples in terms of corrosion. For a more detailed examination, metallography of the samples before and after heat treatment was performed using an optical microscope. Observations of the aforementioned images in the weld zone showed that the ferrite phase with a Widmann-Stätten structure containing needle-shaped ferrites and parallel pearlite plates transformed after heat treatment into a needle-shaped ferrite structure with larger grains and almost no intergranular pearlite plates. Using the scanning Kelvin probe technique, the small difference in potential difference between the weld zone and the base metal was investigated. To quantitatively investigate the corrosion properties, electrochemical impedance spectroscopy was used in a ۳% by weight sodium chloride solution at ۲۵°C for ۳ hours. It was found that after tempering heat treatment, the corrosion susceptibility in the joint area was eliminated and the corrosion behavior of this area became similar to that of the base metal. However, the corrosion rate of the weld area was still higher than that of the base metal. Finally, the Tafel polarization test in a ۳% sodium chloride solution at ۲۵°C after ۴ hours of immersion showed that the corrosion rate of the base metal was reduced by heat treatment and the corrosion rate in the interface and weld areas became almost uniform.

کلیدواژه ها:

Plain carbon steel - Weld corrosion behavior - Tempering heat treatment ، electrochemical evaluation ، فولاد ساده کربنی- رفتار خوردگی جوش- عملیات حرارتی بازپخت ، ارزیابی الکتروشیمیایی