Effect of Cooling Rate on Pitting Corrosion Behavior of 904L Austenitic Stainless Steel in a Simulated Flue Gas Desulfurization Solution

다국어 초록 (Multilingual Abstract)

904L super austenitic stainless steel is prone to harmful secondary phase precipitation, which reduces corrosion resistance.
The cooling rate during the solidification of steel is one of the critical factors affecting the precipitation of brittle phases instainless steel metals. In this paper, the effect of the cooling rates (6, 50, 100, 500, and 1000 °C min−1) on the initial corrosionbehavior of 904L steel in a simulated flue gas desulfurization (FGD) solution was studied by electrochemical measurementsand microscopic morphology observation. The results show that as the cooling rates increases, the primary solidification temperatureand the secondary dendrite arm spacing decrease. The precipitated phase in the steel is a σ-phase mainly distributedinterdendrites and forms zones of chromium and molybdenum depletion, reducing pitting resistance. With the increase in thecooling rate, the corrosion resistance increases first and then decreases, and reaches the maximum at 100 °C min−1. At thesame time, different cooling rates result in different contents of Cr and Mo in σ phase. At 100 °C min−1, the concentrationgradient of Cr and Mo near the interdendrites is the lowest compared with other cooling rates, which inhibits the growthrate of the σ phase nuclei and produces a more uniform microstructure. Corrosion test results show that pitting corrosion issensitive to the increase in the contents of Cr and Mo in the σ phase. The higher the content of Cr and Mo in the σ phase, themore serious the depletion of Cr and Mo near the interdendrites, and the worse the corrosion resistance.