Effect of Cooling Rate on Solidification and Segregation Characteristics of 904L Super Austenitic Stainless Steel

To study and understand the solidification behavior of super austenitic stainless steel under different cooling rates and segregation laws of alloying elements is of great significance to optimize the subsequent diffusion annealing homogenization treatment process and improve product quality. According to Thermo-Calc thermodynamic simulation results and combined with high temperature laser confocal scanning electron microscope (HT-CSLM), the tissue morphology of 904L super austenitic stainless steel was observed in-situ during solidification. The solidification path of the test steel was determined via calculation with the Scheil-Gulliver model. Microscopy techniques, including true color microscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron probe microanalyzer (EPMA) were used to analyze the influence of different cooling rates (6 ℃/min, 50 ℃/min, and 100 ℃/min) on the solidification structure and determine the main distribution law of alloying elements. This analysis determined that the solute distribution coefficient (K) of Cr, Mn, Mo, Cu, and Si elements is less than 1 during the solidification process, which means that they will accumulate in the liquid phase. Among them, elemental Mo segregation is the most severe, while elemental Ni hardly segregates. As the cooling rate increases, the crystallization temperature of the test steel decreases, and the secondary dendrite arm spacing λ2 decreases, the concentration of Mo in the residual liquid phase increases.