Dicalcium silicate is one of the main mineral phases of steel slag. Ascribed to the characteristics of hydration and carbonation, the application of slag in cement production and carbon dioxide sequestration has been confirmed as feasible. In the current study, the precipitation process of the dicalcium silicate phase in steel slag was discussed. Meanwhile, the study put emphasis on the influence of different crystal forms of dicalcium silicate on the hydration activity and carbonation characteristics of steel slag. It indicates that most of the dicalcium silicate phase in steel slag is the γ phase with the weakest hydration activity. The hydration activity of γ-C2S is improved to a certain extent by means of mechanical, high temperature, and chemical activation. However, the carbonation activity of γ-C2S is about two times higher than that of β-C2S. Direct and indirect carbonation can effectively capture carbon dioxide. This paper also summarizes the research status of the application of steel slag in cement production and carbon dioxide sequestration. Further development of the potential of dicalcium silicate hydration activity and simplifying the carbonation process are important focuses for the future.

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Critical for flanging of square tributary junction on cylindrical steel tube is to determine the shape and sizes of pre-machined hole. In order to investigate precise shape and sizes of the pre-machined hole, an optimized design model is established. The forming process during flanging is simulated with the aid of FE-simulation software, and the target function for optimized design is calculated based on results of the simulations. In order to increase the convergence rate of the optimized design, a mathematical model of pre-machined hole for flanging on the tube is established based on isoline theory, the results are used as initial values for optimized design. To verify its accuracy the optimized design is carried out based on a typical flanging of square tributary junction on cylindrical steel tube. The results of the optimized design meet the technological requirements.

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