2020 Volume 106 Issue 11 Pages 777-787
Important large components such as rotors for power generation steam turbines, pressure vessels and reaction vessels are manufactured by the ingot casting. However, it is difficult to manufacture the materials with sufficient properties due to macro-segregation of ingots.
For the purpose of developing effective and versatile macro-segregation countermeasures in the casting of large steel ingots for manufacturing large parts for power plants, the insert casting in vacuum atmosphere, in which a core material with the same composition as the base steel is placed at the center of the steel ingot, was studied. The effectiveness of the proposed insert casting as a macro-segregation countermeasure was verified in laboratory experiments. In addition, it has been clarified that good bonding between the core material and the base material can be realized even under conditions where bonding by normal insert casting in air atmosphere is difficult.
The smelting behavior of the core material and the solidification behavior of the molten steel in the experiments of macro-segregation reproduction casting and the insert casting were analyzed by the direct finite difference method. The mechanism by which this method suppresses the formation of macro-segregation and the solidification conditions for the suppression, the reasons and conditions for good bonding in this insert casting are clarified by the analyses.
Furthermore, in the experiments of insert casting, the cause of internal cracks generated in the solidified shell on the core material surface was considered, and guidelines for preventing the internal cracks were presented.
