2006 Volume 78 Issue 1 Pages 14-20
The semi-solid process for cast iron using a cooling slope was investigated. Significant improvements were seen in structural refinement and globularity of the primary austenite size compared with mechanical stirring. However, casting defects such as gas entrapment occurred due to the high viscosity of the slurry. A new semi-solid process combining a cooling slope and pressurization was developed to solve the problem of the casting defects caused by gas entrapment. In this process, molten cast iron is poured using a cooling slope on to a metal die between the liquidus and solidus temperatures, followed by pressurization. The defects reduced, the microstructure was refined, and the mechanical properties improved. The following merits were also seen ; The heat treatment time reduced apparently due to the promotion the decomposition of ledeburite and the precipitation of graphite by the refinement of the microstructure. Filling ability at the edge of die also improved and net-shape forming could be achieved by this process. The hardness increased from the center to the edge of the pressurized sample, indicating that the material may have developed on inclination fanction.
