One-dimensional solidification analyses of casting based on the relationship between the degree of undercooling and the increasing rate of solid fraction were carried out for cast iron and aluminum casting. Analytical solutions of the cooling curve showed that the degree of undercooling during solidification increased, with decreasing thickness of plate-type casting and the coefficient of undercooling for the increasing rate of solid fraction. By taking into account undercooling, it is possible to simulate the pattern of mushy-type solidification in which the surface and central part of the casting solidify almost at the same time, even for alloys with small solidification range. The difference in solidification time between the surface and center of casting for aluminum casting was smaller than that for cast iron. The solidification characteristics of aluminum casting were also more remarkable than those of cast iron. In cylindrical and spherical casting, the degree of undercooling near the completely solidified point was larger than that during solidification. The acceleration of the velocity of solid-liquid interface near the center of the casting was observed particularly in aluminum casting.
Residual stress in welded spheroidal graphite cast iron was measured by the inherent strain method. Spheroidal graphite cast iron plates, which are equivalent to JIS-FCD400 and FCD700, were welded using SUS309 stainless steel and carbon steel wires by the MIG bead-on-plate method. Distribution of residual stress through out the bead and substrate was estimated precisely using a small cut-off specimen by the inherent strain method. The residual stress distribution corresponded closely to the structure in the welded cast irons. The residual stresses in the welded bead and the heat-affected zone (HAZ) were tensile and compressive, respectively. On the other hand, the residual stress in the bead was compressive when welded using carbon steel wire. The compressive residual stress in HAZ was derived by the formation of martensite. The residual stress in the cast iron welded with carbon steel was released by annealing at 873K for 10.8ks, whereas the cast iron welded with SUS309 stainless steel remained as the residual stress caused by the difference in shrinkage between the SUS309 steel and cast iron after annealing at 873K for 10.8ks.
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.
Nirayama reverberatory furnace is located at lzunokuni-city of lzu-Peninsula, Shizuoka-Prefecture. Hagi reverberatory furnace exists at Hagi-city, Yamaguchi-Prefecture, but Nirayama's one is the only one architectures that could make cast iron cannon. There are still remained some unknown matters as follows ; (1) whether cast iron was really melted or not, (2) what kind of pig-iron was used, (3) whether blowing of bellows were utilized or not, (4) what kind of fuels were used, (5) where firebricks were made, etc. On this Nirayama reverberatory furnace, the possibility of casting of cannon with iron was investigated, with melting experiment from a foundry engineering standpoint. The followings are presumed from the investigation. Firstly, at least three cannons of cast iron were manufactured. Secondly, high Silicon contained pig-iron could not be available, so casting of iron cannon was not well done. Finally, the melting time by reverberatory furnace, from preheating to pouring completion, was about eight hours and melting temperature was above 1623K.