抄録
Recently, the permanent mold process has been employed for producing iron castings on a large scale because of its economic and technical advantages. The short service life of the cast iron molds, however, hinders the development of the process. In general, the same kind of material is used in iron castings as in metal mold material. This prevents cracks in the castings due to differences of expansion and contraction coefficients between the metal mold and the castings during solidification and cooling. However, the cast iron metal molds are themselves destroyed by cracks which are caused by thermal effects. Diffusion impregnating is one means of preventing destruction of the metal mold. The author discovered that cast iron siliconized by the powder method using Fe-Si-Cr alloy with high purity did not have such defects as rough surface and a porous layer: a layer obtained by using Fe-Si-Cr alloy powder containing 20-30% Si and 30-40% Cr and by heating at 1, 100° in H2 for 4-10 hours had about 9% Si and about 2% Cr, and 30-80 microns in thickness. Chromium in the alloy powder reduces the diffusion rate of silicon in the Fe-Si layer. The applicability of the siliconized cast iron as a new metal mold material was studied by examining oxidation and thermal shock resistances, thermal stability, microhardness at elevated temperatures etc. The siliconized cast iron is superior as a new metal mold material and siliconizing extends not only mold life but also durability of errosion-resistant coatings on the mold. It is expected that the siliconized metal mold contributes greatly to the further development of the casting iron by metal mold.
