The purpose of the present work has been to develope a high corrosion and wear resistant cast iron. This has been realized as a stainless spheroidal carbide cast iron.
  The typical chemical composition of the new cast iron, in which spheroidal carbides distribute in γ matrix, is Fe-3 % C-10 % V-18 % Cr-8 % Ni-1 % Mn. Corrosion tests, carried out in 1NHCl, HNO₃, H₂SO₄ at room temperature and in boiling 7N-H₂ SO₄, show that this cast iron has an excellent corrosion resistance which stands comparison with that of stainless steel. Further, wear resistance tests show that this cast iron has excellent wear resistance. These new cast irons have already been used practically in several cases where high corrosion and wear resistances are simultaneously needed, and the results have been confirmed to be highly satisfactory.

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  To improve of the surface hardness on Al alloy castings, the cast bonding of quench hardening steel insertion at near the surface on Al alloy castings was carried out by method used flux. The flux consists mostly of potassium fluo-aluminate, and was coated on steel insertion. By preheating at 473 K for 3.6 ks for dehydration, commercial base flux was possible to use on cast bonding. The condition on cast bonding of Al alloy and steel insertion was improved remarkably by using flux. On this method, the cast bonding used molten Al alloy containing Mg over 0.2 mass % was difficult because Mg reacts with flux to form a compound higher melting temperature. The hardness of quench hardening carbon steel (SK3, S45C) insertion decreased by temper softening with cast bonding, but then, these influence on alloy tool steel (SKD61) insertion with resistance of temper softening were nothing.

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  Abnormal graphite layers are often observed in the surface of spheroidal graphite iron castings pouring into the furan resin sand mold. The primary cause of the layer formation is considered to be the thermal decomposition of sulfuric gases from the binder and the sulfur diffusion in the iron melt. The alteration of cast iron structure from flake to spheroidal by the application of metal-mold interface reaction was considered by the author, changing the concept of suppressing the occurrence of abnormal graphite. Spheroidal graphite iron melt was poured into green sand mold with the cylindrical furan or phenol resin sand core containing commercial FeS powder. Flake and/or CV graphite layer formed by the contact with the core increased with the increase of the FeS content added to the core. The production of hybrid graphite iron castings with the graphite structure from flake to spheroidal can be expected by using this technique.

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  The internal structure of graphite in Ca treated SG iron, rare-earth treated SG iron, Mg-Ti treated CV iron and gray iron was studied by a high performance SEM with EDS. In each case, regardless of the graphite shape, sulfide inclusions containing fine oxide particles were found near the center of the graphite. These sulfide inclusions are considered to work as the heterogeneous nuclei for graphite. The graphite morphology is significantly dependent on the crystallographic features and the shape of sulfide as well as the attached inclusions such as TiCN.

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  CO₂ laser beam was applied to the cladding of hastelloy C on cast iron using a preplaced powder method. The hardness and microstructure of the clad layer were investigated by changing the laser power and number of clad layers. The average hardness of the clad layer obtained was 300∼350 HV0.1, when the conditions were as follows : laser power of 2300 W to 2700 W, clad number of one layer to two layers (thickness of clad layer ; 0.85∼1.90 mm), cladding speed of 400 mm/min, defocusing distance of 30 mm, oscillation width of 7 mm and argon as the shielding gas. The microstructure of clad layer was completely transformed into the fine dendritic structure (secondary dendrite arm spacing; 3μm) and eutectic structure by the rapid solidification. A heat affected zone was produced on the surface of the cast iron. The heat affected zone was heat treated with electric furnace at 873 K; the martensitic structure of the heat affected zone was transformed into pearlite. The hardness of the clad layer was unchanged with heat treatment. EPMA line analysis indicated that an alloyed layer (thickness ; 60μm) exists between the clad layer and base metal. These results show that CO₂ laser beam cladding of hastelloy C serves as a new surface treatment process for cast iron.

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  Cast-in insertion is an advanced technique for producing hybrid materials. The diameter of the cylindrical sand mold was changed in this experiment. Flake graphite cast iron melt with a chemical composition of 3.8%C and 2.0%Si was poured around a spheroidal graphite cast iron shaft which was cut from a continuous casting rod (JIS FCD 450). Better bonding conditions were investigated by thermal analysis, microscopic examination and EPMA analysis concerning the effects of the mold diameter, coolant shaft and run-off. The graphite structure of the interface changed from spheroidal, eutectic, rosette type to flake under the better bonding conditions.

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