Boronizing in the fluidized bed was performed on the surface treatment of austenitic spheroidal graphite cast iron. Tests were carried out on the hardness, microscopy. X-ray diffractometry, electron microprobe X-ray analysis, glow discharge spectrometry, friction and wear characteristic, and the corrosion behaviors in boronized specimens. As a result, the boride layer in the austenitic spheroidal graphite cast iron produced by fluidized bed was 1400 HK in hardness and consisted of two intermetaltic compounds (FeB, Fe₂B), The enrichment of Si and Ni excluded from the horonized compound was detected like the stripe. The boride layer more improved friction properties and the wear resistance of austenitic spheroidal graphite cast iron than those of SUS304 and Al₂O₃. The corrosion resistance against 0.1 N HCl and 0.1 N H₂SO₄ of the boronized specimen was more improved compared to untreated specimens. It was found that the boronizing method in fluidized bed could be successfully applied to the surface treatment of austenitic spheroidal graphite cast iron.

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  The effects of alloying elements on the solidification process of high carbon high speed steel type alloy were investigated by using a series of hypo-eutectic alloys of Fe-2% C-5% Cr-5% Mo-5.5% V-0/5% W-0/5% Co-0/5% Ni and a hyper-eutectic Fe-2.3% C-5% Cr-5% Mo-9% V-5% W-5% Co alloy. The solidification process of each alloy was investigated by thermal analysis and quenching experiments. In each hypo-eutectic alloy, crystallization proceeds in the order of primary γ, γ + MC eutectic, γ + M₂C eutectic, while the primary MC instead of γ crystallizes in the hyper-eutectic alloy. The amount and distribution of each carbide are explained with the phase diagram and the redistribution of alloying elements during solidification. The hardness of quenched alloy was maximum at an austenitizing temperature between 1273 K and 1373 K since the hardness depends on both the amount and hardness of martensite, that is the carbon content of austenite. Each alloy was found to exhibit a temper hardening, Co in particular enhanced the hardness when the alloy was tempered at around 823K.

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  A compact method for testing the thermal fatigue resistance of cast irons has been developed, where an emphasis is put on the evaluation of materials for the automobile exhaust manifold. The testing procedure using a newly fabricated tester is explained. Thermal fatigue tests were carried out in a temperature range between 373K and 1173K for several cast irons and steels. It was found that thermal fatigue lives obtained by the present method show good agreements with those obtained by conventional methods. Thermal fatigue fracture behavior in two cast irons is also reported.

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  CO₂ laser beam was applied to the cladding of stellite on cast iron by using beam scanner. The hardness and microstructure of clad layer were investigated by changing the laser power and number of clad layer. The average hardness of clad layer obtained was 480∼510 HV 0.1, when the conditions were laser power from 2200 W to 2600 W, clad number from one layer to four layers (thickness of clad layer ; 0.9∼4.7mm), cladding speed of 400mm/min, defocusing distance of 30mm, oscillated width of 7mm and argon as the shielding gas. The microstructure of clad layer was completely transformed into a fine dendritic structure (secondary dendrite arm spacing; 5.0μm) and eutectic carbide by the rapid solidification conditions. The remelted zone was produced on the surface of cast iron (base metal) and a primary dendrite and ledebulite could be observed. EPMA line analysis indicated that alloyed layer (thickness ; 150∼200 μm) existed between clad layer and base metal. These results show that CO₂ laser beam cladding serves as a new surface treatment process for cast iron in foundry industries.

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  The structure of spheroidal graphite in an magnesium treated spheroidal graphite cast iron was studied by a combined use of the high performance microscopic instruments : SEM with EDS, EPMA, AES and TEM. A spherical sulfide (Mg, Ca) S of about 1μm diameter is found near the center of graphite spheroids and is regarded as a nucleus for the graphite. A spherical MgO of about 0.2 μm diameter is found in the sulfide and is speculated to be a nucleus for the sulfide.

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  Test procedure for evaluating internal shrinkage tendency, excluding liquid state and external shrinkage, is investigated. The gate thickness of plate castings has been changed in order to vary the order of solidification time among plate, gate and riser. The optimum gate thickness has been decided so as to keep the gate in molten state while the riser feeds only liquid shrinkage of the plate and also to minimize external shrinkage of the plate. Thus internal shrinkage of the plate is properly evaluated by X-ray photography. Using these test castings, effects of carbon content of the melt and green sand mold strength on the shrinkage tendency have been studied. Additionally, comparison of the shrinkage tendency between green sand mold and metal-back shell mold, and spheroidal and flake graphite cast iron have been made. It was revealed that spheroidal graphite cast iron shrinks in a later stage of its solidification while flake graphite cast iron expands in the whole duration of its solidification.

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