An impact fatigue test was carried out on spheroidal graphite cast iron using a Hopkinson bar type impact testing machine, which facilitates the measurement of the impact stress wave. The impact fatigue fracture mechanism of spheroidal graphite cast iron was also clarified. The results obtained ware as follows,
(1) When the applied stress exceeded the dynamic yield stress, the S-N diagram formed a curve which was affected by the stress duration time. The fracture surface was a mixture of cleavage fracture and ductile dimple destruction.
(2) When the applied stress was equal to the dynamic yield stress, the cleavage fracture surface rate was dependent on the fracture life (the generation stress), and was the lowest at 10-200 cycles.
(3) When the applied stress was below the dynamic yield stress, the S-N diagram formed a straight line, and no effects of the stress duration time were observed. The fracture surface was similar to the fatigue fracture surface, and the fatigue life was equivalent to the results of the axial load fatigue test.

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  The solidification sequences and the amounts of primary and eutectic carbides were investigated on hyper-eutectic high Cr-Nb-V cast irons containing 3.5 mass %, 4.7 mass % C, 15mass % Cr, 0∼10 mass % Nb and 0∼10 mass % V. Solidification proceeded in the order of primary MC, eutectic γ + MC, and eutectic γ + M₇C₃ in the lower C cast irons, while primary MC was followed by a peritectic reaction L + MC→M₇C₃ and a eutectic reaction L→γ + M₇C₃ in the high C irons. The peritectic M₇C₃ crystallized into a hexagonal columnar structure just like a primary M₇C₃. The total amount of carbides increased more or less linearly with the increase in the C content of iron. On the other hand, the amount of MC was increased with the increase in Nb and V contents and barely influenced by the C content. In the iron containing similar levels of Nb and V, Nb rich MC crystallized first and were surrounded by V rich MC which crystallized next.

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  Oxidation tests of multi-component white cast irons containing 0 % to 10 % mass % cobalt were carried out in air at temperature of 973 K to 1273 K for 36 ks. The mass gain was found to decrease with an increase in the cobalt content at the oxidation temperature of 1073 K and 1173 K. The effects of cobalt on the oxidation behavior at the oxidation temperatures of 1273 K were not revealed due to excessive mass gain. Breakaway oxidation occurs in cast irons containing cobalt and the start of this oxidation is delayed with the increase in the cobalt content. The oxidized layer was found to be separated into the outer and inner portions, and Fe₂O₃ and Fe₃O₄ oxides were identified in the outer layer. Cobalt was concentrated near the surface of the outer layer and at the boundary of the inner layer and cast iron. Observation of the growth of the oxidized layer using SEM, indicated that cobalt promotes the formation of a concentrated oxidized layer and works as a barrier against the diffusion of iron and other element ions from the cast iron to the oxidized layer.

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  The effects of water on the sand-erosive behavior of austempered ductile iron (ADI) were investigated. The amount of weight loss after the specimens were rotated in a mixture of sand and water was determined by wear tests. The effects of water were verified by tensile tests, hardness tests and scratch tests under damp conditions. The results obtained were as follows : Plastic deformation under damp conditions causes considerable embrittlment on ADI. The embrittlement behavior is considered to result from hydrogen embrittlement. The Hardness under damp conditions is higher than under dry conditions on a thin layer near the surface of ADI because embrittlement and hardening occur at the same time. Damping with water on the surface of ADI improves resistance to abrasive wear. Superior resistance to the sand-erosion of ADI results from strain-induced martensitic transformation of retained austenite and the self-hardening behavior by water.

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  The nuclei of spheroidal graphite (here after referred to as SG) was studied using FE-SEM and EDS. Many kinds of SG iron were prepared for the observation, namely, commercial grade Mg- and RE-treated SG iron, pure Fe-C SG iron, pure Fe-C-Ce SG iron and pure Fe-C-Si SG iron. The nuclei of graphite were mainly MgS, RES, FeCl, CaS and SiO₂, respectively. The shape of these nuclei was mainly spherical except for the nucleus of the pure Fe-C SG iron. Their diameter ranged from 0.1 to 1.0μm.
  These observations suggest no common factors in the chemical compositions of these nuclei. This means that the formation mechanism of SG is not based on the nuclei. One common factor was however the low sulfur activity in these irons. The interfacial energy theory for the formation of SG is thus supported and discussed in this paper.

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  The causes of blister defects often occurring in the paint coating of counterweight castings were investigated. Flake graphite near the casting surface oxidizes to form a tube while casting solidifies slowly. In the paint coating process, solvents sometimes permeate into the oxide tube intergranularly due to capillary attraction. Air in the oxide tube discharges though a part with casting defect such as sand or slag inclusion, resulting in blister defects. Vacuum assist sand mold castings, castings of mold dressed with iron oxide coating and spheroidal graphite castings were found to be appropriate alternatives to conventional seasoning.

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