This study aims to clarify the influence of loading speed on toughness in ferritic spheroidal graphite cast iron with various notches. The toughness was measured by means of the Charpy impact test and static bending test. The specimens used were impact and bending test specimens with various notches; un-notch (stress concentration factor:α= 1.0), U-notch with 2 mm depth and 0.5 mm root-radius (α= 3.0), U-notch with 2 mm depth and 0.15 mm root-radius (α=4.8), and fatigue-crack with 2 mm depth. The tests were performed at various loading speeds from 1.67×10^-5 m/s to 5.2 m/s in the temperature range from 123 K to 298 K. The results obtained are as follows:
  In the ductile region, the fracture energy at a higher loading speed is larger than that at a slower loading speed. The transition temperature region of the bending test is lower than that of impact test at any loading speed. Therefore, at the temperature of 223 K, every notched specimen shows that the fracture energy by the bending test is larger than that by the impact test, which is because every specimen of the im-pact test plunges into its transition temperature region at this temperature. Only a small difference is observed in the load-displacement curves of the specimen with a notch of α=4.8 and the specimen wi th fatigue-crack. The transition temperature of the specimen with fatigue-crack is very similar to those of the specimen with notch of α=4.8. The influence of external notches on toughness increases with increasing loading speed.

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  In order to clarify the effects of oxygen on graphitization in cast iron, various pig irons were melted in air and held for various duration under vacuum ranging from 1 Torr to 5 Torr at 1773 K to 1823 K. Molten iron was cast into green sand mould in air, and round bar specimens were made. Fractures and microstructures of round bar affected by oxygen were studied.
  The total oxygen and that dissolved in molten iron were measured. In the first stage of the decompression process, the dissolved oxygen content had a tendency to increase slightly, and decreased as low as 2 massppm afterwards. As the processing time increases, the flake graphite structure changed from type A (or type D plus chill structure) to an increase in the chill structure to inverse chill, and finally to the type D graphite structure (without chill). The molten iron of D which was held for 30 minutes under low pressure was added with 3% Fe-Si-Ca for inoculation. The graphite in irons spheroidized easily.

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  Various pig irons were melted in air and held for various duration in the vacuum state at 1773 K to 1823 K. The total oxygen and that dissolved were measured. Then the melt was treated by Fe-Mg-Si and Fe-Si-Ca alloy. After the nodularizing reaction, the melt was poured into green sand mould with a thickness of 2 mm, 6 mm, and 15 mm. The graphite nodule counts were measured and structures in the sections were observed. The relationship between the nodule count and oxygen content was studied. Two mm thick sections were made without chill structures because the removal of the oxygen corresponds to the oxygen content in melt. In order to obtain the maximum graphite nodule count in the 2 mm thick section, the optimal amount of Mg to be added exists.

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  A method for predicting porosity defects in spheroidal graphite (SG) iron castings with sand mold using critical stress values specific to melt was studied by comparing experimental results with stress distribution obtained by numerical stress analyses including mold strength effects. The elastic perfectly plastic volume pixel finite element method (VOXEL-FEM) was introduced to calculate stress distribution of the castings. The analysis considered elastic deformation of mold and contacts between the mold and casting. Young's modulus of the mold was estimated from the relation between mold elasticity and strength. Porosity volume in the calculation was defined as the volume of element where average stress exceeds the critical stress. As a result of comparing the calculated results with porosity observations under various mold strengths, the critical stress was estimated to be about 3.5 MPa, confirming that defective regions can be quantitatively predicted with this critical stress. Furthermore, the proposed method was applied to a casting with green sand mold. The calculated results showed that green sand mold has little influence on stress distribution and porosity volume of the casting as shown by experimental results.

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  The solidification sequences of three kinds of hypereutectic multi-component white cast irons with 4 to 5 mass% C were clarified for a basic study to apply them to a welding deposit material in the hard facing technique. To reveal the phases crystallized from liquid, quench tests during thermal analysis were Introduced into this experiment.
  In the case of Fe-5% (Cr, V, Mo, W, each)-4-5% C irons, four types of carbides, MC, M₂C, M₇C₃ and M₃C were found to exist in the matrix.
  In the iron with 4% C, MC carbide precipitates as a primary phase, and austenite as a quasi-primary phase. After the precipitation of the two different primary phases, L→γ+MC eutectic reaction takes place, followed by L→γ+M₇C₃ eutectic reaction. Next, L→γ+M₃C eutectic reaction continues and solidification completes with L→γ+M₂C eutectic reaction.
  The solidification sequence of the iron with 5% C is as follows : L₀→Primary MC+L₁, L₁→quasi-primary M₇C₃+L₂, L₂→(γ+M₇C₃) eutectic+L₃, L₃→(γ+M₃C)eutectic+L₄, and finally L₅→(γ+M₂C) eutectic.
  In the case of Fe-5% (Cr, V, each)-2% (Mo, W, each)-4% C iron, γ, MC, M₇C₃ and M₃C exist in the matrix. The following solidification sequence was revealed :
  L₀→Primary MC L₁, L₁→(γ+MC) utectic+L₂, L₂→(γ+M₇C₃) eutectic+L₃and finally L₃→ (γ+M₃C) eutectic.

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