Electrolytic iron and crystalline electrode graphite or non-graphitizing carbon materials (furnace and channel carbon blacks, furan resin carbon and saccharose carbon) with different facility of graphitization compared with electrode graphite, were subjected to carburizing treatment at 1573 K or 1873 K in a high frequency induction furnace in vacuum. The influences of various carbon materials on the properties of cast iron melt were investigated by examining the micro-structure and the average carbon contents of samples obtained. In the case of electrode graphite, although carburizing into solid iron was very difficult, the dispersion of graphite into liquid iron occured easily and thus the electrode graphite promoted the nucleation and growth of stable graphite-γ eutectic. In the case of non-graphitizing carbon materials, although carburizing into solid and liquid iron was easier with a decrease in the degree of graphitization, and the dispersion of carbon matelials into liquid iron were promoted with an increase in the degree of graphitization. The nucleation and growth of graphite-γ eutectic were more difficult with a decrease in the degree of graphitization, while those of the metastable cementite-γ eutectic were promoted. Though carbon content in the melts at 1873 K hardly changed for all carbon meterials, their behavior to the iron differed remarkably by the sort of carbon precursor and graphitization temperature of carbon materials. These facts indicate clearly that the properties of carburized melt (the state of the presence of carbon-microgroups) depend on the structural characteristics of carbon materials.

View full abstract

  As the result of a few examination about the joint strength of ferritic spheroidal graphite cast iron in insert-type electron beam welding, we found out that the mean hardness of fusion zone by 3 passes welding increased markedly in the case of SUS 304 insert (about Hv 618) compared with SUS 310 S insert (about Hv 152). Concerning the tensile strength of welded joint, SUS 310 S was superior in joint strength to SUS 304 and pure nickel. And especially in the case of SUS 310 S, about 100 % joint efficiency was obtained. As to the impact values of base metal and insert-type welds, higher toughness was shown in the case of base metal than insert-type welds in high temperature, but same tendency was shown for both base metal and insert-type welds in low temperature. As the result of the fatigue tests for both SUS 304 and SUS 310 S welded joints, generally base metal was fractured under repeated stress of 225∼350 MPa, while welds had sufficient fatigue strength. And the fatigue limit of 200 MPa was shown for both. Moreover, when the joint strength of SUS 304 welds using as-cast material was compared to that using annealed material, the static strength of annealed material was superior to that of as-cast material and, regarding dynamic strength, as-cast material showed superior joint performance.

View full abstract

  The fatigue strength, the microstructure in the fracture zone, and the fracture surface of Zn-4Al-0∼8Cu-0.02Mg alloys were studied.
  (1) The Cu addition increases the fatigue strength.  (2) The popular alloy for the mold, Zn-4Al-3Cu-0.02Mg, has the fatigue strength of 98 MPa at 1 × 10⁷ cycle.  (3) The crack propagates linearly through the grains.  (4) The quasi-striation patterns are observed at more than 1 × 10⁵ cycles. These patterns become finer at the higher cycles. The Cu additon also fines these patterns.

View full abstract

  A direct simulation method has been developed for the prediction of porosity. The model considers both hydrogen redistribution in melt and solidification contraction. Simulated results were compared with experiments for castings of AC4C (sand mold) and AC8C (metallic mold) alloys. Both the simulation and experimental results showed that regions solidified slowly have a higher amount of porosity. It was found that it is difficult to predict porosity by the temperature gradient method or G⋅t_f^1/2 method, because these methods do not consider the effect of hydrogen. Further, it was also found that calculated and experimental secondary arm spacings show a rather good agreement by taking the time from liquidus temperature to eutectic temperature as the local solidification time.

View full abstract

  Cast-in insert of flake graphite iron around mild steel pipe was made using thermal spraying of a Ni base self-fluxing alloy. The microstructure and basic properties of the bonded region were investigated, and practicalities and problems with this method were discussed. The experiments showed that the bonding in the cast-in insert was quite sensitive to the volume ratio of steel pipe and cast iron, pouring temperature, and other casting conditions; still thermal spraying greatly expanded the region where successful bonding was obtained. The microscopic observation showed that the bonding was metallurgically satisfactory and that there were a carburized layer on the steel pipe, a diffusion zone of sprayed alloy and rapidly solidified cast iron structure. Metal-carbon compounds and martensite formation were also observed in the diffusion zone. The strength of the bonded region was proved adequate by punching tests. Thus, thermal spraying was found effective in cast-in insert.

View full abstract

  Pulsed YAG laser was used for processing of silicon nitride ceramics. Analysis of surface layers of molten material remaining in plane making process was investigated by EPMA (Electron probe X-ray microanalyzer), ESCA (Electron spectroscopy for chemical analysis). The analyzed results indicate that the ejected molten material remaining around the processed region contains oxides of silicon, aluminum and yttrium, but is free from nitrogen. The oxide of silicon is produced by the following oxidation reaction : (1/3)Si₃N₄ + O₂ → SiO₂ + (2/3) N₂. The main source of O₂ in this reaction is atmospheric oxygen. The oxides of aluminum and yttrium added as sintering aids in silicon nitride ceramics are retained in the ejected molten materials.

View full abstract