This innovative molding process is characterized by using an expanded polystyrene(EPS) pattern in which a required amount of inoculant is directly embedded. An untreated melt was poured into this EPS pattern by the ordinary full mold process under reduced pressure. As a result, a sound inoculated iron castings were obtained and the usefulness of this method was proved. The mechanism by which the inoculant in the EPS reacts with the melt is complex. Because Ca contained in the inoculant reacts in a nonoxidizing atmosphere formed from the organic pattern, the inoculation effect of Ca is very efficient as compared with that by the usual process. As compared with the usual inoculation treatment, this “In-pattern Inoculation” process is excellent both economically and technically.

View full abstract

  Effects of heat treatment and copper contents on the fatigue strength of high aluminum zinc alloys cast into metallic mold were investigated using a uni-bending fatigue machine at the rotating speed of 1,800 rpm. Zn-28.2%Al-1.1%Cu-0.02%Mg alloy has the highest fatigue strength (13.5kgf/mm²) at 10⁷ cycles among the as-cast alloy castings tested. Addition of 9.4%Cu does not improve the fatigue strength of as-cast Zn-11.8%Al-1.0%Cu-0.02%Mg alloy. Heat treatment at 360 degC for 20h followed by air cooling results in about 20% improvement of fatigue strength of as-cast Zn-22.2%Al and Zn-28.2%Al-1.1%Cu-0.02%Mg alloys. However, heat treament at 360 degC for 20h followed by water quenching causes a decrease in fatigue strength by 30% of as-cast Zn-22.2%Al-alloys, resulting in the minimum fatigue strength among the alloys studied.

View full abstract

  The pressurizing mechanism of unbonded sand of the full mold process with reduced pressure was studied both theoretically and experimentally. Pressure distribution in sand was expressed theoretically by Jansen's equation in which the bulk density of sand and pressure coefficient evaluated from the experimentally obtained ratio of horizontal to vertical stresses were introduced. Some experiments were carried out with unbonded sand filled in a flask, 300mm square by 450mm deep, to verify the theoretical analysis. Surcharge of sand was effected by the use of either mold weights or reduced pressure, while pressure distribution was measured by pressure sensors installed at various. The theoretically predicted values agreed well with the experimental results. It was found that the pressure distribution changes remarkably with a change in the cross sectional area of the flask, due to the friction between sand and the flask wall.

View full abstract

  Austempered ductile iron (ADI) contains a great deal of retained austenite which contributes to an improvement of impact strength. It is also suspected that the retained austenite transforms to martensite with the propagation of fatigue crack, giving various influences on the fatigue properties of ADI. In the present study, ductile irons cast in sand or metal mold were austempered for various times at 400 degC or 380 degC, and some specimens were held at -196 degC for 30 min after the austempering. The rotate-bending fatigue test and fatigue propagation test using CT specimens were performed. Influences of the quantity and stability of the retained austenite upon the fatigue properties, such as fatigue limit and fatigue propagation rate, were discussed.
  The sand-cast ductile iron austempered for 20 min has the maximum content of the retained austenite. But, the retained austenite is less stable than that in the iron austempered for 180 min, because the carbon content of the former is less uniform. Therefore, the fatigue properties of the iron austempered for 180 min are better than those for 20 min. The retained austenite in the iron cast in metal mold is more stable than that in the iron cast sand mold, because it is finer and has more uniform high carbon content. Therefore, the fatigue properties are better than those of the iron cast in sand mold. Specimens, which were held at -196 degC to obtain martensite transformed from the retained austenite at low temperature, showed a high crack propagation rate. And iron austempered for longer time to eliminate retained austenite showed even higher crack propagation rate. It was found that the stable retained austenite helps to improve the fatigue properties of austempered ductile iron.

View full abstract

  Recently there has been an increasing use of liquidized gas in various industries, resulting in increases of the weight and wall thickness required for compressor casing, valve flange and other equipments for high pressure uses. A study was made to develop a new steel alloy for castings for such low-temperature services. Based upon the type SCS5 cast steel, the optimum chemistry was selected and the effect of heat treatment on notch impact properties was investigated. It was shown that toughness of the cast steel with the base composition of 12Cr-5Ni-0.5Mo was improved by increasing Ni and Mo content and by lowering C, Si, P and S. When this new alloy was normalized and tempered at around 600 degC, a superior low temperature toughness could be obtained. Toughness was further improved by adding a heating in the (α/γ) temperature range between the normalizing and tempering. It was shown that the low temperature toughness was dependent on hardness and the quantity of retained austenite. The newly developed steel possessed a good combination of tensile strength of more than 70 kgf/mm² and fracture toughness of more than 300 kgf⋅mm-3/2.

View full abstract

  Wear characteristics, microstructure and impact values of austempered ductile iron (ADI) containing chromium and vanadium were investigated. By the addition of Cr and V eutectic carbides appeared in the matrix and the number and area fraction of graphite nodules decreased. Retained austenite was increased remarkably by the addition of Cr and the bainitic structure became finer by the addition of V. Sliding were rate of the ADI containing Cr and V was very low as compared with unalloyed ones. This high wear resistance was supposed to be due to the reduced scratching and adhesive wear caused by hard carbides dispersed in the matrix. Abrasive wear resistance of the ADI containing Cr and V was also superior to FCD50, S53C and unalloyed ADI, but inferior to SKD11. The latter fact is considered to be caused by graphite nodules broken off in collision with abrasive particles. Impact values of the ADI containing Cr and V were 40 to 50 percent of those of the unallyed ones.

View full abstract