WC particles were inserted near the surface of gray irons. Particles of three different sizes were inserted individually or mixed with the particles of other alloy elements, The inserted layer was observed from the vertical section with an EPMA. It was confirmed that an inserted layer of about 4 mm thick can be formed without any defects near the surface of gray irons. The base metal of the inserted layer was usually the same as the mother gray iron. However, the Cr or Mo alloying favored the formation of white cast irons. Microstructures of the layer inserting coarse WC particles were different from that of the fine WC particles. The coarse WC particles were bridged by the γ + M₃C eutectic layers, however, fine WC particles dispersed uniformly in both eutectic phases. The hardness of the mother gray irons ranged from Hv120 to 200 while the hardness of the Cr alloying inserted layer increased more than Hv700.

View full abstract

  In squeeze castings, molten metal is forcibly fed for shrinkage. In this study, in order to find the most suitable squeeze timing, the outflow ability of the molten metal during solidification under pressure was investigated.
  The outflow ability of aluminum alloys was found to depend on the solid fractions and the species of the solid phase. For example, the outflow volume from pressurized molten metal was found to decrease with the increase of the solid fractions, after which the outflow volume becomes constant and small. At this inflection point, the solid fractions of Al-4% Si alloy with many primary dendrite crystals were smaller than that of the Al-8% Si alloy. This outflow ability of alloys which solidifiy into mushy state can be improved by grain refinement, because the outflow ability depends on the state of the solid phase in the molten metal.

View full abstract

  Effect of upset conditions on the friction welding characteristics of spheroidal graphite cast iron (FCD) to mild steel (S20C) were examined. Friction welding was carried out under various welding conditions of forge pressure and break timing. The dimensions of the test pieces were 15 mm in diameter and 70 mm in length, respectively.
  Micro and macroscopic observations were carried out to examine the changes in the area of the deformed layer of spheroidal graphite (DLSG). The tensile strength and forge length were also investigated.
  The area of DLSG, tensile strength, and forge length were found to be influenced by the forge pressure and break timing. The tensile strength was very high under the appropriate forge pressure and break timing.

View full abstract

  We examined the formation mechanism of chunky graphite generated in heavy section spheroidal graphite cast iron. Chunky graphite is generated according to Ce contents. Moreover, it is generated mainly at the eutectic cell boundary, suggesting chunky graphite is generated due to the concentration of Ce with the progress of eutectic solidification. In this study, the solidification conditions of heavy casting were reproduced by maintaining a small quantity of molten metal at the eutectic temperature for a long time. Next, the electronic diffraction image and microstructure of various graphites were examined by TEM. As a result, chunky graphite was found to generate according to the eutectic solidification time and increase in the Ce content. It was also confirmed that chunky graphite was formed by X=1-exp (-b⋅tⁿ) and generated by the growth of graphite with sufficient spherodizing ability in the direction where the basal plane expands predominantly.

View full abstract

  In order to establish the optimum system of hot return sand cooling in a fluidized bed with a water-cooled pipe, a mathematical model including heat transfer was constructed and numerical calculation was carried out. The present study especially aimed to clarify the effects of inlet sand temperature, water temperature, feed rate of hot sand, coolant air velocity and cooling water on sand cooling behavior. From the calculation, the heat transfer between hot sand and cooling water pipes was found to be the principal process. The control of temperature and feed rate of water is very important for ensuring reasonable sand cooling in addition to the control of convective heat transfer around the cooling pipe.

View full abstract

  In the control of green sand by oolitics, it is necessary to quantify oolitics accurately. For this, the quantity of quartz in green sand is quantified first, then oolitics is quantified after calibrating the base sand which is silica sand for calibration and for core used in green sand. However, since certain kinds of base sand are used in recent green sand, calibration and consequently the quantification of oolitics are not possible. The authors therefore developed a new method for quantifing oolitics. Feldspar and quartz are analyzed quantitavely at the same time by X-ray diffractometric analysis by reason of which base sand is quantitatively calibrated for the purpose of calibrating feldspar in silica sand. Quartz is calculated from the integrated intensity of the diffraction peak 20.9° and feldspar is calculated from the sum of each diffraction peak from 26.9° to 28.0°. The oolitics quantity in green sand can be calculated accurately by this method. The average value of oolitics in 67 different kinds of system sand was 6.9 mass% and the standard deflection was 3.7 mass%. The accurate quantification of oolitics enables control of green sand.

View full abstract