The purpose of this study is to clarify the influence of Mo and austenitizing temperature to the heat treatment aracteristics, using five (5) kinds of low alloyed ductile cast irons containing 0-2mass% of Mo. The specimens were austenitized at 1223K-900s and 1323K-900s, and the range of cooling time from Ac₃ to 773K was approximately 3-4000s. Each transformation regions of ferrite, pearlite, bainite and martensite existed in CCT diagrams for ductile cast iron use. And almost the same tendency at the austenitizing temperature of 1223K and 1323K was recognized. The ferritic and pearlitic transformation region in the CCT diagram shifted to a longer cooling time side with increasing Mo content because of the impurity solute drag effect of Mo. The bainitic transformation region existed even at a longer cooling time side in CCT diagrams in case of adding Mo. Ms temperature of low alloyed ductile cast iron was not influenced by Mo. With increase in austenitizing temperature, the ferritic transformation region in the CCT diagram shifted a little bit to the longer cooling time side, while the perlitic transformation region shifted to shorter cooling time side. It is considerable that it caused by increasing the amount of C in the austenite with rising austenitizing temperature. The bainitic transformation region was not influenced by austenitizing temperature. Ms temperature shifted slightly to the lower temperature by increasing the amount of C in the austenite with rising austenitizing temperature. For the both austenitizing temperature of 1223K and 1323K, the quenching hardness of 0Mo cast iron was 600 ～ 630HV10, and that of 2Mo cast iron was 700HV10. It is thought that the difference between these hardness is based on the increase in the amount of Mo carbide. When Mo was separately added to the low alloyed ductile cast iron, the influence of Mo on hardenability was little, and its influence of austenitizing temperature was also little.

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  Austempered ductile iron (ADI) possesses superior strength with good ductility, and is used for many applications requiring wear resistance. However, ADI has been found to suffer from so-called water embrittlement effect, which causes marked decrease in tensile strength and elongation in ADI in contact with water compared to ADI under dry conditions. This water embrittlement effect occurs in ADI but not ferrite matrix. This paper intends to provide a possible solution to the water embrittlement effect of ADI by means of producing a mixed microstructure of ausferrite and fine ferrite grains, which can be obtained by controlling austenitizing and austempering temperatures. ADI specimens with this kind of microstructure were found to have a superior resistance against water-embrittlement effect compared to ordinary ADI specimens. Mechanical properties in wet condition were assessed with tensile specimens whose surfaces were wrapped with wet tissue paper. The results showed that specimens whose microstructure contains fine ferrite grains exhibited superior resistance against water-embrittlement effect. However, specimens containing such high strength structure as martensite showed marked water embrittlement effect. These experimental results indicate that the stress-induced transformation of austenite to martensite is related strongly to the water embrittlement effect of ADI.

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  In general, most semi-solid slurries are obtained by either the electromagnetic stirring or mechanical stirring of molten alloys during alloy solidification. The advantages of the semi-solid process are low casting temperature, good fluidity of the slurry, and fine solidified structures. However, both processes are costly and require very large equipment. We used a simple inclined cooling plate to produce semi-solid slurry, and many seeds were generated and flowed onto the cooling plate. In this investigation, we cast 7075 aluminum semi-solid slurry and observed the microstructures of products. The microstructures exhibited granular, fine and homogeneous primary aluminum crystals, except in the top area. The top area contained small liquid pools before casting. Dendrite crystals appeared when an inclined cooling plate was not used. The best fraction of solid in the slurries was less than 20% in this process.

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  The mechanical properties of thin wall die castings of Zn-Al-Cu alloys containing higher amounts of aluminum and copper than that of generally used ZDC2 alloy were investigated, in the aim to realize high strength in thin wall die castings. The thin wall die castings were cast into square specimens measuring 70mm by 100mm with a 0.2mm thickness using a hot chamber die casting machine applying an undiluted commercial oil-type die lubricant. The tensile strength of binary eutectic Zn-Al alloy with high copper content and ternary eutectic alloy was found to increase 25% more than that of ZDC2. Furthermore, the strength was found to decrease slightly at the overflow side. Hyper eutectic Zn-Al alloys with high copper content are 50 to 70% better than ZDC2 because of the following two factors ; precipitation of fine primary crystals of β(Al) phase and solid-solution hardening with higher aluminum and copper contents. In addition, these alloys show lower elongation. The mechanical properties of thin wall die castings are significantly governed by microstructural distribution. When segregation of massive primary crystals takes place in hyper eutectic alloy due to inadequate solidification, the properties of die castings degenerate.

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