The purpose of this study is to clarify the continuous cooling transformation behavior and heat treatment characteristics for four kinds of ductile iron containing 0.5mass%Cr to 3.5mass%Cr. The specimens were austenitized at 1223K-900s, and the range of cooling time from Ac₃ to 773K was about 3s to 4000s.
  The volume of crystallized carbide in the low alloyed ductile iron containing 3.5mass%Cr ranged from 25% to 28%. The ferrite transformation region in CCT diagrams for ductile irons containing Cr less than 1mass% shifted to a longer cooling time, and did not exist for ductile irons containing Cr more than 2mass%. The pearlite transformation region in CCT diagrams shifted to a higher temperature and a shorter cooling time with increasing Cr content of ductile iron. The bainite transformation region existed only in CCT diagrams for ductile iron with 0.5mass%Cr. The martensite transformation region less than 2mass%Cr moved to a lower temperature with an increase in Cr content. The hardness of quenched ductile irons containing 0.5mass%Cr to 2mass%Cr was about 630HV10 and that of the ductile iron containing 3.5mass%Cr was about 800HV10. The effects of Cr on hardenability for low alloyed ductile irons were small.

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  Ultrasonic measurement was carried out with specimens made by aluminum alloy die-cast plates (ADC12) having a cold flake to observe echoes reflected from the surface, bottom and cold flake. The echo reflected from the cold flake had the same phase as that of the surface echo, and it was found that the ultrasonic wave was reflected from the oxide layer of the cold flake. This means that the cold flake and the matrix are not separated but stick together or join together. Next, ultrasonic measurement was carried out with specimens containing cold flake transversely to the tensile direction during tensile testing with a water bag to examine the change in the echo reflected from the cold flake. In the case of the specimen containing coarse cold fake, the phase of the echo reflected from the cold flake was reversed in the tensile testing, and it was found that debonding occurred between the cold flake and matrix to open the crack at the cold flake. And in some cases, the echo reflected from the cold flake approached to the surface 0.1mm or less with increasing tensile deformation. Similar results were obtained with specimens containing rather smaller cold flake. These results show that a crack initiates at the cold flake in the tensile deformation of the aluminum alloy die-casts, and also suggests that a crack may grow shortly before final failure.

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  CAC804 copper alloy, a type of lead free copper alloy, has higher strength. The effects of cooling rate on microstructures and mechanical properties were investigated for alloy cast into a shell mold with a stepped cavity. With increasing cooling rate, the microstructure of the alloy became finer, resulting in increased hardness. The tensile strength tended to increase and the elongation decrease with increasing cooling rate. This was thought to be due to micro defects formed during the casting process. CAC804 alloy casting prepared with a cooling rate of 10K/s had Vickers hardness of 135Hv, tensile strength of 500MPa and elongation of 30%. It was found that CAC804 copper alloy is effective for manufacturing thin-walled castings.

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