Tohru Arai1, Takuo Ito1 and Noboru Komatsu1
1Toyota Central Research and Development Laboratories, Inc., Nagoya
A simple measuring apparatus was contrived to determine isothermal and continuous cooling transformations of steels with simple procedures by the method of differential thermal analysis. Specimens and references 1 mm in diameter were prepared, respectively, and a thermocouple was welded to each of them. This apparatus comprises an austenitizing and cooling furnace and an isothermal salt bath.
The TTT diagram and the Ms temperature of SUJ 2 bearing steel were determined by this method, and the results were in good agreement with those obtained by the metallographic or Greninger-Troiano method. The CCT diagram of S 45 C structural carbon steel was also, found to have satisfactory accuracy for practical purposes. In this method, it was permissable for the specimens to be subjected to plastic deformation during the measurement, so that the CCT diagram for the steel being thermomechanically treated could be obtained. The method can also be used for obtaining the CCT diagram for cast iron cooled from the molten state. The DTA method for measuring transformations seems to be of great practical value in obtaining transformation diagrams which are required not only for heat treatment but also for thermomechanical treatment, welding and casting.
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