The tempering process of high carbon martensite was investigated by means of the electrical resistivity measurement, dilatometry, and transmission electron microscopy. The first stage of tempering is not the precipitation of ε-carbide, but is probably the pre-precipitation stage such as the segregation of carbon atoms to the lattice defects or the carbon cluster formation. The second stage is the precipitation of ε-carbide which is related to the martensite by Jack's orientation relationship. The retained austenite decomposed into lower bainite in the temperature range between 230° and 330°C. Tempering up to 330°C produced χ-carbide on the twin interfaces and this exhibited the monoclinic Pd5B2 type structure determined by Duggin. Further tempering up to 400°C, the in-situ transformation of χ-carbide into cementite occurred.
(Received November 9, 1970)
* This paper was presented at the Autumn Meeting of the Japan Institute of Metals in October, 1970.
** Central Research Laboratories, Sumitomo Metal Industries, Ltd., Amagasaki, Japan.
© 2002 The Japan Institute of Metals
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