2211.     MATUSHITA, T., AND NAGASAWA, K.  Mechanism of the Tempering of Steels.  Jour. Iron Steel Inst. (London), vol. 10, 1927, 12 pp.; Chem. Abs., vol. 21, 1927, p. 3876.

        The change in electric resistance and intensity of magnetization are determined for a quenched C steel containing 1.02% C, 0.33% Si, 0.30% Mn, 0.015% P, and 0.022% S, and it is found that during the decomposition of martensite, the electric resistance decreases and the intensity of magnetization increases, both in 2 steps below 300°.  It is concluded that there are 2 kinds of martensite, a and β, of which during the heating at a normal rate, the first decomposes at 100°-170° and the second at 170°-300°.  In decomposing, martensite yields free C rather than cementite, and this combines with Fe in the interval 300°-400° to form cementite.  This formation of cementite is believed to explain the second contraction in the thermal expansion curve as well as the sharp increase in magnetic hardness between 300° and 400°.  This also is illustrated with a W steel containing the double carbide 4Fe₃C.WC.  The authors propose the following classification of the tempered structure of quenched C steels; martensite+troostite—100°-300°; troostite—300°; troostite+sorbite—300°-400°; sorbite (osmondite)—400°; sorbite+granular pearlite—400°-550°; granular pearlite—550° to Ac₁ point.  This is only valid for a normal rate of heating.