3683. ---------------. [WHITELEY, J. H.] Solution of Cementite in a-Iron and Its Precipitation. Jour. Iron Steel Inst., No. 14, 1927, 11 pp.; Engineering, vol. 124, 1927, pp. 472-473; Chem. Abs., vol. 21, 1927, p. 3872.
Basic steel of the Armco type, acid-steel plate heated to 1,000° and air-cooled, and acid-steel plate heated to about 1,400° and cooled very slowly were the specimens examined. The results indicate that above 630°, a-Fe dissolves an appreciable amount of cementite, which is retained in a solid solution on quenching. On tempering at or below 250°, precipitation of this cementite occurs in the ferrite grains, and on further heating, the cementite particles travel to the grain boundaries at high velocity. The solubility of cementite increases above 630°, being above 0.03% at 720°. Decrease in purity of the ferrite slightly raises the initial temperature of solution, the acid-steel samples showing no solubility below 750°. Photomicrographic examination shows that the carbide precipitated at lower temperatures was always uniformly distributed in the ferrite grains in parts well away from pearlite areas, indicating a very rapid rate of diffusion. During slow cooling, the dissolved carbide is deposited on existing crystals. The presence of dissolved C has a distinct hardening effect. Thus, the sample of basic steel untreated showed a Brinell number of 89, whereas heated to 680°, quenched, and reheated to 550° the Brinell number was 91, and quenched from 680° it was 105.