3675.     WEVER, F., AND NAESER, G.  [Manner in Which Carbon is Bound in Hardened and Tempered Steels.]  Mitt. Kaiser Wilhelm Inst. Eisenforsch., Düsseldorf, vol. 16, 1934, pp. 201-206; Chem. Abs., vol. 29, 1935, p. 2491.

        Object was to determine, by analyzing the residues of tempered steels obtained by electrolysis in FeCl₂ solutions, the manner in which C is bound in steel at different temperatures.  The residues are separated magnetically into 2 parts, one essentially highly dispersed C with H₂O and the other a gray-black powder, which, in dry state, ignites in air.  The C content of the unseparated residues decreases with increasing tempering temperatures from very high values in untempered steels to that of the composition Fe₃C at 700°, whereas the C content of the purified residues is mostly FeC up to about 300° and Fe₂C between 300° and 600°-700°.  Residues of steels transformed directly from the austenite state have lower C contents than tempered steels and correspond to Fe₂C for transformation temperatures of 400°-500°.  The existence of the carbides FeC and Fe₂C in tempered steels is considered to be established.  23 references.