High-carbon iron alloys containing carbide formers of chromium and molybdenum were rapidly solidified by means of a single roller method. In the alloy containing a high level of both chromium and molybdenum (10Cr-5Mo) and a critical carbon content of about 4 pct, the metastable phases, ε phase and austenite, are retained after solidification. The ε phase could contain a large amount of carbon in solid solution so that during tempering at about 900 K, it decomposes to very fine ferrite and carbide, which bring about an enhanced hardness of 1300 DPN. Even after tempering at a high temperature around 1100 K, the hardness hardly deteriorates due to a remarkable dispersion of fine M3C and M7C3 carbides. Thus, coaddition of chromium and molybdenum is effective in obtaining high hardness. © 1991 The Minerals, Metals and Materials Society, and ASM International.