The scope of this paper is perhaps best limited or defined by the the statement that it covers the high-chromium iron alloys which at the same time carry sufficient nickel (or manganese or both) as normally to exist dominantly in the form of a solid solution of the austenite type (in gamma iron) and which are rolled or forged rather than cast into form for use. The carbon content is in general very low, the more recently preferred compositions carrying less than 0.10 per cent in most cases. Similar to most high-chromium alloys, these materials are remarkably strong and, in addition, due perhaps to their crystal structure, are comparatively very ductile alloys. Their resistance to many types of corrosion attack is of course their outstanding characteristic, and accompanying this property is the unique resistance to oxidation at high temperature. For this high-temperature applicability the chromium is largely responsible, presumably by virtue of its contribution of a thin, continuous, adherent film of oxide which is, at the same time, impermeable. It is of special importance that chromium contributes, in addition to ordinary strength, the valuable property of strength at high temperatures. The nickel present doubtless adds somewhat to the resistance to chemical action of the metal but it is thought that its principal contribution is through the agency of crystal structure modification in developing workability.