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As a consequence of a nickel shortage in the early 1930's, German investigators undertook the development of austenitic chromium-manganese stainless steels. These investigators established the composition limits for the iron-chromium-manganese system, and their results are discussed. American investigators were able to obtain higher chromium contents in austenitic steels by the use of nitrogen. Using both nickel and nitrogen in combination with manganese, these investigators developed the steels that are accepted today as AISI Types 201 and 202. Further work in America indicated that fully austenitic steels containing over 18 per cent chromium, using manganese and nitrogen as austenite formers, were possible. In this paper the structural diagrams for the iron-chromium-manganese-nitrogen system are presented. These diagrams permit the establishment of composition limits for fully austenitic chromium-manganese-nitrogen stainless steel.
The melting, processing, mechanical properties, and corrosion resistance of one of the chromium-manganese-nitrogen austenitic stainless steels is described. This steel contains upward of 0.40 per cent nitrogen with the result that its room-temperature mechanical properties are twice those of the conventional chromium-nickel austenitic stainless steels. Data are presented showing the effect of cold rolling on the room- and elevated-temperature tensile strength and compressive strength. In addition, data are presented illustrating the fatigue strength of this material in the annealed and cold rolled condition. The results of laboratory and service corrosion tests indicate that the corrosion resistance of the chromium-manganese-nitrogen stainless steels is equivalent to that of 17 per cent chromium Type 430 stainless steel in all environments tested and is similar to Type 304 stainless steel in many of the environments tested. Although the stress corrosion resistance of the chromium-manganese-nitrogen stainless steel is erratic, it is always superior to that of the chromium-nickel austenitic stainless steels, such as Type 304. The possibility, therefore, exists that some slight modification in the chromium-manganese-nitrogen stainless steel will provide the long-wished-for austenitic stainless steel having immunity to transgranular stress corrosion cracking.
Heger, J. J.
Chief research engineer, Personal Member, ASTM, Stainless Steel Applied Research U. S. Steel Corp., Pittsburgh, Pa.