An ultrahigh carbon steel having a composition of carbon in an amount of from about 0.8 weight percent up to the maximum solubility limit of carbon in austenite, aluminum in an amount of from about 0.5 to about 10 weight percent, an effective amount of a stabilizing element acting to stabilize iron carbide against graphitization, and the balance iron. Preferably, the aluminum is present in an amount of from about 0.5 to about 6.4 weight percent and the stabilizing element is chromium. The steel has excellent ductility and is readily hot, warm and cold worked without cracking. It is particularly useful in superplastic forming operations, and may be processed to a suitable microstructure by any technique which reduces its grain size to about 10 microns or less, and preferably to about 1 micron. Such a very fine grain size is readily acheived with the steel, and the aluminum and stabilizing additions act to retain the fine grain size during superplastic processing.
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