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<p>The research deals with a cobalt-chrome steel of the following composition: C, 1.75%; Mn, 0.26%; Co, 2.90%; Cr, 15.0%. Samples were cooled from a constant temperature of about 900°C. at varying rates. As the rate of cooling is increased the temperature Ar' gradually falls from 770° to 700°, with a cooling rate of 0.7 deg. C. per sec. The lowered point Ar' makes its appearance at a cooling velocity of 0.15 deg. per sec., falling from 450° to 380° as the speed of quenching is increased to 1.2 deg. C. per sec. Between the limits 0.15 and 0.7 deg. C. per sec. both Ar' and Ar' are found; above the latter limit only Ar'. The heating curves show the Ac1-3 and Ac2 points at fairly constant temperatures, b
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