Thus, sudden cooling from a red heat leaves the carbon not in definite combination as cementite, but actually dissolved in (3and 7-allotropic iron, in the conditions known as martensite and austenite, not granitic but glass-like bodies, of which the " hardened " and " tempered " steel of our cutting tools in large part consists.
These freezing-point curves and transformation curves thus divide the diagram into 8 distinct regions, each with its own specific state or constitution of the metal, the molten state for region 1, a mixture of molten metal and of solid austenite for region 2, austenite alone for region 4 and so on.
Austenite, gamma ('y) iron.-Austenite is the name of the solid solution of an iron carbide in allotropic y-iron of which the metal normally consists when in region 4.
On cooling into region 6 or 8 austenite should normally split up into ferrite and cementite, after passing through the successive stages of martensite, troostite and sorbite, Fe 0 C= Fe 3 C +Fe(i 3).
But this change may be prevented so as, to preserve the austenite in the cold, either very incompletely, as when high-carbon steel is " hardened," i.e.