- (Osmond.) Martensite (black) in austensite (white).
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.
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).
Martensite, Troostite and Sorbite are the successive stages through which the metal passes in changing from austenite into ferrite and cementite.
Martensite, very hard because of its large content of (3-iron, is characteristic of hardened steel, but the two others, far from being definite substances, are probably only roughly bounded stages of this transition.