Martensitic transformation in iron

Abstract

1. The formation of martensite in iron (0.03% C) occurs at high temperatures (700–650°) and obeys well-known [5] rules established for the formation of martensite in steels—in particular, the initial martensitic transformation temperature is independent of the austenite grain size and the cooling rate. 2. The growth rate of martensite crystals is low (∼3 μ/sec for iron and 2 μ/sec for low-carbon steel) and does not depend on the temperature. 3. Martensite formation is not a thermally activated process—the low rate at which martensite is formed at high temperatures is due to the fact that the growth of martensite platelets occurs in a narrow range in which relaxation processes occur rapidly. Evidently the occurrence and relaxation of stresses is the principal factor determining the mechanism and rate of the martensitic transformation.