Martensite is a body-centered cubic form of iron in which some carbon is dissolved. Martensite forms during quenching, when face centered cubic austenite changes to the body centered cubic structure without the precipitation of cementite. Instead, the carbon is retained in the iron crystal structure, which is stretched slightly so that it is no longer cubic. Martensite is more or less ferrite supersaturated with carbon. Compare the grain size with tempered martensite.