At cooling rates faster than 140 C/s the transition is to a metastable material known as martensite. Between 35 and 140 C/s the system at room temperature is a mixture of these two materials. The ...

The micrographs below show the effect of annealing at different temperatures on a sample of Fe - 0.7 wt % C steel in which martensite has been formed by quenching. Because of the low carbon content ...