Full TTT Curves for Steel
Cooling to low temperatures (below the nose of the TTT curve) means that diffusion rates are greatly reduced
Under such conditions it is not possible to form pearlite and a different phase, bainite is formed
Bainite consists of needles with a ferrite matrix containing elongated particles of Fe3C
Cooling to very low temperatures without transformation to pearlite or bainite allows a shear transformation to martensite to occur