Structural alloy steels were studied to show the different banding behavior by the isothermal and step heat treatment at various isothermal treating temperatures around the nose of the TTT-curves. The banding behavior could be quantitatively observed by the author's new definition of the degree of banding as the amount of the phase localization.
In the cases of the isothermal heat treatments, the degree of banding at the nose temperature was negligible among the different isothermal treating temperatures. It was caused by too short transformation time to redistribute the carbon atoms at this temperature. In the cases of the step heat treatments, after the proeutectoid ferrite was transformed at the upper or lower region of the nose, the pearlite was transformed at the nose temperature. On the other hand, after the proeutectoid ferrite was transformed at the nose temperature, the pearlite was transformed at the upper or lower region of the nose. The degrees of banding in the step heat treatments were decreased by about half of that which both the proeutectoid ferrite and the pearlite were transformed at the upper or lower region of the nose.
On accounts of these, the farther isothermal treating temperture from the nose, the worse banding behavior was developed. The banding behavior was thought to be a function of the isothermal treating temperature.
