ON THE TTA (TIME-TEMPERATURE-AUSTENITIZATION) DIAGRAM IN THE CARBON STEELS.

The TTA (Time-Temperature-Austenitization) diagram was determined for a commericial pure iron, a eutectoid steel and various hypo-eutectoid steels, using a newly designed experimental apparatus previously described. It was observed that, in the TTA diagram, the starting time of the transformation shifts to the left side with increased over-heating and finally reaches 0 sec at 950 degree C in commercial pure iron, and, at 840 degree C, in the hypo-eutectoid and eutectoid steels. Therefore, it is concluded that there exists an upper limiting temperature at the zero-time axis that coincides with the upper limit of the transformation start on super rapid heating.