PREDICTING THE ONSET OF TRANSFORMATION UNDER NONCONTINUOUS COOLING CONDITIONS .2. APPLICATION TO THE AUSTENITE PEARLITE TRANSFORMATION

A detailed review of the additivity principle with respect to the incu bation of the austenite decomposition was summarized in Part I of this two-part series and led to the concept of an ''ideal'' time-temperatu re-transformation (TTT) diagram. This curve is characteristic of the c hemistry and austenite grain size in the steel and allows nonisotherma l behavior to be described assuming additivity holds. The derivation o f mathematical relationships between the ideal and experimental coolin g data was presented in the first article. In this second article, an ideal curve for the austenite-to-pearlite transformation was derived f rom cooling data. The applicability of the ideal TTT curve for predict ing the start of transformation under continuous cooling conditions wa s assessed for a range of cooling rates. Experiments were conducted un der both isothermal and varying temperature conditions, including an i ndustrial cooling schedule, using a Gleeble Thermal Simulator. Reasona ble agreement was found between the predictions and the observed trans formation start temperatures; predictions were consistent and compared favorably against other methods which have been frequently used to es timate the transformation start temperature for nonisothermal conditio ns.