Effect of cold rolling on the precipitation behavior of δ phase in INCONEL 718

Systematic research has been undertaken on the effect of cold rolling on the precipitation kinetics of delta phase in INCONEL 718. Above 910 degrees C, cold rolling promotes the precipitation of delta phase. Below 910 degrees C, the precipitation of delta phase is still preceded by the gamma " precipitation in cold-rolled INCONEL 718. Cold rolling promotes not only the precipitation of gamma " phase but also the gamma " --> delta transformation. The relationship between the weight percentage of delta phase and aging time follows the Avrami equation. Below 910 degrees C, as cold rolling reduction and temperature increase, the time exponent (n) decreases, whereas the rate of delta precipitation increases. The apparent activation energy of delta precipitation varies in the range of 1113 to 577 kJ/mol for 25 to 65% cold-rolled INCONEL 718 and decreases as cold rolling reduction increases. Precipitation-time-temperature (PTT) diagrams have been determined for the four cold-rolled INCONEL 718. The noses of the PTT curves are located at about 910 degrees C. These curves are shifted significantly to longer times as cold rolling reductions decrease.