A creep technique for monitoring the aging precipitation in Cu-Nb bainitic steels

A creep technique was applied on a Gleeble-1500 thermal simulator for monitoring the aging precipitation in ultra-low carbon steels containing various coppers. The aging hardening curve was obtained by the hardness testing. With the aid of an optical microscope and TEM, the microstructure and the aging precipitates were detected. The results indicate that when the precipitation occurs during the creep a plateau will appear on the creep curve; the left-hand and right-hand endings of the plateau correspond to the precipitation start (P_s) and finish (P_f) times, respectively. The P_f obtained from the creep curve coincides with the peak hardness time (t_p) at the aging hardening curve. A precipitation-time-temperature (PTT) diagram of the steel can be obtained.