Effect of Pre-deformation on Nanoscale Precipitation and Hardness of a Maraging Stainless Steel

The effect of pre-deformation on nanoscale precipitates and hardness of a maraging stainless steel strengthened by the co-precipitation of Ni₃Ti, Mo-enriched and Cr-enriched precipitates was systematically studied using electron back scattered diffraction, transmission electron microscopy and atom probe tomography (APT). Hardness measurements showed that the hardness of specimen with a deformation ratio of 90% peaked at HV 718 aged for 24 h, which is higher than that in the undeformed specimen (HV 603) aged for 72 h at 480 °C. APT characterization revealed that pre-deformation could shorten the incubation time of the Mo-enriched and Cr-enriched precipitates. At the early-aged stage, pre-deformation increased the stain energy that inhibited the nucleation of Ni₃Ti precipitates, but accelerated the rejection of Mo from Ni–Ti clusters. Besides, the strengthening model indicated that strain hardening (43%) makes a larger contribution to the hardness at the early-aged condition, while precipitation hardening (58%) has most contribution to the hardness at the peak-aged conditition.