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 coprecipitation of Ni3 Ti,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 ℃.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.