Abstract: Three-dimensional atom probe (3DAP) and thermal aged method were used to characterize precipitation of Cu-rich clusters in pressure vessel model steel. Pressure vessel model steel specimens were quenched at 880 °C , then aged at 400 °C and 500 °C for different time. The results of hardness test show that peak hardness reached for 100 h aged at 400 °C and 5 h aged at 500 °C, respectively. Analysis results of 3DAP indicate that the number density of Cu-rich clusters increases from 1.5×10²³ m^-3 to 6.2×10²³m^-3, and equivalent diameter of the biggest clusters increases from 2 nm to 3.5 nm after aging 100 h and 300 h at 400 °C . It shows that the growth of Cu-rich clusters is very slow. The content of Cu in Cu-rich clusters is about 20%. Both Mn and Ni atoms are also segregated in Cu-rich clusters and distribution riched at the αFe matrix/clusters interfaces.

Key words: 3-dimensional atom probe, Cu-rich cluster, thermal aging
, pressure vessel steel