Refinement mechanism of nanoscale Cu-rich precipitates by Mo addition and its effect on strength-toughness of Cu-bearing low carbon high strength steel

Effect of Mo element on the precipitation behavior of nanoscale Cu-rich particles in Cu-bearing low carbon high strength steels was investigated in this work. The addition of 0.82 wt% Mo refined the size of grain interior Cu-rich particles (ICRPs) from 12 nm to 8 nm, accompanied by the structure changed from 3R-Cu to 9R-Cu. Mo also inhibited the formation of grain boundary Cu-rich particles (BCRPs) with the size of ∼30 nm. The calculation of phase field method indicated that Mo was repelled from Cu-rich particles and enriched in α-Fe matrix, which suppressed the diffusion of Cu atoms and merger of Cu-rich particles. The measured yield strength of CuMo-bearing steel increased by 87 MPa, mainly due to the refinement of ICRPs. The reduction of BCRPs suppressed the crack initiation and propagation at grain boundaries, which contributed to the increment of absorbed energy at −40 °C by 41J.