Effects of NiAl on precipitation behavior and mechanical properties of M2C strengthened secondary hardening steel

A novel dual-precipitation steel was developed by introducing NiAl into secondary hardening ultrahigh strength steel. This steel exhibited a yield strength of 1.9 GPa, an ultimate tensile strength of 2.3 GPa, and an elongation of 9%. These exceptional mechanical properties can be primarily attributed to the synergistic strengthening effects of nanoscale NiAl and M 2 C dual-precipitates during the aging process. The influence of NiAl on the precipitation behavior of M 2 C and its precipitation strengthening effect were studied using atom probe tomography, transmission electron microscopy, and first-principles calculations. The results indicate that the precipitation of NiAl in the steel induces M 2 C nucleation around NiAl, preventing the coarsening behavior typically observed when M 2 C precipitates alone, where precipitates aggregate along dislocations. The high number density of NiAl increases the number density of M 2 C and reduces their size. Furthermore, at higher aging temperatures, the precipitation of NiAl in the steel inhibits the coarsening of M 2 C, thereby delaying the trend of strength reduction in the steel. Under the dual-precipitation strengthening effect of nanoscale NiAl and M 2 C, the yield strength of the steel can be increased by up to 1130 MPa, which is significantly surpassing the strengthening effect from the single precipitation of M 2 C during the aging process.