Effects of Matrix Microstructure on the Nanoscale Precipitation and Precipitation Strengthening in an Ultra-high Strength Steel

Matrix microstructure and nanoscale clusters are the two main factors influencing the mechanical properties of nanocluster strengthened steels. Here, an ultra-high strength steel with a tensile strength of ~1.64 GPa and an elongation of ~14% has been developed through a combination of fine matrix microstructure and precipitation strengthening. Matrix microstructure was primarily controlled by annealing treatment. After annealing treatment at 750 °C for 1 h, the hot-rolled microstructure changes to the layered sorbite-like structure. The precipitation strengthening contributes a similar yield strength of ~494 MPa in both hot-rolled and annealed steels. The results indicate that there is no effect of matrix microstructure on the subsequent precipitation of nanoscale clusters and precipitation strengthening. The matrix microstructure and the precipitation of nanoscale clusters are independent and can be controlled separately.