Effect of microalloying elements Ti and Nb on impact property of high-strength engineering structural steel

Comparing the properties of Q345E steels of two different components, it is found that the yield strength and tensile strength of Q345E increase with the additions of microalloying elements Nb and Ti, but the low-temperature impact performance reduces.The results of the equilibrium phase calculation of Nb-Ti steel and C-Mn steel using thermodynamic software Thermo-Calc reveal that the main difference between them is the precipitation of (Nb, Ti) (C, N) phase.Furthermore, three titanium containing high-strength test steels were designed to observe the microtopography of the fracture and the second-phase particles of steels after impact test under scanning electron microscopy.With the increase of Ti, the low-temperature impact performance of steels reduced, and a number of large particles were gathered in the fracture, which were found to be (Nb, Ti) (C, N) using energy dispersive spectrometer (EDS) analysis, resulting in reduced impact energy.The results indicate that Ti deteriorates the low-temperature impact performance of low-alloy high-strength steel Q345E;therefore, it is necessary to control the size of the second-phase particles using controlled rolling and cooling or component design.