Abstract:ZrO₂ dispersion-strengthened Q345 steel with different ZrO₂ contents (0%, 0.5% and 1.2%, mass fraction) was fabricated through combining middle frequency induction furnace melting and cored-wire injection technologies. The microstructure and fracture surface morphology of ZrO₂ dispersion-strengthened Q345 steel in casting, normalizing and quenching states were observed using optical microscopy, scanning electron microscopy and transmission electron microscopy. Also, strengthening and fracture mechanisms of the alloys were analyzed. Results showed that the dispersed ZrO₂ particles added into Q345 matrix significantly enhanced its strength, and the main strengthening mechanism was the formation of dislocation cells and pinning effect caused by the addition of ZrO₂ particles. Apart from that, the hard martensite phase, grain refinement and high ZrO₂ particles content also played important roles in strengthening effect. Furthermore, the nanoindentation was also performed to further reveal the strengthening effect and mechanism of dispersed ZrO₂ particles in Q345 steel. Results showed that the hardness of ZrO₂ dispersion-strengthened Q345 steel increased with the increase of ZrO₂ content.

Key words: Q345 steel; ZrO₂ particles; dispersion strengthening; microstructure; mechanical properties