Research on the mechanisms for enhancing strength and toughness in 1000 MPa hydroelectric steel influenced by V elements

This research aims to enhance the characteristics of hydroelectric steel with a grade of 1000 MPa by examining how varying vanadium (V) levels (0, 0.05%, 0.09%) influence its microstructure and mechanical attributes. Through the implementation of specific rolling techniques and heat treatment processes, microstructural analysis was conducted using optical and scanning electron microscopy, while mechanical performance was assessed via tensile and impact testing. Findings reveal that both tensile and yield strengths show a marked increase with higher V concentrations, although elongation initially declines before rising again. The enhancement in yield strength is mainly attributed to the strengthening of grain boundaries and precipitation effects. At lower temperatures, the impact energy first rises and then falls as V content increases. Steel with 0.05% V demonstrated the best low-temperature toughness, recording impact energies of 201 J at -40°C and 186 J at -60°C. On a microstructural scale, vanadium and carbon combine to create fine VC carbides that restrict martensite development, refine grain structures, and enhance the density of dislocations. The primary precipitation phase identified is the ternary (Nb, V, Ti)C, with the strengthening mechanism transitioning from being dominated by Nb pinning to V dispersion strengthening, resulting in effective precipitation hardening. Additionally, raising the V content to 0.05% leads to significant changes in the Compact Precipitate (CP) group, increasing the amount of bainite present. The differing frequencies of bainite in these groups can be interpreted as high-angle grain boundary dislocations (HAGBs), which improve crack resistance and overall toughness.