YAN Zhongting, MENG Yue, LIANG Enpu, XU Le, WANG Maoqiu
With the large-scale development of wind power generation equipment, higher performance requirements are imposed on fasteners for wind turbines. As a typical bolt steel, 42CrMoVNb contains strong carbide-forming elements such as Nb and V, making its precipitation evolution sensitive to heat treatment, which directly affects the service performance of bolts. To establish the optimal heat treatment process window matching the service requirements of wind power fasteners, Thermo-Calc thermodynamic software was used to simulate the precipitation behavior of 42CrMoVNb bolt steel. The types of precipitated phases in the steel were investigated, with a focus on calculating and analyzing the precipitation behavior of MC phases during tempering. The results show that under equilibrium conditions, 42CrMoVNb bolt steel containsaustenite, ferrite, MC, M23C6 phases, and cementite. During tempering, (Mo,V)C is the dominant precipitated phase. When the holding time is 120 min, as the tempering temperature increases from 500 to 650 ℃, the size of (Mo,V)C phases coarsens significantly: the size of (Mo,V)C phases precipitated within grains increases from 2.5 to 20.1 nm, that precipitated at dislocations increases from 2.6 to 156.8 nm, and that of phases precipitated at grain boundaries increases from 2.5 to 194.1 nm. Meanwhile, the volume fraction of (Mo,V)C phases increases markedly: the volume fraction of phases precipitated within grains increases from 2.6×10-5 to 8.9×10-3, thatprecipitated at dislocations increases from 6.8×10-12 to 1.8×10-4, and that precipitated at grain boundaries increases from 2.1×10-10 to 2.7×10-3. These differences are primarily attributed to the combined effects of nucleation energy barriers at different crystal defects, atomic diffusion rates, and carbide coarsening rates.
