Effect of Precipitates on Austenite Grain Growth Behavior in a Low-Carbon Nb-V Microalloyed Steel

摘要

The effect of precipitates on austenite grain growth behavior in a Nb-V microalloyed steel was investigated. The precipitates were identified by selected area electron diffraction(SAED) and energy dispersive spectrometer(EDS) analysis. Because of pinning effect of NbC and/or VC on austenite grain boundaries, grains grew slowly at 850℃-1000℃. However, when temperature reached 1050 ℃, abnormal grain growth was observed, which was attributed to dissolution of NbC particles. The NbC precipitates dissolved significantly at 1150 ℃. However, grain sizes were still very small. Thus, austenite grains grew rapidly at 1050-1150 ℃. The fully dissolution temperature of this steel was 1150-1250℃. Finally, the relationship between grain coarsening temperature(T_(GC)) and fully dissolution temperature(T_(DISS)) could be illustrated as follows: 100 ℃≤T_(DISS) -T_(GC)≤200 ℃. When heating temperatures were 850-1050 ℃ and 1050-1250 ℃, grain growth activation energies (0 were 59945 J/mol and 135813 J/mol, respectively. The different grain growth models were mainly caused by the gradual dissolution of NbC particles.