通过理论计算并结合实验研究了低碳Nb微合金钢中NbC析出相与Nb固溶原子共同作用对再结晶后奥氏体晶粒长大的影响. 结果表明, Nb的溶质原子拖曳与NbC析出相钉扎共同作用阻碍晶粒长大晶界的迁移, 高温时NbC析出相的钉扎起主要作用, Nb的溶质拖曳效应并不明显, 而相对低温时Nb拖曳对晶粒长大产生明显地抑制作用, 理论计算与实验结果吻合良好; 溶质原子拖曳和析出相的钉扎对抑制晶粒长大的效力可以用p因子来表征, 当p=0时, 以NbC析出的Nb与固溶Nb的量之比达到最优, 抑制晶粒长大效果最好, 当p>0时, 析出相的钉扎能更有效地阻碍晶粒长大, 而p<0时, 溶质原子的拖曳对抑制晶粒的长大更有效; 在常规热轧温度区间或者奥氏体化温度区间内, 只有尺寸不大于10 nm的细小的NbC析出相对再结晶后的晶粒长大才能起到较好抑制作用.
A kinetic equation for austenite grain growth has been derived concerning the mutual effect of NbC and Nb solute in low carbon Nb-microalloyed steels. It is shown that both solute drag of Nb in solid solution and pinning of NbC particles inhibit the grain boundary migration during grain growth after recrystallization in low carbon Nb-microalloyed steels. At high temperatures the NbC pinning plays a dominate role for retarding the austenite grain growth with less Nb solute drag effect. An obvious Nb solute drag restraint was, however, observed at relatively low temperatures. Also, the theoretical calculations are in good agreement with experimental results. The effectiveness of drag effect of soluble atoms and pinning effect of precipitates can be characterized by a p factor. The pinning of precipitates and solute drag of soluble atoms are more effective for suppressing grain growth as p>0 and p<0, respectively. And the ratio of Nb in solute and Nb in precipitate as p=0 reaches the priority and most effectively retards the grain growth. In the traditional hot rolling or< austenitizing temperature range, a strong suppression for grain growth after recrystallization could be obtained due to those fine NbC particles smaller than 10 nm in Nb-microalloyed steels.
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