变形条件和冷却速率对低碳含Nb钢的相变及纳米析出的影响

利用Gleeble 3800热模拟试验机，研究了奥氏体再结晶和未再结晶组织对低碳含Nb钢连续冷却转变行为的影响，并对不同变形温度及冷却速率下Nb(C, N)的纳米析出行为进行了研究。结果表明，未再结晶区奥氏体的变形能够为多边形铁素体提供更多的相变形核点，扩大铁素体相变区，并且能够细化铁素体晶粒；相比于再结晶区1050℃单道次变形，未再结晶区的第二道次变形能够促进Nb(C, N)的析出，其中910℃变形时Nb(C, N)的析出量最多，850℃次之；冷却速率的增大能够抑制Nb(C, N)在奥氏体中的析出，但能够促进其在铁素体中析出；对于本试验钢，10℃/s的冷却速率即可抑制Nb(C, N)的析出；Nb(C, N)的析出粒子平均粒径随着冷却速率的增加而减小。

Effect of deformation and cooling rate on transformation characteristic and nanoscale precipitation in a low carbon Nb micro-alloyed steel

Effects of austenite recrystallization and unrecrystallization structure on continuous cooling transformation behavior of low carbon Nb micro-alloyed steel were studied by Gleeble 3800 thermal simulator, and the nano precipitation behavior of Nb(C,N) at different deformation temperatures and cooling rates was analyzed. It is found that the plastic deformation in un-recrystallization region of austenite accelerates the ferrite transformation and the ferrite transformation zone is enlarged. The deformation also refines the ferrite grain size. Compared with the single-pass deformation at recrystallizing 1050 ℃, the second deformation in the unrecrystallized zone can promote the precipitation of Nb(C, N), and the precipitation of Nb(C, N) at 910 ℃ is the largest, followed by that at 850 ℃. The increase of cooling rate can inhibit the precipitation of Nb(C, N) in austenite, but can promote its precipitation in ferrite. And the size of precipitates is refined with the increase of cooling rate. When the cooling rate reaches 10 ℃/s, the nucleation of precipitation is totally inhibited during cooling process.