铌微合金化抗震钢筋形变奥氏体连续冷却转变

 为了研究铌对高强抗震钢筋生产过程中组织转变的影响,通过热模拟试验对比研究了无铌碳素钢筋及铌微合金化钢筋(铌质量分数为0.03%)形变奥氏体在不同冷却速率下的组织和相变规律,获得动态CCT曲线。研究结果表明,添加0.03%铌使试验钢奥氏体连续冷却转变有明显变化。从连续冷却曲线(CCT)可看出,添加铌后,发生先共析铁素体、珠光体相变的冷却速度范围减小,铁素体、珠光体转变温度降低;贝氏体相变的冷却速度区间整体右移。添加铌能细化组织,各冷却速度下含铌钢的硬度均大于无铌钢。利用TEM对不同冷却速度下含铌钢中析出相进行观察,发现Nb(C,N)弥散分布于钢中,随着冷却速度的增加,析出的Nb(C,N)逐渐减少,析出相尺寸呈先减小后增大的规律,2 ℃/s冷却速度冷却得到的析出相尺寸细小且数量较多。

Deformed austenite continuous cooling transformation in Nb microalloyed anti-seismic rebar

In order to study the effect of niobium on the microstructure transformation of high strength anti-seismic rebar,the microstructure and phase transformation of deformed austenite in Nb-free carbon steel bars and niobium microalloyed steel bars (0.03% niobium) at different cooling rates were studied by thermal simulator and dynamic continuous cooling curves,CCT of the tested steel were obtained. The results show that the addition of 0.03% Nb causes a significant change in the continuous cooling transformation of austenite in tested steels. It can be seen from CCT that after the addition of Nb,the cooling rate range of ferrite and pearlite phase transformation decreases,the ferrite and pearlite transformation temperature decreases. Cooling rate interval for the bainite transformation is shifted to the right as a whole. The addition of Nb can refine the microstructure,and the hardness of the niobium containing steel is greater than that of the Nb-free steel. The TEM was used to observe the precipitates in the niobium containing steel at different cooling rates. It was found that Nb(C,N) was dispersed in the steel. With the increase of cooling rate,the precipitation of Nb(C,N) gradually decreased,and the size of the precipitated phase decrease first and then increase. Size of precipitates obtained is finer and the number of precipitates is larger at cooling rate of 2 ℃/s.