Nb元素对含Ti低碳微合金钢连续冷却转变及析出行为的影响

采用热模拟试验机研究了Nb元素对含Ti低碳微合金钢的动态连续冷却转变行为的影响，利用OM和TEM对等温淬火工艺处理后实验钢的显微组织和析出行为进行观察和分析。结果表明：Nb元素使得含Ti低碳微合金钢的动态CCT曲线整体向右下方移动，大大减小了先共析铁素体和珠光体相变区，同时扩大了针状铁素体和贝氏体相变区，在较低冷速时能得到较多的针状铁素体；含Nb- Ti和含Ti两种实验钢经等温淬火工艺处理后的显微组织均由铁素体和马氏体两相组成，铁素体相中析出物平均尺寸分别为6.8、4.2 nm，利用Orowan机制对析出强化量进行计算得出析出强化量分别为90.6、142.3 MPa。

Effect of Nb on continuous cooling transformation process and precipitation behaviors of the Ti- bearing low- carbon steel

The effect of Nb on austenite phase transformation behavior during its dynamic continuous cooling transformation process was investigated. The microstructure and precipitation behaviors of experimented steels treated by isothermal quenching process had been investigated by using optical microscopy and field- emission- gun transmission electron microscopy. The results show that Nb makes the overall CCT curve of the Ti- bearing low carbon steel move to the bottom right, which greatly reduces the eutectoid ferrite and pearlite transformation area, while expands the acicular ferrite and granular bainite transformation area. Thus the Nb- Ti- bearing steel can get more acicular ferrite at a lower cooling rate. The microstructure of the Nb- Ti bearing and Ti- bearing steel treated by isothermal quenching process mainly consists of ferrite and martensite. The size of the precipitation has been determined to be 6.8 nm and 4.2 nm, respectively. The contribution of the precipitation hardening to the yield strength have been identified to be 90.6 MPa and 142.3 MPa, respectively, based on the Orowan mechanism.