含硼超低碳贝氏体钢焊接热影响区组织性能及其硼分布

Microstructure and Property and Boron Distribution of HAZ in an Ultra-low Carbon Bainitic Steel Containing Boron

用Ｇｌｅｅｂｌｅ－１５００热模拟机研究了超低碳贝氏体（ＵＬＣＢ）钢经不同工艺处理后ＨＡＺ的组织与性能。结果表明，适量Ｎｂ，Ｂ合金化的ＵＬＣＢ钢在不同焊接条件下都能获得具有良好冲击韧性的口氏体组织。但焊接工艺的不同也直接造成焊后组织的差异而使低温断裂行为有所不同。通过对二次裂纹的直接观察。探讨了裂纹在不同组织中的扩展机制。二次循环明显使ＨＡＺ晶粒细化，而且随加热速率的增大，虽然韧脆转变温度略有提高，但其低温冲击韧性却明显改善。径迹显微照相试验结果表明，奥氏体化条件不同会造成硼在奥氏体晶界偏聚状态的不同，而使相交后贝氏体组织在形态及性能上出现差异。

The microstructures and properties of HAZ with different technology treatment in the ULCB steel were investigated by means of Gleeble-1500 thermal simulator. Results indicated that bainite structure of high toughness can be obtained under different welding conditions in the ULCB steel microalloyed with an appropriate addition of Nb and B. Welding process makes the difference in microstructure, thus leading to the different fracture behavior at low temperatures. direct observations on subsidiary cracks showed the mechanism of crack extension in different structures. Grain refinement can be gained by a second thermal cycle, and low temperature impact toughness is well improved with the increase of heating rate, despite of a little increase ofFATT. Results of Particle Tracking Autoradiography showed that boron segregation at austenite grain boundaries changes with austenization conditions, which causes the difference in morphology and property of bainite structure.