TiNb钢焊接热影响区微观组织与冲击性能演变规律

Evolution of microstructure and impact property in welding HAZ of TiNb steel

关键词:  TiNb微合金钢  高热输入焊接  焊接热影响区  粗晶区  冲击性能

Key words:  TiNb steel  high heat input welding  welding heat affected zone  coarse grained region  impact property

摘要:

利用热模拟技术研究了焊接热循环参数对高热输入焊接用TiNb钢焊接热影响区粗晶区的组织及冲击韧性的影响规律. 结果表明，TiNb钢焊接热循环峰值温度升高，珠光体和铁素体的含量明显减少，贝氏体的含量增多，贝氏体板条组织明显粗化，导致冲击韧性下降；高温停留时间延长，贝氏体和珠光体含量大幅降低，多边形铁素体含量增加，高温停留时间为10 s以上时，多边形铁素体组织粗化严重，冲击韧性急剧降低. 在合适的冷却时间条件下，以晶粒细小的针状铁素体组织为主，冲击韧性达到最大值. 较低的热循环峰值温度、较短的高温停留时间和合适的冷却时间，可以获得晶粒细小的铁素体组织，从而可以显著提高热影响粗晶区的冲击韧性.

Abstract:

The influence of welding thermal cycle parameters on the microstructure and impact property of the coarse grain zone in the HAZ of TiNb steel for large-line energy welding was studied by thermal simulation technology. The results show that the coarse-grained microstructure of the heat-affected zone of TiNb steel is mainly composed of bainite, ferrite and pearlite. When the peak temperature of thermal cycle increases, the content of pearlite and ferrite decreases, and the content of bainite increases, the slab structure is obviously roughened, resulting in the decrease of impact toughness, the prolonging of high temperature residence time, the reduction of bainite and pearlite content, and the increasing of polygonal ferrite content. The high-temperature ferrite structure is thick when the high temperature residence time is above 10 s. Then the impact toughness is drastically reduced. Under the appropriate cooling time conditions, the main microstructure is fine acicular ferrite structure, and the impact toughness reaches the maximum. With a lower thermal cycle peak temperature, a shorter high temperature residence time and a suitable cooling time, a fine grained ferrite structure can be obtained, which can significantly improve the impact toughness of the heat affected coarse grain zone.