X80管线钢焊接接头TEM观察下的断裂行为对比

对X80管线钢焊接接头3个区域的试样在透射电子显微镜（TEM）下进行原位拉伸试验，通过观察各个区域裂纹的萌生与扩展过程，对其微观断裂行为进行了研究和分析。结果表明：母材区中，裂纹萌生扩展主要以多裂纹起裂为主，表现为沿晶扩展的断裂形式，最后造成在切应力作用下的剪切脆性断裂;热影响区内，主裂纹首先在切应力作用下以45°方向起裂，整个扩展过程是主裂纹钝化、位错发射、主裂纹前方无位错区形成、微裂纹形核、主裂纹与微裂纹连接扩展这一多尺度过程不断重复的过程，最后导致准解理穿晶断裂;焊缝区中，从主裂纹分支出多条裂纹，裂纹均以与拉伸轴成45°的方向起裂，表现为沿晶与穿晶混合的断裂模式，最后造成穿晶脆性解理断裂。

Comparison of Fracture Behaviors of X80 Pipeline Steel Welded Joints under TEM Observation

Three specimens of X80 pipeline steel welded joint regions were in situ TEM tensile test by observing initiation and propagation of cracks in each region, the micro mechanical behaviors were studied and analyzed. The results show that, in the base metal zone, the crack initiation and extension are mainly composed of multiple crack, in the mode of intergranular extension, finally cause shear brittle fracture under the action of shear stress. In the heat affected zone, the main crack extension is in the direction of 45°, the whole expansion process including the main crack blunting, dislocation emission, formation of dislocation free zone in front of the main crack, microcrack nucleation, connection of main crack with microcracks, the multiscale process constantly occurrence, finally leads to quasi cleavage transgranular fracture. In the weld zone, cracks branch off from the main crack which extend to the direction of 45°, in the mixed fracture mode of intergranular and crystalline, finally lead to the transgranular brittle cleavage fracture.