X70M管线钢焊接接头CTOD断裂韧性研究

Research on CTOD fracture toughness of welded joints of X70M pipeline steel

采用CTOD(裂纹尖端张开位移)试验对X70M直缝埋弧焊管焊接接头的焊缝中心、熔合线和热影响区进行断裂韧性测试,并使用OM、SEM和EBSD对CTOD试样裂纹扩展区的微观组织进行观察。结果显示,X70M直缝埋弧焊管焊接接头的CTOD断裂韧性为:焊缝中心良好,熔合线波动大,热影响区最佳。焊缝中心的组织细小均匀,断裂韧性稳定;熔合线附近的组织形态和晶粒大小差异大,大角度晶界比例较低,链状M-A组元诱发应力集中,造成CTOD特征值离散性大,并且出现薄弱点;等效热影响区中的针状铁素体含量增多,有利于提高韧性。

Fracture toughness of weldpipeline steel welded joints producing bythree-point crack tip opening displacementseam, fusion line and heat affected zone （HAZ） in X70Mlongitudinal submerged-arc welded was investigated by（CTOD） test, and microstructure near fracture zones wereobserved by means of OM, SEM and EBSD. The results indicated that fracture toughness of HAZ wasthe best, and fracture toughness of fusion line was far more volatile than that of weld seam. Themicrostructure of weld seam center was uniform with good toughness ; the microstructure of fusion linewas not uniform with less high-angle grain boundaries, and the chain M-A constituents caused stressconcentration so that CTOD results of fusion line were discrete and vulnerability; the content ofacicular ferrite in HAZ increased and was favorable for fracture toughness.