国产X80管线钢管焊接接头的力学性能

Mechanical Properties of Welded Joint of Domestic X80 Pipeline Steel Pipes

对"西气东输"二线工程现场的X80钢直缝埋弧焊管的焊接接头,分别进行了显微组织观察、常温下的硬度测试和单轴拉伸性能测试。结果表明:在焊接接头的熔合区附近出现了焊接硬化现象,在细晶区出现了焊接软化现象;熔合区附近粒状贝氏体(GB)晶粒严重粗化,含有大尺寸的硬脆组织马氏体/奥氏体(M/A)岛,同时熔合线两侧组织发生渗透,它是焊接接头的断裂危险区域;焊接接头采用了高强匹配,母材金属具有良好的形变强化能力,焊缝金属由于含有魏氏组织(WF),导致塑性较差,韧性不佳,屈强比为93.55%,断后伸长率为14.2%;热影响区整体上具有较高的强度和塑性,力学性能较好,抗拉强度669.30MPa,屈强比为89.45%,断后伸长率为22.8%。

The welded joint of a longitudinally submerged arc welded（LSAW）pipeline of X80 steel at the job site of the second project of natural gas transmission from west to east China was studied by microstructure observation,hardness testing,uniaxial tensile testing at room temperature.The results show that welding hardening happened near the fusion zone of the welded joint and welding softening happened at the fine-grained heat affected zone.The grains of granular bainite near the fusion zone coarsened severely and contained large hard-brittle inclusions of M/A constituents,meanwhile mutual permeation between the microstructure on both sides of the fusion line happened,so the fusion zone was the fracture risk zone of the welded joint.The welded joint of X80 steel was overmatched,and the base metal had a good capacity of deformation strengthening.The weld metal had poor plasticity and toughness because of widmanstatten ferrite（WF）,with the ratio of yield strength to tensile strength of 93.55% and breaking elongation of 14.2%.The heat affected zone overall possessed relatively high strength and plasticity,and good mechanical properties with tensile strength of 669.30 MPa,the ratio of yield strength to tensile strength of 89.45% and breaking elongation of 22.8%.