LNG储罐用钢06Ni9DR焊接接头弯曲试验断裂失效分析

Fracture failure analysis of 06Ni9DR steel welded joint for LNG storage tank in bending test

在进行LNG储罐用钢06Ni9DR焊接工艺评定试验时,会出现弯曲试件开裂的现象,为了查找弯曲试样失效原因,保障LNG储罐焊接质量,采用不同热输入工艺对06Ni9DR钢板进行手工焊条电弧焊接,对焊接接头开展了拉伸试验、弯曲试验、-196℃低温冲击等试验。通过金相显微镜和扫描电镜对焊缝、热影响区,以及弯曲失效断口进行观察和分析,结果表明,采用ENiCrMo-6焊条焊接的焊缝组织中均散布较多大小不一的夹渣,热输入控制在12.5~26.5 kJ/cm范围内对焊接接头的力学性能、塑性以及低温冲击性能影响不明显;但采用较小热输入焊接时,更易产生夹渣、咬边缺陷,较大夹渣和轻微咬边缺陷是导致弯曲试件失效的主要原因。

In the process evaluation test of 06Ni9DR steel for LNG storage tank,cracking of bending specimen often appears.In order to find out the failure cause of bending specimen and ensure the welding quality of LNG storage tank,manual arc welding of 06Ni9DR steel was carried out with different heat input processes.Tensile test,bending test,and low temperature impact test at-196℃were carried out on the welded joint.The weld,heat affected zone and bending failure fracture were observed by metallographic microscope and scanning electron microscope.The results show that there are a lot of slag with different sizes scattered in the weld microstructure of ENiCrMo-6 electrode,and the mechanical properties,plasticity and low temperature impact properties of welded joints are not significantly affected when the heat input is controlled within the range of 12.5~26.5 kJ/cm.However,when smaller heat input is used for welding,it is more likely to produce slag inclusion and undercut defects.Larger slag inclusion and slight undercut defects are the main causes leading to failure of bending specimens.