9%Ni钢薄板焊条电弧焊弯曲试验开裂分析及改善

Analysis and Improvement of the Cracking of Bending Test by Electrode Arc Welding based on 9%Ni steel sheet

LNG船用9%Ni钢进行薄板(≤5 mm)焊接时,横向弯曲试验易产生开裂。采用有限元分析与工艺试验相结合的方式,研究X7Ni9钢薄板采用焊条(ENiCrMo-6)电弧焊工艺进行焊接后,在执行接头横向弯曲试验时弯曲拉伸面易产生超标开裂(弯曲面裂纹长度≥3 mm)甚至是试样断裂的原因。结果表明:弯曲拉伸面开裂的主要原因是母材和焊材为异质材料,其屈服强度差异大,当试板厚度过小时,横向弯曲试验过程中焊缝金属弯曲面过度拉伸,超过4倍厚度弯心的试验标准要求,被强制拉裂,导致评价失真;采用ENiCrMo-6系焊材进行根部焊道焊接时,当焊缝熔合情况不好时,易在该区域产生气孔缺陷,其与弯曲过程中产生的外表面开裂共同作用下会导致整个试样的断裂。工艺改进措施为:采用窄而厚的焊缝形态,增加单层的排道数量,从而增加焊缝整体宽度,以此保证焊缝考察面受拉伸时具有足够的塑性储备;通过控制焊道成形保证焊缝的熔合情况(根部焊道背面微透),以减少焊缝内部的气孔缺陷。

The w(Ni)=60 nickel-base type(Ni-Cr-Mo)series alloy is widely used for LNG(liquefied natural gas)Marine vessels 9%Ni steel welding.For thin plate(thickness less than 5 mm)welding,the transverse bending test is easy to produce cracks.The research on this problem is lacking.In this paper,this study would investigate the reasons for the easy occurrence of unqualified cracking(bend surface crack length more than 3 mm),through the combination of finite element analysis and process test the X7Ni9 steel sheet welded by manual(ENiCrMo-6)arc welding process.The results show that the main reason of bending cracking is that the base material and welding material are heterogeneous materials.The yield strength varies greatly.When the test plate thickness is too thin,the weld metal is overstretched and forced cracking beyond 4t requirement of the standard during the lateral bending test,which distorts the test results.The weld orifice defect are easy to occur on root weld by manual(ENiCrMo-6)arc welding process with poor weld formation under combined action of.which and crack lead to the sample fracture.The process improvement measures:increase the weld width to ensure sufficient plastic reserve when stretching,control the weld duct molding to improve the weld orifice defects;adopt longitudinal bending instead of transverse bending test.The process improvement measures are:increase the weld width to ensure sufficient plastic reserve when stretching;control the weld duct forming to improve the weld orifice defect.