焊后热处理对NiCrMo-3熔敷金属腐蚀行为的影响

Effect of post welding heat treatment on corrosion behavior of NiCrMo-3 deposited metal

以NiCrMo-3合金熔敷金属为研究对象,通过扫描电子显微镜、透射电子显微镜、X射线衍射仪等研究了原始焊态与690℃保温8 h热处理态熔敷金属的耐腐蚀性能差异.结果表明,与焊态试样相比,热处理试样具有良好的耐晶间腐蚀性能,在HNO3溶液中浸泡不同的时间发生了点蚀和晶间腐蚀;热处理态金属除了点蚀与晶间腐蚀还发生了部分枝晶间腐蚀行为.热处理后的试样由于NbC,Laves相数量及尺寸的增加导致腐蚀敏感性升高.析出相NbC,Laves相与基体的电位差导致在腐蚀介质作用下发生点蚀.晶界析出物导致Ni,Cr元素含量的降低,从而增加了熔敷金属晶间腐蚀敏感性.热处理后由于元素再分配导致枝晶间Nb,Mo等元素的富集和Ni,Cr等元素的贫化,引起枝晶间腐蚀.创新点:(1)利用衍射花样标定确定析出相的晶体结构,结合X射线衍射分析得出析出相类型.(2)对热处理前后埋弧焊焊接接头的析出相数量和尺寸进行统计,阐明析出相对耐腐蚀性能的影响.

In this paper,the difference of corrosion resistance for NiCrMo-3 deposited metal with as-welded and as-PWHT(post welding heat treatment)at 690℃for 8 h was investigated by scanning electron microscope,transmission electron microscopy and other characterization methods.The results show that the as-welded specimens have better intergranular corrosion resistance than that of as-PWHT specimens.Pitting corrosion and intergranular corrosion occur when the specimens were immersed in HNO3 solution for different times.In addition to pitting corrosion and intergranular corrosion,partial inter-dendrite corrosion occurs in as-PWHT deposited metal.The increase of the number and size of NbC and Laves phase leads to the increase of corrosion sensitivity of the speci-mens after heat treatment.The potential difference between precipitated phase NbC,Laves phase and matrix leads to pitting corrosion under the action of corrosive medium.The contents of Ni and Cr elements decrease due to grain boundary precipitates,which increased the intergranular corrosion sensitivity of deposited metal.After heat treatment,the elements redistribution leads to the enrichment of Nb,Mo elements and depletion of Ni,Cr elements,resulting in inter-dendrite corrosion.Highlights:(1)The crystal structure of the precipitated phase was determined by diffraction pattern calibration,and the type of precipitated phase was obtained by X-ray diffraction analysis.(2)The quantity and size of precipitated phase of submerged arc welding joints before and after heat treatment were statistically analyzed,and the influence of precipitated phase on corrosion resistance was clarified.