双金属复合管Inconel625合金堆焊层表面黑斑形成原因及其对材料性能的影响

 为探究双金属复合管Inconel625合金堆焊层表面局部出现黑斑的原因，通过对试样进行理化性能分析，结合堆焊工艺，对黑斑位置与正常位置进行了对比研究。结果表明，与正常位置相比，黑斑位置的基管Fe元素向堆焊层扩散程度加大，局部形成元素偏析，故堆焊层表面黑斑可能与较高热输入量下的高稀释率有关。另经检测分析，黑斑位置的化学成分、金相组织、弯曲性能、硬度、耐蚀性能均符合API 5LD—2015标准要求，但黑斑位置的晶间腐蚀与点腐蚀速率均高于正常位置，故黑斑现象对合金堆焊层的耐腐蚀性能存在不利影响。

Forming Causes of Black Spots of Inconel625 Alloy Surfacing Layer of Bimetal Composite Pipe and Its Effect on Material Properties

 In order to find out the forming causes of black spots on the surfacing layer of Inconel625 alloy for bimetal composite pipe, the black spots on the surface of the surfacing layer were obtained by means of the physical and chemical properties analysises and the black spots positionss were compared with the normal position by combining with the surfacing process. The results show that compared with the normal position, the diffusion degree of Fe element in the base pipe at the black spot position increases to the surfacing layer. Therefore, the black spots on the surface of surfacing layer may be related to the high dilution ratio under higher heat input. In addition, the chemical composition, metallographic structure, bending property, hardness and corrosion resistance of black spots positions can meet the requirements of API 5LD—2015 standard. However, the rates of intergranular corrosion and pitting corrosion at the black spots positions are higher than those at the normal position, so the black spot has an adverse effect on the corrosion resistance of the alloy surfacing layer.