Inconel625合金及焊缝在Na2SO4-NaCl熔盐中热腐蚀行为研究

Hot Corrosion Behavior of Inconel625 Alloy and Welds in Na2SO4-NaCl Molten Salt

摘要:

对Inconel625母材与焊缝金属进行750℃下的75% Na2SO4-25%NaCl混合熔盐热腐蚀实验，并对腐蚀产物的物相、表面形貌、腐蚀失重速率及腐蚀机理等进行研究分析。结果表明:Inconel625接头母材处组织为奥氏体等轴晶，焊缝处组织为树枝晶；母材与焊缝金属失重曲线均遵循抛物线规律，其失重速率常数分别为3.43和4.18；焊缝金属因为富Nb第二相的析出，导致其与母材相比耐蚀性较差，腐蚀表现出“不均匀性”；两种状态下的Inconel625有着相同的腐蚀层结构均为，外层NiO颗粒和片层状NiCr2O4，中层致密Cr2O3氧化层，内层“蜂窝”状Ni2S3硫化层的3层结构；Inconel625合金在750℃下75%Na2SO4-25%NaCl混合盐中的主要腐蚀机理为:“硫化-氧化”腐蚀。

Abstract:

Inconel 625 base metal and weld metal were subjected to 75% Na2SO4-25% NaCl mixed molten salt hot corrosion experiments at 750°C. The physical phase, surface morphology, corrosion weight loss rate and corrosion mechanism of corrosion products were studied and analyzed. The results show that the organization of Inconel 625 joints is austenitic equiaxial crystal at the base material and dendrite at the weld. The weight loss curves of both base metal and weld metal follow parabolic laws with weight loss rate constants of 3.43 and 4.18, respectively. The weld metal is less resistant to corrosion compared to the base material due to the precipitation of Nb-rich second phase, and corrosion exhibits "inhomogeneity". Inconel 625 in both states has the same corrosion layer structure, the outer layer of NiO particles and lamellar NiCr2O4, the middle layer of dense Cr2O3 oxide layer, and the inner layer of "honeycomb" Ni2S3 sulfide layer of the three-layer structure. The main corrosion mechanism of Inconel 625 alloy in 75% Na2SO4-25% NaCl mixed salt at 750°C is: "sulfidation-oxidation" corrosion.