| Lead-based reactor is one of the fourth-generation nuclear reactors.Liquid metals(lead or lead-bismuth eutectic)are used as system coolant or scattering target,which have strong corrosive effect on the structural material.The development of lead(leadbismuth)corrosion-resistant structural material is the key to the development of leadbased reactor.The ferritic/martensitic steel(F/M steel)bearing antioxidant element Si is an important direction in the development of structural materials resistant to lead(lead bismuth)corrosion.Welding is an important thermal process in reactor construction,and the welds often show different corrosion resistance from the base material.The corrosion behaviors of 9Cr-Si F/M steel deposited metal in static leadbismuth eutectic(LBE)at 550℃ were investigated in this study to lay the foundation for developing the lead-bismuth corrosion-resistant welding fillers.Four kinds of 9Cr-Si F/M steel wires with different Si contents were designed and fabricated,and the deposited metals were manufactured by multi-layer and multi-pass welding by TIG(Tungsten inert gas arc welding).The deposited metal samples were placed in static LBE with oxygen-saturated(Co,max=1.8×10-3 wt.%)and controlled oxygen(Co=10-6～5×10-6 wt.%)at 550℃ for corrosion experiments.SEM-EDS,EPMA,TEM,XPS,and XRD were used to analyze the structure of the oxide scales formed on the corrosion samples.The corrosion behaviors of 9Cr-Si F/M steel deposited metal with different Si contents in static LBE were systematically studied.The main work and results of the paper are as follows.9Cr-Si F/M steel deposited metal in 550℃ static oxygen-saturated LBE forms an oxide scale with three-layer structure,including outer layer,inner layer,and inner oxide zone(IOZ).A three-stage corrosion mechanism is proposed for the 9Cr-Si F/M steel deposited metal in static oxygen-saturated LBE at 550℃.The thickness of oxide scale and exposure time have a parabolic relationship.There are two parabolic constants in the early and the later stages of corrosion,respectively.The early parabolic constant is larger.IOZ presents emergence,disappearance,and regeneration and inner layer divides into two sublayers in the corrosion process.Si forms oxides(SiO2 and Fe2SiO4)in inner layer and IOZ which impede the outward diffusion of Fe in the matrix and promotes the generation of Cr-rich oxides.The increase in Si content reduces the growth rate of oxide scale and improves the corrosion resistance of the deposited metal in oxygensaturated LBE.9Cr-Si F/M steel deposited metal in 550℃ static oxygen-controlled LBE forms a discontinuous passivation layer and a double(or triple)oxide scale with uneven thickness,including outer layer,inner layer and partially emerged IOZ.Si is mainly enriched in the passivation layer and the inner layer/substrate interface.The increase of Si content improves the continuity of the passivation layer,impedes the generation of IOZ in oxidation aggravation regions and further oxidation of the substrate,improving the corrosion resistance of the deposited metal in oxygen-controlled LBE.Without dissolution corrosion,reducing the oxygen concentration in LBE promotes the formation of the passivation layer and reduce the corrosion rate of the deposited metal.The passivation layer fails by penetration and film breakdown mechanisms during the corrosion process. |
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