Oxide Scale Formation on Ultrafine-Grained Ferritic-Martensitic Steel During Pre-Oxidation and Its Effect on the Corrosion Performance in Stagnant Liquid Pb-Bi Eutectic
Oxide Scale Formation on Ultrafine-Grained Ferritic-Martensitic Steel During Pre-Oxidation and Its Effect on the Corrosion Performance in Stagnant Liquid Pb-Bi Eutectic
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DOI：
10.11900/0412.1961.2020.00451
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发表时间：
2021-08-01
影响因子：
2.3
通讯作者：
Rong Lijian
中科院分区：
文献类型：
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作者：
Chen Shenghu;Rong Lijian
液态铅和铅铋共晶(LBE)因其良好的热物性和化学性质，被认为是先进铅快堆冷却剂的主要候选材料，也是加速器驱动系统冷却剂和散裂靶材的首选材料。然而，液态铅和LBE表现出严重的结构材料腐蚀，这被认为是液态铅或LBE应用中的关键挑战之一。在减少腐蚀影响的有效方法中，仔细控制液体中的溶解氧含量在结构材料的表面引入了一层保护性的氧化层。质量分数为(9%~12%)的铁素体-马氏体钢被认为是先进的铅快堆和加速器驱动系统中很有前途的结构材料。在含氧LBE中，在(9%~12%)铬铁素体-马氏体钢上形成了具有双重结构的氧化膜，但氧化膜的生长速度很快，足以引起衬底衰退。近年来，为进一步改善LBE的腐蚀性能，人们提出了预氧化处理。据报道，在没有化学变质的情况下，晶粒细化促进了氧化膜的形成。然而，对(9%~12%)铬铁素体-马氏体钢氧化膜的细化作用尚不清楚，预氧化处理后的氧化膜对LBE腐蚀性能的影响更是鲜见报道。利用扫描电子显微镜、X射线衍射仪、电子探针和X射线光电子能谱分析了9Cr2WVTa铁素体-马氏体钢在650℃空气中预氧化过程中不同冷旋锻变形速率后的氧化膜形成行为，并进一步研究了预氧化膜对静止氧饱和LBE腐蚀性能的影响。结果表明，随着压下率的增加，材料在空气中的高温抗氧化性得到提高。63%变形后抗氧化性略有提高，而94%变形量制备的超细晶样品的抗氧化性显著提高。在空气氧化过程中，变形63%的样品与回火样品相比，其氧化物颗粒尺寸略有减小，但都形成了(Fe，Cr)(2)O-3氧化物颗粒。超细晶样品中的氧化物颗粒明显细化，富锰氧化物(MnCr2O4和Mn2O3)增多。具有良好稳定性的富锰氧化物的存在提高了氧化膜的致密性。650℃预氧化20h的超细晶样品上致密的氧化膜有效地抑制了LBE的腐蚀和在550℃停滞氧饱和LBE中暴露500h后Fe通过预氧化膜向外扩散。锰在预氧化膜中的逐渐溶解和LBE的腐蚀导致了预氧化膜的破裂，这是由于在停滞的氧饱和LBE中暴露2000h后形成的连续腐蚀产物层支持的。
Liquid lead and lead-bismuth eutectic (LBE) are considered primary candidate materials for coolant in advanced lead fast reactors, and also, for coolant and spallation target in accelerator-driven systems because of their favorable thermal-physical and chemical properties. However, liquid lead and LBE exhibit substantial structural material corrosion, which is considered one of the critical challenges in the liquid lead or LBE application. Among the effective methods to reduce the corrosive effect, careful control of the oxygen content dissolved in the liquid introduces a protective oxide layer on the surface of the structural material. Ferritic-martensitic steels with (9%-12%)Cr (mass fraction) have been considered promising structural materials in the advanced lead fast reactor and accelerator-driven system. Oxide scale with duplex structure is formed on the (9%-12%)Cr ferritic-martensitic steels in oxygen-containing LBE, but the oxide scale grows rapidly enough to cause the substrate recession. Recently, pre-oxidation treatment was proposed to further improve the corrosion performance in LBE. As reported, grain refinement promoted the formation of oxide scale without chemical modification. However, grain refinement effects on the oxide scale formation of (9%-12%)Cr ferritic-martensitic steels are not clear, and the effect of oxide scale through pre-oxidation treatment on the corrosion performance in LBE is rarely reported. In this study, the oxide scale formation behavior during pre-oxidation in air at 650 degrees C on the 9Cr2WVTa ferritic-martensitic steel after different cold rotary-swaging deformation rates was analyzed using SEM, XRD, EPMA, and XPS, and the effect of pre-oxide scale on the corrosion performance in stagnant oxygen-saturated LBE was further investigated. The results demonstrated that the high-temperature oxidation resistance in air was enhanced by increasing the diameter reduction. A slight improvement in oxidation resistance was observed after 63% deformation, while significant enhancement in oxidation resistance was present in ultrafine-grained sample fabricated by 94% deformation. The oxide particle size was slightly reduced in the sample produced after 63% deformation during air oxidation compared with the tempered sample, but (Fe, Cr)(2)O-3 oxide particles were formed on both samples. The size of oxide particles was significantly reduced and Mn-riched oxide (MnCr2O4 and Mn2O3) was promoted in the ultrafine-grained sample. The presence of Mn-riched oxide with good stability improved the oxide scale compactness. The compact oxide scale on the ultrafine-grained sample using pre-oxidation treatment at 650 degrees C for 20 h effectively suppressed the corrosive attack of LBE and the outward diffusion of Fe through the pre-oxide scale after exposure for 500 h to stagnant oxygen-saturated LBE at 550 degrees C. The higher solubility of Mn in LBE promoted the dissolution of the Mn-riched pre-oxide scale. The gradual dissolution of Mn in pre-oxide scale and corrosive attack by LBE led to the breakdown of the pre-oxide scale, which was supported by the formation of a continuous corrosion product layer after exposure for 2000 h to stagnant oxygen-saturated LBE.