###### Abstract  
The corrosion of nuclear-grade steels in lead-bisamuth eutectic (LBE) complicates the realization of high coolant temperatures. Corrosion tests of T91, HT9, and SS316L were performed in static cells at 600 \({}^{\circ}\)C for 2000 h at an oxygen level of \(10^{-6}\) wt.%. The obtained corrosion surfaces of post-processed samples were characterized by several microscopy methods. Up to 1000 h, all the alloys exhibited an evolution of duplex oxide layers, which were spalled until 2000 h due to their increased thickness and decreased integrity. Following the spallation, a thin internal Cr-rich oxide layer was formed above the Cr-depleted zone for T91 and HT9. SS316L was penetrated by LBE down to 300 um in severe cases. A comparison on the corrosion depths of the materials with regard to the parabolic oxidation law with abundant literature data suggests that it may lose its validity once the duplex layer is destroyed as it allows LBE to penetrate the metal substrate. LBE; lead-alloy-cooled fast reactor; high-temperature corrosion; stainless steel; HT9; T91; SS316L +
Footnote †: journal: Applied Sciences  
nature at high temperatures on various nuclear-grade steels also makes it challenging to achieve [12; 13]. Corrosion in LBE depends on several distinct mechanisms including the dissolution of alloying elements due to their dissimilar solubility limits to the liquid metal, the oxidation of the elements with dissolved oxygen, and erosion given by shear stress exerted by LBE flow [14]. To cope with the corrosive effect of LBE, numerous approaches have been investigated. For instance, Russia developed a Si-oxide-forming alloy and dissolved oxygen control technique [15]; however, the diffusion of chemical species across the Si-oxide layer exponentially accelerates with increasing temperature. To solve this issue, a protective Al\({}_{2}\)O\({}_{3}\) layer was applied to FeCrAl coatings, followed by pulsed electron beam mixing, which is basically FeAl-based coating and surface modification named GESA (GepulsteElektronenStrahlAnlage) [16; 17]. [PERSON] and his colleagues also developed Al\({}_{2}\)O\({}_{3}\)-forming FeCrAl ferritic steels [18; 19]. Both Si-containing ferritic/martenstic steels and Al-containing ferritic steels may exhibit significant radiation embrittlement due to the segregation of Si/Al to grain boundaries and the formation of a Cr-rich \(\alpha^{\prime}\)-phase at temperatures of 300-500 \({}^{\circ}\)C [20; 21; 22]. To achieve corrosion resistance while preserving desirable mechanical properties, a hybrid fuel cladding tube has been suggested by [PERSON] and his colleagues in the case of Si-containing alloys on radiation-resistant ferritic/martenstic steels [23]. To ensure the fabricability and reliability of structural materials exposed to LBE, the corrosion behaviors of American Society of Mechanical Engineers (ASME) code-certified materials were studied [24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34]. Ferrritic/martenstic steels (e.g., HT9 and T91), having a maximum swelling temperature of 400-420 \({}^{\circ}\)C and exhibiting swelling of less than 2% [35], displaying higher resistance to 200 dpa irradiation than austenitic stainless steels [36]. Corrosion tests were also performed for silicon-added 9 Cr steels at 450-550 \({}^{\circ}\)C, with improved performance observed at low temperatures [21; 37; 38; 39; 40]. However, previously reported data on the corrosion of ASME code-certified materials at higher temperature such as 600 \({}^{\circ}\)C are limited. Herein, we present our corrosion test results on some ASME code-certified ferritic/martensitic stainless steels, T91 and HT9, and an austenitic stainless steel, SS316L, conducted in static LBE-containing cells at 600 \({}^{\circ}\)C for 1000 and 2000 h at an oxygen level of 10\({}^{-6}\) wt.%. The post-processing results on the specimens are characterized by the means of several microscopic analysis methods.