The dissolution of austenitic steel in liquid lead-based alloys can induce a phase transformation characterized by a sharp dissolution front separating ferrite and austenite grains, a process commonly referred to as ferritization. Although widely reported, the mechanism driving this transformation remains under debate. This study re-examines ferritization as a discontinuous reaction via a migrating liquid film and proposes a thermodynamically consistent model for the initiation and propagation of the dissolution front. The proposed mechanism is supported by experiments at 500–550°C, literature evidence, and diffusion calculations. Under low oxygen conditions, Cr transport through liquid Pb channels is identified as the rate-limiting step, setting the theoretical corrosion rate in stagnant environments. High-speed erosion-corrosion tests show enhanced corrosion rates, driven by erosion-limited channel lengths that locally boost mass transport. In contrast, under moderate oxygen concentrations relevant for lead-cooled fast reactor (LFR) operation, the rate-limiting step shifts to metal transport across a nanometer-scale amorphous oxide layer at the reaction front. Other Ni-containing austenitic steels, including alumina-forming austenitic (AFA) alloys and Ni-based high-entropy alloys (HEAs) can also be susceptible to discontinuous reactions under direct contact with liquid Pb-based alloys, lacking the self-healing oxide protection as observed in alumina-forming ferritic steels. This limitation may present a concern for the long-term use of bare austenitic steel in liquid Pb environments.

Erosion-corrosion experiments were carried out a chromia-forming steel (316L) alumina-forming ferritic, austenitic and martensitic steels and coated 316L at 480-520 °C in liquid lead. Testing was done under low oxygen conditions (10-7-10-8 wt.% O) for times up to 1392 hours using a purpose-built Erosion Corrosion rig (ECO). It was found that uncoated 316L suffered from Ni dissolution to a depth of 140 µm and severe erosion-corrosion attack. After coating with alumina oxide via Detonation Gun (DG) and Pack Cementation (PC) methods, the 316L remained unaffected. The commercial alumina forming alloys containing multiple reactive elements, Kanthal EF 100, Alkrothal 14 and Kanthal APMT, performed well and were minimally affected by erosion-corrosion. However, Kanthal AF, which contains only the single reactive element Y, lost a similar amount of mass as the 316L sample. The experimental alumina forming austenitic alloy denoted AFA 3 showed very poor resistance to erosion-corrosion, suffering from severe mass loss and with signs of Ni dissolution to a depth of 25 µm. The experimental alumina-forming martensitic steel, AFM, on the other hand, remained unaffected by erosion-corrosion. Hydrodynamic simulations were carried out using ANSYS FLUENT to determine the relative velocity between the HLM and the samples, calculating the highest velocity to be 9.9 m/s. It also demonstrated a good qualitative alignment between the experimental result and the simulations. This indicates that the erosion damage originated from a combination of the turbulence created inside the ECO-rig and particle erosion.

Three new multi-phase alumina-forming steels with compositions Fe-(10–14.5)Cr-(10–12)Ni-3.5Al (wt.%) were exposed to stagnant lead at 550 and 650 °C for up to 1000 h The experimental alloys formed stable and protective alumina (Al2O3) layers at both temperatures, crucial for preventing lead penetration and material degradation. In contrast, 316 L and T91 steels, candidate materials for nuclear applications, showed significant oxidation and lead penetration, particularly at the higher temperature. The designed alloys retained their mechanical properties after exposure, with one of them even increasing yield strength due to phase transformations. The findings highlight the potential of these new alloys with no reactive elements and no thermomechanical treatments, to operate in environments with high-temperature liquid lead, such as Gen IV nuclear reactors or high-temperature concentrated solar power plants.

Liquid metal embrittlement was observed in an alumina-forming martensitic (AFM) steel tested in both liquid Pb and lead-bismuth eutectic (LBE) in the temperature range 350-550 °C and 150-550 °C, respectively, using slow strain rate testing (SSRT) in a low oxygen environment ( ~10-11 wt.% O dissolved in Pb). A significant decrease in the total elongation to failure (TEF) could be observed in both environments, with LBE yielding the lowest measured TEF of 0.9% strain at 150 °C. The elongation to failure followed the classic pattern of a ductility dip, gradually recovering with increasing testing temperature so that fully ductile behaviour was restored at 550°C. There may be a potential to improve the performance of the AFM alloy by optimizing the microstructure through adjustments to the austenitizing, quenching and tempering conditions. 

Liquid metal embrittlement was observed in an alumina-forming martensitic (AFM) steel tested in both liquid Pb and lead–bismuth eutectic (LBE) in the temperature range 350–550 °C and 150–550 °C, respectively, using slow strain rate testing (SSRT) in a low oxygen environment (∼10-11 wt% O dissolved in Pb). A significant decrease in the total elongation to failure (TEF) could be observed in both environments, with LBE yielding the lowest measured TEF of 0.9 % strain at 150 °C. The elongation to failure followed the classic pattern of a ductility dip, gradually recovering with increasing testing temperature so that fully ductile behaviour was restored at 550 °C. There may be a potential to improve the performance of the AFM alloy by optimizing the microstructure through adjustments to the austenitizing, quenching and tempering conditions.

Liquid metal embrittlement (LME) in three newly developed alumina-forming austenitic (AFA) alloys, two 50 kg batches and one 5-ton heat, was studied in the temperature range 350–600 °C in liquid Pb and 140–600 °C in LBE using slow strain rate testing (SSRT) in a low-oxygen environment. No significant decrease in the engineering strain was observed in either environment. However, the presence of secondary cracks along the length of the specimen and brittle intergranular areas on the fracture surfaces indicates that the AFA alloys do show a minor degree of embrittlement above 570 °C. This appears to be related to grain boundary wetting by Pb/LBE. At temperatures below 570 °C, this wetting effect does not seem to be strong enough to induce LME in the alloys, and their ability to form a sufficiently protective oxide means that they remain unaffected by LME. The results indicate that the AFA alloy group can perform sufficiently well in liquid Pb/LBE environments, and long-term testing should be carried out to determine their viability as candidate materials for use in Pb- and LBE-based cooling systems.

The use of molten lead as a heat exchange fluid poses important critical issues, both in terms of corrosion resistance and creep resistance, due to the temperatures and structural stresses reached during operation. The objective of this work has been the investigation of the corrosion resistance and mechanical properties of new experimental compositions of alumina-forming stainless-steel candidates for these applications. The exposures to stagnant liquid lead were carried out for 500 and 1, 000 hours, at temperatures of 550 and 650 °C, with controlled amounts of oxygen dissolved in the liquid lead. In comparison with the AISI 316L and T91 both tested as reference materials, the studied alloys showed highly promising corrosion behavior and mechanical properties. According to these results, the proposed steels are appropriate for components that will operate in liquid lead at elevated temperatures without corrosion, while maintaining good mechanical properties.

Liquid metal embrittlement (LME) of a Fe-10Cr-4Al ferritic steel was studied at 375 degrees C in liquid Pb-Bi alloys. Slow strain rate testing (SSRT) in low oxygen conditions was used to evaluate the ductility as a function of Bi concentration. It was found that susceptibility to LME increased strongly with the Bi concentration. The steel showed a reduction in its total strain to failure, which started at 3-5 wt.% Bi. The alloying elements (Fe, Cr, and Al) have a higher solubility in Bi than pure lead (Pb), so they are expected to dissolve more readily when Bi is added to the Pb. This is believed to be part of the explanation for the observed increase of LME. Lead with up to 3 wt.% Bi induced no LME in the studied corrosion resistance FeCrAl alloy.

The susceptibility of Fe-10Cr-4Al steel to liquid metal embrittlement (LME) in low oxygen liquid lead and lead-bismuth eutectic (LBE) environments has been investigated using a newly developed slow strain rate testing (SSRT) technique that can be employed at elevated temperatures. This study showed that the Fe-10Cr-4Al steel suffered embrittlement when exposed to LBE over a wide temperature range. The embrittlement, here measured as a reduction in fracture strain, was observed at the melting temperature of LBE and reached a maximum at approximately 375 degrees C. At temperatures above 425 degrees C, the material's ductility regained its original levels. The exposures in liquid lead showed no indications of embrittlement, but a ductile behavior over the entire tem-perature range studied (340-480 degrees C).

In this paper, the possibility of applying different welding strategies to overlay an FeCrAl layer against corrosion from heavy liquid metal on a plain plate made of 316L austenitic stainless steel was investigated. This technology could be used in manufacturing the main vessel of CiADS, which may be considered as a more economic and feasible solution than production with the corrosion-resistant FeCrAl alloy directly. The main operational parameters of the laser welding process, including laser power, weld wire feeding speed, diameter of the welding wire, etc., were adjusted correspondingly to the optimized mechanical properties of the welded plate. After performing the standard nuclear-grade bending tests, it can be preliminarily confirmed that the low-power pulse laser with specific operational parameters and an enhanced cooling strategy will be suitable to surface an Fe-10Cr-4Al-RE layer with a thickness of approximately 1 mm on a 40 mm-thick 316L stainless steel plate, thanks to the upgraded mechanical properties incurred by refined grains with a maximum size of around 300 mu m in the welded layer.