Honeycomb structure with oxygen-poor pores at the top of magnetite layer on a martensitic steel CLAM exposed to lead-bismuth eutectic at 500 ºC.

Localized regions at the top of the magnetite layer on a 9 %Cr martensitic steel CLAM were honeycombed after exposure to lead-bismuth eutectic (LBE) at 500 ºC for 500–2000 h. The honeycomb structures were composed of many oxygen-poor pores and surrounding net-like branches. Low oxygen concentrations promoted the formation of honeycomb structures in a shorter time and more areas. A model based on the local dissolution of magnetite crystals was proposed to explain the formation process. Honeycomb structures can lead to much oxygen loss in the spinel layer, which may induce pitting corrosion and promote its development. • Honeycomb structures in the oxide scale of martensitic steel are rarely reported in LBE. • Honeycomb structures were composed of net-like branches and oxygen-poor pores. • Low oxygen concentrations promoted the formation of honeycomb structures. • Honeycomb structures led to oxygen loss in spinel layer and may induce pitting corrosion. • Honeycomb structures may be an indicator of local low oxygen concentrations. [ABSTRACT FROM AUTHOR]