Corrosion properties of welded ferritic-martensitic steels in liquid lead-bismuth AT 600C

A static corrosion test for ferritic-martensitic steel HCM12A with three types of welding in lead-bismuth eutectic (LBE) was conducted at 600°C for 500 h. The specifications of TIG welding, YAG laser welding and electron beam welding were 40A/12V of electrical conductance, 278W/14.3J of heat input and 5.0 mA of beam electric current, respectively. Oxygen concentration was controlled to be about 4.7×10^-6wt% by injecting Ar-H2-H2O gas mixture into LBE. After corrosion test, cross sections of the specimens were analyzed by using optical microscope and SEM/EDX. Toughness profiles of fusion zone and base metal were determined by using Vickers hardness tool. The results show coarse grain structure in fusion zone (FZ) and typical ferritic-martensitic grain structure in base metal (BM). It was found that those Cr-rich spinel oxide layer and diffusion zone were formed on the surface. The total thickness of oxide layer and diffusion zone on and in the fusion zone was about 18-30μm. It was much thicker than 10-15μm on BM. The hardness was higher in the fusion zone than in the BM.