Corrosion behaviour of welds and Ta in liquid lead

Abstract

Four specimens, P91 welded by friction stir welding with and without post heat treatment, P91 electromagnetic pulse welded (EMP) and 14Cr ODS (explosive welding) were exposed at 550 °C for up to 2131 h to Pb containing 10−6 wt% oxygen. After the exposure none of the samples showed dissolution attack, all were protected by an oxide layer at the surface. Nearly no effect on the oxidation due to welding was found in both friction stir welded specimens. Severe deformation and partial melting during explosive welding result in a slower oxide layer growth within the welding zone. The EMP sample was tested as delivered without post-heat treatment. No Pb penetrated into the tiny gap between the welded parts. After the test, the gap is filled up with oxides.Additionally, Ta, discussed as a pump impeller material, was exposed to Pb and PbBi at different temperatures (400–900 °C) and oxygen concentrations in liquid metal (saturated, 10−6 wt%, 10−8 wt% and reduced (<<10−8 wt%). Only the Ta specimens exposed to Pb with highly reduced oxygen content showed nearly no attack. All the others exhibited oxide scale formation that becomes severe above 400 °C test temperature.