Hydrogen re-embrittlement of high strength steel by corrosion of cadmium and aluminium based sacrificial coatings

Abstract

When high strength steels absorb hydrogen during corrosion of a sacrificial coating they can fail by a process termed hydrogen re-embrittlement. This paper compares the levels of re-embrittlement caused by coatings of electroplated cadmium and two possible alternative aluminium based coatings. Slow strain rate tests were performed on coated tensile specimens exposed to 3·5%NaCl solution or pre-exposed to a coastal marine atmosphere. Permeation experiments were used to measure the absorption of hydrogen over a range of potentials, including those typical of the corroding sacrificial coatings. The severity of re-embrittlement was shown to be controlled not only by the corrosion potential of the coating but also by its barrier properties, which can limit hydrogen uptake by the steel substrate.

Keywords:

• HYDROGEN EMBRITTLEMENT
• CADMIUM PLATING
• ALUMINIUM COATINGS
• SLOW STRAIN RATE TEST