SEDL / STP / STP978-EB / STP26190S

Hydrogen Embrittlement of Plated High-Strength 4340 Steel by Galvanic Corrosion

Pollock, WJ
Principal research scientist and senior research scientist, Aeronautical Research Laboratories, Defence Science and Technology Organization, Department of Defence, Melborne, Victoria

Hinton, BRW
Principal research scientist and senior research scientist, Aeronautical Research Laboratories, Defence Science and Technology Organization, Department of Defence, Melborne, Victoria

Pages: 16    Published: Jan 1988

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Abstract

Slow strain rate methods are used to quantify the degree of embrittlement in high-strength 4340 steel after coating with porous electroplated cadmium or ion-vapor-deposited aluminum and subsequently exposing to aqueous sodium chloride environments for various times. Porosity in the coatings is primarily responsible for the establishment of galvanic couples at the steel/coating interface, resulting in the generation and absorption of hydrogen in the steel. Data from hydrogen permeation and galvanic corrosion experiments are used to establish a model for hydrogen generation in coated tensile specimens. Estimates of the total hydrogen absorbed in cadmium-plated tensile specimens are consistent with the results of slow strain rate tests whereas similar calculations grossly underestimate the total hydrogen absorbed in aluminum-coated specimens where localized corrosion processes are believed to enhance the rate of hydrogen generation.