High-strength steels plated with cadmium for protection against corrosion were found to fail unexpectedly at high stress levels. A definite connection between this phenomenon and the introduction of hydrogen into the steel through pickling and plating was determined. Tests were made to determine the effect of hydrogen concentration and notch radius on the delayed failure of aircraft quality SAE-AISI 4340 steel samples. As might be expected, hydrogen concentration exerted a potent influence on the static fatigue curve.
The kinetics of crack initiation and propagation were studied by an electrical resistivity method. The existence of an incubation period for crack initiation and a period of apparently controlled crack growth were apparent. Data on the reversibility of the incubation period were reported.
Baking to eliminate hydrogen from steel was effective with thin plates, but thickly plated parts still exhibit embrittlement. A new recovery treatment was developed to solve this problem without increasing baking times on temperatures for thicker plates. This method involves double electroplating of cadmium and depends for its effectiveness on the ability of cadmium to delay the passage of hydrogen. 3.2.2
