Sustained load tensile testing has been made while under cathodic charging with hydrogen using notched sheet specimens of an 18% Ni maraging steel. Two kinds of specimens as to the way of processing prior to aging have been prepared; R-specimens which were cold rolled after solution treatment, and S-specimens undeformed after solution treatment. Aged S-specimens have shown characteristic delayed failure, accompanied with subcritical intergranular fracture surfaces. No. fracture has been observed below a stress called the lower critical stress, at which the local concentration stress at notch roots is found to be identical to the yield stress of the specimens.
Cold rolling prior to aging has resulted in great suppression of hydrogen induced intergranular cracking, and the fracture lives are increased even by 70 times with rolling reductions up to 30%. The effect, however, is being saturated in the heavier reduction of 80%, where the delaminations along rolling planes have been observed. From fractographic evidence, apparent Kc has been found to decrease greatly in 5-specimens during the testing, but not remarkably in R-specimens.
No delayed failure has been observed in 80%-rolled R-specimens when the age-hardening is confined within the strength level of conventionally treated (i.e. non-deformed and peak-aged) S-specimens.