Book excerpt: Three grades of unalloyed titanium were studied to determine the effect of variations in O and N contents on delayed cracking. The bar stock was analyzed for interstitial content, then vacuum annealed to remove most of the H. Large samples of the 1/2-in.-diam vaccum-annealed stock were subsequently hydrogenated to about 90 and 160 ppm H levels. Hydrogen-induced strainaging embrittlement at ambient temperatures in interstitial-containing alphi Ti was not indicated by the results of stress-rupture tests. The results indicate that strain-aging embrittlement does not occur in unalloyed Ti having up to 0.38 wt-% O with as much as 160 ppm H content. However, a noticable effect of H on notch sensitivity of the materials, in the alpha-annealed and especially in the beta-annealed conditions, was observed. It appears probable that H was concentrated in the critical areas by a thermaldiffusion process to create an ultrasensitive zone. Failure might have occurred subsequently as a result of simple overstressing, or by accidentally applied impact stresses, or by a more complicated low-cycle fatigue mechanism. (Author).