Abstract
Near-surface hydrogen segregation with a concentration that is at least three times higher than that in the internal layers is detected in D16 and AK4-1 alloy rods subjected to standard hardening heat treatment. When AK4-1 alloy rods are stored, hydrogen from the segregation region propagates into the metal volume via two dissolved hydrogen waves moving toward the volume and surface of a rod rather than via a classic diffusion way. The segregation region with an initially high hydrogen content eventually becomes almost free of hydrogen. Both the directions and anomalously high velocities of low-temperature uphill (against the concentration gradient) hydrogen flows in the rods are explained by the effect of internal stresses in the alloys.
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