Deformation-induced defects controlling fracture toughness of steel revealed by tritium desorption behaviors

Defects induced by plastic deformation have been revealed by means of room temperature desorption and thermal desorption spectroscopy of tritium with regards to the ductile crack growth resistance and brittle fracture initiation in steels in the ductile-to-brittle transition region. Tritium, as a probe for detecting defects, was introduced into non-deformed or deformed samples. Three steels, the microstructures of which are characterized by the constraint factor for slip extension, were employed. The residual tritium in a specimen after three days at room temperature increased to the extent corresponding to the constraint factors when plastic deformation was applied. The thermally desorbed tritium, with a peak desorption rate around 150°C, also increased according to the constraint factors. Referring to the previous analysis of the R-curves, the constraint for the extension of slip across grain boundaries is shown to control both the ductile crack growth resistance and the brittle fracture initiation through the deformation microstructures that evolve vacancy clusters or microvoids.