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 initiat ion in steels in the ductile-to-brittle transition region. Tritium, as a pr obe for detecting defects, was introduced into non-deformed or deformed sam ples. Three steels, the microstructures of which are characterized by the c onstrains factor for slip extension, were employed. The residual tritium in a specimen after three days at room temperature increased to the extent co rresponding to the constraint factors when plastic deformation was applied. The thermally desorbed tritium, with a peak desorption rate around 150 deg rees C, also increased according to the constraint factors. Referring to th e previous analysis of the R-curves, the constraint for the extension of sl ip across grain boundaries is shown to control both the ductile crack growt h resistance and the brittle fracture initiation through the deformation mi crostructures that evolve vacancy clusters or microvoids. (C) 2000 Acta Met allurgica Inc. Published by Elsevier Science Ltd All rights reserved.