THE HEALING OF HYDROGEN-INDUCED MICROCRACKS IN IRON - 3% SILICON.
STANFORD UNIV CA DEPT OF MATERIALS SCIENCE AND ENGINEERING
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High-temperature annealing treatments are investigated. The cleavage fracture strength at -196 C of precracked material has been found to increase from 50 ksi as-cracked to 65 ksi after annealing for six hours at 900 C, and to 67 ksi after annealing for five hours at 1000 C. This effective healing appears to result from an increase in the critical strain necessary for reinitiation of the stopped microcracks, an increase in the tip radii of curvature of the microcracks, or both of these effects. In addition, the effective healing of microcracks results in an increase in tensile ductility of precracked material above the transition temperature range, coupled with a lowering of the transition temperature. These effects appear to result from a lowering of the effective strain concentration factor of the microcracks after annealing. Individual small microcracks have occasionally been observed to heal completely disappear. The mechanism for this complete healing is believed to involve a combination of recovery a disperson of polygonization to the crack surface and sintering capillarity-induced mass transport at or to the crack surface.
- Properties of Metals and Alloys
- Fabrication Metallurgy