112 Self-healing of Creep Damage in Austenitic Stainless Steel

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In austenitic stainless steels, creep cavities nucleate at grain boundaries by long time use at high temperatures. These creep cavities grow along grain boundaries, form grain boundary cracks by linking up each other and cause the premature and low ductility fracture. Therefore long time creep rupture life and ductilities chiefly depend upon the behavior of nucleation and growth of creep cavities. If the growth of creep cavities could be suppressed, creep rupture life and ductilities should be improved remarkably. Present work is intended to propose a self-healing process for the cavitation and improve the creep rupture properties due to the suppression of creep cavity growth by a self-healing process. Ordinary austenitic stainless steels contain sulfur as impurity and segregates to creep cavity surface because of its high surface activity. It is possible to remove sulfur almost completely by doping cerium and adding titanium to the austenitic stainless steels. By adding boron and nitrogen, boronnitride precipitates on creep cavity surface. It was thought that the boronnitride on creep cavity surface supresses creep cavity growth and improves creep rupture life and ductilities by its healing effect on creep cavities.
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