Behavior of Subcritical and Slow-Stable Crack Growth Following a Post-Irradiation Thermal Anneal Cycle.

摘要

This report presents the experimental results of Phase I of a Small Business Innovation Research Program which investigated the response of environmentally-assisted monotonic and cyclic crack growth following a simulated anneal of a reactor-pressure vessel weld. Unirradiated steels were used in this (initial) Phase I of the program. Fatigue cracks were grown in several specimens of a submerged arc weld deposit in pressurized, high-temperature reactor-grade water. The specimens were removed from the environment, and annealed for one week at either 399C or 454C. Fatigue crack growth in high-temperature water was resumed on several annealed specimens and unannealed controls. No effect of the anneal was noted on the fatigue crack growth rates, which continued with about the same degree of environmental assistance as exhibited before the anneal. An elastic-plastic fracture specimen, tested in 93C air at a very slow loading rate, showed that neither annealing nor the slow rate had a significant effect on the J-R curve characteristics. However, conducting the tests at a slow loading rate in 93C PWR water resulted in a 25% to 30% decrease in J sub Ic and a small decrease in T(avg). Examination of the oxides on the fatigue fracture surfaces showed that magnetite (formed during the crack growth in pressurized, high-temperature water) was the predominant oxide specie.