引張変形されたオーステナイト系不銹鋼薄肉管の渦流検査

抄録

Eddy current testing is one of the most effective nondestructive test methods in the fields of thin-tube inspection and the theoretical foundation on its nature is already analysed in detail. However, published practical data on the testing are comparatively few. Therefore, the changes of the current flowing in a annular coil (7 KC) on a tensile-deformed thin tube (initial tube dimension; O.D. 8.56 mm, I.D. 7.50 mm) of AISI-304 type austenitic stainless steels were investigated. The main results obtained were as follows: (1) The current change (the only phase component) caused by tensile deformation of the tube specimen increased in accordance with the increase of unstability of the austenitic phase of the initial tube. (2) The electrical resistivity and the magnetic property can be considered as factors affecting the current change. The measurement showed that the former change is comparatively small and the latter change is predominant. This means that the measured change is caused by a precipitation of ferrite phase in the austenite phase by deformation. (3) The current change is affected by heat-treatment before deformation. Generally speaking, the change of annealed specimen is larger than that of solutionized specimen (in annealed specimen it became to the maximum at the annealing temperature of ca. 650°C). (4) Recovery of the current change takes place at the temperature of 400∼650°C. The activation energy of recovery decreases continuously with increasing gross recovery.