Development of nondestructive techniques for micro-damages; Measurement of ferrite quantity by barkhausen noise method

Sakamoto, Yoshihiko ; Kawasaki, Hirotsugu

For the establishment of life and residual life evalution method for FBR, the development of nondestructive technique by barkhausen noise (hereafter refferred to as BHN) method has been carried out as one of the method of detecting damages in materials nondestructively. In this study, two examinations using the specimens which contained various quantities of ferrite and which was SUS304 steel exposed in sodium was carried out by use of BHN system for the purpose of clarifying the relation between BHN and the ferrite quantity in austenite steel and investigating the possibility of detecting a ferrite layer in sodium exposed surface respectively. The results is as follows. (1)The values corresponding to the ferrite quantity was obtained by use of the parameter of the BHN maximum amplitude and the area of frequency band as a result of the examination using the specimens which the ferrite quantity was known such as Mod.9Cr-1Mo steel (F4 heat) or the standard specimen for ferritescope. (2)In the case of using the parameter of the BHN maximum amplitude, it was difficult to find ferrite below 10%, because the value of BHN maximum amplitude was as same as noise when no specimen was attached to the BHN sensor. In the case of using the parameter of the area of frequency band, ferrite below 10% could be detected as different values from the noise. (3)BHN was detected remarkably at a part in the specimen of SUS304 steel exposed in sodium. The ferrite layer caused by dissolution of Ni was observed in the region of a few micron depth from surface at this part. As a result, the BHN method is a effective method to detect a ferrite layer in a surface of materials.