高感度磁気センサを用いた熱時効したインコネル600合金の磁気的非破壊評価

抄録

Ni base alloy, Inconel 600, has high strength and high corrosion resistance, and is therefore widely used for steam generators tubing in power generation plant. During long term plant operation at higher temperature, sensitization occurs along grain boundary, which will induce stress corrosion cracking. The alloy is paramagnetic basically, however it transforms into ferromagnetic along grain boundaries when Cr depletion occurs. Since Cr depletion is attributed to sensitization of the material, nondestructive testing for sensitization using changes in magnetic properties will be possible. Here, Inconel 600 alloy was heat treated at 600℃ from 0 to 400 hours to occur sensitization. Then magnetic field sensor with relatively higher sensitivity scanned over the sensitized specimen. The change in the magnetic field near the surface of specimen is related to the degree of chromium carbides progressing sensitization. The obtained results suggest that scanning with magnetic field sensor is effective to assess sensitization due to heat treatment for Ni base alloy.