Abstract
Sensitization of Ni-based Alloy 600 was discussed by means of magnetic susceptibility measurements. In Alloy 600, the magnetic susceptibility responds quite sensitively to the chromium content. Magnetic susceptibility of Alloy 600 increases with the sensitization as the result of the formation of chromium carbide precipitates. Alloy 600 with various carbon contents was sensitized at temperatures from 773 to 1073 K after solution annealing and the magnetic susceptibility measurements were carried out over the temperature range from 123 to 773 K.
The results are as follows: (1) Throughout the sensitization and recovery stage, the magnetic susceptibility was consistent with the result of 40%HNO3 test. (2) Sensitized Alloy 600 showed an increase of the Curie point up to a temperature of 523 K compared with that in the solution annealed condition. (3) From the increase of the Curie point at higher temperature, the chromium content in the chromium depleted region was determined. The minimum chromium content was estimated at less than 3% in the most sensitized condition and the chromium content increased in the recovery stage.
