A Study of Cellular Decay in Austenite Alloys Using an Applied Eddy-Current Transducer

The eddy-current parameter f 0 of the N36K10T3 invar has been studied in the range of aging temperatures from 600 to 900°C. The maximal drop in f 0 has been observed at the temperature T ag = 800°C, and the drop in this parameter was the larger, the longer the aging process. The drop in this parameter is caused by the cellular decay process in the solid solution, which depletes the austenite of nickel and titanium. The parameter f 0 increases notably (from 4 to 46 kHz) when crystals of lowtemperature martensite (α-phase) are generated in samples of the N26T3 steel with 100% cellular decay. This high value (f 0 = 46 kHz) persists at T ag < 400°C and drops by a factor of 4.5 over the interval 400 < T ag < 600°C because the ferromagnetic α-phase transforms to the paramagnetic phase-hardened austenite (α → γph). Aging of the phase-hardened austenite in the steel with cellular decay at T ag = 700°C increases the parameter f 0 by a factor of two (from 10 to 20 kHz) because the ferromagnetic α-phase is generated when the aged phase-hardened austenite transforms to the martensite (γph → α) as a result of cooling the steel from the aging to room temperature.