Microstructurally and Electromagnetically Evaluations of Aging Phenomenon in 2304 Duplex Stainless Steel

Microstructural ‎and Electromagnetically Methods were performed for evaluation of aging phenomenon in 2304 duplex stainless steel. The artificial aging process were carried out at temperatures of 700, 800 and 900 °C and at 15, 60 and 120 minutes. For microscopic and hardness evaluations, optical microscopy equipped with image analysis software, scanning electron microscopy equipped with chemical analyzer, X-ray diffraction device and Vickers method were used. Then, for electromagnetic evaluation, the eddy current test at 100 kHz was performed, and the data were presented and evaluated as an impedance plan. The microscopic studies showed that with increasing aging intensity by increasing aging temperature and time, reduced the amount of ferrite phase. In contrast, the secondary phases of M23C6 carbide, Cr2N nitride, and secondary austenite form and grow in the microstructure. These secondary phases are formed within the ferrite phase and lead to a reduction in the volume fraction of the ferrite phase relative to the annealed sample. The most sever changes were observed at 900 °C and 120 min. The results of electromagnetic evaluation have shown that with increasing the aging temperature and time, formation of more destructive phases and a sharp decreasing of ferrite content in the microstructure, the electromagnetic responses change appropriately by further reducing the inductive reactance and impedance index and further increasing the resistance index. Therefore, the severity of the aging phenomenon in the steel can be seen from its impedance plan.