The potential of NDE by magnetic methods in SUS 304 stainless steel

摘要

The present work demonstrates that magnetic non-destructive evaluation techniques can be useful for detecting the presence and extent of ferromagnetic α' martensitic phase induced in SUS 304 stainless steel specimens due to plastic deformation after annealing at various temperatures and heat treatment sensitization. The amount of α' martensite phase transformation is found to be dependent on annealing temperature and the increase in martensitic phase is observed at annealing temperature between 1003 and 1103 K. A remarkable increase in α' martensitic phase transformation is observed at annealing temperature of 1553 K. A good correlation between ferromagnetic martensitic phase and magnetic field has been obtained. Saturation magnetization is increased and coercive is decreased depending on the volume of ferromagnetic phase transformation. Chromium carbide is precipitated along the grain boundaries during sensitization at 950 to 1023 K and at the same time, a zone depleted of chromium and carbon is formed in the region adjacent to chromium carbide. The ferromagnetic martensitic phase is also induced in the specimen by sensitization at temperature between 950 and 1023 K and high value of saturation magnetization is obtained at sensitization temperature of 1023 K. The magnetic transition indicates that enough volume of ferromagnetic martensitic phase is formed in the specimen at 1023 K. The ferromagnetic phase percentage decreases to a low value above 1023K.