Josinaldo Pereira Leite

Evaluation of the magnetic permeability for the microstructural characterization of a duplex stainless steel

Non-destructive testing has been commonly used to assess the presence of discontinuities that may affect the integrity of materials in service. In this study, a Hall-effect sensor is used in a methodology developed to study, in a non-destructive manner, the microstructural variations of a material that occur because of the single-phase decomposition. The material selected was the UNS S31803 duplex stainless steel, particularly because of its behavior at temperatures below 525°C. Measurements of magnetic permeability based on Hall voltage values were performed, as well as hardness measurements and x-ray diffraction studies. The results confirm that the magnetic permeability can be used to successfully track the formation of α′ phase from α phase in a duplex stainless steel.

Sigma phase detection in duplex stainless steel by induced magnetic field

Duplex stainless steels when subjected to temperatures above 600 ° C have its tenacity decreased by the formation of sigma phase. This phase has high hardness and is rich in chromium and reduces the matrix of this element. In this study, field line density measurements, obtained in the reversibility region of magnetic domains, and application of artificial neural networks are used to monitor the formation of this undesirable phase. Samples of a stainless steel SAF 2205 were subjected to aging at temperatures of 800 ° C and 900 ° C, in order to obtain different amounts of sigma phase. The amount of this phase was obtained by image processing and the density of field lines through a Hall Effect sensor. Charpy impact tests were performed. The field lines densities were used for training of an artificial neural network and correlated with the presence of sigma phase and embrittlement of the material. The results showed that the method was able to correlate the parameters studied with the presence of the sigma phase and toughness of the material studied in both temperatures.