Non-destructive characterization on multiphase structures of duplex stainless steel using multi-frequency electromagnetic sensor

Signals of multi-frequency electromagnetic sensor is of great significance for in-line monitoring microstructure transformations during duplex stainless steel (DSS) manufacture. The key is to accurately evaluate the relative permeability value of DSS as it dominates sensor signals at low frequencies and can be used to characterize microstructure transformations. In this paper, a micro finite element (FE) model of DSS microstructures for analyzing and calculating relative permeability is proposed. The relative permeability value is input into a macro multi-frequency electromagnetic sensor model and the modelling sensor signal shows a good agreement with the experimental validation. Effects of phase composition, phase distribution and grain numbers on the relative permeability value are investigated using the model. A 3D microstructural model is also established and results compared with the 2D model are discussed. Results show that the relative permeability value of DSS can be determined using the model and steel microstructures can be characterized using the multi-frequency electromagnetic sensor. •Macro and micro FE models to study non-destructively electromagnetic evaluation on steel microstructures.•Novel method of constructing microstructure model for steels and calculating its relative permeability value.•Explicitly discussions on influence of microstructural elements for relative permeability values.