Duplex stainless steel (DSS) has a wide application in industrial structures that needs strong corrosion resistance. The properties that make this class of steel very attractive for the oil refinery industry are: high strength, toughness, ductility, stress corrosion cracking resistance, even in H₂S containing environments, allied to low cost when compared to conventional stainless steel. DSS are two-phase materials which microstructure consists of grains of ferrite (δ) and austenite (γ). Nonetheless, a drawback is pointed out: exposition to temperatures in the range 300°C - 1000°C may lead to precipitation of a deleterious phase, named sigma (σ). When this occurs, the material becomes brittle and its corrosion resistance to H₂S is severely impaired. Eddy currents (EC) testing can be successfully employed to detect and quantify σ phase. The study of magnetic behavior of DSS allows a better understanding of the technological problem of detecting and quantifying the σ phase. The main focus is to understand the difference in EC signals for the different samples with σ phase, because it may be related to either the precipitation of the paramagnetic σ phase or to the decrease of the ferromagnetic δ phase. The present work is a first attempt to understand the origin of the changes observed in EC technique. We considered the hysteresis behavior as the key to understand the differences in magnetic permeability, initially at room temperature. EC measurements were made with a customized probe. It was observed that the changes in the signal of EC are predominantly from deleterious phase