Effect of microstructure evolution on magnetic incremental permeability response in DP590 steel during annealing process

This is the authors' abstract. We don't add key points for this paper.

Real-time monitoring of microstructural evolution during annealing is important for quality control and performance prediction of materials. However, existing methods are mainly confined to room-temperature measurements, which limits the understanding of microstructural evolution under high-temperature conditions involving multi-factor coupling and phase transformation. To address this, a high-temperature magnetic incremental permeability (MIP) measurement method based on the Epstein frame is established, providing the MIP evolution throughout the entire annealing thermal cycle (heating, holding, and cooling). The MIP responses at three annealing temperatures (550 °C, 750 °C, and 950 °C) are systematically compared, and the differences between heating and cooling stages are analyzed. Quantitatively, compared with the virgin specimen, μ max increases by approximately 114%, 164%, and 213% after annealing at 550 °C, 750 °C, and 950 °C, respectively, while H cμ decreases by 12%, 37%, and 66%. A harmonic-excitation MIP model is constructed based on the Jiles-Atherton (J-A) hysteresis framework. The simulated MIP curves reproduce the experimental trends well, and the extracted J-A parameters provide a physical interpretation for the observed changes in MIP characteristics. Combined with high-temperature confocal laser scanning microscopy (HT-CLSM) and electron backscatter diffraction (EBSD) observations, the distinct effects of phase transformation and grain size evolution on MIP signals are clarified, explaining the underlying microstructural mechanisms. This work offers a potential basis for online monitoring and microstructural assessment during annealing.