Nondestructive study on σ phase precipitation in duplex stainless steel using the multi-frequency electromagnetic characterization

During high-temperature processes, σ phase precipitation in duplex stainless steel (DSS) leads to the degradation of mechanical properties and corrosion resistance. Therefore, it is of great significance to measure the microstructural changes (σ phase precipitation) online during the DSS production process, as this can enable real - time monitoring and adjustment of the production process, helping to optimize product quality and performance, and ultimately reducing the risk of product failure caused by σ phase precipitation. Traditional microstructure inspecting methods suffer from destructiveness and insufficient real-time monitoring capabilities. This study proposes a non-destructive characterization method based on the multi-frequency electromagnetic technology. The correlation mechanisms of electromagnetic responses, microstructures and mechanical properties were systematically analyzed through experimental measurements and finite element modeling. The multi-frequency electromagnetic sensor can effectively distinguish specimens with different σ phase contents within a specific lift-off distance range. The low-frequency characteristic signals showing a strong correlation with microstructural states and mechanical properties. The developed macro-micro coupled model confirms that electromagnetic responses can achieve real-time mapping of microstructural changes and property degradation induced by σ phase precipitation, providing a non-destructive solution for online monitoring and quality control of σ phase precipitation in DSS during industrial production.