Magnetic detection of α′-martensite in 316L austenitic steel: Toward safer hydrogen applications

The formation of ferromagnetic α′-martensite in 316L austenitic stainless steel poses a significant threat to the structural integrity of hydrogen-related components, particularly under mechanical loading and hydrogen exposure. This study compares and analyses four advanced magnetic non-destructive testing techniques, magnetic Barkhausen noise, magnetic incremental permeability, eddy current testing, and Magnetic Flux Leakage (MFL) via Nitrogen-Vacancy center (NV-center) magnetometry, for their ability to detect α′-martensite in plastically deformed 316L specimens. Energy-dispersive X-ray diffraction was used as a reference to quantify near-surface α′-martensite content, while finite element simulations of plastic strain and residual stress provided supporting mechanical context. Among the tested methods, NV-center magnetometry exhibited a very strong linear correlation with XRD-based martensite quantification (r = 0.99), reflecting its sensitivity to plastic strain, which closely governs α′-martensite formation. Other techniques showed lower correlations (r < 0.4), with magnetic incremental permeability notably influenced by mechanical stress rather than martensite content. In addition to its sensitivity, NV-center MFL also demonstrated excellent spatial resolution, fast acquisition, and high robustness, making it a promising technique for α′- martensite detection in 316L components. • NV-center magnetometry shows high sensitivity to α′-martensite in 316L steel. • NV-center method achieves strong correlation (r = 0.99) with XRD measurements. • NV-center offers high spatial resolution and fast magnetic flux leakage mapping. • MBN and MIP techniques mainly respond to mechanical stress, not martensite content. • NV-center magnetometry is promising for hydrogen system integrity monitoring.