Abstract
Recently, we have developed a spin Hall magnetoresistance (SMR) sensor featuring high-sensitivity, low-noise, zero-offset, and negligible hysteresis. Here, we demonstrate that the SMR sensor can be used to map the self-magnetic leakage field (SMLF) of stainless steel sheets. The SMLF serves as an effective knob for probing magnetism in steel sheets induced by either stress or composition inhomogeneity, which, in turn, affects its mechanical properties and corrosion resistance. However, the SMLF is typically quite weak, and thus the high-sensitivity and low-noise SMR sensor is uniquely suited for this application. The self-magnetic flux leakage mapping experiments have been conducted on SUS304 steel sheets with emphasis on the lift-off effect. Both analytical model and finite element modeling have been used to account for the experimental results. Although the SMLF mapping alone is unable to pinpoint the root cause of magnetism, i.e., whether it is due to stress or composition inhomogeneity, it does provide an efficient way for pre-screening of steel sheets to prevent defect formation at early stages.
Highlights
Austenitic stainless steels (ASSs) are widely used in various industries, including chemical, food and beverage, transportation, and energy, owing to their favorable mechanical strength and excellent corrosion resistance.1–3 The fatigue life of ASS is significantly affected by tensile residual stress and chemical composition distribution
We show that the spin Hall magnetoresistance (SMR) sensor can be used to measure the self-magnetic leakage field (SMLF) of steel sheets directly without any external field or complicated signal processing
This shows that the actual pattern of composition inhomogeneity is not necessarily the same as what is to be revealed by stray field mapping
Summary
Austenitic stainless steels (ASSs) are widely used in various industries, including chemical, food and beverage, transportation, and energy, owing to their favorable mechanical strength and excellent corrosion resistance. The fatigue life of ASS is significantly affected by tensile residual stress and chemical composition distribution. Stress in the matrix usually arises from the manufacturing process of metals or external loads during service It can result in the degradation of mechanical properties and reduce fracture toughness. When the ASS is used for hydrogen storage in fuel cell vehicles, composition inhomogeneity causes the local microstructure more sensitive to hydrogen embrittlement, which tends to accelerate fatigue crack growth.. When the ASS is used for hydrogen storage in fuel cell vehicles, composition inhomogeneity causes the local microstructure more sensitive to hydrogen embrittlement, which tends to accelerate fatigue crack growth.8,9 When it is used in aggressive environments at elevated temperatures, inhomogeneous elemental distribution is of concern due to different local corrosion resistance.. Compared to the SMLF caused by manufacturing processes or fatigue, the stray field due to compositional distribution is harder to detect, depending on the degree of inhomogeneity. Effect of lift-off, which is the distance between the SMR sensor and the specimen, on mapping results is discussed analytically and is investigated with the assistance of three-dimensional (3D) finite element modeling (FEM)
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