Abstract
This paper presents magnetic force imaging (MFI) – a method for spatially resolved quantitative assessment of the ferrite/martensite fraction in austenitic stainless steel or similar materials. This method exploits the force interaction between a magnetic tip and the surface of a specimen, similar to magnetic force microscopy (MFM). It differs from MFM in the size of the tip and close-to-saturation magnetization of the sample under investigation. In this study, AISI 347 (1.4550/ X6CrNiNb18-10) austenitic stainless steel was analyzed in the as-delivered state, i.e., 30 mm diameter round bars. The MFI results show a distinct resemblance of an inhomogeneous structure that forms bands in the rolling direction. This structure retains its initial square cross-section from which the material was hot rolled and has been detected due to the formation of α′-martensite. The information depth of MFI proved to go beyond the depth of α′ formed due to surface preparation only. The material was further characterized by standard methods, including EBSD, EDX, and hardness measurements.
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