Austenite stainless steel is the most widely used stainless steel material. Martensitic transformation is easy to occur during processing and service, which changes the mechanical and corrosion resistance of the material. In this paper, we observed martensite transformation amount, electrical conductivity and surface magnetic induction of austenitic stainless steel by slow (5*10-4s-1) uniaxial stretching tests at different temperatures. Meanwhile thermally induced martensitic phase transformation was used as a control test to explore the influence of the two on the deformation of martensite. It was found that the coupling of both thermally induced and phase transformation induced can greatly promote martensitic transformation. With the same test parameters, 2.5% ultra-low temperature uniform the amount of martensite transformation induced by 20% homogeneous stretching at room temperature can be achieved with the same test parameters. Low temperature aging treatment can induce a small part of austenite to undergo martensitic transformation. With increasing aging time, the martensite content increases slowly. The amount of martensite is 3.2% at -196℃ and aging time 36 hours. And by observing the metallographic diagram of the specimen section, it was found that the amount of martensite precipitated at the surface was more than that at the middle position. At the same time, by measuring the electrical conductivity and micro magnetic signal of the tested material, it was found that the electrical conductivity of stainless steel continued to decrease with the increase of martensite content, which was analyzed to be caused by the generation of dislocations, slips and twins within the material. Subsequently, the three-dimensional magnetic induction intensity of the specimen surface was measured by a high-precision three-axis fluxgate magnetometer with the geomagnetic field as the excitation source, and it shows that the magnetic field component perpendicular to the specimen plane had a good linearity with the martensite content, the reason why is that some paramagnetic austenite transform into the ferromagnetic martensitic, and the magnetic domain boundary wall in the horizontal plane was destroyed during the stretching process and could not be recovered after plastic deformation. Under the weak magnetization of the geomagnetic field, it leads to the total direction of some of the magnetic domains pointing in the normal direction and can be detected by high-precision instruments. However, when the martensite content in austenite exceeds 50%, the magnetization intensity of the specimen surface decreases steeply. Therefore, the scope of use of the method for the characterization of martensite by micro-magnetic detection needs further experimental investigation.

Study on Characterization Method of Martensitic Transformation Magnetic Signal of Austenitic Stainless Steel

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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