The production of rotationally symmetrical workpieces by flow forming allows the manufacture of a wide range of components with applications in industries such as transportation and aerospace [1]. The use of metastable austenitic steel as raw material makes the production of high-performance products possible, since during plastic deformation of these steels, not only changes of geometry but also on microstructure occur. Particularly, phase transformation from metastable austenite to martensite modifies the magnetic and mechanical properties of final products [2, 3]. The development and calibration of novel micromagnetic sensors to monitor those microstructural changes is crucial for the implementation of online closed-loop control systems during the production process [4]. By means of offline characterization techniques such as magneto-optical Kerr effect microscopy is possible to correlate the relationship between the evolution of the microstructure and properties and corresponding magnetic structures [5]. Thus, a better understanding of the operational principles of the micromagnetic sensors for online measurements can be achieved.