Induction coil as sensor for contactless, continuous in-process determination of steel microstructure by means of Magnetic Induction Spectroscopy (MIS)
In hot forming and machining process chains heat treatment of steels is controlled by temperature and time. The process parameters significantly influence the material microstructure, which is important for the final component properties. The dependence between the predominant microstructure and the magnetic properties can be determined by means of Magnetic Induction Spectroscopy (MIS). In this paper, we propose to use the induction coil as an in-process sensor element to implement MIS in induction heating processes with subsequent cooling of steel sheets. This novel approach enables contactless, continuous in-process measurement of complex inductance and allows a non-destructive determination of steel microstructure. The novel measurement method can differentiate discrete microstructural states and determine phase transformation points during continuous heating and cooling, by analysing the inductance curve. The realized combination of sensor and actuator features enab les both process monitoring and closed-loop control of production processes with integrated heat treatment.