By means of the eddy current method, small defects in components can be detected non-destructively and conclusions can be made about the physical and mechanical/technological properties of the component and its microstructure. In addition to detecting material mix-ups in production, this allows the heat treatment condition to be controlled and, for example, incorrectly hardened workpieces to be identified. Furthermore, high-temperature sensor technology can be used to determine the microstructure evolution and with it the component properties during the cooling phase. In addition to quality assurance, this allows real-time process control in order to set a defined microstructure in a controlled manner.