Grain Size Measurement Using Barkhausen Noise Method
Grain size is one of the most important parameters which determine the mechanical properties, e.g. tensile strength and yield strength of steel sheet. Therefore, it is necessary for quality control in the steel sheet production process to measure the grain size continuously.
Nondestructive methods for measuring grain size, such as the coercive force method, the ultrasonic attenuation method, and the ultrasonic backscattering method have been reported. However, these methods are not suitable for continuous measurement in the production line.
An advanced magnetic Barkhausen noise method has been developed for evaluating the grain size of steel sheet. The steel sheet is magnetized at low frequency (5Hz) by an electromagnet on one side of the sheet, and a ferrite cored coil, set on the opposite side, picks up the magnetic flux. The detected magnetic flux consists of the flux transmitted through the sheet and the high frequency flux generated by the Barkhausen effect. Since these fluxes have different frequency components, each flux is easily discriminated by frequency filters. By combining the Barkhausen noise and the transmitted flux a grain size measuring method that is highly accurate and insensitive to disturbances has been developed. The experimental results show the measuring accuracy of ± 0.5 in ASTM units.
KeywordsMagnetic Flux Steel Sheet Size Number Path Line Line Speed
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