Xinjiang Hao

Monitoring microstructure changes in rod online by using induction spectroscopy

Abstract This paper describes the application of a new multifrequency sensor system to an industrial rod mill. The system operates by analysing the response of the rod to an excitation signal which contains a range of frequencies. The sensor system is able to successfully monitor the transformation of the material. Sensor configurations that could be deployed online have been considered and a prototype system has been built and tested in the Stelmor section of the Scunthorpe Rod Mill fitted in the enhanced cooling zone. Initial results are shown, demonstrating that the phase spectra is essentially unaffected by variations in lift-off and the lay pattern of the rod on the run-out table. The system was also able to detect different phase spectra from different grades of steel and also to detect features of the process which are known to affect microstructure.

Measurement of electromagnetic properties of power station steels

Accurate measurement of electromagnetic properties of steels is of significant importance as EM properties are indicative of microstructure and hence properties of the material. In this paper, we present the measurement of cylindrical power station steel samples in different microstructural states representative of their initial condition and after service exposure. Cylindrical air cored sensors were used. Analytical and numerical methods (Finite Elements Methods) were employed to calculate the sensor response of these samples. Experimental results were obtained for a range of samples and their electromagnetic properties inferred by fitting finite element models to the measured results. In addition, sensitivity and error analysis were carried out to evaluate the accuracy of the method.

Measurement and modelling of ACFM response to multiple RCF cracks in rail and wheels

Abstract This paper presents the experimental and model results of the response of an alternating current field measurement (ACFM) sensor to clusters of rolling contact fatigue (RCF) cracks typical of those found in rails and rail wheels. Both artificial and real cracks occurring in rails taken from service are considered. Currently, commercially available ACFM software is capable of producing an estimate of crack pocket length for isolated cracks, assuming they are regularly shaped. The results presented are part of continuing work to link the ACFM signal to the whole range of complex shaped RCF cracks that appear in rail and rail wheels, including those appearing in clusters. The challenges in accurately sizing clustered RCF cracks using the ACFM technique are discussed.

Measurement of Permeability and Ferrite/austenite Phase Fraction Using a Multi-frequency Electromagnetic Sensor

This paper presents the measurement of ferrite/austenite phase fraction using a multi-frequency electromagnetic sensor. A simple analytical model was established that can describe the response of the sensor for samples containing varying fractions of ferromagnetic phase over a wide range of frequencies (100 Hz to 1 MHz). In particular, a new feature, the peak frequency of the imaginary part of the inductance, is found to be able to distinguish between samples across the whole range of the ferrite percentages. FEM models were used to simulate representative real microstructures from the samples and to relate the relative permeability to the ferrite fraction. Experimental results suggest that the accuracy of ferrite/austenite percentage measurement is within 8%.