Non-destructive characterisation of steel microstructures using electromagnetic sensors

Zhou, Lei (2015). Non-destructive characterisation of steel microstructures using electromagnetic sensors. University of Birmingham. Ph.D.

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Abstract

Steel properties are controlled by its microstructural parameters, such as grain size, phase balance and precipitates. It is desirable to monitor microstructural changes during processing, allowing in-situ feedback control, or microstructure characterization in a non-contact and non-destructive manner. Electromagnetic (EM) sensors are sensitive to changes in magnetic (relative permeability- dominant effect) and electrical (resistivity minor effect) properties, which in steels, vary with microstructure and temperature. EM sensors have been shown to have great potential for assessing steel microstructures (austenite to ferrite transformation or decarburisation). However, the influence of key microstructural parameters is not yet fully understood. This thesis presents a study of the effect of individual microstructural parameters on relative permeability and hence sensor output. In particular the ferrite grain size, pearlite interlamellae spacing, as-quenched martensite carbon content and phase balance were independently studied. The relative permeability of certain steel microstructures was determined using a finite element (FE) model fitted to experimental data. These values agreed with the literature and were used to predict the relative permeability of complex microstructures using an embedded microstructure FE model. Finally a case study on commercial steels was carried out, where the phase balance and tensile strength of dual phase steels were accurately predicted.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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