Measured and modelled low field relative permeability for dual phase steels at high temperature

Abstract

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Local magnetic flux density measurements for temperature control of transient and non-homogeneous processing of steels

“…It is worth mentioning that even though the whole processed volume of the steel specimens is kept below the Curie temperature the Δ moves slightly away from the baseline. This phenomena of sensitivity of the magnetic measurement to different temperatures below the T C is reported by other authors 50–52 .…”

Multifunctional Induction Coil Sensor for Evaluation of Carbon Content in Carbon Steel

“…The interaction between induction coil and the tested steel would change the electrical properties of coil, such as impedance. Davis et al [10] used this characteristic estimated the fraction of ferrite in dual phase steel accurately. Hence, the electrical properties could also be a potential method to evaluate the carbon volume in steel.…”

Real-time in-line steel microstructure control through magnetic properties using an EM sensor

“…A 3D FE macro model developed using COMSOL Multiphysics, for the commercial EMspec TM sensor is described, along with its verification using measurements for different steel microstructures at room temperature. Using this model the sensor output of zero crossing frequency (ZCF) can be predicted, using inputs of low field permeability values, determined from the microstructure model [8] and resistivity values that are either measured or reported in the literature [9]. High temperature dynamic cooling tests using a laboratory bespoke furnace and ROT system have been carried out and the model prediction (for known transformation behaviour determined independently using dilatometry) compared with the measurement.…”

“…The low field relative permeability of bainite at elevated temperatures is required to predict the full transformation microstructure response as the Cr-Mo steel transforms from austenite to bainite microstructure at the cooling rate used. The low field relative permeability of bainite was estimated using the relationship between low field relative permeability and temperature for pearlitic steel from the FE micro model and experimental results[8]: a parallel trend to that observed for the fully pearlite microstructure low field relative permeability with temperature curve was assumed for the bainitic steel using the measured room temperature low field relative permeability values of 59 for the 0.8 wt% C pearlitic steel and 88 for the 2.25 Cr-Mo bainitic steel. This assumption was made on the basis that both these microstructures have a large number of domain pinning sites -finely spaced carbides / lath boundaries for bainite compared with ferrite/cementite lamellae boundaries in pearlite and parallel trends with respect to temperature can also be observed for 0.17, 0.38 and 0.80 wt% carbon steels (ferrite-pearlite microstructures with different pearlite fractions) up to 600 °C[8].…”

“…Magnetic and electrical properties used in the model.The full 3D FE model was established to predict the ZCF for a range of steel grades at room and high temperatures, which meant the magnetic permeability can vary from hundreds to thousands, e.g. 90% ferrite-austenite microstructure has a permeability of about 100 at room temperature but it can go up to 2000 at 700°C[8]. It was found that the initial full 3D FE model used had insufficient mesh elements (limited by local computer workstation capability to solve the model: CPU: Intel Xeon E5-1620 3.70GHz; RAM: 64.0 GB) to accurately predict the ZCF for high permeability samples (e.g.…”