Characterization of Decarburization of Steels Using a Multifrequency Electromagnetic Sensor: Experiment and Modeling

Abstract

A potential online nondestructive method using a multifrequency electromagnetic (EM) sensor to measure the decarburization of steels has been proposed and tested. Online (hot) testing was simulated, using composite samples comprised of a 316 stainless steel (paramagnetic) core and a surrounding tube of ferritic steel (ferromagnetic), with thicknesses between 100 and 600 lm. The sensor can detect the decarburization and quantify the depth. Offline (cold) measurement of decarburized high-carbon steel rods was also carried out and compared with the online measurement. The relationship between the sensor output and the decarburized layer type/thickness has been modeled using finite element methods (FEMs).

Measurement of microstructure changes in 9Cr–1Mo and 2.25Cr–1Mo steels using an electromagnetic sensor

“…Multi-frequency EM sensors have proved sensitive to the change of ferrite/austenite fraction [4,5], shown using model alloys, in-situ analysis and modelling, and decarburisation [6,7], shown for high carbon steels for on-line and off-line monitoring.…”

“…A cylindrical EM sensor, similar to that used in [6], consisting of one exciting coil and one sensing coil both wound around an insulating tube of 5.5 mm and 6.5 mm inner and outer diameters respectively was used. EM sensor tests were carried out on the same cylindrical specimens as for the resistivity measurements.…”

Magnetic Evaluation of Microstructure Changes in 9Cr-1Mo and 2.25Cr-1Mo Steels Using Electromagnetic Sensors

“…A cylindrical EM sensor, similar to that used in [28], consisting of one exciting coil and one sensing coil both wound around an insulating tube of 5.5 mm and 6.5 mm inner and outer diameters respectively was used in this study. EM sensor tests were carried out on the same cylindrical specimens as for the resistivity measurements.…”

“…The model is broadly similar to that described in [28] and exploits the inherent cylindrical symmetry of this sensor design. The resistivity values of modeled samples were taken from the experimental measurements and the relative permeability values determined by fitting the modeled real inductance with the experimental measurement based on a non-linear least square method with 51 frequency points from 10 Hz to 1 MHz (logarithmically spaced) in Comsol LiveLink for Matlab.…”

“…Prototype EM sensors are being used for in-situ monitoring of the γ → α transformation during steel processing [27]. EM sensors have also been used to detect decarburisation [28,29], shown with high carbon steels for on-line and off-line monitoring. The theory as to how the relative permeability and resistivity of a sample affect the multi-frequency EM response, for any sensor geometry, is presented elsewhere [30].…”