Method for the electromagnetic and real-time measurement of the percentage of austenite contained in steel strip in continuous motion during the in-line manufacture or transformation thereof, by means of a device consisting of said steel strip and of a measuring device comprising at least: - an alternating-current generator; - a first coil supplied by the alternating-current generator, called the transmitting coil, and a second coil, called the receiving coil, the first and second coils (1, 2) being arranged parallel to each other or coaxial and on both sides of the steel strip, the distance between the coils being fixed and comprised between 10 and 200mm; - a core of ferromagnetic material (6, 7) constituting the center of each coil (1, 2), respectively; - at least one voltage-measuring device connected to the terminals of the receiving coil, in the form of a multimeter or of an electronic acquisition system comprising an analog-digital converter coupled to a computer, to obtain the percentage of austenite contained in the steel strip after prior calibration of the device; - means for prior calibration of the device; so that the magnetic field produced by the alternating current flowing in the transmitting coil produces in the steel strip induced currents that generate an induced magnetic field creating in the receiving coil an electromotive force Vs that can be measured by the voltage-measuring device, the amplitude of this electromotive force being a function of the voltage Vp applied to the transmitting coil and of the nature of the steel of the strip; said method being characterized at least by the following steps: - a cooling system is implemented for the coils (1, 2) in order to bring them to ambient temperature; - a steel strip of unknown austenitic fraction is scrolled between the coils (1, 2) and the voltage Vs generated at the terminals of the receiving coil is measured for a given voltage Vp applied to the transmitting coil in a voltage range where the ratios between the voltages Vs and Vp remain constant if the voltage in the transmitting coil Vp is modified; - taking into account prior calibration of the device, the austenitic fraction of the steel strip is determined as a function of the generated voltage Vs. - an alternating-current generator; - a first coil supplied by the alternating-current generator, called the transmitting coil, and a second coil, called the receiving coil, the first and second coils (1, 2) being arranged parallel to each other or coaxial and on both sides of the steel strip, the distance between the coils being fixed and comprised between 10 and 200mm; - a core of ferromagnetic material (6, 7) constituting the center of each coil (1, 2), respectively; - at least one voltage-measuring device connected to the terminals of the receiving coil, in the form of a multimeter or of an electronic acquisition system comprising an analog-digital converter coupled to a computer, to obtain the percentage of austenite contained in the steel strip after prior calibration of the device; - means for prior calibration of the device; so that the magnetic field produced by the alternating current flowing in the transmitting coil produces in the steel strip induced currents that generate an induced magnetic field creating in the receiving coil an electromotive force Vs that can be measured by the voltage-measuring device, the amplitude of this electromotive force being a function of the voltage Vp applied to the transmitting coil and of the nature of the steel of the strip; - a cooling system is implemented for the coils (1, 2) in order to bring them to ambient temperature; - a steel strip of unknown austenitic fraction is scrolled between the coils (1, 2) and the voltage Vs generated at the terminals of the receiving coil is measured for a given voltage Vp applied to the transmitting coil in a voltage range where the ratios between the voltages Vs and Vp remain constant if the voltage in the transmitting coil Vp is modified; - taking into account prior calibration of the device, the austenitic fraction of the steel strip is determined as a function of the generated voltage Vs.