Comparing Permeability and Ferrite Content

Permeability measurement and ferrite content measurement are two different methods used in materials science and metallurgy to characterize materials, especially steels. Both measurements have different objectives and are used in different contexts.

Permeability Measurement

Definition
Permeability measures the ability of a material to conduct a magnetic field. It is a measure of a material's magnetic conductivity.
Measurement
To measure permeability, a magnetic field is passed through the material and the strength of the magnetic field generated inside the material is measured. The relative permeability of a material is the ratio of the magnetic induction (B) to the magnetic field strength (H) in the material. The µr value of the material is measured here. The maximum µr value that can be measured by this method is µr = 5.0; higher permeabilities cannot be measured by this method because it would require much higher magnetic fields. This is only possible with a complex device to record the entire hysteresis curve.
Application
This measurement is used to study the magnetic properties of weakly magnetic materials such as stainless steel and alloys. It provides information about how magnetic the material is.

Ferrite Content Measurement

Definition
Ferrite content is the percentage of ferrite in a steel (usually duplex or austenitic). Ferrite is a special phase in steel that is magnetic.
Measurement
The ferrite content is also measured using an external magnetic field generated in the probe, similar to the permeability measurement, although the sensitivity of the measurement is lower in order to display higher ferrite content values on austenitic steels. This measurement is based on the Basel standard ISO 8249 and determines the ferrite content number FN or the percentage ferrite content in Fe%.
Application
The ferrite content is important to control the mechanical properties of the steel, such as toughness and corrosion resistance. In duplex steels, a certain ferrite content is required to achieve the desired balance between toughness and strength.

Magnet Permeability Meter FerroPro compact	Ferrite Content Meter FERRITE-CHECK 240

Magnet Permeability Meter FerroPro compact

For permeability measurements List-Magnetik offers the new, precise FerroPro compact with an extended measuring range of µr = 1 - 5. During the measurement a permanent magnetic field is induced in the material. The perturbing effect of the material on the magnetic field can be measured and the permeability derived.

The new permeability tester has a high-resolution LCD color display for visualization of scan measurement curves and graphs and replaces the previous Ferromaster. It can automatically store and display peak values and graph and store permeability curves. The instrument measures permeability in accordance with EN 60404-15 and MIL-1-17214 standards, where the excitation field strength of the probe is different when measuring permeability; DIN-EN-60404-15 has an excitation field strength of 30 kA/m according to PTB, BN-EN-60404-15 has one of 25 kA/m according to NIST calibration, and MIL-1-17214 has one of 200 Oe. For the first time, FerroPro compact offers the ability to accurately measure permeability to all three standards by converting the field strength in the instrument.

The measuring system has a built-in data logger for a maximum of 10,000 measured values, where measurement curves, single values or peak values can be recorded on site for later processing. Another unique feature is the ability to remotely control the instrument via a USB SCPI interface, e.g. with LabView or other SCPI programs, so that the instrument can be integrated into a production line. At the same time, the instrument has a Bluetooth 5.0 interface for transferring stored data or for online measurement with the supplied PC or application software. Data and graphs can be exported to Microsoft Excel for further quality assurance.

The system offers a scan measurement for continuous graphical recording of measured values with display of minimum-maximum and statistical values, and a peak measurement for measuring the peak value.

The new permeability meter offers a variety of advantages in different applications, especially the new measurement evaluation options and the extended measurement range with different calibration curves for different excitation field strengths. All instruments are supplied with a manufacturer's certificate.

Ferrite Content Meter FERRITE-CHECK 240

Ferrite scopes are one way to measure ferrite content. They are based on magnetic induction and determine the ferrite content by measuring the magnetic properties of the material. List-Magnetik offers the very practical FERRITE-CHECK 240 with a measuring range of 0.2 - 140 FN, which precisely measures the ferrite content.

The device is identical in construction to the FerroPro compact just described. However, the probe has a completely different design. The FERRITE-CHECK 240 provides a fast and accurate measurement of the ferrite content of stainless steels and duplex steels according to the Basel standard DIN EN ISO 8249 using the magnetic induction method. The instrument displays the measurement in FN and Fe%. The measuring range is FN 0.2 - 140 (or 0.2 - 100 Fe%).

To detect a weld seam on smooth or polished surfaces, the instrument can be switched to scan measurement. As the probe is placed and moved along the surface, readings are continuously stored and statistics are displayed for the minimum, maximum, and average of the series of readings. The instrument has a built-in data logger for up to 10,000 readings.

Measuring ferrite content is especially important for welded duplex steels to know if the weld has sufficient ferrite content for adequate strength. If there is insufficient heat input or cooling in the weld area, the ferrite content may be too low.

This instrument also has a built-in Bluetooth 5.0 interface for transferring the stored data or for online measurement with the supplied PC or application software. Data and graphs can be exported to Microsoft Excel for further quality control.