The Elcometer 111-7F is a hand-held magnetic gauge for checking the delta ferrite content in stainless steel weld metal. It is pre-calibrated and simple to use. The readings are in Ferrite Number (FN) in accordance with WRC and IIW recommendations.

Place the nose of the gauge onto the weld metal and rest the middle of the gauge on adjacent parent metal. Turn the central wheel to the zero end of the scale, now turn it in the opposite direction until the magnet clicks off. Read the value.

A minimum ferrite content in austenitic stainless steel weld metal prevents microfissures and hot cracks. Too much ferrite can lead to corrosion or embrittlement at high temperatures. It is a magnetic material in an essentially non-magnetic metal and so can be measured by the force of attraction due to a magnet.

After much testing around the world, it has been decided that it is impossible to determine accurately the true ferrite content of stainless steel weld metals. Previous figures of percentage content were very dependent on their source, the measuring instrument used ands its calibration. So Ferrite Numbers were established to define ferrite quantity and are related to the ferrite quantity of an equivalently magnetic weld metal

The calibration of a gauge is such that the ferrite reading can be related to the seperation of the gauge's magnet from low carbon mild steel plate. The primary standard is thickness and the secondary standard is ferrite samples, and the Calibration Certificate supplied with the Elcometer 111-7F relates the gauge reading to both standards.