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Industrial processing and chemical plants work at high temperatures and pressures, often with aggressive media and stainless steel is often the material of choice for these applications. If the ferrite content of the steel is too low, then welding of stainless material may crack at elevated temperature or with high stress or vibration.
Alternatively, if the ferrite content is too high, the weld may be weaker and corrode. To address the need to measure the amount of ferrite in a sample the Welding Research Council introduced the Ferrite Number (FN) as a standardised value which related to the ferrite content of an equivalently magnetic weld metal.
The volume percentage of ferrite can be estimated as about 70% of the FN but the relationship depends upon the type and origin of the stainless steel used and the measurement technique.
The Diverse Ferrite meter MF300F+ measures the Ferrite number (FN) of austenitic and duplex stainless steel weld material. It has a probe that is sensitive to ferrite content in a 10 mm area to a depth of approximately 1 mm. The instrument is calibrated using the secondary world standards held at The Welding Institute.
All 16 standards are used in the calibration giving an instrument with a measurement range from 0 to 115 FN. Transfer standards are supplied with the instrument allowing performance to be verified at any time. A variety of measurement modes are supported to ensure that good repeatable measurements can be made.