Thermocouple iron is used for the positive leg of thermocouples type J and L. The alloy is also used as the positive leg of compensating cables type KCA (WX).
The alloy is transformed magnetically at 770°C (1420°F) and a crystallographic transformation occurs at 900°C (1650°F). Both transformations affect the thermoelectric properties of the alloy.
Iron can not be exposed to sulphur-containing atmospheres and to temperatures below zero. Thermocouple iron wire is supplied copper-coated to prevent oxidation.
Thermocouple type J and L are frequently used because of their high emf output and their low cost. Compensating cables of type KCA are used together with thermocouples of type K.
|C %||Si %||Mn %||Fe %|
|Wire size||Yield strength||Tensile strength||Elongation||Hardness|
|Electrical resistivity at 20°C Ω mm2/m||0.13|
|Temperature coefficient of resistance between 20°C and 100°C x 10-6/K||5000|
|Temperature °C||Thermal Expansion x 10-6/K|
|20 - 100||11.7|
|W m-1 K-1||66.2|
|kJ kg-1 K-1||0.445|
|Melting point °C||1535|
|Magnetic properties||The material is magnetic|
|Wire size Ø||3.26||1.63||1.00||0.50||0.25|
|Bare wire °C||760||760||720||650||560|
|Protected wire °C||760||760||760||760||670|
Note that the indicated temperatures should be considered as guide values
Iron is used as positive leg in thermocouples of type J, L and in compensating type KCA. The emf values vs the negative thermocouple leg are listed in the data sheets for the respective thermocouples.