Ferromagnetic Annealing and In-Process Heat Treating
Core Iron (VIM VAR)
Magnetic properties of the fabricated magnetic core parts from the mill product can be improved by thermal heat treatment. Heat treating temperatures of 730°C (1350°F) or higher should be used to obtain part uniformity of magnetic properties. With increasing temperature, DC magnetic properties improve provided no surface contamination of carbon, sulfur, oxygen or nitrogen is encountered.
The heat treating atmosphere is a very important factor. Further improvement in DC magnetic properties can be achieved by employing an atmosphere capable of decarburizing and desulfurizing the material. Degree of material purification is also a function of time at temperature.
Heat Treating for Best DC Magnetic Properties
Heat charge in a wet hydrogen atmosphere with a dew point of approximately 25°C (75°F) to 850°C (1562°F) and hold at temperature for 2 to 4 hours. Cool at a rate of 100°/170°C (180°/306°F) per hour to 540°C (1000°F). and at any rate thereafter.
Other atmospheres, including pack anneal, vacuum, dry hydrogen, argon, forming gas (nitrogen and hydrogen) may be used with a treating temperature in the 730°/1180°C (1350°/2150°F) range.
Do not use we hydrogen above 950°C (1740°F) as this will not improve the soft magnetic properties.