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Stress relief annealing is a process that is carried out to acquire desired magnetic properties of electrical steel sheets by relieving stress generated in the process of shearing and punching at a proper temperature for a certain period of time.

If the annealing temperature is too low, it is difficult to acquire adequate magnetic properties and if the temperature is too high, it may erode surface insulation and degrade insulation properties The optimum annealing temperature for grain-oriented electrical steel is 780°C to 840°C and 750°C to 800°C for non-oriented electrical steel for improved magnetism.

Annealing time means the in-furnace time of materials at the highest temperature during the annealing process. During this time, the materials in the furnace should be evenly heated.. The annealing time varies depending upon amount of materials or type of furnace. Generally, the annealing time is between 1.5 to 2.5 hours.

Abrupt heating and cooling must be avoided to prevent any deformation of the iron core. Slow cooling must be applied until it reaches 300~350°C before air cooling is applied.

Furnace atmosphere should be controlled to minimize carburization or oxidization which can diminish magnetic properties. Therefore a pure nitrogen atmosphere is ideal and the dew point of gas should be maintained as low as possible, below 0°C is adequate. The oil used in shearing and punching should be removed completely. Otherwise both sides of piled-up core will be damaged during the annealing process, deteriorating the work capacity.