Tips for bright heat treatment of metals in oxidizing atmosphere furnace
It is to burn off the oxygen in the airtight container where the workpiece is placed to form a stable solid compound, so that the metal product is heated under oxygen-free and low vacuum conditions.
The specific method is to put the metal spring products (single piece or batch) in an iron (low carbon steel) container, and put a small piece of metal sodium or lithium into the container at the same time, and then cover the lid to weld the seam. . Heat the sealed container in an air oven. When the container is heated to a low temperature, the sodium or lithium burns and the oxygen in the container (accounting for 21% of the container volume) combines to form a stable solid compound. The reaction is as follows:
Further heating is carried out in pure nitrogen below atmospheric pressure, and after heating is maintained, it is cooled in the furnace or taken out of the furnace. That can make the metal achieve the purpose of bright annealing or normalizing. After processing, take out the workpiece with gas cutting method.
The amount of sodium or lithium (XNa, Xli) put in the container can be calculated according to the volume (V. in L) of the container,
That is to say, only 0.86gNa or 0.26gLi is required for a 1L container. However, in actual applications, the calculated value should be slightly excessive, such as adding 105%.
Attention should be paid to the application of this method for heat treatment:
1. When welding a closed container, cooling measures should be taken to prevent sodium and lithium from burning in advance.
2. Metal sodium and lithium are easily oxidized in the air, so they must be stored in gasoline, kerosene or inert gas when not in use.