Deformation of Mold Components

After the molds are used actually for injection molding for some time, the mold components that use carbon steels and alloy tool steels and that have been heat-treated may generate warps, deformations, or their dimensions may have increased slightly.
The phenomenon of changes occurring in the dimensions after the passage of time in this manner is called "aging".
The main cause of changes with time occurring in carbon steels of alloy tool steels is known to be the expansion in volume caused when the austenite structures remaining during quenching changes to martensite structures.
The process of quenching is that of changing the austenite structure to the martensite structure by suddenly cooling from the quenching temperature (about 800°C, but this varies depending on the type of steel).
While the sudden cooling is done using water, oil, or a salt bath, although the conversion to martensite is promoted when the temperature C, if the temperature is not that low, a small quantity°is less than 0 of austenite structure remains within the martensite structure. This remaining part is called "remained austenite". It has been known that this remained austenite gradually changes to martensite structure with the passage of time as mentioned above, and at that time the volume also expands. As a consequence, if the quantity of remained austenite is large, it can be assumed that the trend is that of a large change with time.
In order to reduce the remained austenite, it is effective to carry out deep cooling treatment (subzero treatment) by creating a low temperature environment of about -80°C using a coolant such as Freon (the user of Freon cannot be recommended due to environmental protection), and to carry out sudden cooling in that environment.
If liquid oxygen or liquid nitrogen is used, although it is possible to cool down to -180°C to -190°C, since the cost becomes high this is only done under special cases.
Therefore, in the case of components that should not undergo changes with time, it is recommended to carry out subzero treatment.
However, although the remained austenite would have become small in a subzero treated steel, at the same time, since even the hardness would have increased and the internal strain would have become large, appropriate annealing processing will be required. (There are recommended values for the conditions of annealing depending on the type of steel.)