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Frequently Asked Question
When is a temperature considered to be cryogenic?It is not possible to answer this question categorically as no universally accepted definition exists about the limit below which a temperature is considered to be cryogenic. One of the most common criteria is to consider that the limit is at 120 K or -150 ºC, which is a temperature that is quite close.
Aside from these references, it must remain clear that subzero treatments are not cryogenic treatments. These processes are quite common in the industry of conventional treatments and are used on certain types of steel immediately after quenching to achieve a more complete transformation of austenite to martensite. They are normally relatively short processes which are carried out at around -80 ºC in order to improve the dimensional stability of certain components. Some companies offer this type of processes by incorrectly calling them cryogenic treatments when neither their execution nor their effects are the same.
The CRYOBEST® multi-stage cryogenic process is performed at much lower temperatures (below -170 ºC) for longer times. As well as improving dimensional stability, it increases wear resistance, extends fatigue life, improves the conductivity, etc.
In general it is not necessary. Multi-stage cryogenic treatment affects the whole volume of the material without significantly altering the hardness. Therefore, materials subjected to the treatment can be machined, rectified, sharpened, etc. without losing the effects. In many cases it is even beneficial to perform the CRYOBEST® process before finishing as this enables better, more precise finishes to be obtained. Furthermore, in this way the risk of damaging a completely finished tool or piece due to any incident that may occur during its transport or handling is greatly reduced.
Obviously, we have to take into account that if the material needs to be subjected to any kind of heat treatment at very high temperatures (e.g. quenching) the CRYOBEST process should not be performed prior to this treatment as the effects would disappear.
If the piece to be treated will be coated (PVD, CVD, etc.), this coating can normally be applied either before or after the cryogenic process and, in most cases, the results will be similar.
In most applications, the CRYOBEST® treatment can be performed in various different phases of the manufacturing process, which means which means the most suitable option for each case can be selected. For more detailed information please do not hesitate to contact us.
This is not a treatment to increase the hardness of the material. In the case of steel, if the hardness needs to be increased, a quenching process will need to be performed.
The multi-stage cryogenic treatment does not significantly modify the hardness of the material. In certain cases, such as the steel grades which after quenching contain a lot of remaining austenite, there may be a slight increase in the hardness as a result of the transformation of part of that austenite into martensite. What is often observed is that, after performing the CRYOBEST® process, the hardness of the material is more homogeneous.
No. The multi-stage cryogenic treatment does not alter the dimensions of materials. On the contrary, components treated usually gain in service dimensional stability. The appearance is not altered either and no corrosion is produced as the process is performed in an inert (nitrogen) atmosphere. Therefore, the treatment is undetectable in practice.
Only in the case of certain steels which after hardening still contain a high percentage of remaining austenite could there be a minimum growth in the material due to the fact that the volume of the martensite crystal is slightly larger than the austenite crystal. In any case, it would be an imperceptible alteration in most applications which, if necessary, could be corrected in most cases (see previous questions).
When the piece to be treated is composed of various different elements joined together certain precautions must be taken, particularly if they are made of different materials. Different materials have different expansion coefficients and this means that, at cryogenic temperatures, very significant tensions can be created. The materials are usually more fragile when the temperature drops and, therefore, these tensions could lead to breakages (special care with plastic elements). Whenever possible, it is recommended to dissemble or loosen the joints under tension. If in doubt, it would be recommendable to carry out a previous test to ensure there are no problems.
Special care must be taken when there are elements glued with precision as practically no adhesives maintain their performance at cryogenic temperatures. This may make the treatment unviable in some applications.
As the temperature drops materials usually become more fragile. However, this behaviour is reversible and when they return to room temperature they regain their previous resistance.
On the other hand, to prevent the possibility of causing damage to the material due to sharp changes in temperature (thermal shock); the CRYOBEST® process is performed in specially designed processors with fully controlled gradients. It is a “dry” process in which the components to be treated never come into contact with the liquid nitrogen.
We must point out that the CRYOBEST® multi-stage cryogenic treatment is not a laboratory process that is only suitable to treat expensive and delicate components. Quite the opposite, it is an industrial process that can be used efficiently and economically in applications of all kinds.
Cryobest’s own technology and its ability to design and manufacture cryogenic processors means that the size and capacity requirements rarely pose a problem. It will almost always be possible to adapt or make the necessary equipment to meet each customer’s requirements.
Furthermore, the CRYOBEST® process has a fundamental advantage compared to other conventional cryogenic treatments. Given that the process is much shorter, the equipment is much more productive. For that reason, it is the ideal solution for the treatment of large quantities of material.
