This method can be considered as an evolution of conventional cryogenic treatments that, basically, are isothermal processes in wich the materials are slowly cooled, then maintained for a long time at a constant cryogenic temperature (usually around -180°C) and, finally, slowly heated back to ambient temperature. Tipically, the time required to complete one of these processes is more than two days.
Compared wit conventional cryogenic treatments, the multistage strategy provieds two main advantages:
The total process time is much shorter (usually it does not exceed 15 hours).The results are usually better.
Tec-proceso-2These treatments neither alter the apearance nor the dimensions of the components. They are carried out in inert atmosphere and do not generate rust or color change. In fact, these treatments are virtually undetectable in practice since the changes in the material are very subtle, only affecting in the microstructural scale.
Cryogenic treatments can be applied to a wide variety of materials such as:
Steels (alloyed, tool steels, HSS, cemented, stainless steels, etc.) both wrought and from powder-metallurgyCast ironCemented carbideAluminium alloysCopper and its alloys (bronze, brass…)Other metals and special alloysCeramic materials, composites, certain polymers, etc.
Obviously, the effects produced by cryogenic treatments are linked to the material and, in practice, also to the application. These are only some of the features or properties that can get to be improved:
Resistance to different wear mechanisms.Resistance to fatigue and creep.Hardness.Residual stresses and dimensional stability.Tensile properties.Toughness.Thermal / electrical conductivity.
We should not forget that we are talking about a heat treatment and, therefore, the whole volume of the material is affected. This means that a deep cold treated tool or component can be modified (by machining, grinding, etc.) without suffering any loss in performance. It will not be necessary to apply the treatment again.
These processes do not replace the standard treatments used for steel hardening (quenching + tempering) though could sometimes be considered as an extension of them. Another feature of cryogenic is not only their compatibility but also their complementarity with many other processes commonly used in industry to increase the life and performance of the materials (PVD coatings, case hardening, nitriding, etc.).
Finally and just for clarification, it is important to distinguish these processes from the standard subzero treatments (also known as shallow cryogenics), performed at temperatures around -80°C, that are sometimes used after quenching to reduce the amount of residual austenite in components made of certain steel grades. Obviously, this effect is also achieved with deep cryogenic treatments, performed at temperatures below -150°C (the threshold to be considered criogenic in this field)