Cryogenic treatment is a thermal process in which the material is subjected to cryogenic temperatures below -153 ºC. CIC marGUNE, the Co-operative Research Centre into High-performance Manufacturing, is coordinating the DURASTEEL line of research that is endeavouring to produce more efficient steels by applying the right thermal treatment routes in order to maximize their performance.
The automotive, aerospace, metalworking and mining industries, and industry in general, are constantly on the lookout for more reliable, longer-lasting tools. But to get the most out of tooling steels, it is necessary to apply the right thermal treatments. However, the limited development in this field contrasts with the advances that have taken place in that of steels over the last few years. In other words, even though cryogenic treatment has displayed an unquestionable potential to improve the performance of a wide variety of materials and applications, its application in industry remains thin on the ground. "There's somewhat of a gap between experience and theory," pointed out Luis Ángel Álava, coordinator of the line of research at CIC marGUNE and of the area of Cryogenic Treatments at IK4-Azterlan. "One of the reasons is the lack of understanding of the microstructural changes that take place in the steels as a result of the low temperatures, as well as of the mechanisms that cause them," he explained. Nevertheless, the research activity in this field has increased considerably over the last few years.
Conventional cryogenic treatment consists of slowly cooling the material to about -180 ºC, keeping it at that temperature for a long period of time and then reheating it to ambient temperature. The fact that it takes so long is a clear problem.
To solve this problem, one of the alternatives that is currently being explored is multi-phase cryogenic treatment. It is based on the repetition of short, fast, cryogenic cycles. It allows the processing time to be considerably reduced, which enables consumptions and costs to be cut. What is more, "the results achieved with this type of process are, on the whole, better than the ones achieved using conventional cryogenic treatments," stressed Álava.
In general, cryogenic treatments are applied at the end of a tooling production process. Nevertheless, at IK4-Azterlan they are also exploring the application of cryogenic treatment between hardening and tempering. Right now, "we are gathering data to see what scope it could have," added Álava.
Greater durability and lower cost
Cryogenic treatment affects the whole material, not just the surface. On the whole, "it produces changes in the improvement of parameters like wear resistance, fatigue life, toughness, conductivity, etc.," he added. On the other hand, these changes are perfectly compatible with most of the coatings in industry. Basically, "it's a straightforward, easy way of improving the characteristics of materials and what is more, it is economic," pointed out Álava.
The cryogenic treatment of materials has demonstrated its considerable potential for altering the properties of a wide variety of materials. "The applications are endless and can be found in practically any industrial field. Wherever there's a problem of wear or fatigue, there will be a possibility if using processes of this type successfully," explained Álava. In the case of steels "we are looking for fresh approaches for applying processes of this type so that, besides improving the characteristics of the products, it will be possible to come up with the development of more efficient thermal treatment processes."
Álava highlighted the fact that "it is a process that is totally environmentally friendly because while it is being applied, it produces no waste whatsoever. Since wear and fatigue resistance are increased, the consumption of materials is reduced and so are the energy and the environmental costs associated with its production and transformation," he pointed out. Apart from the obvious reduction in the consumption of materials that can be achieved by means of this technology, "nitrogen is a non-toxic, inert gas that is extracted from the air and liquefied so that it can be stored. During cryogenic treatment the liquid nitrogen evaporates and returns to the atmosphere, thus closing the cycle," explained Álava.
This line of research seeks to promote a qualitative leap forwards in the technology of thermal treatments of steels.
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