TECHNOLOGY

Cryogenic treatment provides for slower wearing down and improved lifetime of gears, tools, components and castings, which results in significant cost savings and increase in productivity.

It is a dry process during which parts never come into contact with liquid nitrogen. Parts are cooled down very slowly and then are kept at a temperature of approx. -184°C for 24-36 hours and gradually warmed up to room temperature. Different materials and cross sections require different cycles. This is how the entire material is treated (not only the surface). The structure of the entire material is not changed by the subsequent treatment (grinding, honing, milling); it remains constant for the lifetime of the tool or component.

In the course of material treatment, the following three main changes take place:
1) The material microstructure changes into structures with increased resistance to wear. The residual austenite changes into martensite in the structure. Austenite is relatively soft and unstable and is not sufficiently resistant to wear. Martensite is hard and fragile until it is tempered. Thus, parts must be tempered after cryo-treatment. As a result, a “tempered martensite“ structure will arise which is a desirable structure for its good properties in terms of toughness and resistance to wear.
2) In the course of processing, small particles of hard metal develop called “eta” parts of hard metal. This process is known as “hard metal separation”. These particles form from alloyed parts which are present in steel. Thus, interstitial (inserted) microparticles in the peripheral area and “micro-emptiness“ in the structure form a more coherent crystalline structure.
3) Reduction in the volume of random residual compressive and tensile stresses, which may be caused by heat processing or machining. Such random stresses are significantly eliminated by changes in the structure and by uniform expansion and contraction which are achieved by the thermomechanical cycle. This results in improved dimensional stability and resistance to fatigue.

Such improvements may be accompanied by increased tensile strength, toughness and stability associated with the release of residual stresses.

Not all materials respond to cryogenic treatment. To give a partial list of materials and a table of some steels with percentage improvement at various temperatures: carbon steel, alloy steel, tool steel, martensitic steel and austenitic stainless steel, cast iron (grey), manganese steel, aluminium, brass, wolfram high-speed steel.

Our company uses exclusively the technology and software of 300 Below, Peta Paulina, with its office at Decatur-IL, USA, from which we received training in such technological procedures.

Increase in resistance to wear after cryogenic tempering (%)