Cryogenic Process

In the cryogenic process, materials are cooled to very low temperatures (-196 ºC) to achieve the desired metallurgical and microstructural properties. Reducing these temperatures is possible by feeding computer-controlled liquid nitrogen (N2) into the system and using the most suitable insulation materials. Cryogenic process is divided into two main categories: “deep” and “shallow”. Although there is a significant improvement in the mechanical properties of the materials by reducing the temperature of the materials to around -150 ºC in the shallow cryogenic process, the desired properties cannot be fully achieved. In the deep cryogenic process, materials are cooled to -196 ºC, and the effects of this process increase significantly compared to the shallow cryogenic process.

Application of Cryogenic Process

Cryogenic processing can be applied to a wide range of materials such as steels, cast irons, non-ferrous metals, alloys, carbides, plastics, ceramics. The process is cooled at a rate of 1-2 ºC/min and is carried out between 36 and 72 hours and may vary depending on the material type and weight. There are 3 cycles in the cryogenic process. These cycles can be briefly thought of as controlled cooling, holding and controlled heating. Since the system is computer controlled and prevents liquid nitrogen-part contact, any change in part dimensions is prevented and the risk of cracking in the part is eliminated or greatly reduced. This special process is not a surface treatment and can create the same effect at every point of the material.

Effects of Cryogenic Process

Cryogenic process has many effects. Its effects can basically be grouped under a few main headings. These are briefly; These can be listed as transformation of the residual austenite phase into martensite, change in carbide forms, refinement in the grain structure, and elimination of internal stresses.

Converting Residual Austenite Phase to Martensite

In traditional heat treatment applications, the austenite phase is first obtained in order to harden steels. It is desired to obtain the martensite phase by rapidly cooling this phase. However, as a result of traditional heat treatment, not all of the austenite phase can turn into martensite. At this point, the cryogenic process comes into play, converting approximately the entire residual austenite phase into martensite.

Change in Carbide Forms

In traditional hardening methods, carbides can enter the crystal structure and cause stresses in the crystal structure. During the cryogenic process, carbide particles can break free from the crystal lattice and disperse within the material. In this way, residual stresses are significantly reduced and high hardness carbide structures are formed, which can lead to high increases in wear resistance.

Thinning in Grain Structure

The atoms that make up the alloy want to stay where they are most stable in the structure. These atoms can achieve optimum alignment thanks to the cryogenic process and cause thinning in the grain structure. In this way, molecular bonds are strengthened and the wear resistance of the material may increase.

Relieving Internal Stresses

Due to the rearrangement of atoms and therefore the thinning of the grain structure, atomic gaps (errors) in the crystal structure can be eliminated and the atomic density in the unit volume can be increased. In this way, internal stresses in the material can be significantly reduced. As a result of microstructural changes, the strength, toughness and hardness of materials increase and wear resistance increases. In particular, increases in wear resistance can reach 800%. As a result, material life increases significantly.