Cryogenic treatment
Encyclopedia
A cryogenic treatment is the process of treating workpieces to cryogenic temperatures (i.e. below -190 C) to remove residual stress
es and improve wear resistance on steel
s.
The process has a wide range of applications from industrial tooling to improvement of musical signal transmission. Some of the benefits of cryogenic treatment include longer part life, less failure due to cracking, improved thermal properties, better electrical properties including less electrical resistance, reduced coefficient of friction, less creep and walk, improved flatness, and easier machining.
d bulk materials from its bulk counterpart at cryogenic temperatures. It can be defined as rolling that is carried out at cryogenic temperatures. Nanostructured materials are produced chiefly by severe plastic deformation processes. The majority of these methods require large plastic deformations (strain
s much larger than unity). In case of cryorolling, the deformation in the strain hardened metals is preserved as a result of the suppression of the dynamic recovery. Hence large strains can be maintained and after subsequent annealing
, ultra-fine-grained structure can be produced.
Residual stress
Residual stresses are stresses that remain after the original cause of the stresses has been removed. They remain along a cross section of the component, even without the external cause. Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment...
es and improve wear resistance on steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
s.
The process has a wide range of applications from industrial tooling to improvement of musical signal transmission. Some of the benefits of cryogenic treatment include longer part life, less failure due to cracking, improved thermal properties, better electrical properties including less electrical resistance, reduced coefficient of friction, less creep and walk, improved flatness, and easier machining.
Cryogenic rolling
Cryogenic rolling, also known as , is one of the potential techniques to produce nanostructureNanostructure
A nanostructure is an object of intermediate size between molecular and microscopic structures.In describing nanostructures it is necessary to differentiate between the number of dimensions on the nanoscale. Nanotextured surfaces have one dimension on the nanoscale, i.e., only the thickness of the...
d bulk materials from its bulk counterpart at cryogenic temperatures. It can be defined as rolling that is carried out at cryogenic temperatures. Nanostructured materials are produced chiefly by severe plastic deformation processes. The majority of these methods require large plastic deformations (strain
Strain (materials science)
In continuum mechanics, the infinitesimal strain theory, sometimes called small deformation theory, small displacement theory, or small displacement-gradient theory, deals with infinitesimal deformations of a continuum body...
s much larger than unity). In case of cryorolling, the deformation in the strain hardened metals is preserved as a result of the suppression of the dynamic recovery. Hence large strains can be maintained and after subsequent annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
, ultra-fine-grained structure can be produced.
Advantages
Comparison of cryorolling and rolling at room temperature:- In Cryorolling, the strain hardening is retained up to the extent to which rolling is carried out. This implies that there will be no dislocation annihilation and dynamic recovery. Whereas in rolling at room temperature, dynamic recovery is inevitable and softening takes place.
- The flow stressFlow stressFlow stress is defined as the instantaneous value of stress required to continue deforming the material - to keep the metal flowing. It is the yield strength of the metal as a function of strain, which can be expressed:* Yf = Flow stress, MPa...
of the material differs for the sample which is subjected to cryorolling. A cryorolled sample has a higher flow stress compared to a sample subjected to rolling at room temperature. - Cross slip and climb of dislocationDislocationIn materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials...
s are effectively suppressed during cryorolling leading to high dislocation density which is not the case for room temperature rolling. - The corrosion resistance of the cryorolled sample comparatively decreases due to the high residual stress involved.
- The number of electron scattering centres increases for the cryorolled sample and hence the electrical conductivity decreases significantly.
- The cryorolled sample shows a high dissolution rate.
- Ultra-fine-grained structures can be produced from cryorolled samples after subsequent annealing.