Cryogenic treatment

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A cryogenic treatment is the process of treating workpieces to cryogenic temperatures (i.e. below −190 °C (−310 °F)) in order to remove residual stresses and improve wear resistance in steels and other metal alloys, such as aluminum. In addition to seeking enhanced stress relief and stabilization, or wear resistance, cryogenic treatment is also sought for its ability to improve corrosion resistance by precipitating micro-fine eta carbides, which can be measured before and after in a part using a .

The process has a wide range of applications from industrial tooling to the 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.^[1]

Processes[]

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Cryogenic hardening[]

Cryogenic hardening is a cryogenic treatment process where the material is slowly cooled to very low temperatures. By using liquid nitrogen, the temperature can go as low as −196 °C. It can have a profound effect on the mechanical properties of certain materials, such as steels or tungsten carbide. In tungsten carbide (WC-Co), the crystal structure of cobalt is transformed from softer FCC to harder HCP phase whereas the hard tungsten carbide particle is unaffected by the treatment.^[2]

Applications of cryogenic processing[]

• Aerospace & Defense: communication, optical housings, weapons platforms, guidance systems, landing systems.
• Automotive: brake rotors, transmissions, clutches, brake parts, rods, crank shafts, camshafts axles, bearings, ring and pinion, heads, valve trains, differentials, springs, nuts, bolts, washers.
• Cutting tools: cutters, knives, blades, drill bits, end mills, turning or milling^[3] inserts. Cryogenic treatments of cutting tools can be classified as Deep Cryogenic Treatments (around -196 °C) or Shallow Cryogenic Treatments (around -80 °C).
• Forming tools: roll form dies, progressive dies, stamping dies.
• Mechanical industry: pumps, motors, nuts, bolts, washers.
• Medical: tooling, scalpels.
• Motorsports and Fleet Vehicles: See Automotive for brake rotors and other automotive components.
• Musical: Vacuum tubes, Audio cables, brass instruments, guitar strings^[4] and fret wire, piano wire, amplifiers, magnetic pickups,^[5] cables, connectors.
• Sports: Firearms, knives, fishing equipment, auto racing, tennis rackets, golf clubs, mountain climbing gear, archery, skiing, aircraft parts, high pressure lines, bicycles, motor cycles.

Cryogenic machining[]

Cryogenic machining is a machining process where the traditional flood lubro-cooling liquid (an emulsion of oil into water) is replaced by a jet of either liquid nitrogen (LN2) or pre-compressed carbon dioxide (CO2). Cryogenic machining is useful in rough machining operations, in order to increase the tool life. It can also be useful to preserve the integrity and quality of the machined surfaces in finish machining operations. Cryogenic machining tests have been performed by researchers since several decades,^[6] but the actual commercial applications are still limited to very few companies.^[7] Both cryogenic machining by turning^[8] and milling^[9] are possible.

Cryogenic deflashing[]

Cryogenic deburring[]

Cryogenic rolling[]

Cryogenic rolling or cryorolling, is one of the potential techniques to produce nanostructured 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 (strains 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 . Hence large strains can be maintained and after subsequent annealing, 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 and dynamic recovery. Where as in rolling at room temperature, dynamic recovery is inevitable and softening takes place.
• The flow stress 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 dislocations are effectively suppressed during cryorolling leading to high 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 .
• Ultra-fine-grained structures can be produced from cryorolled samples after subsequent annealing.

References[]

External links[]

• [1]
• Cryogenics Society of America
• CSA Cryogenic Treatment Database of Research Articles
• https://ctpcryogenics.com
• 300 Below - Founder of Commercial Cryogenic Industry (Since 1966)
• Understanding how Deep Cryogenics works, and what applications are most effective