Cryogenic treatment

Last updated

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 on steels and even composites. 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 quantimet.

Contents

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

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 dynamic recovery. 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 dislocation annihilation 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 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.

Related Research Articles

Cryogenics Study of the production and behaviour of materials at very low temperatures

In physics, cryogenics is the production and behaviour of materials at very low temperatures.

Martensite

Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation.

Stress–strain curve

In engineering and materials science, a stress–strain curve for a material gives the relationship between stress and strain. It is obtained by gradually applying load to a test coupon and measuring the deformation, from which the stress and strain can be determined. These curves reveal many of the properties of a material, such as the Young's modulus, the yield strength and the ultimate tensile strength.

Carbon steel Steel in which the main interstitial alloying constituent is carbon

Carbon steel is a steel with carbon content from about 0.05% up to 2.1% by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

Creep (deformation) Tendency of a solid material to move slowly or deform permanently under mechanical stress

In materials science, creep is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods and generally increases as they near their melting point.

High-speed steel Subset of tool steels

High-speed steel is a subset of tool steels, commonly used as cutting tool material.

Quenching Rapid cooling of a workpiece to obtain certain material properties

In materials science, quenching is the rapid cooling of a workpiece in water, oil or air to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phase transformations, from occurring. It does this by reducing the window of time during which these undesired reactions are both thermodynamically favorable, and kinetically accessible; for instance, quenching can reduce the crystal grain size of both metallic and plastic materials, increasing their hardness.

Work hardening

Work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context.

Tempering (metallurgy) Process of heat treating used to increase toughness of iron-based alloys

Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys. Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air. The exact temperature determines the amount of hardness removed, and depends on both the specific composition of the alloy and on the desired properties in the finished product. For instance, very hard tools are often tempered at low temperatures, while springs are tempered at much higher temperatures.

Cryogenic hardening is a cryogenic treatment process where the material is cooled to approximately −185 °C (−301 °F), usually using liquid nitrogen. It can have a profound effect on the mechanical properties of certain steels, provided their composition and prior heat treatment are such that they retain some austenite at room temperature. It is designed to increase the amount of martensite in the steel's crystal structure, increasing its strength and hardness, sometimes at the cost of toughness. Presently this treatment is being practiced over tool steels, high-carbon, high-chromium steels and in some cases to cemented carbide to obtain excellent wear resistance. Recent research shows that there is precipitation of fine carbides in the matrix during this treatment which imparts very high wear resistance to the steels.

Hardening is a metallurgical metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain. A harder metal will have a higher resistance to plastic deformation than a less hard metal.

Lüders band

Lüders bands, also known as "slip bands" or "stretcher-strain marks," are localized bands of plastic deformation in metals experiencing tensile stresses, common to low-carbon steels and certain Al-Mg alloys. First reported by Guillaume Piobert and W. Lüders, the mechanism that stimulates their appearance is known as "dynamic strain aging," or the inhibition of dislocation motion by interstitial atoms, around which "atmospheres" or "zones" naturally congregate.

In metallurgy and materials science, annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for an appropriate amount of time and then cooling.

Burr (edge)

A burr is a raised edge or small piece of material that remains attached to a workpiece after a modification process.

Eglin steel (ES-1) is a high-strength, high-performance, low-alloy, low-cost steel, developed for new generation of bunker buster type bombs, e.g. the Massive Ordnance Penetrator and the improved version of the GBU-28 bomb known as EGBU-28. It was developed in collaboration between the US Air Force and the Ellwood National Forge Company.

Cryogenic grinding

Cryogenic grinding, also known as freezer milling, freezer grinding, and cryomilling, is the act of cooling or chilling a material and then reducing it into a small particle size. For example, thermoplastics are difficult to grind to small particle sizes at ambient temperatures because they soften, adhere in lumpy masses and clog screens. When chilled by dry ice, liquid carbon dioxide or liquid nitrogen, the thermoplastics can be finely ground to powders suitable for electrostatic spraying and other powder processes. Cryogenic grinding of plant and animal tissue is a technique used by microbiologists. Samples that require extraction of nucleic acids must be kept at −80 °C or lower during the entire extraction process. For samples that are soft or flexible at room temperature, cryogenic grinding may be the only viable technique for processing samples. A number of recent studies report on the processing and behavior of nanostructured materials via cryomilling.

TRIP steel are a class of high-strength steel alloys typically used in naval and marine applications and in the automotive industry. TRIP stands for "Transformation induced plasticity," which implies a phase transformation in the material, typically when a stress is applied. These alloys are known to possess an outstanding combination of strength and ductility.

Dynamic strain aging (DSA) is an instability in plastic flow of materials, associated with interaction between moving dislocations and diffusing solutes. Although sometimes dynamic strain aging is used interchangeably with the Portevin–Le Chatelier effect, dynamic strain aging refers specifically to the microscopic mechanism that induces the Portevin–Le Chatelier effect. This strengthening mechanism is related to solid-solution strengthening and has been observed in a variety of fcc and bcc substitutional and interstitial alloys, metalloids like silicon, and ordered intermetallics within specific ranges of temperature and strain rate.

Peening

Peening is the process of working a metal's surface to improve its material properties, usually by mechanical means, such as hammer blows, by blasting with shot or blasts of light beams with laser peening. Peening is normally a cold work process, with laser peening being a notable exception. It tends to expand the surface of the cold metal, thereby inducing compressive stresses or relieving tensile stresses already present. Peening can also encourage strain hardening of the surface metal.

USAF-96 is a high-strength, high-performance, low-alloy, low-cost steel, developed for new generation of bunker buster type bombs, e.g. the Massive Ordnance Penetrator and the improved version of the GBU-28 bomb known as EGBU-28. It was developed by the US Air Force at the Eglin Air Force Munitions Directorate. It uses only materials domestic to the USA. In particular it requires no tungsten.

References

  1. ASM Handbook, Volume 4A, Steel Heat Treating Fundamentals and Processes. ASM International. 2013. pp. 382–386. ISBN   978-1-62708-011-8.
  2. Padmakumar, M.; Guruprasath, J.; Achuthan, Prabin; Dinakaran, D. (2018-08-01). "Investigation of phase structure of cobalt and its effect in WC–Co cemented carbides before and after deep cryogenic treatment". International Journal of Refractory Metals and Hard Materials. 74: 87–92. doi:10.1016/j.ijrmhm.2018.03.010. ISSN   0263-4368.
  3. Thamizhmanii, S; Mohd, Nagib; Sulaiman, H. (2011). "Performance of deep cryogenically treated and non-treated PVD inserts in milling". Journal of Achievements in Materials and Manufacturing Engineering. 49 (2): 460–466.
  4. "Archived copy". Archived from the original on 2015-09-03. Retrieved 2015-07-30.CS1 maint: archived copy as title (link)
  5. "Zephyr Tele".
  6. Zhao, Z; Hong, S Y (October 1992). "Cooling Strategies for Cryogenic Machining from a Materials Viewpoint". Journal of Materials Engineering and Performance. 1 (5): 669–678. Bibcode:1992JMEP....1..669Z. doi:10.1007/BF02649248.
  7. Richter, Alan. "Cryogenic machining systems can extend tool life and reduce cycle times". Cutting Tool Engineering.
  8. Strano, Matteo; Chiappini, Elio; Tirelli, Stefano; Albertelli, Paolo; Monno, Michele (2013-09-01). "Comparison of Ti6Al4V machining forces and tool life for cryogenic versus conventional cooling". Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture. 227 (9): 1403–1408. doi:10.1177/0954405413486635. ISSN   0954-4054.
  9. Shokrani, A.; Dhokia, V.; Newman, S. T.; Imani-Asrai, R. (2012-01-01). "An Initial Study of the Effect of Using Liquid Nitrogen Coolant on the Surface Roughness of Inconel 718 Nickel-Based Alloy in CNC Milling". Procedia CIRP. 45th CIRP Conference on Manufacturing Systems 2012. 3: 121–125. doi: 10.1016/j.procir.2012.07.022 .