Cryogenic tempering Cryogenic tempering is a two-phase metal treatment that involves a descent and ascent phase, including a cryogenic treatment process, known as "cryogenic processing", where the material is slowly cooled to ultra low temperatures, typically around -300 °F / -184 °C, which then optionally reheated slowly, typically up to +325 °F / 162 °C. Materials do not "harden" during the temperature descent or ascent, rather their molecular structures are compressed together tightly in uniformity through a computer controlled process that typically uses liquid nitrogen to slowly descend temperatures.
Invention history of cryogenic processing and cryogenic tempering The cryogenic treatment process was invented by Ed Busch (CryoTech) in Detroit, Michigan in 1966, inspired by NASA research, which later merged with 300 Below, Inc. in 2000 to become the world's largest and oldest commercial cryogenic processing company after Peter Paulin of Decatur, IL collaborated with process control engineers to invent the world's first computer-controlled "dry" cryogenic processor in 1992 (where he was featured on the Discovery Channel's Next Step TV Show for his invention). Whereas the industry initially submerged metal parts in liquid nitrogen by dunking them or pouring liquid nitrogen over the parts, the earliest results proved inconsistent, which led Mr. Paulin to develop 300 Below's "dry" computer-controlled cryogenic processing equipment to ensure consistent and accurate treatment results across every processing run by introducing liquid nitrogen into a chamber above its boiling point, in a "dry" gaseous state, to ensure that parts in a chamber are not
thermally shocked by direct exposure to ultracold liquid. A "dry" cryogenic process does not submerge parts in liquid, but rather ensures that temperatures are slowly descended at less than one degree per minute using short bursts of cold gas being introduced via a solenoid-metered pipe, which is controlled by a computer equipment paired with highly accurate RTD (Resistance Temperature Detector) sensors.
Science behind dry cryogenic processing and cryogenic tempering Because all changes to metals take place on the quench, the first phase of the initial descent is called cryogenic processing and by adding a second phase to heat the materials after an initial molecular re-alignment, both processes together are called cryogenic tempering. By using liquid nitrogen, the temperature can go as low as −196 °C, though, the typical dwell temperature of cryogenic processing equipment is slightly above the boiling point of liquid nitrogen, closer to -300 °F / -184 °C, due to being injected into the processing chamber as a gaseous state and making every attempt not to introduce liquid into the chamber that could cause parts to become thermally shocked. Cryogenic processing, especially cryogenic tempering, can have a profound effect on the mechanical properties of certain materials, such as
steels or
tungsten carbide, but the heating phase in cryogenic tempering is typically omitted for softer metals like brass in musical instruments, for piano strings, in certain aerospace applications, or for sensitive electronic components like vacuum tubes and transistors in high-end audio equipment. In tungsten carbide cobalt (WC-Co), the crystal structure of cobalt transforms from softer FCC to harder HCP phase, whereas the hard tungsten carbide particle is unaffected by the treatment.
Applications of cryogenic processing • Aerospace and defense: communication, optical housings, satellites, weapons platforms, guidance systems, landing systems • Automotive: brake rotors, transmissions, clutches, brake parts, rods,
crankshafts, camshafts, axles,
bearings, ring and pinion, heads, valve trains, differentials, springs, nuts, bolts, washers • Cutting tools: cutters, knives, blades, drill bits, end mills, and
turning and
milling 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, and fret wire, piano wire, amplifiers,
magnetic pickups, cables, connectors • Sports: firearms, knives, fishing equipment, auto racing, tennis rackets, golf clubs, mountain climbing gear, archery, skiing, aircraft parts, high-pressure lines, bicycles, motorcycles
Cryogenic machining Cryogenic machining is a machining process where the traditional flood lubro-cooling liquid, an emulsion of oil in water, is replaced by a jet of either liquid nitrogen (
LN2) or pre-compressed carbon dioxide (). 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 for several decades, but the actual commercial applications are still limited to very few companies. Both cryogenic machining by turning and milling are possible. Cryogenic machining is a relatively new technique in machining. This concept was applied on various machining processes such as turning, milling, drilling, etc. Cryogenic turning technique is generally applied on three major groups of workpiece materials—superalloys, ferrous metals, and viscoelastic polymers/elastomers. The roles of cryogen in machining different materials are unique.
Cryogenic deflashing Cryogenic deburring Cryogenic rolling Cryogenic rolling or '''', 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. ==Cryogenic treatment in specific materials==