Cryogenic ductility

Microstructural analysis revealed that solution treating the Inconel 718 at 1255 K did not dissolve these particles. The inferior cryogenic ductility, fracture toughness, and FCGR properties demonstrated by cold-worked and 1255 K STD A Inconel 718 verified this observation. 

PCTFE plastic is compatible withHquid oxygen, remains ductile at cryogenic temperatures (16—22), and retains its properties when exposed to either uv or gamma radiation. PCTFE exhibits a refractive iadex of 1.43 (ASTM D542) and an amorphous sheet can provide over 90% transmittance. 

Select storage/service materials and joints with care, allowing for the reduction in ductility at cryogenic temperatures. Provide special relief devices as appropriate. 

Gray cast irons do not have the abrupt ductile to brittle fraction transition down to -40°C as takes place in steels. Special austenitic nodular cast iron similar to the AUS 203 grade, but with a higher manganese content of about 4%, has been obtained for cryogenic purposes for temperatures down to -253°C. 

Aluminum and its alloys are excellent for low temperatures as well as for cryogenic applications because their tensile strength and ductility are increased at low temperatures. 

Nickel Alloys Alloy C-4 (16 Cr, 16 Mo, Balance Ni) and alloy C-276 (16 Cr, 16 Mo, 3.5 W, 5 Fe, balance Ni) have been used for closure seals on cryogenic gas cylinders because the alloys retain all their ductility down to -327°C (—557°F). The impact strength at liquid nitrogen temperatures is the same as that at room temperature. 

The selection of materials for high-temperature applications is discussed by Day (1979). At low temperatures, less than 10°C, metals that are normally ductile can fail in a brittle manner. Serious disasters have occurred through the failure of welded carbon steel vessels at low temperatures. The phenomenon of brittle failure is associated with the crystalline structure of metals. Metals with a body-centred-cubic (bcc) lattice are more liable to brittle failure than those with a face-centred-cubic (fee) or hexagonal lattice. For low-temperature equipment, such as cryogenic plant and liquefied-gas storages, austenitic stainless steel (fee) or aluminium alloys (hex) should be specified see Wigley (1978). 

At cryogenic temperatures, ductile gaskets (indium, Kapton, vacuum grease) are to be preferred (see Fig. 1.25). 

Grayish, soft metal with a white luster on polished surfaces ductile and very malleable at room temperature also highly ductile at cryogenic temperatures body-centered cubic crystals density 8.66 g/cm at 20°C melts at 2,468+10°C vaporizes at 5,127°C electrical resistivity 13.2 microhm-cm at 20°C becomes superconducting at 9.15K thermal neutron-capture cross section 1.1 barns insoluble in water insoluble in hydrochloric acid, nitric acid and aquaregia soluble in hydrofluoric acid soluble in fused alkah hydroxide. 

It is most convenient to classify metals by their lattice symmetry for low-temperature mechanical properties considerations. The fee metals and their alloys are most often used in the construction of cryogenic equipment. Aluminum, copper, nickel, their alloys, and the austenitic stainless steels of the 18-8 type are fee and do not exhibit an impact ductile-to-brittle transition at low temperatures. Generally, the mechanical properties of these metals im-... 

An extensive compilation and evaluation of mechanical, electrical, and thermal properties of six commercially available polymers was performed by Reed et al. [14]. It was shown in their summarized data that polypyromellitim-ide (PPMI), which is obtained by the polycondensation between pyromellitic acid and aromatic diamine, exhibits excellent mechanical properties at both high and low temperatures and retains ductility even at cryogenic temperatures, as seen in Fig. 1. 

Stainless steels can usually be used safely down to about cryogenic temperatures. Tanker ships carrying liquefied natural gas (LNG) are typically made of steel with 9% nickel added to impart cold temperature ductility properties. 

Among low-temperature procedures widely used in the powder production of ductile materials are various kinds of cryodispersion or cryomilling methods based on mechanical comminution of materials at cryogenic temperatures. A decrease of the comminution temperature is accompanied by a corresponding... 

Conversely, mills with impact and attrition modes often do poorly with heat-sensitive materials where the materials become ductile as they heat up. Impact and attrition mills cause significant heating at the point of impact, and it is not uncommon for heat-sensitive materials (e.g., plastics) to stick to the device rather than being ground. In the worst cases, cryogenic grinding can be necessary for highly ductile or heat-sensitive materials. 

Materials such as austenitic stainless steels, nickel-based alloys, and titanium alloys can be used as materials for pressure vessel components in cryogenic applications at temperatures as low as 200°C. Alloy steels have brittle transition points making their impact properties at low temperatures unsuitable for pressure applications. Closures and bolts must also be made of materials that remain ductile at low temperatures. 

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