Ductility at low temperatures

The hexagonal-close-packed (hep) metals generally exhibit mechanical properties intermediate between those of the fee and bcc metals. For example Zn encounters a ductile-to-brittle transition whereas Zr and pure Ti do not. The latter and their alloys with a hep structure remain reasonably ductile at low temperatures and have been used for many applications where weight reduction and reduced heat leakage through the material have been important. However, small impurities of O, N, H, and C can have a detrimental effect on the low temperature ductihty properties of Ti and its alloys. 

Steels lose their ductility at low temperatures and can become subject to brittle failure. There are specific requirements for metals to be used for refrigerated storage tanks in API 620, Appendices Q and R. 

Low-temperature p-hydrogen requires the use of materials that retain good ductility at low temperatures. Austenitic stainless steel (e.g. AISI 316L and 304L) or aluminum and aluminum alloys (Series 5000) are recommended. Polytetrafluor-oethylene (PTFE, Teflon) and 2-chloro-l,l,2-trifluoroethylene (Kel-F) can also be used. 

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. 

Significant strengthening is observed up to 2700 K (2427 °C). Above this, rapid particle coarsening occurs, and the strengthening effect fades. Additions of rhenium provide ductility at low temperatures by decreasing the DBTT. 

A white metal, malleable and ductile at low temperature, brittle when heated which accompanies Zn in certain of its ores. It resembles zinc in its physical as well as its chemical characters. It is used in certain fusible aUoye, and its iodide is used in photography. 

Di(2-ethyl hexyl) phthalate (DOP) and diisooctyl phthalate (DIOP) are largely used for PVC and copolymers of vinyl chloride and vinyl acetate as they have an affinity to these polymers, produce good solvation, and maintain good flexibility of finished products at low temperature. The use of M-octyl-n-decyl phthalate in the production of plastics materials also allows good flexibility and ductility at low temperature. Diisodecyl phthalate (DDP), octyl decyl phthalate (ODP), and dicapryl phthalate (DCP) have a lower solvency and are therefore used in stable PVC pastes. Butyl octyl phthalate (BOP), butyl decyl phthalate (BDP, and butyl benzyl phthalate (BBP) have a good solvency and are used to adjust melt viscosity and fusion time in the production of high-quality foams. They are highly valued for use in expandable plasticized PVC. 

Such a possibility is of practical importance for evaluating the residual strength of cracked structures under conditions other than those studied experimentally. Condition (5) can be used as a structural criterion of brittle fracture for a wide combination of test conditions of thin sheets of medium-strength metals, which remain ductile at low temperature. 

This section deals with the features of ductile ceramics and, in some cases, the modifications in composition that induce ductility at low temperatures, as well as additives to base ceramics, such as metals, which also promote ductility. 

Although tantalum is by far the most widely used of the refractory metals to impart corrosion resistance to chemical-process vessels and components, there are some applications where molybdenum has been used with great success. Molybdenum support structures have replaced graphite in the processing of high-purity alcohols. Molybdenum-rhenium alloys, first developed because of their vastly improved ductility at low temperatures and in the recrystallized condition, have been used as vessel lining and piping components for the manufacture of Freon replacements. ... 

ADVANTAGES AND DISADVANTAGES OF THE BLEND Excellent chemical resistance, impact strength, one of the most abrasion resistant plastics, one of the lowest coefficient of friction, ductility at low temperatures. 

Dry carbon dioxide liquid and gas is compatible with most metallic piping materials. The primary hazards are elevated pressure and the loss of piping ductility at low temperature. Low-pressure liquid carbon dioxide is typically stored at temperatures ranging from 0°F to -20°F (-17.8°C to -28.9 C), and rapid depressurization will cause the liquid to autorefriger-ate. Piping temperatures can decrease to as cold as -109.3°F (-78.5°C) when dry ice is formed. 

The use of n-octyl n-decyl phthalate in the production of plastic materials allows good flexibility and ductility at low temperature. Its volatility is low and it is often used mixed with other phthalates. 

The aluminum alloy, 5086 (4,0 per cent Mg, nominal), which was developed for structural use and particularly for welded structures, has been found to be one of the strongest as well as one of the most ductile of the aluminum alloys. Because this alloy was expected to exhibit a higher strength but still retain most of its ductility at low temperatures, a program was undertaken which involved the testing of both the parent and welded metals down to 20 K,... 

Process industries. In the chemical industries aluminum is used for the manufacture of hydrogen peroxide and the production and distribution of nitric acid. It is also used in the manufacture and distribution of liquefied gases, because it retains its strength and ductility at low temperatures, and its lower density is also an advantage over nickel steels. 

The bubble chamber itself is made of a 6300-lb stainless steel casting. The chamber material must have high strength and good ductility at low temperature because of the impact load. High electrical resistivity at low temperature is desirable to reduce eddy current forces should the magnet power fail. Also the permeability of the chamber must remain below about 1.05 between room temperature and 20°K to reduce distortions in the magnetic field. 

One major reason for reluctance in using any new alloy in cryogenic equipment is thefear of brittle fracture at low temperatures. Many structural alloys do suffer amarkedlossof ductility at low temperatures. Such ductile—brittle metals, at low temperatures, become sensitive to stress concentrations caused by accidental notches or by necessary changes in the shape of a part. As a result, local failures at a point of stress concentration start easily and propagate almost instantaneously into complete failures. 

Remain ductile at low temperatures, if ductile at room temperature Become brittle at low temperatures... 

---