Temperature embrittlement

Sensitization temperatures (under -320°F). Room temperature embrittlement is nominal. and vessels. stabilized (Types 321,347) and extra low carbon (304 L, 316L) grades. into grain boundaries, with depletion of chromium in contiguous grain boundary areas. austenitic stainless steels. 

The main use of this type steel is for situations in which the process material may not be corrosive to mild steel, yet contamination due to rusting is not tolerable and temperatures or conditions are unsuitable for aluminum. However, prolonged use of these steels in the temperature range of 450 to 550°C causes low-temperature embrittlement of most ferritic steels with more than 12% chromium [16]. 

Low temperature. Low-temperature processes (below 0°C) contain large amounts of fluids kept in the liquid state by pressure and/or low temperature. If for any reason it is not possible to keep them under pressure or keep them cold, then the liquids will begin to vaporize. If this happens, impurities in the fluids are liable to precipitate from solution as solids, especially if equipment is allowed to boil dry. Deposited solids may not only be the cause of blockage but also in some cases the cause of explosions. It is necessary, therefore, to ensure that the fluids entering a low-temperature plant are purified. A severe materials-of-construction problem in low-temperature processes is low-temperature embrittlement. Also, in low temperature as in high-temperature operations, the equipment is subject to thermal stresses, especially during start-up and shutdown. 

A material of construction problem in low temperature plants is low temperature embrittlement. The material requirements are however well understood. The problems arise from the installation of incorrect materials or flow of low temperature fluids to sections of plant constructed in mild steel. These both refer to inherent safety problems. 

Specific heat (J/(kg K)d Thermal degradation temperature, °C Low temperature embrittlement, °C Water absorption, %... 

One faces the problems of low-temperature embrittlement of steel claddings of SRU fuel elements, CPS absorbers as well as SRU steel structures potentially complicating the process of SNF unloading from land-based containers and subsequent shipment to the reprocessing plant ... 

Low impact values at cryogenic temperatures (under -320°F). Room temperature embrittlement is nominal. 

Low-temperature embrittlement occurs in carbon and low-alloy steels at temperatures below their brittle-ductile transition temperature range. The effect is reversible when the alloy is heated above the transition range, ductility is restored. This embrittlement is avoided by following the Charpy impact test requirements of the relevant engineering codes. The need to test depends primarily on the material, its thickness and the minimum design temperature. 

Duplex stainless steels are susceptible to 885°F (475°C) embrittlement and to sigma-phase formation, and they are usually not selected for temperatures above 650°F (345°C). Because of their ferrite content, they are susceptible to low-temperature embrittlement. However, the duplex stainless steels tend to have relatively low brittle-ductile transition temperatures. The engineering codes typically require the duplex stainless steels to be qualified for low-temperature service by impact testing. They can be susceptible to hydrogen embrittlement, but are less susceptible than are the ferritic and martensitic stainless steels. 

High alloys with little exception suffer some embrittlement if exposed to sustained high-temperature service due to the formation of intermetallic compounds. Conditions and rates of embrittlement vary with the alloy. Check with alloy manufacturers for specific information. High alloys containing enough nickel to ensure an austenitic microstructure are, like austenitic stainless steels, unaffected by low-temperature embrittlement. 

If degradation processes such as high-temperature embrittlement or autorefrigeration will affect operating procedures such as pressurization during start-up, indicate such limitations as general notes to the MSD. 

A weldable austenitic stainless steel for liquefied natural gas tankage applications has been developed in the USSR. In the United States, ferritic 9% nickel alloy steels and 5083-0 aluminum are used for similar applications. The USSR alloy composition, Fe-13%Cr-19%Mn-0.2%N-0.8%Ni, has a low nickel content. Substantial amounts of nickel are traditionally required in ferrous alloys to resist low-temperature embrittlement. The substitution of nitrogen and manganese for nickel results in a relatively high-strength austenitic alloy. 

RPV integrity is of great importance. Problems related to the low temperature embrittlement of RPV metal and welds are well known. 

The low-temperature embrittlement found to occur in USS Tenelon makes its value doubtful as a low-temperature structural material. The impact transition encountered in this material is not common in alloys with a face-centered-cubic lattice, although low-temperature embrittlement of certain of the high Mn-austen-itic stainless steels is a fairly well-known fact [9-11]. 

The second important factor affecting low temperature embrittlement of the 7000 series aluminum alloys is that of primary working. The degree of primary working of the metal is important as maybe seen by comparing the properties of the 7079 T6 sheet and 7079-T6 billet material. Their analyses were nearly identical however, the billet material experienced much more severe embrittlement at lower temperatures than the sheet material. This may be explained by the cored structure present in the 7079-T6 billet (Fig. 10), which was not broken up by primary working. No effects of heat treatment were detected since all materials tested were of the same temper and improper heat treatment was not apparent from the tensile data or microstructures. 

Crum, J. R., Smith, G. D., Flower, H. L., Resistance of Automobile Exhaust Flexible Coupling Alloys to Hot Salt Attack, Stress Corrosion Cracking and High Temperature Embrittlement, SAE1999-01-0372, SAE International, Warrendale, PA, 1999. 

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