High-temperature strength steel

A final consideration is the fan operating temperature and environmental conditions. Most axial fans contain the motor, bearings, and drive components within the duct. Thus, the gases must be noncorrosive, at a low tenqjerature (-34 to 82 C) (-29.2 to 180 °F) [1], nonflammable and without any particulate matter. At low or high temperatures, most steels lose their strength [8]. Thompson and Trickier [8] discuss some elements of duct-system design. Table 5.3 summarizes efficiencies for approximate sizing of the fans that have been described. 

High-Temperature Steels. For applications affording superior high-temperature strength and high-temperature creep resistance, austenitic and Cr-alloyed tungsten steels containing also Mo and V are in use (see Table 8.3, rows 7 and 8). 

More Mo is consumed annually than any other refractory metal. The major use for Mo is as an alloying element in alloy steels, tool steels, stainless steels, Ni-based and Co-based superalloys. In these materials, it increases the hardenability, toughness, high-temperature strength, and corrosion resistance. Molybdenum is important in the missile industry, where it is used for high-temperature structural parts, such as nozzles, leading edges of control surfaces, support vanes, struts, reentry cones, radiation shields and heat sinks. In the electrical and electronic industries. Mo is... 

Alloy Steels. These contain a iittie carbon, and sometimes siiicon, but they mainiy contain added metais, such as manganese (hardness), nickei (strength), moiybdenum (improved wear), tungsten (high temperature strength), chromium (corrosion resistance), and vanadium (toughness). 

The external case of the rocket motor supports the mechanically and thermally induced stresses, which are due to internal gas pressure, vibration, acceleration, thrust vector control, and differential thermal expansion of component materials. To accommodate these factors, the structural material should have high strength, adequate modulus, and resistance to buckling. Either a continuous glass filament wound epoxy plastic or a high temperature metal (steel, titanium, or aluminum) case serves as the exterior structural member. 

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