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Alloy 718ST (Inconel 718)

Alloy 718ST (Inconel 718)

ALLOY718 is a precipitation-hardenable Ni-Cr-Fe alloy containing significant amounts of Nb & Mo as well as lesser amounts of Al+Ti. The alloy has good ductility in the

annealed condition and high strength up to 700 ‹C (1300 ‹F).

good fabrication characteristics in the annealed condition
good tensile, fatigue and creep-rupture strengths
high-temperature strength up to 700 ‹C (1300 ‹F)
good oxidation resistance up to 1000 ‹C (1830 ‹F)
excellent mechanical properties in cryogenic environments
excellent corrosion resistance at high and low temperatures and good resistance to stress-corrosion cracking and pitting corrosion
good weldability by arc and resistance welding processes without susceptibility to post-weld cracking

Corrosion resistance

The high chromium and molybdenum contents of Alloy 718 impart excellent resistance to uniform and localized corrosion, such as pitting in many media at both high and low temperatures. The chromium also enables it to withstand chloride-ion stress-corrosion cracking which makes it an excellent alloy for service in oil and sour gas (H2S containing) environments as well as seawater.

Alloy 718 is generally only used for applications not exceeding 700 ‹C (1300 ‹F). However, oxidation resistance up to 1000 ‹C (1830 ‹F) is particularly high and comparable to that of other gamma-prime (ƒÁ') strengthened superalloys

Due to its high-temperature strength up to 700 ‹C (1300 ‹F), excellent corrosion resistance and ease of fabrication ALLOY718 finds applications in many fields. Initially it was used as a turbine disk material in aircraft jet engines. Here resistance to creep and stress rupture was most important.

Because of its properties, fabricability and cost effectiveness it has since gained wider acceptance. To-day applications vary from highly stressed rotating and static components in gas turbines and rocket engines to high-strength bolting, springs and fasteners, components in nuclear reactors and space vehicles as well as high-temperature tooling for extrusion, of for example copper, and shearing. Another more recent important application involves pump shafts and other highly stressed well head and downhole components in offshore

and marine engineering. Particularly useful is the alloy for drilling equipment in sour (containing H2S, CO2 and chlorides) oil and gas wells.