Incoloy 800HT

Incoloy 800HT also referred to as the UNS N08811/W.Nr. 1.4959 alloy.

Incoloy 800HT is an iron-nickel-chromium alloy having the same basic composition as Incoloy alloy 800, with significantly higher creep rupture strength.

Special Metals knew the importance of maintaining the aluminum and titanium contents in the upper portion of the specified material range. This resulted in higher creep and stress rupture properties than competitive alloy 800H. Therefore, to maintain higher allowable design stresses, the company introduced a variation of INCOLOY alloy 800H which is called INCOLOY alloy 800HT (UNS N08811). INCOLOY alloy 800HT has a restricted chemistry, within the limits of alloy 800H, and requires a heat treatment of 2100°F (1149°C) minimum. The carbon is 0.06 to 0.10% (alloy 800H is 0.05 to 0.10%), the Al + Ti is 0.85 to 1.20% (alloy 800H is 0.30 to 1.20% Al + Ti).

The major differences between alloys 800, 800H and 800HT are mechanical properties. The differences stem from the restricted compositions of alloys 800H and 800HT and the high-temperature anneals used for these alloys. In general, alloy 800 has higher mechanical properties at room temperature and during short-time exposure to elevated temperatures, whereas alloys 800H and 800HT have superior creep and rupture strength during extended hightemperature exposure.