Incoloy 800H/HT (UNSN08810/N08811)
Introduction
INCOLOY 800H and 800HT have significantly higher creep and rupture strength than INCOLOY 800. The three alloys have nearly identical chemical composition limits. The base elements in all three alloys are the same. However, chemical composition limits vary with carbon, aluminum and titanium. The carbon content of INCOLOY 800 (UNS N08800) is 0.10% max with no limit on the lower end. The carbon content for INCOLOY 800H (UNS N08810) is 0.05 to 0.10%, which is the upper end of the 0.10% maximum specified for INCOLOY 800. The chemical limits for INCOLOY alloy 800HT (UNS N08811) are even more restrictive yet still within the limits specified for INCOLOY alloy 800H. The carbon content for INCOLOY alloy 800HT is further restricted  to 0.06 - 0.10%. Additionally, the Al plus Ti content of INCOLOY alloy 800HT  is restricted to 0.85 - 1.20%. Note that the chemical compositions for INCOLOY alloy 800HT will always be within the limits of INCOLOY alloy 800H. Note also that the limits for INCOLOY alloy 800H may or may not be within the limits of INCOLOY 800HT
Character
High temperature strength
High creep rupture strength
Resistant to oxidation and carburization in high temperature environments
Good corrosion resistance in many acidic environments
Good resistance to many sulfur-containing atmospheres
Application
Ethylene furnace quench boilers
Hydrocarbon cracking
Valves, fittings and other components  exposed to corrosive attack from 1100-1800° F
Industrial furnaces
Heat-treating equipment
Chemical and petrochemical processing
Super-heater and re-heaters in power plants
Pressure vessels
Heat exchangers

Limiting Chemical Compositions, %, for INCOLOY alloys 800, 800H and 800HT