Alloy 800 (UNS N08800),Incoloy 800H (UNS N08810),800HT (UNS N08811),1.4876 Stock

Alloy 800 (UNS N08800), Alloy 800H (UNS N08810) and Alloy 800HT (UNS N08811) are nickel-iron-chromium alloys designed to resist oxidation and carburization at elevated temperatures. The nickel content 32% makes the alloys highly resistant both to chloride stress-corrosion cracking and to embrittlement from precipitation of sigma phase. The general corrosion resistance is excellent. In the solution annealed condition, Alloys 800H and 800HT have superior creep and stress rupture properties.

General Properties:
All three versions of the basic Alloy 800 have been approved as materials of construction under ASME Boiler and Pressure Valve Code Section I-Power Boilers Section III-Nuclear Vessels and Section VIII-Unfired Pressure Vessels.
Alloy 800, Alloy 800H and Alloy 800HT are identical except for the higher level of carbon (0.05 to 0.10 percent) in Alloy 800H and the addition of up to 1.00 percent aluminum + titanium in Alloy 800HT. Alloy 800 is normally used in this service at temperatures to approximately 1100F (593C). Alloy 800H and Alloy 800HT are normally used above approximately 1100F where resistance to creep and rupture is required.

Chemical Analysis:
Typical Analysis (Weight %)
C Mn P S Si Cr Ni Ti Al Ti + Al Cu
Alloy 800 0.02 1.00 0.020 0.010 0.35 21.0 32.0 0.40 0.40 - 0.30
Alloy 800H 0.08 1.00 0.020 0.010 0.35 21.0 32.0 0.40 0.40 - 0.30
Alloy 800HT 0.08 1.00 0.020 0.010 0.35 21.0 32.0 - - 1.00 0.30

Standards:
ASTM........... B 409
ASME.......... SB 409
AMS ........... 5871

Mechanical Properties:
Typical room temperature mechanical properties of Alloys 800, 800H and 800HT are shown. Alloy 800 was annealed at 1800F (928C) and Alloys 800H and 800HT were annealed at 2100F (1149C). The different anneal temperature used contributed to the difference in strength of the materials.
Short Time Elevated Temperature Properties
The above tables illustrate the short time high temperature tensile properties of Alloys 800, 800H and 800HT. The strength of Alloys 800H and 800HT is lower, because the heat treatment of Alloys 800H and 800HT at 2100F (1149C) results in a larger grain size to provide better creep and stress rupture resistance. The 1800F (982C) anneal of Alloy 800 results in a finer grain size to provide better cold formability.

Corrosion Resistance:
The chromium and nickel contents of Alloys 800, 800H and 800HT are higher than those of the familiar Alloy 304 stainless steel alloy. Under many conditions of service, the performance of Alloys 800, 800H 800HT and Alloy 304 are similar. For example, comparable behavior can be expected in most rural and industrial atmospheres and in chemical media such as nitric acid and organic acids. Neither Alloys 800, 800H and 800HT nor Alloy 304 are suggested for sulfuric acid service except at lower concentrations and temperatures. Like the austenitic stainless steels, Alloys 800, 800H and 800HT are subject to sensitization (precipitation of chromium carbides at grain boundaries) if heated for excessive time in the 1000-1400F (538-760C) temperature range. The sensitized metal may be subject to intergranular attack by certain corrosive agents including pickling acids or the boiling 65% nitric acids (Huey) test.
Alloy 800 is highly resistant although not totally immune to stress-corrosion cracking. In extensive field experience, Alloy 800 has shown excellent service performance in many types of equipment in the petroleum chemical food and pulp and paper industries. Thus Alloy 800 may offer a distinct advantage for use in moderately corrosive environments where service experience has indicated a tendency toward stress corrosion cracking of other austenitic stainless steels. However, the alloy is not immune to stress corrosion cracking as judged by the extremely severe magnesium chloride test.

Oxidation Resistance:
The alloys are particularly well suited for high temperature applications, such as furnace parts and related heating equipment for petrochemical reforming units and isocracker tubs and for handling superheated steam in nuclear and conventional power plants. With the specified high levels of chromium and nickel, the alloys offer superior resistance to oxidation and scaling and to carburization as well.
The following oxidation data for Alloy 800 was obtained by exposing samples to the indicated temperature for 100 hours in still air and cooling. In general, total weight gains greater than 10mg/cm2 indicate that additional exposure at these temperatures will lead to failure.

Welding:
Alloys 800, 800H and 800HT can be joined by tungsten arc (GTAW) gas consumable electrode (MIG) or by stick electrode welding techniques commonly used on stainless steels. A number of welding rods and wires are commercially available for joining the alloys. Since these alloys form tightly adhering scales which can be removed only by grinding inert gas shielding is desirable.

Applications:
Chemical and petrochemical processing equipment
Power generation
Thermal processing fixtures
Steel production