Incoloy alloy 800 UNS N08800/W.Nr. 1.4876 ASTM B408 bar sheet tube

Overview

INCOLOY alloy 800 (UNS N08800/W. Nr. 1.4876) is a widely used material for construction of equipment requiring corrosion resistance, heat resistance, strength, and stability for service up to 1500°F (816°C). Alloy 800 offers general corrosion resistance to many aqueous media and, by virtue of its content of nickel, resists stress corrosion cracking. At elevated temperatures it offers resistance to oxidation, carburization, and sulfidation along with rupture and creep strength. For applications requiring greater resistance to stress rupture and creep, especially at temperatures above 1500°F (816°C), INCOLOY alloys 800H and 800HT are used.

INCOLOY alloy 800 is used in a variety of applications involving exposure to corrosive environments and high temperatures. It is used for heat-treating equipment such as baskets, trays, and fixtures. In chemical and petrochemical processing, the alloy is used for heat exchangers and other piping systems in nitric acid media especially where resistance to chloride stress-corrosion cracking is required.

In nuclear power plants, it is used for steam-generator tubing. The alloy is often used in domestic appliances for sheathing of electric heating elements. In the production of paper pulp, digester-liquor heaters are often made of alloy 800. In petroleum processing, the alloy is used for heat exchangers that air cool the process stream.

Limiting Chemical Composition, %

Nickel ..................................................................................................................................................................................30.00-35.00

Chromium............................................................................................................................................................................19.00-23.00

Iron...........................................................................................................................................................................................39.50min.

Carbon.....................................................................................................................................................................................0.10 max.

Manganese.............................................................................................................................................................................1.50 max.

Sulfur.....................................................................................................................................................................................0.015 max.

Silicon......................................................................................................................................................................................1.00 max.

Copper.....................................................................................................................................................................................0.75 max.

Aluminum................................................................................................................................................................................0.15-0.60

Titanium...................................................................................................................................................................................0.15-0.60

Physical Constants

Mechanical properties

INCOLOY alloy 800 has high mechanical strength over a broad temperature range. In general, alloy 800 is used for its strength characteristics at service temperatures up to about 1500°F (816°C). At those temperatures, equipment design is usually based on tensile properties. For applications that require high creep or rupture strength, INCOLOY alloys 800H and 800HT are used.

Corrosion Resistance

INCOLOY alloy 800, like many austenitic stainless steels, can be sensitized, or made susceptible to intergranular attack in some aggressive media, by exposure to the temperature range of 1000 to 1400°F (540–760°C). The Huey test determines susceptibility to sensitization. The test involves exposure of a specimen to boiling 65% nitric acid for five consecutive 48-hour periods. An average corrosion rate for the five periods of substantially over about 24 mils penetration per year (0.61 mm/yr) indicates that the specimen is sensitized to some degree. The timetemperature-sensitization diagrams in Figures 12 and 13 show Huey test rates for alloy 800 annealed at two different temperatures and exposed to a range of sensitizing treatments.

When INCOLOY alloy 800 is exposed to heat from welding or other operations, care should be taken to avoid sensitization if the material is to be pickled or subjected to other aggressive environments. Sensitization is not a problem in most high-temperature applications.

Heating and Picking

All material to be heated must be clean. Oil, paint, grease, shop soil and other foreign substances must be removed prior to the heating operation.

Heating must be performed in a low-sulfur atmosphere. Open heating must be done with low-sulfur fuel, and the furnace atmosphere must be maintained in a reducing condition to prevent excessive oxidation

Because of the readiness with which chromium is oxidized into a refractory oxide by air, carbon dioxide or water vapor, alloy 800 cannot be bright annealed in the usual industrial annealing furnace. Under closely controlled conditions, the alloy can be bright annealed in dry, pure hydrogen (dew point of -73°F (-58°C) or lower, less than 0.004% by volume water, and less than 0.007% by volume air).

INCOLOY alloy 800 is normally annealed in box or muffle furnaces using prepared reducing atmospheres. A satisfactory atmosphere is formed by the products of combustion from low-sulfur natural gas burned with a deficiency of air. It produces a thin, adherent, green-black film of oxide on the material. Oxidizing atmospheres produce a heavy black scale that is difficult to remove.

Removal of such scale often requires considerable grinding.

Specific annealing procedures depend on the amount of cold work and cross section of the material. The mechanical properties of heavily cold-worked material are only slightly affected by temperatures below 1000°F (540°C). Stress relief begins at about 1000°F (540°C) and is virtually complete after 1½ hours at 1600°F (870°C). Softening by annealing begins at about 1400°F (760°C) and is reasonably complete after 10 to 15 minutes at 1800°F (980°C).

Appreciable grain growth may occur at temperatures over 1800°F (980°C). A satisfactory anneal, however, can usually be obtained by 2 to 5 minutes heating at 1900°F (1040°C).

Available Forms

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● Bar & Rod

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