Incoloy 800 Round Annealed Nickel Alloy Products For Elevated Temperature Service

Forged corrosion resistant nickel alloy Incoloy 800 round bar for elevated temperature service

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.

The chromium in the alloy imparts both aqueous and heat resistance. Iron provides resistance to internal oxidation. The nickel content maintains a ductile, austenitic structure. Thus, alloy 800 is readily formed, welded, and machined.

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.

Chemical composition, %

Nickel ..................................................................................30.0-35.0

Chromium............................................................................19.0-23.0

Iron.......................................................................................39.5 min.

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

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

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

Silicon ...................................................................................1.0 max.

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

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

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

Microstructure and metallurgy

INCOLOY alloy 800 is an austenitic, solid-solution alloy. Titanium nitrides, titanium carbides, and chromium carbides normally appear in the alloy’s microstructure. The nitrides are stable at all temperatures below the melting point and are therefore unaffected by heat treatment.

Chromium carbides precipitate in the alloy at temperatures between 1000 and 2000°F (540 and 1095°C). Consequently, alloy 800 is similar to other austenitic alloys in that it can be rendered susceptible to intergranular corrosion (sensitized) in certain aggressive environments by exposure to temperatures of 1000 to 1400°F (540-760°C).

An important property of alloy 800 is its relative freedom from chloride stress-corrosion cracking. Extensive studies of stress-corrosion cracking of austenitic alloys in chloride solutions have shown that the tendency to crack decreases with increasing nickel content of alloy. For example, INCONEL alloy 600, with a nickel content of 76%, is considered to be immune to chloride-ion stress corrosion cracking. INCOLOY alloy 800 (32.5% Ni) can be made to crack in severe laboratory tests, but it has such high resistance that it is commonly used to replace materials that have failed in service from stress-corrosion cracking.

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 time temperature-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.

Working instructions

The various mill forms of INCOLOY alloy 800 are fabricated into finished articles and equipment by standard procedures. The alloy is readily formed by either hot working or cold working, and it has good weldability and machinability.

Hot and cold forming

Hot forming of INCOLOY alloy 800 is done in the temperature range of 1600 to 2200°F (870 to 1200°C). Heavy forging should be done at temperatures from 1850°F to 2200°F (1010°C to 1200°C). Forming at temperatures between 1200 and 1600°F (650-870°C) can result in cracking of the workpiece.

The rate of cooling following hot forming is not critical with respect to thermal cracking. However, the alloy is subject to carbide precipitation in the 1000-1400°F (540-760°C) temperature range and should be cooled rapidly through that range to avoid sensitization.

Cold forming of alloy 800 is done by procedures similar to those used for INCONEL alloy 600 and stainless steel. The work-hardening rate for alloy 800 is higher than the rate for mild steel but lower than that for Type 304 stainless steel. The work-hardening rate for INCOLOY alloy 800 is essentially the same as the rate for INCONEL alloy 600.

Machining

Alloy 800 is readily machined by standard methods.

Turning operations can be performed with high metal removal rates, good tool life, and good surface finish using coated carbide tools. Good results have also been obtained with high-speed-steel tools, which are better for interrupted cutting. Coated carbide tools have shown good life at cutting speeds of 110-190 sfpm (33.5-57.9 m/min) and a feed of 0.008-0.035 ipr (0.20-0.89 mm/rev.). High speed steel tools have been shown to have good life at cutting speeds of 35- 95 sfpm (10.7-29.0 m/min) and a feed of 0.008-0.035 ipr (0.20-0.89 mm/rev.).

Available products and specifications

INCOLOY alloy 800 is designated as UNS N08800 and Werkstoff Number 1.4876. It is listed in NACE MR0175 for oil and gas service. Alloy 800 is available as pipe, tube, round bar, flat

Rod, Bar,

Forgings

ASTM B 408 & ASME SB 408 (Rod & Bar), ASTM B 564 & ASME SB 564 (Forgings), ASME Code Case 1325 (All Product Forms), ASME Code Case 1949 (Forgings), SAE/AMS 5766 (Rod & Bar), ISO 9723 (Rod & Bar), ISO 9724 (Wire), ISO 9725 (Forgings), BS 3076NA15 (Rod & Bar), BS 3075NA15 (Wire), VdTÜV 412 (All Products)

Pipe and Tubes

ASTM B 163 & ASME SB 163 (Seamless Condenser & Heat Exchanger Tubes), ASTM B 407/B 829 & ASME SB 407/SB 829 (Seamless Pipe & Tubes), ASTM B 514/B 775 & ASME SB 514/SB 775 (Welded Pipe), ASTM B 515/B 751 & ASME SB 515/SB 751(Welded Tubes), ASME Code Case 1325 (All Product Forms), ASME N-20 (Cold Worked Seamless Condenser and Heat Exchanger Tubes for Nuclear Service), BS 3074NA15 (Seamless Pipe & Tubes), VdTÜV 412 (All Products), ISO 6207 (Seamless Tubing)

Product size range
Diameter: 100mm - 600mm
Length: on request
 
Production Process