UNS N08890 Forgings Forged bars, seamless rolled rings, flanges, discs, sleeves and shafts in Alloy 890

Key facts about UNS N08890

What a buyer or design engineer normally checks before releasing a UNS N08890 forging order.

What is UNS N08890?

UNS N08890 is a solid-solution nickel-iron-chromium alloy for continuous service at high temperature. The nominal 42.5 % nickel holds an austenitic structure across the full working range. The 25 % chromium builds a chromium-oxide scale that resists oxidation in air and in combustion gases, and rebuilds itself when the scale is damaged. The alloy is not precipitation hardened, so it is supplied and used solution annealed rather than aged.

The N08xxx block of the Unified Numbering System covers the nickel-iron-chromium grades, among them Alloy 800 (N08800), Alloy 800H (N08810), Alloy 800HT (N08811) and HR-120 (N08120). The same ASTM specifications handle all of them. Those specifications split the group by service class: grades used below 1100 °F (593 °C), and grades used above it where creep and stress rupture set the design limit. UNS N08890 sits in the second class, and is annealed to a controlled grain size for that range.

Why UNS N08890 is forged rather than cast or fabricated

Open-die forging breaks down the as-cast ingot structure, closes centreline porosity and lays the grain flow along the shape of the part. For components that run above 593 °C, such as retorts, radiant tube hangers, heat-treatment fixtures, pigtails, header connections and turbine casings, that matters more than the cost of forging. A forged and annealed UNS N08890 ring responds to creep loading more evenly than a welded fabrication with a heat-affected zone running through the highest-stress section.

On UNS N08890 the anneal is not a finishing step, it is the property-setting step. We forge to shape, then solution anneal at 1149 °C minimum and check grain size on every heat, because grain size is what carries the creep life in this alloy.

Chemical composition of UNS N08890

UNS N08890 contains nominally 42.5 % nickel, 25 % chromium and the balance iron, with 1.5 % molybdenum, 1.8 % silicon, 0.4 % niobium, 0.2 % tantalum, 0.1 % aluminium and 0.1 % carbon. Manganese and titanium are capped at 1.0 %, copper at 0.75 %, phosphorus at 0.03 % and sulphur at 0.015 %. All figures are weight percent. Order-specific limits come from the applicable ASTM specification and from any purchaser supplement, and are reported per heat on the mill test certificate.

What each addition does

• Nickel, 42.5 %. Holds the austenitic structure stable from room temperature to the top of the service range, and gives resistance to chloride stress-corrosion cracking.
• Chromium, 25 %. Forms the protective Cr₂O₃ scale behind the alloy's oxidation and sulphidation resistance.
• Silicon, 1.8 %. Reinforces that scale and improves resistance to carburising atmospheres. The cost is some hot workability.
• Molybdenum, 1.5 %. Solid-solution strengthening, which is what carries load once the alloy is past the temperature where precipitation hardening is useful.
• Niobium and tantalum, 0.4 % and 0.2 %. Tie up carbon as MC carbides and limit chromium-carbide precipitation at grain boundaries.
• Carbon, 0.1 %. Deliberately kept at the top of the family range. Carbides pinning the grain boundaries are part of how this class of alloy resists creep rupture.

Physical and mechanical properties of UNS N08890

Physical properties

The density of UNS N08890 is 7.94 g/cm³, equal to 0.287 lb/in³. Its melting range is 1309 to 1383 °C, or 2388 to 2521 °F. The structure is austenitic and face-centred cubic.

Tensile properties from 22 °C to 1100 °C

At 22 °C, solution-annealed UNS N08890 hot-rolled plate gives a 0.2 % yield strength of 272 MPa (39.4 ksi), a tensile strength of 652 MPa (94.6 ksi), 46.6 % elongation and 62.7 % reduction of area. Cold-drawn tubing tested at the same temperature reaches a higher yield of 334 MPa at the same 652 MPa tensile strength. Tensile strength then drops to 132 MPa at 870 °C, 92 MPa at 980 °C and 62 MPa at 1100 °C. Forged product is normally tested to ASTM B408 at room temperature; the elevated-temperature figures are for design rather than acceptance.

How strength and ductility trade off with temperature

Between 22 °C and 1100 °C the tensile strength of UNS N08890 falls to about 9.5 % of its room-temperature value, while reduction of area climbs from 62.7 % to 91.8 %. Solid-solution heat-resistant alloys behave this way. They give up strength as they heat and gain formability, which is why parts in this alloy are shaped hot, and why design above 593 °C runs on creep and rupture allowables rather than short-term tensile figures.

Specifications and heat treatment for UNS N08890

UNS N08890 is a listed grade in three ASTM product specifications, each covering a different wrought form: ASTM B407 for seamless pipe and tube, ASTM B408 for rod and bar, and ASTM B409 for plate, sheet and strip. ASTM B906 gives the general requirements for flat-rolled product. ASME adopts the same documents under SB numbers for pressure-equipment work.

Solution annealing requirement

ASTM B409 specifies a minimum final heat-treatment temperature of 2100 °F (1149 °C) for UNS N08890. That is the same minimum as UNS N08811, above the 2050 °F (1121 °C) minimum for UNS N08810 and below the 2150 °F (1177 °C) minimum for UNS N08120. Annealing at or above that temperature dissolves the carbide network and produces the controlled, relatively coarse grain size that carries creep and rupture strength in service above 1100 °F (593 °C).

Forging practice

UNS N08890 is hot worked in the same window used across the Fe-Ni-Cr heat-resistant family. We heat stock to approximately 1180 °C, forge with generous reductions to break down the cast structure, and finish above about 950 °C to keep the alloy out of the range where it is prone to cracking. Every forging is then solution annealed at 1149 °C minimum and cooled rapidly.

UNS N08890 forged product forms we manufacture

Jiangyin Jiangnan Metal Co., Ltd. produces UNS N08890 by open-die forging and seamless ring rolling. Parts are made to customer drawing or to a standard dimension list, and can be delivered as-forged, rough-machined or finish-machined. The size ranges below are the normal working envelope. Larger pieces are quoted case by case.

Surface condition options are as-forged and descaled, shot blasted, pickled, rough turned, or machined to a drawing tolerance. Marking is by hard stamp or vibro-etch with heat number, grade and purchase-order reference.

Where UNS N08890 forgings are used

UNS N08890 is chosen when a component has to hold shape and resist oxidation for long periods above 593 °C, and where cheaper heat-resistant stainless grades such as 310S would scale, distort or lose creep life too quickly.

• Industrial furnaces and heat treatment. Retorts, muffles, radiant tube supports, roller hearths, fixtures, baskets, trays and hangers exposed to repeated thermal cycling.
• Petrochemical and refining. Reformer pigtails, header connections, transfer-line components and hot-gas piping fittings.
• Power generation. Combustor and duct hardware, expansion joints and support rings in the hot gas path.
• Chemical process plant. Vessels and internals handling hot oxidising or sulphur-bearing atmospheres, where chromium scale stability sets the service life.
• Waste incineration and calcining. Grates, skids, seals and rotary-kiln hardware in combustion gases.

Below 593 °C, Alloy 800 (UNS N08800) is usually the cheaper correct answer. Above that line the choice sits between UNS N08890, Alloy 800H, Alloy 800HT and HR-120, and is normally settled on creep-rupture allowables and on how corrosive the specific atmosphere is, not on room-temperature strength.

UNS N08890 compared with related nickel-iron-chromium alloys

UNS N08890 carries nominally 42.5 % nickel and 25 % chromium, more of both than Alloy 800H at roughly 30 to 35 % Ni and 19 to 23 % Cr. Its 1149 °C minimum final anneal matches Alloy 800HT, sits above the 1121 °C required for Alloy 800H, and below the 1177 °C required for HR-120. All four grades are covered by ASTM B407, B408 and B409, and all four are used above 1100 °F (593 °C).

Values are nominal and indicative. Confirm them against the current edition of the governing specification. Related grade pages: Incoloy 800H (UNS N08810) forgings, Incoloy 800HT (UNS N08811) forgings, Incoloy 800 (UNS N08800) forgings.

Testing, inspection and certification

Every UNS N08890 forging leaving our works is traceable to a single heat number and ships with a mill test certificate covering the tests listed below. The scope is agreed at order stage and printed on the order acknowledgement.

Standard scope

• Chemical analysis. Full product analysis by optical emission spectrometry, reported element by element against the specification limits.
• Tensile test. 0.2 % yield, tensile strength, elongation and reduction of area at room temperature.
• Hardness. Brinell or Rockwell as required by the specification or purchase order.
• Grain size. Determined to ASTM E112. For this alloy it is the key evidence that the solution anneal was effective.
• Heat treatment record. Furnace chart showing soak temperature, hold time and cooling method.
• Dimensional report. Measured against the drawing or the standard dimension table.

Available on request

• Ultrasonic testing to ASTM A388 or EN 10228-3, with the acceptance class stated on the order.
• Dye penetrant to ASTM E165, and magnetic particle examination where applicable.
• Impact testing at room or sub-zero temperature.
• Intergranular corrosion testing to ASTM G28 method A or B.
• Elevated-temperature tensile and stress-rupture testing to customer-defined conditions.
• Positive material identification on every piece.

Certification

Standard supply is with an EN 10204 3.1 certificate issued by the works inspection department, independent of production. EN 10204 3.2 certification witnessed and countersigned by a third party, such as SGS, Bureau Veritas, TÜV or Lloyd's Register, is available on request, as are customer-specific documentation packages and material traceability records.

How to request a quotation for UNS N08890 forgings

An accurate quotation for a UNS N08890 forging needs four things. Sending all four in the first email saves a round of questions.

1. Drawing or dimensions. A 2D drawing, a 3D model, or the finished OD, ID, length or thickness, plus the machining allowance you expect on each surface.
2. Specification and delivery condition. Confirm UNS N08890, the governing standard such as ASTM B408, the delivery condition, and any customer or end-user specification that applies.
3. Testing and certification. The mechanical tests, non-destructive testing and acceptance class you need, the certification level under EN 10204, and whether third-party inspection is required.
4. Quantity and destination. Piece quantity, required delivery date and destination port, so the quotation carries the correct lead time and Incoterms.

Send it to sales@steelforgepieces.com, or call +86 189 2135 9659. If the drawing is not ready, a sketch with the three main dimensions is enough for a budget price.

Cite this page

References and further reading

1. ASTM B407, Standard Specification for Nickel-Iron-Chromium Alloy Seamless Pipe and Tube. ASTM International. astm.org
2. ASTM B408, Standard Specification for Nickel-Iron-Chromium Alloy Rod and Bar. ASTM International.
3. ASTM B409, Standard Specification for Nickel-Iron-Chromium Alloy Plate, Sheet, and Strip. ASTM International. Source of the 2100 °F (1149 °C) minimum final heat-treatment temperature for UNS N08890.
4. ASTM B906, Standard Specification for General Requirements for Flat-Rolled Nickel and Nickel Alloys Plate, Sheet, and Strip. ASTM International.
5. ASTM E112, Standard Test Methods for Determining Average Grain Size. ASTM International.
6. EN 10204, Metallic products, types of inspection documents. CEN.
7. Unified Numbering System for Metals and Alloys. Wikipedia
8. Forging, process overview. Wikipedia