Chemical composition
Composition limits for UNS N09902 in weight percent. Every heat we forge is supplied with its own ladle analysis on the mill certificate. Where a product analysis is required, state it on the enquiry.
| Element | Symbol | Minimum | Maximum |
|---|---|---|---|
| Nickel + cobalt | Ni + Co | 41.00 | 43.50 |
| Chromium | Cr | 4.90 | 5.75 |
| Titanium | Ti | 2.20 | 2.75 |
| Aluminium | Al | 0.30 | 0.80 |
| Manganese | Mn | – | 0.80 |
| Silicon | Si | – | 1.00 |
| Carbon | C | – | 0.06 |
| Phosphorus | P | – | 0.040 |
| Sulphur | S | – | 0.040 |
| Iron | Fe | Balance | |
Specifications also control the combined value Cr + (Ti − 4C), normally to 7.10–8.10 %, because that relationship governs how far the thermoelastic coefficient can be shifted during ageing. Iron is the balance. Alloy 902 is an iron-base alloy carrying about 42 % nickel, not a nickel-base superalloy.
Physical and mechanical properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.05 g/cm³ | 0.291 lb/in³ |
| Electrical resistivity (20 °C) | 51.0 µΩ·cm | 307 Ω·circ mil/ft |
| Tensile modulus of elasticity | 165–200 GPa | 24–29 × 10³ ksi |
| Torsional (shear) modulus | 62–69 GPa | 9–10 × 10³ ksi |
| Constant-modulus range | −45 to +65 °C | −50 to +150 °F |
| Magnetic behaviour | Ferromagnetic at ambient temperature, low magnetostriction | |
The modulus figures span a range because the modulus is not fixed for this alloy. It is set by processing, which is the whole reason the grade exists.
| Condition | Tensile strength | Service temperature |
|---|---|---|
| Annealed | 450–650 N/mm² (65–94 ksi) | −45 to +65 °C (−50 to +150 °F) |
| Solution treated + aged | Substantially higher. The exact level depends on prior cold work and ageing cycle | −45 to +65 °C (−50 to +150 °F) |
Before you design to a number. In Alloy 902 the strength and the thermoelastic coefficient are set together by the same cold work and ageing cycle, so you cannot specify one and ignore the other. Tell us the thermoelastic coefficient or the modulus stability you need. The acceptance values are agreed first and then reported on the EN 10204 3.1 certificate for your heat.
Forged forms and sizes
We do not hold this grade as a stock product. Every piece is forged to the drawing, so the ranges below describe the envelope we work within rather than a stock list.
| Forged form | Outside diameter | Section / thickness | Piece weight |
|---|---|---|---|
| Seamless rolled rings | 100–1200 mm | 15–200 mm wall | 1–600 kg |
| Round bars | Ø 16–400 mm | up to 3000 mm long | 1–500 kg |
| Discs and blanks | 80–800 mm | 20–300 mm | 1–500 kg |
| Forged flanges | to 900 mm | per drawing | 1–300 kg |
| Sleeves, bushings, hollow bars | 80–700 mm | 15–150 mm wall | 1–400 kg |
| Shafts and stepped shafts | Ø 30–350 mm | up to 3000 mm long | 1–500 kg |
Delivery condition is your choice: as-forged, rough-machined with grinding allowance, or finish-machined to drawing. Rough machining before heat treatment is usually worth it on this grade, because it removes the forged skin before the ageing cycle fixes the properties.
Melting, forging and heat treatment
Melting route
Alloy 902 is melted by EAF + VOD followed by ESR remelting. The remelt step matters here. Titanium and aluminium are the elements that make the alloy age-hardenable, and they are also the elements most easily lost or segregated. ESR gives the clean, uniform ingot that a precision elastic component needs. Where a programme calls for VIM + VAR material, we will source it and forge to your specification.
Forging
Billets are heated and forged on open-die hammers and presses with controlled reduction ratios, to break down the cast structure and give a worked, directional grain flow. The alloy work-hardens at a rate similar to austenitic stainless steel, so finish temperature and reheat schedule are controlled rather than left to the operator.
Heat treatment
| Step | Temperature | Time | Cooling |
|---|---|---|---|
| Solution anneal | 980–1040 °C (1800–1900 °F) | Section-dependent | Water quench |
| Cold work (optional) | Ambient | Reduction set by the required coefficient | – |
| Precipitation age | 525–675 °C (980–1250 °F) | 3–8 h | Air cool |
Ageing temperature is the main control. Move it and the thermoelastic coefficient moves with it, so we set the cycle against your requirement rather than taking it from a handbook. Confirm the target at enquiry stage and we will propose the cycle in writing before we cut metal.
Testing, NDT and certification
- Chemical analysis. Ladle analysis on every heat, product analysis on request.
- Mechanical testing. Tensile, hardness and, where specified, impact testing on test pieces representing the forging.
- Ultrasonic testing. To EN 10228-3, SEP 1921, ASTM A388 or your own acceptance class.
- Surface NDT. Dye penetrant inspection to ASTM E165 for the crack-sensitive faces.
- Dimensional report. Against the drawing, with machining allowance recorded.
- Certification. EN 10204 3.1 as standard. EN 10204 3.2 with third-party witness (SGS, BV, TÜV, Lloyd's or your own inspector) on request.
- Traceability. Heat number hard-stamped or vibro-etched, with marking position to your instruction.
Where Alloy 902 forgings are used
Alloy 902 costs more than stainless steel and is harder to machine, so it is worth using in one situation: an elastic component whose stiffness has to stay constant while the temperature moves. For anything that is not an elastic, precision part, a cheaper alloy will do the job.
Pressure and force measurement
Bourdon tubes, diaphragms, aneroid capsules, load cells and pressure transducers, where modulus stability sets the accuracy of the instrument.
Precision springs
Hairsprings for timing devices, helical and leaf springs in weighing machines, where deflection has to be independent of temperature.
Mechanical resonators
Tuning forks, vibrating reeds and electro-mechanical filters, where resonant frequency must not shift with ambient temperature.
Geophysical and downhole instruments
Sensing elements in survey and logging tools that see wide swings in temperature between surface and depth.
Aerospace and cryogenic sensing
Sensor diaphragms and elastic members, including service at cryogenic temperatures.
Instrument housings and fittings
Forged bodies, seat rings, sleeves and flanges machined from the same heat as the elastic element, for matched thermal behaviour.
What to send with your enquiry
Send these six items and we can quote a firm price and lead time without coming back for more information:
- Drawing or dimensions. PDF, STEP or DWG. For rings, OD × ID × height.
- Quantity. Prototype piece count and the series quantity you expect afterwards.
- Delivery condition. As-forged, rough-machined, or finish-machined.
- Heat-treatment condition. Including the thermoelastic coefficient or modulus stability you are designing to.
- Specification. AMS 5221, your own material standard, or the customer spec you must satisfy.
- Testing and certificate. UT class, NDT scope, EN 10204 3.1 or 3.2.
Send it to sales@steelforgepieces.com or call +86 189 2135 9659. Drawings are treated as confidential and are not shared outside the quotation team.
Frequently asked questions
What is NI-SPAN-C Alloy 902?
NI-SPAN-C Alloy 902, designated UNS N09902, is a precipitation-hardenable nickel-iron-chromium alloy containing 41.0 to 43.5 % nickel plus cobalt, 4.90 to 5.75 % chromium and 2.20 to 2.75 % titanium, with iron as the balance. Additions of titanium and aluminium make it age-hardenable, and the titanium content gives it a controllable thermoelastic coefficient, which is the property the alloy is chosen for.
Who supplies NI-SPAN-C Alloy 902 forgings in China?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, forges NI-SPAN-C Alloy 902 into rings, bars, discs, sleeves, shafts and flanges. Enquiries go to sales@steelforgepieces.com or +86 189 2135 9659.
What are the equivalent designations for UNS N09902?
The alloy is covered by AMS 5221, AMS 5223 and AMS 5225 depending on product form, and also carries the designation AWS 080. The Chinese equivalent grade is 3J53, also written Ni42CrTiAl. NI-SPAN-C is a trademark of the Special Metals Corporation group of companies. We supply the alloy to the UNS N09902 composition and to the applicable AMS specification.
How is Alloy 902 different from Invar?
They control different things. Invar (Fe-36Ni) is chosen for its very low coefficient of thermal expansion, so it changes size very little with temperature. Alloy 902 is chosen for its low thermoelastic coefficient, so it changes stiffness very little with temperature. Use Invar when a part must not grow or shrink. Use Alloy 902 when a spring or diaphragm must not read differently as it warms up.
Is NI-SPAN-C Alloy 902 magnetic?
Yes. It is an iron-nickel base alloy and is ferromagnetic at ambient temperature, so it is not a substitute where a non-magnetic material is required. It does have low magnetostriction, which is why it suits resonators and sensing elements. If your application is magnetically sensitive, say so on the enquiry so the heat-treatment condition can be discussed.
How corrosion resistant is Alloy 902?
Moderately. With about 5 % chromium it sits well below stainless steel in corrosion resistance and it will rust in moist air. Exposed outdoors it develops an adherent red-brown oxide film, and reported corrosion rates in industrial and marine atmospheres are under about 0.001 inch per year. For service in a corrosive medium, plate it, coat it, or choose a different alloy.
Can Alloy 902 be machined and welded?
It machines much like the harder stainless grades and work-hardens quickly, so it needs sharp tooling, rigid setups, positive feed and no dwelling in the cut. It can be joined by TIG, electron-beam and resistance welding, and by brazing and soldering. Brazing is normally done on heat-treated material to avoid cracking. Any welding on a precision elastic component should be agreed before the heat-treatment cycle is fixed.
What is the minimum order quantity and lead time?
We forge single pieces for prototypes as well as series quantities. Lead time depends on whether suitable material is on hand and on the heat-treatment and testing scope. Typical open-die lead times for this grade run 4 to 8 weeks from drawing approval. Ask for a confirmed date with your quotation.
About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin City, Jiangsu Province, China, supplying forged rings, bars, discs, shafts, sleeves and flanges in carbon steel, alloy steel, tool steel, stainless steel and nickel alloys. Work is quoted from drawings, forged in-house, heat treated and tested to the customer's acceptance standard, and released with EN 10204 3.1 or 3.2 certification.
Jiangyin Jiangnan Metal Co., Ltd.No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone: +86 189 2135 9659
Email: sales@steelforgepieces.com
Web: www.steelforgepieces.com