What this alloy is, and what it is not
Alloy 330 lives on this page under the stainless steel heading because buyers search for it as "330 stainless", but every primary datasheet classifies it as a nickel-iron-chromium alloy rather than a stainless steel. Sandmeyer Steel calls it an austenitic nickel-iron-chromium alloy developed to provide excellent resistance to carburizing and oxidizing atmospheres at elevated temperatures. High Temp Metals calls it an austenitic nickel-chromium-iron-silicon alloy. If you are comparing it against 310S or 309, you are in the right place; if you are comparing it against 304 or 316 for water service, you are not, and our stainless steel and nickel alloy sections will serve you better.
The alloy's value is almost entirely about temperature. Sandmeyer notes it performs well under cyclic heating and cooling and in alternate carburizing and oxidizing atmospheres, and that any scale which forms is tightly adherent, particularly under cyclic conditions. Sandmeyer is also explicit that it is not intended for strongly reducing acid environments. Rolled Alloys, whose RA330 is the long-standing proprietary version of this chemistry, calls it the workhorse of the heat resistant alloys.
Chemical composition
| Element | Specified minimum | Specified maximum | Typical |
|---|---|---|---|
| Nickel | 34.0 | 37.0 | 36 |
| Chromium | 17.0 | 20.0 | 19 |
| Silicon | 0.75 | 1.50 | 1.13 |
| Manganese | — | 2.00 | 2 |
| Carbon | — | 0.08 | 0.080 |
| Phosphorus | — | 0.030 | 0.040 |
| Sulfur | — | 0.030 | 0.030 |
| Iron | Balance | 42 | |
Two points matter commercially. First, silicon is a deliberate alloying addition with a floor of 0.75 percent, not a residual, because Sandmeyer attributes the enhanced oxidation resistance directly to it. A heat that is low on silicon is not this alloy however well the nickel and chromium read. Second, the AZoM typical phosphorus figure of 0.040 sits above the 0.030 maximum in the specified analysis, which is a reminder to buy against a standard and read the certificate rather than relying on typical tables.
Mechanical properties
Three published data sets circulate for this alloy and they answer different questions. The ASTM minimum is what a certificate has to beat. The mill annealed typical range is what material actually delivers. The single-point annealed figures are what reference tables quote.
| Property | ASTM minimum | Typical, mill annealed | Annealed reference |
|---|---|---|---|
| Tensile strength | 483 MPa, 70.0 ksi | 552–586 MPa, 80–85 ksi | 550 MPa |
| Yield strength, 0.2% offset | 207 MPa, 30.0 ksi | 207–296 MPa, 30–43 ksi | 260 MPa |
| Elongation | 30% in 4D | 40–45% in 2 in | 40% in 50 mm |
| Hardness | — | 70–85 HRB | — |
| Modulus of elasticity | — | 196 GPa, 28.5 × 106 psi | 197 GPa |
| Poisson's ratio | — | — | 0.27–0.30 |
Room temperature strength is modest and largely beside the point. This alloy is bought for what it does after thousands of hours at temperature, where creep strength and the stability of the oxide scale decide service life. Where your design is creep governed, send us the duty cycle with the drawing and state which creep data set your calculation used, so the forging route and final anneal can be matched to it.
Physical properties
| Density | 8.08 g/cm3, 0.292 lb/in3 (Sandmeyer). AZoM gives 8 g/cm3; Rolled Alloys gives 0.287 lb/in3 for RA330 |
|---|---|
| Melting range | 1343–1393 °C, 2450–2540 °F (Rolled Alloys, RA330) |
| Specific heat | 460 J/kg·°C at 0–100 °C, 0.11 BTU/lb·°F at 32–212 °F |
| Coefficient of thermal expansion | 14.4 µm/m·°C, 8 µin/in·°F (AZoM) |
| Magnetic permeability | 1.02 at 20 °C. Rolled Alloys gives µ = 1.009 annealed at H = 2810 oersted for RA330 |
| Electrical resistivity | 1.017 µΩ·m at 24 °C, rising to 1.245 µΩ·m at 982 °C |
Thermal conductivity against temperature
| °F | 75 | 400 | 800 | 1200 | 1600 | 1800 |
|---|---|---|---|---|---|---|
| °C | 24 | 204 | 427 | 649 | 871 | 982 |
| W/m·°C | 12.4 | 15.6 | 19.3 | 23.4 | 28.6 | 31.2 |
Conductivity rises steeply with temperature, roughly two and a half times between room temperature and 982 °C, while the expansion coefficient stays comparatively low. High Temp Metals highlights that combination of low thermal expansion with good oxidation resistance, and it is a large part of why the alloy survives thermal cycling that distorts or cracks cheaper furnace materials.
Temperature capability: read the limits carefully
Quoted maximum temperatures for this alloy range from 1095 to 1200 °C depending on who is writing and what they are measuring, and that spread is wide enough to matter in a design. The honest position is to give you all of it rather than pick the most flattering number.
| Source | Stated limit | Criterion |
|---|---|---|
| Sandmeyer Steel | about 1095 °C, 2000 °F | Resists scale formation up to this temperature |
| Sandmeyer Steel, FAQ | 1149 °C, 2100 °F | Oxidation resistance |
| Rolled Alloys, RA330 | 1148 °C, 2100 °F | Good strength, carburization and oxidation resistance |
| High Temp Metals | 1204 °C, 2200 °F | Resistance to oxidation and carburization, with high strength |
| AZoM | 1200 °C, 2200 °F | High strength and resistance to carburization and oxidation |
In practice, design to the lower figures where tight scaling control or mechanical load is involved, and treat the 2200 °F figures as a short-excursion or lightly loaded ceiling. If your furnace runs continuously above 1100 °C under load, tell us and we will discuss whether a higher-nickel grade is the better buy rather than sell you a forging that will not last.
Carburization, nitridation and green rot
Sandmeyer attributes the excellent carburization resistance to the roughly 35 percent nickel content together with the silicon addition, and states that in alternating carburizing and oxidizing atmospheres the alloy shows excellent resistance to the green rot phenomenon, the selective internal chromium carbide attack that destroys lesser alloys cycling between those two atmospheres. Nitridation resistance is good where oxygen content is low, which is why the alloy is used extensively in components handling cracked ammonia. The high nickel also suppresses sigma phase embrittlement, which is what allows these parts to be cycled for years rather than going brittle in service.
How we forge and heat treat it
The published guidance from Sandmeyer Steel and High Temp Metals is consistent, and we work to it:
- Heat uniformly to 1120–1180 °C (2050–2150 °F) as the starting temperature. Uniform is the operative word on heavy sections; a cold core in a thick billet is where cracks start.
- Finish above 950 °C (1750 °F). AZoM narrows the hot working window further, to 1149–1177 °C.
- Stay out of 650–870 °C (1200–1600 °F) for any forming or bending. Both sources identify this as the low ductility range where austenitic alloys suffer intergranular tearing. This is the single most important rule on the page.
- Cool by water quench or as fast as possible after hot working.
- Anneal after hot working to secure maximum corrosion resistance and optimum grain structure. Where a full anneal is specified: 1020–1120 °C (1870–2050 °F), water quenched for optimum creep resistance, or rapid air cooling to below 425 °C (800 °F). AZoM quotes a wider annealing band of 1121–1204 °C.
Welding and machining
Sandmeyer states the alloy can be welded by GTAW, SMAW and plasma arc, with GTAW preferred for optimum corrosion resistance, and sets out the practical conditions: material in the annealed condition, clean and free of scale and grease, a zone about one inch either side of the joint ground to bright metal, interpass temperature not exceeding 150 °C (300 °F), and neither pre-weld nor post-weld heat treatment required. It welds readily to a range of dissimilar metals, which is useful on fabricated furnace assemblies. For machining, High Temp Metals recommends rigid mounts, sulfurized lubricants, positive feeds and slow speeds. We can supply forgings rough-machined with weld prep already cut if that saves you a handling operation.
Standards and documentation
| Specification | Scope |
|---|---|
| ASTM B511 | Nickel-iron-chromium-silicon alloy bars and shapes. The specification normally applied to forged bar and forged shapes, and therefore the one most relevant to this page |
| ASTM B536, ASME SB-536 | Plate, sheet and strip. Named together with AMS 5592 as the standards on the Sandmeyer specification sheet |
| ASTM B535 | Seamless pipe and tube |
| ASTM B546 | Welded tube |
| ASTM B512 | Nickel-iron-chromium-silicon alloy castings |
| ASTM B366 | Factory-made wrought fittings |
| ASTM B739 | Bar rounds, listed by Carpenter Technology for grade 330 |
| AMS 5592, AMS 5716 | Aerospace material specifications |
Standard supply is a chemical analysis and mechanical test report to EN 10204 3.1. Because this grade usually goes into pressure or furnace assemblies that someone has to sign off, we can add ultrasonic testing, PMI, dye penetrant, grain size determination, hot tensile testing at your service temperature and third-party witness inspection. Ask at enquiry stage so the testing is planned into the heat rather than bolted on afterwards.
Where it gets used
The published application lists converge tightly, which tells you this alloy has a well-defined home. Sandmeyer groups the uses under chemical and petrochemical processing, naming cracked ammonia components, petrochemical furnace parts, waste remediation units, heat exchangers and flares; under ore processing, naming perlite systems; under power generation, naming boiler fixtures and gas turbine components; and under thermal processing, naming heat-treat furnace containers and components, high temperature fans and salt pots. High Temp Metals adds furnace parts, heat-treat components and containers and boiler fixtures. AZoM lists gas turbines, heat exchangers, general heat treating equipment and neutral and cyanide salt pots.
In forged form the enquiries we see most often are retort and muffle flanges and end sections, radiant tube return bends and hubs, fan hubs and shafts for high temperature circulation fans, rolled rings for furnace door frames and seal faces, heavy discs and tubesheets for heat exchangers in hot gas duty, salt pot bodies and fittings, and replacement grid, basket and fixture components where fabricated 310S assemblies have distorted or carburized in service.
AISI 330 forged products
| Category | Items |
|---|---|
| Bars | Round bars, rods, square bars, rectangular and flat bars, hexagonal bars, forged shafts and step shafts |
| Hollow and tubular | Hollow bars, sleeves, bushings, forged pipe and tube sections, retort and muffle bodies, casings, shells, cylinders, hubs, housings |
| Rings | Forged rings, seamless rolled rings, door and seal frames, ring flanges, retaining rings |
| Flat and solid | Discs, blocks, forged plates, tubesheets, cover plates |
| Fabrication inputs | Forged blanks and near-net shapes, rough-machined and finish-machined components, parts supplied with weld preparation |
There is no fixed size catalogue. Send the drawing or a dimensioned sketch together with the quantity, the governing specification, the service temperature and the furnace atmosphere. The last two are not formalities on this grade: atmosphere decides whether N08330 is the right answer at all, and a short conversation at enquiry stage is cheaper than a failed part.
Get a price for AISI 330 forgings
Send the drawing, the quantity and the governing standard, and tell us the service temperature and atmosphere. We will quote our best price, and say so plainly if we think a different grade suits the duty better. Enquiries are answered within 24 hours, Monday to Saturday, China Standard Time (UTC+8).
Jiangyin Jiangnan Metal Co., Ltd., Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Tel +86-189-2135-9659 · Email sales@steelforgepieces.com
Questions we are asked about this grade
What is AISI 330 alloy?
An austenitic nickel-chromium-iron-silicon alloy, UNS N08330, with 34 to 37 percent nickel and 17 to 20 percent chromium. High Temp Metals describes outstanding resistance to oxidation and carburization with high strength; Sandmeyer Steel notes the high nickel keeps it resistant to chloride stress corrosion cracking and sigma phase embrittlement. Non-magnetic when annealed, and not hardenable by heat treatment.
Is AISI 330 a stainless steel or a nickel alloy?
Commercially it is sold both ways, which is why it appears in stainless steel listings. The datasheets treat it as a nickel-iron-chromium alloy, and with 34 to 37 percent nickel that is the more accurate description. Buy it against ASTM B511 or B536 and the label matters less than the certificate.
How hot can it run?
Between 1095 and 1200 °C depending on the source and the criterion, as set out in the temperature table above. Design to the lower end where scaling control or mechanical load matters.
At what temperature is it forged?
Start at 1120 to 1180 °C, finish above 950 °C, cool as fast as possible, and anneal afterwards. Never form or bend between 650 and 870 °C, which is the low ductility range where intergranular tearing occurs.
Can it be hardened?
No. Only cold working raises room temperature strength, and cold working is difficult because of the alloy's work hardening rate. A hardness requirement on an N08330 drawing is usually an error worth querying.
How does it compare with 310S?
Both are heat resistant austenitics, but the mechanism differs: 310S relies mainly on its 25 percent chromium, while N08330 relies on 34 to 37 percent nickel plus a deliberate silicon addition, which is what the sources credit for its carburization resistance and its resistance to green rot in alternating atmospheres. Where carburizing or cracked ammonia atmospheres and thermal cycling are the problem, N08330 is the stronger candidate. Where the duty is straightforward high temperature oxidation, 310S is often the cheaper answer. We forge both and have no reason to push you either way.
Can you supply one piece?
Yes. Open-die forging suits single prototypes and replacement parts as readily as batches. Send the drawing to sales@steelforgepieces.com and we will confirm feasibility, forged weight and lead time, usually within one working day.
Other grades we forge
Sources used on this page: Sandmeyer Steel Company, Alloy 330 (UNS N08330) specification sheet overview and plate FAQ; High Temp Metals, Alloy 330 technical data; AZoM, Stainless Steel Grade 330 (UNS N08330) datasheet; Rolled Alloys, RA330 data sheet and product page; Carpenter Technology grade 330 alloy listing; MakeItFrom UNS N08330 specification list. RA330 is a registered trademark of Rolled Alloys.
Compiled by the technical sales department, Jiangyin Jiangnan Metal Co., Ltd. Figures on this page are for guidance and are drawn from third-party datasheets. The values that govern your order are those on the EN 10204 3.1 certificate issued with the goods.