Nitrogen-strengthened austenitic stainless steel
Nitronic 33 Forgings UNS S24000 · XM-29 · forging stock to ASTM A314
Nitronic 33 is a nitrogen-strengthened, high-manganese austenitic stainless steel, numbered UNS S24000 and designated XM-29. It carries high yield strength with good ductility and toughness, holds up at cryogenic temperatures and has low magnetic permeability. Nominal chemistry is 17 to 19 percent chromium, 11.5 to 14.5 percent manganese, 2.25 to 3.75 percent nickel and 0.20 to 0.40 percent nitrogen, balance iron.
We melt this grade ourselves. The electric arc furnace, ladle furnace and vacuum oxygen decarburisation vessels feed the presses and the ring mill on the same site, so nitrogen is controlled at the furnace and the certificate traces a finished ring back to its melt number.
- Grade
- Nitronic 33
- UNS
- S24000
- ASTM
- XM-29. Forging stock to A314
- Tensile
- 690 MPa / 100 ksi minimum
- Yield
- 379 MPa / 55 ksi minimum
- Elongation
- 40 percent minimum
- Melting
- EF, LF, VOD. ESR on request. 60 t heat
- Max piece
- 30 t. Rings to OD 6,000 mm
- Min order
- 10 kg, no minimum piece count
- Lead time
- 20 to 60 days
Chemical composition
Composition limits for UNS S24000. Single figures are maximums. We verify chemistry at the furnace by optical emission spectrometry to ASTM E415, and again on the finished part by portable analyser, so the number on the certificate is measured rather than carried over from a billet supplier.
| Element | Content |
|---|---|
| Chromium, Cr | 17.00 - 19.00 |
| Manganese, Mn | 11.50 - 14.50 |
| Nickel, Ni | 2.25 - 3.75 |
| Nitrogen, N | 0.20 - 0.40 |
| Silicon, Si | 0.75 max |
| Carbon, C | 0.08 max |
| Phosphorus, P | 0.06 max |
| Sulfur, S | 0.03 max |
| Iron, Fe | Balance |
Mechanical and physical properties
Annealed condition. Strength and elongation are specification minimums; hardness and physical figures are typical. Test pieces are taken from a representative section and pulled on our own 600 kN machine to ASTM A370.
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 690 MPa min | 100 ksi min |
| Yield strength, 0.2 percent | 379 MPa min | 55 ksi min |
| Elongation | 40 percent min | 40 percent min |
| Hardness | 241 HB | 100 HRB |
| Density | 7.775 g/cm³ | 0.2808 lb/in³ |
| Thermal expansion, 26 to 93 °C | 16.074 µm/m·°C | 8.93 µin/in·°F |
Specifications listing this grade
Nitronic 33 appears as XM-29 across the ASTM stainless specifications. For forged work the relevant one is A314, which covers billets and bars for forging.
| Form | Specification |
|---|---|
| Billets and bars for forging | ASTM A314, XM-29 |
| Plate, sheet, strip | ASTM A240, XM-29 |
| Bars and shapes | ASTM A276, A479, A580, XM-29 |
| Pipe and tube | ASTM A249, A269, A312, A688, A813, A814 |
| Other | ASTM A412, XM-29 |
Forging and heat treatment
Nitrogen-strengthened austenite is strong hot and it work-hardens quickly. Both facts shape how this grade is handled on the press.
Forging temperatures
The stock goes to 1093 °C (2000 °F) and soaks until the section has equalised, then it is reheated to 1177 °C (2150 °F) and equalised again before the first blow. On heavy open-die sections that second equalising soak is the step that matters. An uneven through-thickness temperature in this grade shows up as surface tearing, because the cooler skin will not move with the hot core. Our car-bottom furnaces take work up to 8,000 by 2,000 by 2,000 mm, so sections stay in the furnace long enough to come to temperature rather than being rushed to the press.
Annealing
Soak at 1038 to 1121 °C (1900 to 2050 °F), then quench rapidly in water or air. Where forming is done in stages and cold-work stresses have to come out between them, the intermediate anneal is 1065 °C (1950 °F). Long shafts are quenched vertically in one of the two 15 m well-type furnaces, which keeps distortion down on slender sections.
Hardening
This grade hardens by cold work alone. It does not answer to thermal hardening, so any strength above the annealed minimums has to come from cold working. If a drawing calls for properties above 690 MPa tensile, say so at enquiry stage and we will tell you whether it is reachable in your section.
Welding and machining
Welding goes ahead by the usual processes: submerged arc, gas metal arc and gas tungsten arc. For machining, use a resulphurised lubricant, positive feeds and slow speeds. Chips come off stringy and tough, so chip breakers or curlers earn their place. Our own shop runs vertical lathes to 5,000 mm swing, horizontal lathes to 14 m between centres and a deep-hole drill for 1,600 mm by 10,000 mm bores.
What we forge in Nitronic 33
Everything is forged to your drawing or written specification from steel melted here, and supplied as-forged, proof-machined for ultrasonic examination, or finish-machined.
Seamless rolled rings
Rolled on radial-axial mills to 6,000 mm outside diameter. Rectangular or contoured section, including gear ring blanks and slewing rings.
Forged rings
Upset and punched from 50 mm outside diameter, for sections outside the ring-mill envelope and for heavy-reduction work.
Flanges
Weld neck, blind, slip-on, socket weld, lap joint and long weld neck, to ASME B16.5 and B16.47 dimensions.
Shafts and spindles
Stepped, gear, pinion and eccentric shafts to 14,000 mm turned length, quenched vertically in the 15 m well furnaces.
Bars and blocks
Round, flat and square bars, die and mould blocks, the usual feedstock route for machined valve bodies.
Discs and tube sheets
Solid forged discs, tube sheets and covers to 5,000 mm machined diameter, proof-machined for volumetric inspection.
Sleeves, bushings, cylinders
Hollow forged cylinders and bushings bored from solid blanks, to 1,600 mm diameter by 10,000 mm.
Valve parts
Bodies, bonnets, blocks, stems, seat rings and nozzles for ball, gate, globe, check and plug valves.
Capability, testing and certification
The limits below are set by equipment on this site. No forging, heat treatment or machining step is subcontracted.
| Item | Detail |
|---|---|
| Melting route | Electric arc furnace, ladle furnace and vacuum oxygen decarburisation. Protective-atmosphere electroslag remelting where cleanliness is specified. Maximum heat 60 t |
| Forging equipment | 6,300 t, 4,000 t and 2,000 t hydraulic open-die presses; 6 m, 3 m and 1 m radial-axial ring mills; hammers from 750 kg to 5 t |
| Heat treatment | 14 furnaces, including two 15 m well-type furnaces for vertical quenching and three high-temperature car-bottom furnaces for solution annealing |
| Maximum ring | 6,000 mm outside diameter |
| Maximum single piece | 30,000 kg |
| Minimum order | 10 kg, no minimum piece count |
| Chemical analysis | Optical emission spectrometry to ASTM E415; infrared carbon and sulphur to ASTM E1019; portable analyser for material identification |
| Mechanical testing | Tensile on 600 kN and 300 kN machines to ASTM A370 and ISO 6892; Charpy V-notch to minus 60 °C; hardness; grain size to ASTM E112 |
| Non-destructive testing | Ultrasonic to ASTM A388 or EN 10228-3; magnetic particle to ASTM E709; endoscope examination of bores |
| Certification | EN 10204 3.1 as standard. EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector on request |
| Class approvals | CCS, BV, DNV, LR, NK |
| Lead time | 20 to 60 days from order confirmation |
Tests placed outside
A few order-specific tests are not run here and go to an accredited laboratory, with the report issued alongside the mill certificate. Those are intergranular corrosion to ASTM A262 or G28, pitting resistance to ASTM G48, and impact testing below minus 60 °C. State the requirement on the enquiry so it is scheduled before shipment rather than discovered at the end.
Where the grade is used
Published application areas for Nitronic 33 cover tube assemblies, pipes, cable, valves, tanks, generator containment rings and fans. The reason for choosing it is usually one of three: a high yield strength is wanted without going to a high-nickel grade, the part has to stay tough at cryogenic temperature, or the assembly needs a structural stainless that stays close to non-magnetic.
On the work that passes through this plant, that translates into containment and retaining rings for generators, tube sheets and covers for heat exchangers, valve and wellhead components, and shafts and sleeves where a non-magnetic austenitic grade is specified. If your application sits outside the published list, send the service conditions. For corrosive duty in particular, ask us for the figures that apply to your medium rather than relying on a general statement about stainless steel, and we will quote a corrosion test to ASTM G48 or A262 where it is needed to prove the point.
Questions we get asked
How does Nitronic 33 differ from Nitronic 50 and Nitronic 60?
They are separate alloys with separate UNS numbers, not variants of one grade. Nitronic 33 is UNS S24000, a high-manganese grade with 2.25 to 3.75 percent nickel and no deliberate molybdenum. Nitronic 50 and Nitronic 60 are different compositions aimed at different problems. Do not read across between them on corrosion or wear behaviour. We forge all three, so tell us the service conditions and we will quote against the grade your specification names. See Nitronic 50 and Nitronic 60.
Do you buy Nitronic 33 billet, or melt it?
We melt it. The route is electric arc furnace, ladle furnace and vacuum oxygen decarburisation, and the vacuum step is the one that counts here, because it is where nitrogen is held inside the 0.20 to 0.40 percent band instead of being accepted as delivered. Protective-atmosphere electroslag remelting is available where cleanliness is specified. Most forging shops in China buy billet for this kind of grade, which means their certificate starts at a purchased bar. Ours starts at the furnace.
What is the largest Nitronic 33 ring you can roll?
6,000 mm outside diameter on the 6 m radial-axial mill, with 3 m and 1 m mills for smaller sizes and an upset-and-punch route from 50 mm outside diameter. Heaviest single piece is 30 tonnes. In practice the downstream equipment sets the real limit as often as the press does, so send the finished dimensions and we will tell you which step governs.
Can you hold a maximum magnetic permeability figure?
Put the figure on the enquiry. Low permeability is one of the reasons this grade gets specified, but cold work raises permeability in any austenitic stainless, so the value depends on the condition the part ships in as much as on the chemistry. If it is a contractual requirement we will agree the measurement method and the acceptance value before we start, rather than testing for it afterwards.
Will you quote a single piece?
Yes. The minimum is 10 kg by weight, with no minimum piece count, so a one-off is quotable and so is a single large ring. Quantity still moves the unit price, because small parts get grouped into a batch to share furnace and setup time, but it does not decide whether we can take the job.
What do you need in order to quote?
Six things, and sending them in the first email usually gets a price back within two working days: the grade or specification, the dimensions or a drawing in PDF, DWG, DXF or STEP, the quantity and likely repeat volume, the delivery condition, the heat treatment and testing requirements, and the certification and destination port.