Supply summary
Jiangyin Jiangnan Metal Co., Ltd. is an integrated melting and open-die forging works in Jiangyin, Jiangsu, China, operating since 1997. Alloy 33 round bars, seamless rolled rings, flanges, discs, hollow cylinders and valve parts are made to order against ASTM B564, ASTM B462, ASTM B649 or customer drawing, solution annealed in house, with EN 10204 3.1 or 3.2 certificates. Minimum order 10 kg. Enquiries: sales@steelforgepieces.com, 0086-189-2135-9659.
| Trade names | Alloy 33, Nicrofer 3033 |
|---|---|
| UNS | R20033, also quoted as N08033 |
| Werkstoff number | 1.4591 |
| Steel name | X1CrNiMoCuN33-32-1 |
| Type | Austenitic, nitrogen-alloyed, chromium-based |
| Yield strength Rp0.2 | 380 MPa minimum (55.1 ksi) |
| Tensile strength Rm | 720 to 920 MPa (104 to 133 ksi) |
| Elongation | 40 % minimum |
| Hardness | 240 HBW maximum |
| Density | 7.90 g/cm³ |
| Melting range | 1330 to 1370 °C |
| PREN | 50 |
| Hot working range | 1200 to 1000 °C (2190 to 1830 °F) |
| Service approval | Pressure vessel use, −196 to 450 °C (−320 to 840 °F) |
What Alloy 33 is
Alloy 33 is a chromium-based austenitic material intended for duties that defeat ordinary austenitic and super-austenitic stainless steels: hot concentrated sulphuric acid, nitric acid, mixtures of nitric and hydrofluoric acid, strong alkalis and chloride-bearing process water. Its resistance comes from an extremely high chromium content of 33 %, which forms the basis of its performance in oxidising media, rather than from a heavy molybdenum addition.
The published characteristics of the alloy are outstanding resistance to strongly oxidising media, excellent resistance to localised corrosion in halide solutions, excellent resistance to nitric and hydrofluoric acid mixtures, excellent resistance to caustic soda, high strength and toughness, ease of fabrication, good weldability, good metallurgical stability, and approved authorisation for pressure vessel use from −196 to 450 °C. Its resistance to pitting and crevice corrosion in chloride media, and to chloride-induced stress-corrosion cracking, is also reported as outstanding.
For a forge shop three practical consequences follow: a high work-hardening rate that changes machining and cold-forming parameters, a narrow hot-working window, and a mandatory solution anneal with rapid quench after hot work. Each is covered below.
Alloy 33, Nicrofer 3033, 1.4591, X1CrNiMoCuN33-32-1 and UNS R20033 all describe the same material. A parallel datasheet indexed under the Werkstoff number is published on our 1.4591 page.
Designations and equivalents
| System | Designation |
|---|---|
| Trade names | Alloy 33, Nicrofer 3033 |
| UNS | R20033, also quoted N08033 |
| Werkstoff number | 1.4591 |
| DIN steel name | X1CrNiMoCuN33-32-1, also written X1NiCrMoCuN 33-32-1 |
| GB (China) | NS1405 |
| GOST, NF, BS, JIS, SS | No direct national equivalent. Ordered to the ASTM or EN designation. |
Product-form standards
UNS R20033 appears in separate ASTM specifications according to product form. For forgings the governing document is ASTM B564, which covers nickel alloy forgings together with billets and bars for reforging. Flanges, fittings and valve parts are ordered to ASTM B462. ASTM B649 covers bar and wire only, and is often quoted in error for forgings.
| Product form | ASTM | ASME |
|---|---|---|
| Forgings, billets and bars for reforging | B564 | SB-564 |
| Forged or rolled pipe flanges, forged fittings, valves and parts for corrosive high-temperature service | B462 | SB-462 |
| Bar and wire | B649 | SB-649 |
| Plate, sheet and strip, annealed temper | B625 | SB-625 |
| Seamless pipe and tube | B622 | SB-622 |
| Welded pipe | B619 | SB-619 |
| Welded tube | B626 | SB-626 |
Chemical composition
Specified limits are shown with the nominal analysis quoted for the alloy. Iron is the balance, typically about 32 %.
| Element | Symbol | Minimum | Maximum | Nominal |
|---|---|---|---|---|
| Chromium | Cr | 31.0 | 35.0 | 33 |
| Nickel | Ni | 30.0 | 33.0 | 31 |
| Iron | Fe | Balance | 32 | |
| Molybdenum | Mo | 0.5 | 2.0 | 1.6 |
| Nitrogen | N | 0.35 | 0.60 | 0.4 |
| Copper | Cu | 0.3 | 1.2 | 0.6 |
| Manganese | Mn | — | 2.00 | — |
| Silicon | Si | — | 0.50 | — |
| Carbon | C | — | 0.015 | — |
| Phosphorus | P | — | 0.020 | — |
| Sulphur | S | — | 0.010 | — |
Carbon is held to 0.015 % maximum, which is what underpins the good metallurgical stability of the alloy through welding and hot working.
Mechanical properties
Values apply to annealed material at room temperature.
| Property | Metric | Imperial |
|---|---|---|
| Yield strength Rp0.2, minimum | 380 MPa | 55.1 ksi |
| Tensile strength Rm | 720 to 920 MPa | 104 to 133 ksi |
| Elongation, minimum | 40 % | 40 % |
| Hardness, maximum | 240 HBW | 240 HBW |
Acceptance values differ between product-form specifications, so order against the specification that applies to the part rather than against a general figure. Mechanical testing is carried out on a representative test piece taken from the forging and reported on the certificate.
Physical properties
| Property | Value |
|---|---|
| Density | 7.90 g/cm³ |
| Melting point range | 1330 to 1370 °C |
| Structure | Austenitic, face-centred cubic |
| Magnetic response | Essentially non-magnetic in the annealed condition |
Corrosion behaviour and PREN
The alloy was developed for oxidising service. Its high chromium content builds a passive film that holds up in media which dissolve molybdenum-rich nickel alloys, while nitrogen and the modest molybdenum content give chloride pitting resistance in the range of 6 % molybdenum super-austenitic steels. It also has outstanding resistance to corrosion by alkaline media.
Pitting resistance equivalent
The value quoted for Alloy 33 is a pitting resistance equivalent of 50, derived from the nominal 33 % chromium, 1.6 % molybdenum and 0.4 % nitrogen. Where a specification calls for the more conservative formula, chromium plus 3.3 times molybdenum plus 16 times nitrogen, the same analysis returns 44.7. Both figures clear the value of 40 normally required for seawater duty. Because chemistry varies inside the specified limits, the number should be recalculated per heat from the certificate analysis. We will carry out that calculation and state it on the certificate on request.
Surface condition
Surface condition governs performance in service. Optimum corrosion resistance can only be ensured if the material is in clean, bright condition when used. Forging scale, grinding burn, embedded iron and weld heat tint all reduce resistance. Alloy 33 forgings leave this works solution annealed and descaled, and pickled where the order calls for it.
Applications
| Service | Application | Forgings required |
|---|---|---|
| Sulphuric acid | Heat recovery and distribution systems in sulphuric acid production. Pipes and heat exchangers for sulphuric acid contaminated with chlorides. | Flanges, tube sheets, valve bodies, blocks |
| Nitric and mixed acid | Vessels for storage and transport of nitric acid and hydrofluoric acid mixtures. | Rolled rings, flanges, nozzles, hollow cylinders |
| Seawater and brackish water | Seawater conducting pipes, condensers and coolers, selected for resistance to pitting corrosion. | Seamless rolled rings, flanges, pump shafts, sleeves |
| Chlor-alkali | Production and use of sodium hydroxide and potassium hydroxide up to 70 weight percent and a maximum of 170 °C (338 °F). | Flanges, discs, valve internals |
| Fertiliser | Urea solutions in the concentration range 5 to 90 weight percent. | High-pressure flanges, forged fittings, blocks |
| Pulp and paper | Components for the pulp and paper industry, including bleaching plant for chemical pulp. | Rings, shafts, sleeves |
| Petrochemical | Vessels and piping in purified terephthalic acid plants. | Flanges, forged fittings, discs |
Hot working and heat treatment
Alloy 33 takes open-die forging and ring rolling, but the process window is tighter than for standard austenitic stainless steel. The practice below follows the published guidance for the alloy.
Cleanliness before heating
Stock must be free of sulphur, phosphorus, lead and other low-melting metals before it enters the furnace, since these embrittle the alloy at working temperature. They occur in marking paints, temperature-indicating crayons, grease, oil and fuel. Fuel sulphur is kept as low as possible. Electric furnaces are preferred because they give better temperature control and add no combustion products.
Furnace atmosphere
The atmosphere is kept neutral to slightly oxidising and is not allowed to alternate between oxidising and reducing. Flame must not impinge on the work.
Hot forging
Stock is charged into a furnace already at temperature and worked in the range 1200 to 1000 °C (2190 to 1830 °F), with subsequent rapid cooling by water quenching or as fast as the section allows. Finishing below 1000 °C risks cracking, because the alloy is strong hot and work hardens quickly.
Solution annealing
Heat treatment after hot working is not optional where corrosion performance matters. Solution anneal between 1100 and 1150 °C and quench in water, charging into a furnace already at temperature. Soak time is counted from the moment the section reaches temperature and is set against the controlling wall thickness. Over-soaking is less damaging than under-soaking. Rapid air cooling is acceptable only on thin sections.
Cold forming
Cold work only from the solution-annealed condition. The work-hardening rate is much higher than that of standard austenitic stainless steel, so tooling and press capacity have to be sized accordingly. Interstage annealing may be needed for heavy work, and substantial total reduction should be followed by a final solution anneal.
Machining, welding and descaling
Machining
Machine from the solution-annealed condition. Because the work-hardening rate is high, use low cutting speeds, a moderate feed and keep the tool engaged. A tool that dwells leaves a hardened skin that the next pass has to cut through. Depth of cut must be sufficient to get beneath the strain-hardened layer, and generous aqueous coolant keeps the process stable.
Welding
- The alloy is weldable by gas tungsten arc welding using a matching filler of the same composition.
- Weld only annealed material, free of scale, grease and marking media. Degrease the seam faces.
- Because of the increased nitrogen content, interpass temperature should not exceed 120 °C (248 °F).
- Use low heat input and thin stringer beads, which limit porosity in the weld pool.
- Argon shielding with high-purity root protection.
- Post-weld heat treatment is normally not required.
Descaling and pickling
Oxide scale and weld heat tint adhere more tenaciously than on standard stainless steel. Grind with fine abrasives and avoid grinding burn. Before pickling in nitric and hydrofluoric acid, break up the oxide layer by grit blasting, fine grinding or a salt bath pre-treatment, and control bath concentration and temperature. Where the work allows, brushing the weld while still warm removes heat tint without pickling.
Alloy 33 forged products and size limits
This is an integrated works rather than a stockholder. Steel is melted on site through an electric arc furnace, ladle furnace and vacuum oxygen decarburisation, with vacuum induction, vacuum arc and protective-atmosphere electroslag remelting available for clean and superalloy grades. Maximum heat size is 60 tonnes. Forging, ring rolling, heat treatment, machining and testing all take place in the same plant, so the certificate traces a part back to its melt number rather than to a purchased billet.
| Product | Limit | Set by |
|---|---|---|
| Seamless rolled rings | Up to 6,000 mm outside diameter | 6 m radial-axial ring rolling mill, with 3 m and 1 m mills for smaller sizes |
| Rings below ring-mill range | From 50 mm outside diameter | Upset and punch route |
| Forged shafts | Up to 14,000 mm turned length | C61160 horizontal lathe. Two 15 m well-type furnaces allow vertical quenching |
| Discs, tube sheets, blocks | Up to 5,000 mm machined diameter | 5,000 mm vertical turning lathe |
| Bored cylinders and hollow shafts | Up to 1,600 mm by 10,000 mm | CNC deep-hole drilling machine |
| Single-piece weight | Up to 30,000 kg | 60 t heat size and 6,300 t hydraulic press |
| Minimum order | 10 kg, no minimum piece count | Weight-based order limit |
| Lead time | 20 to 60 days | Depends on melting route and witnessed testing |
Delivery condition
- Standard condition: forged, solution annealed, water quenched and descaled.
- Surface: as forged with machining allowance, proof-machined for ultrasonic testing, or finish-machined to drawing.
- Marking: grade, melt number, order number and specification, applied with sulphur-free and chloride-free marking media.
Testing and certification
Chemistry is verified at the furnace rather than taken from a supplier certificate, because the steel is melted here. Release follows a documented route: melt analysis, mechanical testing on a representative test piece, non-destructive examination, dimensional inspection, then certification.
| Category | Scope |
|---|---|
| Chemical analysis | Optical emission spectrometry to ASTM E415, infrared carbon and sulphur analysis to ASTM E1019, handheld alloy verification for positive material identification |
| Mechanical testing | Tensile testing on 600 kN and 300 kN machines to ASTM A370 and ISO 6892, pendulum impact testing with low-temperature bath to −60 °C, hardness measurement |
| Non-destructive testing | Ultrasonic testing to ASTM A388 and EN 10228-3, magnetic particle inspection to ASTM E709, bore inspection by endoscope, dimensional inspection |
| Metallography | Grain size to ASTM E112 with in-house mounting, grinding, polishing and microscopy |
| Corrosion testing | Intergranular corrosion to ASTM A262 or ASTM G28 and pitting resistance to ASTM G48, placed with an accredited third-party laboratory and reported alongside the mill certificate |
| Heat treatment records | Furnace charts covering charge, soak and quench for every lot |
| Certification | EN 10204 3.1 as standard. EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or the customer's own inspector on request |
| Approvals | CCS, BV, DNV, LR and NK classification society approvals |
State corrosion testing, impact testing below −60 °C and witnessed inspection on the enquiry so they are scheduled into the quoted delivery date rather than added to it.
Alloy 33 against other corrosion-resistant grades
Nominal compositions. PREN is shown on the conservative 16 times nitrogen basis so the grades compare on the same footing.
| Grade | UNS | Cr | Ni | Mo | N | PREN | Rp0.2 min | Suited to |
|---|---|---|---|---|---|---|---|---|
| Alloy 33, 1.4591 | R20033 | 33 | 31 | 1.6 | 0.4 | 45 | 380 MPa | Hot concentrated sulphuric acid, nitric acid, nitric and hydrofluoric mixtures, alkalis, seawater |
| Alloy 31, 1.4562 | N08031 | 27 | 31 | 6.5 | 0.2 | 51 | 276 MPa | Reducing acids, phosphoric acid, mixed chloride service |
| 6 % Mo austenitic, 1.4547 | S31254 | 20 | 18 | 6.1 | 0.2 | 43 | 300 MPa | Seawater, chloride pitting, bleach plant |
| 904L, 1.4539 | N08904 | 20 | 25 | 4.3 | — | 34 | 220 MPa | Dilute sulphuric and phosphoric acid |
| Super duplex 2507 | S32750 | 25 | 7 | 3.8 | 0.27 | 42 | 550 MPa | High-strength chloride service, offshore |
| 316L, 1.4404 | S31603 | 17 | 12 | 2.2 | — | 24 | 170 MPa | General chemical and food service |
Where the dominant attack is oxidising, such as concentrated sulphuric acid at temperature, nitric acid or nitric and hydrofluoric mixtures, the 33 % chromium content is what counts and Alloy 33 will outlast higher-molybdenum alloys. Where the attack is from reducing acid, a molybdenum-rich grade such as Alloy 31 or a nickel-base alloy is the better selection. Where chloride pitting is the problem, Alloy 33 and the 6 % molybdenum grades are close, but Alloy 33 carries roughly a quarter more yield strength, which can reduce wall thickness and forging weight.
Questions and answers
Is Alloy 33 the same as 1.4591, UNS R20033 and Nicrofer 3033?
Yes. Alloy 33 and Nicrofer 3033 are trade names, 1.4591 is the Werkstoff number, X1CrNiMoCuN33-32-1 is the steel name and R20033 is the UNS number for the same material. Some suppliers also quote UNS N08033, and the Chinese designation is NS1405.
Is Alloy 33 a stainless steel or a nickel alloy?
By composition it is austenitic with iron as the balance at about 32 %, so it sits at the boundary between super-austenitic stainless steel and the nickel-iron-chromium alloys. ASTM lists it in nickel alloy specifications such as B564, B649 and B625. In purchasing and fabrication it is handled like a super-austenitic stainless steel.
What is the chemical composition of Alloy 33?
Chromium 31.0 to 35.0, nickel 30.0 to 33.0, molybdenum 0.5 to 2.0, copper 0.3 to 1.2, nitrogen 0.35 to 0.60, manganese 2.00 maximum, silicon 0.50 maximum, carbon 0.015 maximum, phosphorus 0.020 maximum, sulphur 0.010 maximum, iron balance. The nominal analysis is 33 % chromium, 32 % iron, 31 % nickel, 1.6 % molybdenum, 0.6 % copper and 0.4 % nitrogen.
What is the PREN of Alloy 33?
The figure quoted for the alloy is 50. Using the more conservative formula of chromium plus 3.3 times molybdenum plus 16 times nitrogen, the nominal analysis gives 44.7. Both exceed the value of 40 normally required for seawater service. Recalculate from the heat analysis on the certificate, since chemistry varies within the specified limits.
Which ASTM specification applies to Alloy 33 forgings?
ASTM B564 covers forgings in UNS R20033, along with billets and bars for reforging. ASTM B462 covers forged or rolled pipe flanges, forged fittings, valves and parts for corrosive high-temperature service. ASTM B649 covers bar and wire, and is sometimes quoted in error for forgings.
What is the hot working temperature range?
1200 to 1000 °C, equivalent to 2190 to 1830 °F, with rapid cooling in water or as fast as the section allows. Do not finish below 1000 °C. A solution anneal between 1100 and 1150 °C followed by a water quench restores corrosion resistance after hot work.
Can Alloy 33 be welded?
Yes. Weldability is good and the alloy is welded by gas tungsten arc welding with a matching filler. Because of the increased nitrogen content the interpass temperature should not exceed 120 °C. Thin stringer beads and low heat input limit porosity in the weld pool. Post-weld heat treatment is normally not required.
What service temperature is the alloy approved for?
It carries approved authorisation for pressure vessel use in the range −196 to 450 °C, equivalent to −320 to 840 °F.
Why is Alloy 33 harder to machine than 316L?
Its work-hardening rate is much higher. A pass that dwells or runs too shallow leaves a hardened skin for the next pass to cut through. Use low cutting speed, sufficient depth of cut to get under the strain-hardened layer, continuous tool engagement and plenty of aqueous coolant, working from the annealed condition.
Do you hold Alloy 33 in stock?
It is melted and forged to order rather than held as stock. Lead time runs 20 to 60 days depending on size, melting route and testing scope. Minimum order is 10 kg with no minimum piece count. Send a drawing, or the dimensions, quantity, specification and test requirements, to sales@steelforgepieces.com.
What certification is supplied?
EN 10204 3.1 mill test certificates are standard, covering melt chemistry, mechanical properties, heat treatment records and non-destructive testing results. EN 10204 3.2 certificates witnessed by BV, DNV, LR, SGS, TUV or your own inspector are available on request. The works holds CCS, BV, DNV, LR and NK approvals, and customer audits are welcome.
Which grades are alternatives to Alloy 33?
Alloy 31 (UNS N08031) for reducing acids, UNS S31254 and N08926 for chloride service, and 904L for milder sulphuric and phosphoric acid duty. In strongly oxidising service none of these matches Alloy 33, because its resistance rests on about 33 % chromium rather than on molybdenum.
References
- VDM Metals International GmbH, VDM Alloy 33 (1.4591 / R20033) and Nicrofer 3033 material data sheet: alloy characteristics, applications, hot working and heat treatment.
- VDM Metals, Welding Consumables catalogue: interpass temperature guidance for UNS R20033.
- ASM International, Alloy Digest Ni-786, VDM 33 high-chromium austenitic alloy.
- ASTM B564, Standard Specification for Nickel Alloy Forgings.
- ASTM B462, Standard Specification for Forged or Rolled Alloy Pipe Flanges, Forged Fittings, and Valves and Parts for Corrosive High-Temperature Service.
- ASTM B649, Standard Specification for Ni-Fe-Cr-Mo-Cu-N Low-Carbon Alloy and Cr-Ni-Fe-N Low-Carbon Alloy Bar and Wire.
- ASTM B625, Standard Specification for Plate, Sheet, and Strip; ASTM B622, B619 and B626 for pipe and tube.
Data is published for engineering guidance and does not constitute a guarantee of properties for a particular application. Selection of material for a given service environment remains with the purchaser. Trade names are the property of their respective owners. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with VDM Metals. Page last reviewed 2 October 2026.