UNS N08028 is a high-alloy austenitic stainless steel of nominally 27 per cent chromium, 31 per cent nickel, 3.5 per cent molybdenum and 1 per cent copper. The chromium and molybdenum together give resistance to both oxidising and reducing acids, and the copper addition raises resistance to sulphuric acid in particular. It carries the EN and Werkstoff number 1.4563, EN name X1NiCrMoCu 31-27-4.

Is UNS N08028 the same as Alloy 28 and Sanicro 28?

Yes. Alloy 28 is the generic name, Sanicro 28 is Alleima's trade name and Incoloy alloy 028 is another designation for the same grade. All correspond to UNS N08028 and EN 1.4563. The property limits that apply to an order come from the product standard quoted rather than from the trade name, so material to ASTM B668 and material to ASTM B709 are the same alloy with different test requirements.

What is the chemical composition of UNS N08028?

To ASTM B668 the limits are carbon 0.030 per cent maximum, silicon 1.00 maximum, manganese 2.50 maximum, phosphorus 0.030 maximum, sulphur 0.030 maximum, chromium 26.0 to 28.0, nickel 30.0 to 34.0, molybdenum 3.0 to 4.0, copper 0.6 to 1.4, with iron as balance. The copper minimum is 0.6 per cent, a figure frequently misprinted as 0.06 per cent.

Which standards cover UNS N08028?

Seamless tube and pipe follow ASTM B668, EN 10216-5, SEW 400, SS 14 25 84 and NF A49-217. Plate, sheet and strip follow ASTM B709 and EN 10088-2. Bar follows EN 10088-3 and EN 10272. Fittings follow ASTM A403 with chemistry and mechanical properties to ASTM B668. The grade is approved by ASME for Section III, for Section I under Code Case 1325-18 and for Section VIII Division 1, holds VdTUV Werkstoffblatt 483, and appears in NACE MR0103 and NACE MR0175 / ISO 15156.

What heat treatment do UNS N08028 forgings receive?

Solution annealing at 1100 to 1160 degrees C, which is 2010 to 2120 degrees F, held 10 to 30 minutes, then quenched in water. Thin sections may be cooled rapidly in air. The alloy does not respond to precipitation hardening or to quench and temper, so strength comes from composition and cold work rather than from heat treatment.

What are the mechanical properties of UNS N08028?

ASTM B668 requires a minimum tensile strength of 503 MPa or 73 ksi, a minimum 0.2 per cent proof strength of 214 MPa or 31 ksi, and minimum elongation of 40 per cent. Published bar data for the solution annealed and quenched condition gives proof strength Rp0.2 of 220 MPa or 32 ksi minimum, tensile strength 500 to 750 MPa, elongation 35 per cent minimum and hardness 220 HB maximum. The bar figures are the more relevant reference for forging stock.

What is the PREN of UNS N08028?

Using PREN equals per cent chromium plus 3.3 times per cent molybdenum plus 16 times per cent nitrogen, the nominal 27 chromium and 3.5 molybdenum composition calculates to about 38.6 before any nitrogen contribution, and the ASTM B668 minimum composition of 26 chromium and 3.0 molybdenum calculates to about 35.9. PREN is an index calculated from chemistry and is not a measured property. Where pitting margin governs the design, critical pitting temperature testing should be specified instead.

Can UNS N08028 be welded, and which filler metal is used?

Weldability is good. Manual metal arc and gas-shielded arc welding are both suitable, with TIG as first choice. Recommended practice is heat input below 1.0 kJ per mm, interpass temperature below 150 degrees C and a string bead technique. For TIG or MIG the filler is ISO 14343 S 27 31 4 Cu L, equivalent to AWS A5.9 ER383. For manual metal arc the electrode is ISO 3581 E 27 31 4 Cu L R, equivalent to AWS A5.4 E383-16.

How difficult is UNS N08028 to machine?

It needs adjusted tooling data. Against a machinability-improved 316 or 316L, cutting speed should be reduced by roughly 50 to 55 per cent when turning with coated cemented carbide tools, with a similar reduction in most other operations. Feeds should be reduced only slightly and with care, because a light feed lets the tool rub and work-harden the surface rather than cut it.

What size UNS N08028 forgings can Jiangyin Jiangnan Metal supply?

Seamless rolled rings from 50 mm up to 6,000 mm outside diameter, forged shafts to 14,000 mm turned length, discs and tube sheets to 5,000 mm machined diameter, bored cylinders to 1,600 mm diameter by 10,000 mm, and single pieces up to 30,000 kg. Minimum order is 10 kg with no minimum piece count, so one-off forgings are accepted. Lead time normally runs 20 to 60 days depending on melt route, forged weight and test scope.

Home / Stainless steel / UNS N08028

Super-austenitic stainless steel · 27Cr 31Ni 3.5Mo 1Cu

UNS N08028 Forgings Alloy 28 / Sanicro 28 / Incoloy 028 / EN 1.4563. Seamless rolled rings, forged rings, flanges, shafts, discs, tube sheets, bushings and bar.

UNS N08028 is a high-alloy austenitic stainless steel containing nominally 27 per cent chromium, 31 per cent nickel, 3.5 per cent molybdenum and 1 per cent copper. The chromium and molybdenum give resistance to both oxidising and reducing acids, and the copper addition raises resistance to sulphuric acid in particular. It is specified mainly for phosphoric and sulphuric acid service, chloride-bearing process streams and sour wells.

We melt this grade in our own furnaces and forge it on the same site. The certificate traces a finished part back to its melt number rather than to a purchased billet, and the chemistry is aimed at the forging it will become instead of accepted as delivered.

Send a drawing Jump to technical data

Grade summaryN08028

Designations: N08028 / 1.4563
Also called: Alloy 28, Sanicro 28, Incoloy 028
Type: Super-austenitic stainless, fully austenitic, not hardenable by heat treatment
Chemistry to: ASTM B668
Condition: Solution annealed 1100–1160 °C, water quenched
Melting: EF + LF + VOD, with ESR where specified
Max ring OD: 6,000 mm
Max piece: 30,000 kg
Certificate: EN 10204 3.1 or 3.2
Min order: 10 kg, no minimum piece count

Designations and standards

The same alloy appears under a generic number, a Werkstoff number and several trade names. What changes between orders is the product standard, because that is what fixes the test requirements and the acceptance criteria.

Table 1. Cross-reference and applicable standards
UNS	N08028
EN number, Werkstoff	1.4563
EN name	X1NiCrMoCu 31-27-4
DIN	X1NiCrMoCuN 31 27 4
ISO	4563-080-28-I
SS, Sweden	2584
AFNOR	Z1NCDU31-27-03
Trade and common names	Alloy 28, Sanicro 28, Incoloy alloy 028
Seamless tube and pipe	ASTM B668, EN 10216-5, SEW 400, SS 14 25 84, NF A49-217
Plate, sheet, strip	ASTM B709, EN 10088-2
Bar	EN 10088-3, EN 10272
Fittings	ASTM A403, with chemistry and mechanical properties to ASTM B668
Code approvals held by the grade	ASME Boiler and Pressure Vessel Code Section III, Section I under Code Case 1325-18, Section VIII Division 1. VdTÜV Werkstoffblatt 483.
Sour service listings	NACE MR0103, NACE MR0175 / ISO 15156

There is no dedicated ASTM forging specification for this grade. Forgings are normally ordered to ASTM B668 chemistry with dimensions, NDT class and mechanical testing agreed on the drawing or purchase specification. State the standard edition you work to on the enquiry.

Chemical composition

Two columns are given. The left is what ASTM B668 permits, the right is the nominal aim published for the grade and the range we work to in the melt shop.

Table 2. Chemical composition, weight per cent
Element	ASTM B668	Nominal aim
Carbon, C	0.030 max	≤ 0.020
Silicon, Si	1.00 max	≤ 0.6
Manganese, Mn	2.50 max	≤ 2.0
Phosphorus, P	0.030 max	≤ 0.025
Sulphur, S	0.030 max	≤ 0.010
Chromium, Cr	26.0 – 28.0	27
Nickel, Ni	30.0 – 34.0	31
Molybdenum, Mo	3.0 – 4.0	3.5
Copper, Cu	0.6 – 1.4	1.0
Iron, Fe	Balance	Balance

The copper minimum is 0.6 per cent. It is frequently printed as 0.06 per cent on trading sites, which is a decimal error. Copper is the element responsible for the grade's behaviour in sulphuric acid, so a heat analysing below 0.6 per cent is out of specification whatever the rest of the certificate says.

Pitting resistance equivalent

Taking PREN as per cent Cr plus 3.3 times per cent Mo plus 16 times per cent N, the nominal 27Cr 3.5Mo composition calculates to about 38.6 before any nitrogen contribution. At the ASTM B668 minima of 26Cr and 3.0Mo the same formula gives about 35.9. A value of 32 is widely used as the rule-of-thumb threshold for seawater pitting resistance, so the grade sits above it across its whole composition range.

PREN is an index calculated from chemistry. It is useful for ranking candidate grades on paper and it is not a measured property. Where pitting or crevice margin governs the design, specify critical pitting temperature or a crevice test on the actual product rather than relying on a calculated number.

Mechanical and physical properties

Figures apply to material in the solution annealed and quenched condition, tested at 20 °C. The bar column is the more relevant reference for forging stock, while the ASTM B668 column is what a tube or fitting order has to meet.

Table 3. Room temperature mechanical properties, solution annealed
Property	ASTM B668 requirement	Published bar data
Tensile strength, R_m	503 MPa (73 ksi) min	500 – 750 MPa
Proof strength, R_p0.2	214 MPa (31 ksi) min	≥ 220 MPa (≥ 32 ksi)
Elongation, A	40 % min	≥ 35 %
Hardness	not specified	≤ 220 HB

Bar elongation is measured on a proportional gauge length, L0 equals 5.65 times the square root of the original cross-sectional area. Elongation measured on a fixed 50 mm gauge length is not directly comparable. Acceptance figures for a specific order are those written on the agreed specification, not those in this table.

Impact strength

The microstructure is fully austenitic, so impact strength stays good at room temperature and at cryogenic temperature, with published producer testing carried out down to minus 196 °C. Our own pendulum machine and low-temperature bath cover Charpy V-notch testing to minus 60 °C. Testing below that is placed with an accredited third-party laboratory and reported alongside the mill certificate, so state the test temperature at enquiry stage if your specification calls for it.

Table 4. Physical properties at 20 °C
Property	Value
Density	8.0 g/cm³ (0.289 lb/in³)
Mean coefficient of thermal expansion, 20 to 100 °C	15 to 16 × 10⁻⁶ /°C
Thermal conductivity	approx. 12 W/(m·K)
Specific heat capacity	approx. 450 J/(kg·K)
Electrical resistivity	approx. 1.0 µΩ·m
Magnetic response	Non-magnetic in the annealed condition

Published thermal conductivity for this grade varies between roughly 10 and 14.5 W/(m·K) at 20 °C depending on the source consulted. Where conductivity feeds a heat transfer calculation, ask us for the figure from the specific producer datasheet in use and treat the value above as indicative only.

Corrosion behaviour

The grade is characterised by very high corrosion resistance in strong acids, very good resistance to stress corrosion cracking and intergranular corrosion, high resistance to pitting and crevice corrosion, and good weldability. The notes below cover the two duties it was developed for.

Phosphoric acid

This is the application the alloy is best known for. Tubing in this grade has been used to replace graphite heat exchangers in wet-process phosphoric acid evaporation. The combination of high chromium with molybdenum and copper is what lets it survive acid carrying the chloride and fluoride impurities that come across from phosphate rock.

Sulphuric acid

Suited to piping and heat exchangers, with the useful windows being roughly 40 to 70 per cent deaerated acid and above 85 per cent. In concentrated acid its resistance is of the same order as a nickel-chromium-molybdenum alloy of the Alloy C type. Copper is the deliberate addition responsible for this behaviour.

Chlorides, pitting and crevice attack

With 26 to 28 per cent chromium and 3 to 4 per cent molybdenum the grade is well placed against pitting and crevice corrosion in chloride-bearing media, which is why it appears in seawater-cooled exchangers, desalination plant and chloride-rich utility water. For a specific stream, confirm with a critical pitting temperature figure rather than a calculated PREN.

Cracking and sour service

The high nickel content gives good resistance to chloride stress corrosion cracking, and the 0.030 per cent carbon maximum keeps intergranular attack in check after welding. The grade is listed in NACE MR0175 / ISO 15156 for oilfield equipment and in NACE MR0103 for refining environments. Listing is not blanket approval. Acceptance still depends on the partial pressure, chloride, temperature, hardness and delivery condition limits those standards set for the application.

Corrosion data is environment-specific. Published figures are a screening tool and are not a warranty of performance in your process stream. Where the consequences of failure are high, qualify the material against the actual medium at the actual temperature.

How we make it

Most forging suppliers in China buy billet. This works starts one step earlier, at the furnace. Nothing in the route below is subcontracted.

MeltEF then LF refining, with VOD for the low carbon and controlled nitrogen this grade needs
RemeltProtective-atmosphere ESR where the order calls for a remelted ingot
ForgeOpen-die press or radial-axial ring mill, 6,300 t and 6 m respectively
Heat treatSolution anneal 1100 to 1160 °C, water quench, in one of 14 furnaces
MachineRough or finish turning, boring and CNC work on site
Test and certifyChemistry, mechanical, NDT, then EN 10204 3.1 or 3.2

Table 5. Quality plan for N08028 forgings
Melting routes available	EF, LF, VOD, IF, VIM, protective-atmosphere ESR, VAR. Maximum heat size 60 t.
Forming	6,300 t, 4,000 t and 2,000 t open-die presses. Radial-axial ring mills at 6 m, 3 m and 1 m.
Heat treatment	Solution anneal 1100 to 1160 °C, 10 to 30 minutes, water quench. Car-bottom furnaces to 8,000 x 2,000 x 2,000 mm and two 15 m deep pit furnaces for vertical quenching of long work.
Chemical analysis	Optical emission spectrometry to ASTM E415, infrared carbon and sulphur to ASTM E1019, handheld PMI
Ultrasonic testing	ASTM A388 or EN 10228-3, class agreed on order. SEP 1921 on request.
Surface NDT	Liquid penetrant to ASTM E165, this grade being non-magnetic
Mechanical testing	Tensile to ASTM A370 on 600 kN and 300 kN machines, Charpy V-notch to minus 60 °C in house, hardness, grain size to ASTM E112
Placed with accredited laboratories	Intergranular corrosion to ASTM A262 or G28, pitting to ASTM G48, impact below minus 60 °C, bench Brinell or Rockwell where the specification requires it
Certification	EN 10204 3.1 mill certificate, or 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector. Class approvals held: CCS, BV, DNV, LR, NK.

Welding

Weldability is good. Manual metal arc and gas-shielded arc processes both work, with TIG the first choice. Keep heat input below 1.0 kJ/mm and interpass temperature below 150 °C, and use a string bead technique rather than wide weaving. For TIG and MIG the filler is ISO 14343 S 27 31 4 Cu L, which corresponds to AWS A5.9 ER383. For manual metal arc the electrode is ISO 3581 E 27 31 4 Cu L R, corresponding to AWS A5.4 E383-16. Matching composition filler is used because an undermatched filler loses the copper and molybdenum that the parent metal depends on.

Machining

Plan for reduced speeds. Against a machinability-improved 316 or 316L, cut turning speed by about 50 to 55 per cent when using coated cemented carbide, and expect a similar reduction in other operations. Reduce feeds only slightly and with care, since a light feed lets the tool rub and work-harden the surface rather than cut it. Rigid setups, sharp positive-rake geometry and generous coolant all help. We allow for this when quoting machined forgings, so a proof-machined N08028 part carries more machining hours than the same geometry in 316.

Forged forms and size envelope

Every item is forged from a single piece of steel melted on site, with no welding, no casting and no purchased billet of unknown origin. The limits below are plant limits rather than catalogue limits.

Table 6. Product forms in UNS N08028 and typical service
Form	Typical service	Size limit
Seamless rolled rings	Chemical and petrochemical plant, pressure equipment, gear and slewing ring blanks	OD 50 to 6,000 mm
Forged rings, retaining and seat rings	Sections outside the ring mill envelope, and heavy reduction work	to 30 t piece weight
Forged flanges and nozzles	Shell and tube exchangers, pressure vessels, process piping	to 5,000 mm
Tube sheets, discs and covers	Exchangers and vessels, supplied proof-machined for volumetric inspection	to 5,000 mm machined dia.
Forged shafts and spindles	Pumps, agitators, compressors, crystalliser and evaporator equipment	to 14,000 mm turned length
Bushings, sleeves and bored cylinders	Subsea and deepwater production equipment, rotating machinery	to 1,600 mm dia. x 10,000 mm
Round bar, blocks and bodies	Valve bodies, bonnets, stems and seat rings for ball, gate, globe, check and plug valves	by drawing
Wellhead and Christmas tree parts	Wellheads, trees, BOPs and risers in sour and chloride-bearing wells	API 6A, NACE MR0175

Minimum order is 10 kg with no minimum piece count, so single prototype forgings are accepted. Lead time normally runs 20 to 60 days depending on melt route, forged weight and test scope.

Common questions

Is N08028 the same as Alloy 28 and Sanicro 28?

Yes. Alloy 28 is the generic name, Sanicro 28 is Alleima's trade name, Incoloy alloy 028 is another designation, and all three are UNS N08028 or EN 1.4563. What differs between orders is the product standard quoted, because that fixes the testing. Material to ASTM B668 and material to ASTM B709 are the same alloy with different acceptance criteria.

Why does the copper minimum matter?

Copper is the element responsible for the grade's behaviour in sulphuric acid, which is a large part of why it gets specified at all. ASTM B668 sets it at 0.6 to 1.4 per cent. Many trading sites print the minimum as 0.06 per cent, which is a decimal error. If a certificate comes back with copper below 0.6 per cent, the material is out of specification regardless of what the rest of the analysis says.

Can you supply forgings with a specific PREN figure on the certificate?

We can report the calculated PREN from the actual heat analysis, which is arithmetic on the certified chemistry. Aiming the melt at the upper end of the chromium and molybdenum ranges to lift that number is also possible if it is stated on the order. What a calculated figure cannot do is substitute for a corrosion test, so if your specification needs a critical pitting temperature or an ASTM G48 result, order it as a supplementary test and we will place it with an accredited laboratory.

What condition are forgings delivered in?

Solution annealed at 1100 to 1160 degrees C, held 10 to 30 minutes and water quenched, unless the order says otherwise. The alloy does not respond to precipitation hardening or to quench and temper, so strength comes from composition and any cold work rather than from heat treatment. Forging and annealing temperatures and the quench route are recorded against the melt number.

Will you forge a single piece, or is there a minimum batch?

Minimum order is 10 kg with no minimum piece count. One-off forgings and prototype rings are normal work here. The practical constraint on a small order in this grade is the melt, so a single small piece is usually taken from an existing heat or a remnant rather than from a dedicated melt, and that affects both price and lead time.

How do I get a price?

Send a drawing, or the finished dimensions with tolerances, to sales@steelforgepieces.com. Include the quantity, the standard you are working to, the NDT class, whether you need EN 10204 3.1 or 3.2, and whether the part should arrive as-forged, proof-machined or finish-machined. With those six items we can quote forged weight, price and lead time without a second round of questions.

Request a quotation

Drawing-to-forging quotations, normally within two working days. Technical questions on this grade go to the same address and are answered by engineering staff rather than by a sales desk.

Jiangyin Jiangnan Metal Co., Ltd.
Open-die forging works, established 1997
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone, WhatsApp and WeChat +86 189 2135 9659
Email sales@steelforgepieces.com
Business hours Monday to Saturday, 08:00 to 17:30 China Standard Time (UTC+8)

Email an enquiry

Data sheet revision October 2026. Composition and mechanical limits quoted from ASTM B668 and from published producer datasheets for the grade. Figures are for guidance in material selection and do not constitute a warranty. The acceptance criteria for any order are those stated on the agreed purchase specification. A plain text version of this page is available at UNS-N08028.md.