Sanicro 28 Forgings, UNS N08028 / EN 1.4563

Open-die forged rings, flanges, bars, discs, sleeves, shafts and valve parts in Alloy 28. Technical data reviewed October 2026.

UNS

N08028

EN / W.Nr.

1.4563

EN name

X1NiCrMoCu31-27-4

Density

8.0 g/cm³

PREN

38 to 39

Max. service temp.

600 °C / 1110 °F

About the grade

Sanicro 28 is an extra-low-carbon austenitic stainless steel carrying high chromium and high nickel at the same time. That combination gives acid resistance close to nickel-base alloys while the material still behaves like an austenitic stainless in the forge shop and on the lathe. The 27% chromium covers oxidising media, the 3.5% molybdenum covers chlorides and pitting, and the 1% copper is the element that lifts performance in sulphuric and phosphoric acid. Carbon at 0.020% maximum keeps the grade free of sensitisation during normal welding.

Published characteristics are 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. Because nickel is above 30%, UNS places the alloy in the N0xxxx series, so you will see it listed as Alloy 28 or Incoloy 28 in some catalogues. Metallurgically it is still an iron-base stainless steel.

Designations

Standards and approvals

Approvals held by the grade: ASME Boiler and Pressure Vessel Code Section I (Code Case 1325-18), Section III and Section VIII Division 1; VdTUV Werkstoffblatt 483 for austenitic rolled and forged steel; NACE MR0103 for sulphide stress cracking resistance in petroleum refining; and NACE MR0175 / ISO 15156 for sour oilfield equipment.

Chemical composition

Pitting resistance equivalent: applying PREN = %Cr + 3.3 x %Mo + 16 x %N to the nominal chemistry gives about 38.5 with no nitrogen credit, and published data for EN 1.4563 lists a PREN near 39. That puts Sanicro 28 at the top of the conventional austenitic range. In seawater specifically, super-duplex SAF 2507 is the more resistant material.

Mechanical properties

Figures below apply to material in the solution annealed and quenched condition at 20 °C (68 °F).

Strength at elevated temperature, t up to 20 mm

Impact toughness

The austenitic structure gives good impact values at room temperature and at cryogenic temperature. Testing has shown compliance with EN 13445-2 (UFPV-2) at 60 J (44 ft-lb) minimum at -270 °C (-455 °F), and with EN 10216-5 and EN 10272 at 60 J (44 ft-lb) minimum at -196 °C (-320 °F).

Physical properties

Corrosion data

Phosphoric acid

Sanicro 28 is the most widely used metallic material for evaporator tubes in wet-process phosphoric acid plants, with units running more than ten years in service, often replacing graphite exchangers that suffered repeated tube breakage. In contaminated 95% superphosphoric acid at 200 °C over 20 days, measured corrosion rates were 0.03 mm/year for Sanicro 28 against 0.10 mm/year for Alloy 904L and 0.23 mm/year for UNS N08020.

Sulphuric acid

Used for piping and heat exchangers, particularly in 40-70% deaerated acid and above 85%. In concentrated 98% sulphuric acid its resistance is roughly the same as Alloy C. In chloride-contaminated sulphuric acid above about 20% concentration it performs better than super-duplex SAF 2507.

Other media

More resistant to hydrochloric acid than lower Cr-Mo stainless steels, and very good in hydrofluoric and hydrofluosilicic acid. In formic acid it is far better than 316L and better than 904L. In the ASTM A262 Practice C Huey test, five periods of 48 hours in boiling 65% nitric acid, corrosion rates stay below 0.15 mm/year. Against sodium hydroxide it is considerably better than 304 and 316, and at moderate temperature and concentration it is a practical alternative to pure nickel, which can suffer erosion corrosion.

Pitting, crevice and stress corrosion cracking

Critical pitting temperature in synthetic seawater is higher than both Alloy 904L and Alloy 825, including in acidified chloride solutions. In ASTM G48 Method B crevice testing in 6% ferric chloride it outperformed Alloy 825. For stress corrosion cracking the 27Cr-31Ni balance works well: in boiling 43% NaOH plus 6.7% NaCl at 142 °C for 500 hours, Sanicro 28 showed no cracking while Alloy 800 and Alloy 904L both cracked. The grade also resists SCC in combined hydrogen sulphide and chloride environments in the solution annealed, cold worked and welded conditions.

Intergranular corrosion

ASTM G28 testing shows Sanicro 28 tolerates at least 30 minutes in the critical 600-700 °C band without intergranular attack. That is far longer than any normal weld thermal cycle, so post-weld intergranular corrosion risk is low. Alloy 904L is more susceptible in the same comparison.

Heat treatment of forgings

Solution annealing: 1100-1160 °C (2010-2120 °F), hold 10 to 30 minutes, water quench. Fast cooling through 600-700 °C is what preserves corrosion resistance. Thin sections can be rapidly air cooled, but forged rings, discs and heavy shafts should always be water quenched. We solution anneal in-house in calibrated furnaces with chart recording, and the time and temperature chart can be issued with the certificate on request.

Our forging route for this grade

High-nickel austenitics such as N08028 have a narrow hot-working window and work harden quickly, so process control matters more than press tonnage. Our route is EAF melting, AOD or VOD refining, then ESR remelting for ingot cleanliness and low sulphur. The ingot is then open-die forged or ring rolled under controlled temperature with enough reduction to break down the cast structure through the full section, solution annealed and water quenched, machined to your tolerance, and finally inspected.

ESR is worth specifying on this grade. Segregation and residual sulphur in a conventionally cast ingot tend to show up later as forging cracks, and as initiation sites in exactly the acid service the alloy was bought for.

Product forms we supply in Sanicro 28

• Seamless rolled rings
• Forged flanges
• Forged round bars
• Forged discs and disks
• Forged sleeves
• Forged bushings
• Forged shafts
• Eccentric shafts
• Tube sheets
• Forged tubes and hollows
• Valve bodies and seat rings
• Valve stems and blocks
• Nozzles
• Gears and spindles
• Forged blocks
• Rolls and wheels

All items are made to your drawing or dimension list, rough forged, proof machined or finish machined. Send a PDF or STEP file together with the governing specification and we will quote weight, tolerance, lead time and price.

Applications

Testing and certificates

Standard scope on Sanicro 28 forgings covers chemical analysis by spectrometer with heat traceability, tensile and hardness testing after solution annealing, Charpy impact testing at ambient or cryogenic temperature on request, ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, PMI verification, dye penetrant examination, intergranular corrosion testing to ASTM A262 Practice C or ASTM G28, and dimensional inspection against your drawing. Certificates are issued as EN 10204 3.1 by default, or EN 10204 3.2 witnessed by TUV, BV, SGS, Lloyd's or another third party you nominate.

Machining and welding

Machining: compared with Sanmac 316/316L, cutting speed has to come down by roughly 50 to 55% when turning Sanicro 28 with coated cemented carbide tooling, and much the same applies to other operations. Reduce feed only slightly and with care. Backing the feed off too far makes the surface work harden instead of cutting. Rigid setups, sharp tools and positive rake are the practical requirements.

Welding: weldability is good. Preferred processes are TIG/GTAW as first choice, then MIG/GMAW and MMA/SMAW. Keep heat input below 1.0 kJ/mm and interpass temperature below 150 °C (300 °F), and use a stringer bead technique. Recommended fillers are ISO 14343 S 27 31 4 Cu L / AWS A5.9 ER383 for TIG and MIG, and ISO 3581 E 27 31 4 Cu L R / AWS A5.4 E383-16 for MMA. No preheat is required. Post-weld solution annealing is only needed when full corrosion performance of a heavily welded assembly has to be restored.

Cold bending: formability is good and small bend radii are achievable without annealing afterwards. For service above 400 °C (800 °F), heat treat after bending to keep long-term ductility.

Common questions

Related grades we forge

• 904L
• A182 F44
• A182 F51
• A182 F53
• A182 F55
• A182 F61
• Alloy 24
• Alloy 31
• Alloy 20
• Incoloy 825
• Incoloy 926
• Hastelloy C-276
• Inconel 625