What 321S51 is
321S51 is a titanium-stabilised austenitic stainless steel to British Standard. Titanium is added so that carbon forms titanium carbide rather than chromium carbide. That keeps chromium in solution at the grain boundaries when the steel is held between 425 and 850 °C, the range in which unstabilised grades sensitise. Stabilised grades are therefore not sensitive to intergranular corrosion after welding or after service at temperature.
The BS 1501-3 carbon range of 0.04 to 0.10 % puts the grade in the higher-carbon H family. AZoM's grade comparison table lists 321S51 against Type 321H, UNS S32109, EN 1.4878 (X10CrNiTi18-10) and JIS SUS 321H. The lower-carbon 321S31 corresponds to standard Type 321, UNS S32100, EN 1.4541.
| System | Designation |
|---|---|
| British Standard | 321S51, also written 321S51-490 and 321S51-510 in BS 1503 |
| AISI or ASTM type | Type 321H |
| UNS | S32109 |
| EN number and name | 1.4878, X10CrNiTi18-10 |
| JIS | SUS 321H |
| Related lower-carbon grade | 321S31, Type 321, UNS S32100, 1.4541, SUS 321 |
| Standard | Scope |
|---|---|
| BS 1501-3 | Steels for pressure purposes. Corrosion- and heat-resisting steels: plate, sheet and strip |
| BS 3059-2 | Steel boiler and superheater tubes with specified elevated-temperature properties |
| BS 1503, 321S51-510 | Steel forgings for pressure purposes |
| BS 1503, 321S51-490 and -520 | Bars and billets for bolting material in pressure-retaining applications |
BS 1503 has been superseded by EN 10222. Forgings are often ordered to the EN or ASTM equivalent while keeping the BS grade reference. Either route can be certified here.
Chemical composition
| Element | 321S51, BS 1501-3 | Type 321H | Type 321 |
|---|---|---|---|
| C | 0.04 to 0.10 | 0.04 to 0.10 | 0.08 max |
| Si | 1.00 max | 0.75 max | 0.75 max |
| Mn | 2.00 max | 2.00 max | 2.00 max |
| P | 0.045 max | 0.045 max | 0.045 max |
| S | 0.025 max | 0.030 max | 0.030 max |
| Cr | 17.00 to 19.00 | 17.0 to 19.0 | 17.0 to 19.0 |
| Ni | 9.00 to 12.00 | 9.0 to 12.0 | 9.0 to 12.0 |
| N | Not specified | Not specified | 0.10 max |
| Ti | 0.80 max | 4(C+N) min, 0.70 max | 5(C+N) min, 0.70 max |
| Fe | Balance | ||
The titanium minimum is the working part of the specification. It is written as a multiple of carbon plus nitrogen so that there is always enough titanium to tie up the carbon present. Chemistry is verified at the furnace by optical emission spectrometry to ASTM E415, with carbon and sulphur confirmed by infrared analysis to ASTM E1019.
Mechanical and physical properties
Acceptance values depend on product form, governing specification and section size. The figures below are the ASTM A240 minima for flat-rolled Type 321H, the closest published reference for 321S51. They are the baseline against which forging requirements are agreed.
| Property | 321H | 321 |
|---|---|---|
| Tensile strength | 515 MPa min | 515 MPa min |
| 0.2 % proof stress | 205 MPa min | 205 MPa min |
| Elongation on 50 mm | 40 % min | 40 % min |
| Hardness, Rockwell B | 95 HRB max | 95 HRB max |
| Hardness, Brinell | 217 HB max | 217 HB max |
Where BS 1503 is invoked the grade carries a strength class suffix, 321S51-490 or 321S51-510, and acceptance values come from that standard rather than from the table above. State the class required and the forging will be tested to it on a representative test piece heat-treated with the part.
| Property | Value |
|---|---|
| Density | 8,027 kg/m³ |
| Modulus of elasticity | 193 GPa |
| Mean coefficient of thermal expansion | 16.6 µm/m·°C at 0 to 100 °C, 17.2 at 0 to 315 °C, 18.6 at 0 to 538 °C |
| Thermal conductivity | 16.1 W/m·K at 100 °C, 22.2 W/m·K at 500 °C |
| Specific heat, 0 to 100 °C | 500 J/kg·K |
| Electrical resistivity | 720 nΩ·m |
Heat treatment of 321S51 forgings
| Treatment | Cycle | Purpose |
|---|---|---|
| Solution annealing | 950 to 1120 °C, cool rapidly | Dissolves carbides and restores maximum corrosion resistance. The standard delivery condition. |
| Stabilising | 870 to 900 °C, 1 hour per 25 mm, air cool | Used for severe service above 425 °C, and where the part was annealed at the top of the annealing range. |
| Stress relief | 700 °C, 1 to 2 hours, air cool | Relieves residual stress after heavy machining or welding. |
Heat treatment runs on site across fourteen furnaces. Car-bottom furnaces take work up to 8,000 by 2,000 by 2,000 mm for rings, discs and blocks. Two 15 m well-type furnaces allow long shafts to be quenched vertically without distortion. Three high-temperature car-bottom furnaces cover the upper end of the solution-annealing range. Charts are issued with the certificate.
Where 321S51 performs and where it does not
In the annealed condition the corrosion resistance of the 321 family is equivalent to Type 304. The advantage over 304 shows up in two cases: a weldment that has not been post-weld annealed, and service between 425 and 900 °C. Outside those two cases there is no corrosion benefit. Where intergranular resistance after welding is the only requirement, 304L is more widely available in most product forms, although 304L has lower hot strength and is not suitable above about 500 °C.
Intergranular corrosion
Not sensitive after heating in the 425 to 850 °C carbide-precipitation range, because titanium ties up the carbon. This is the reason the grade exists.
Oxidation and scaling
Good resistance in intermittent service to 900 °C and continuous service to 925 °C. Above roughly 1100 °C, move to Type 310 or S30815.
Chlorides
Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60 °C. Duplex or super duplex is the alternative.
Potable water
Considered resistant to about 200 mg/L chlorides at ambient temperature, falling to about 150 mg/L at 60 °C.
Claims that do not apply to this grade
Supplier pages for 321S51 often repeat that it has excellent corrosion resistance in hydrofluoric acid and fluorine and good resistance to hot strong alkali. That description belongs to the nickel-copper and nickel-molybdenum alloys, not to a stabilised 18-10 stainless. For hydrofluoric acid duty, ask for a quotation on Monel 400 or a Hastelloy B grade instead. Separately, 321 does not polish well, so it is not a candidate where a decorative finish matters.
Welding and machining
Weldability by all standard fusion methods is good, with or without filler metal, and post-weld annealing is not required. The consumable is not a matching one. Titanium does not transfer well across a high-temperature arc, so 321 is not recommended as a welding consumable. Grade 347 is the standard consumable for welding 321, because the niobium performs the same carbide-stabilisation task and does cross the arc. A high-silicon version of 347 is also used. Like other austenitic grades, 321S51 forms readily and keeps good toughness down to cryogenic temperatures.
321S51 forged products supplied
Every item is forged from a single piece of steel melted at this works. No welded fabrications, no castings, no purchased billet. Parts are supplied as-forged with machining allowance, proof-machined for volumetric inspection, or finish-machined to drawing.
| Product form | Envelope | Typical application |
|---|---|---|
| Seamless rolled rings | OD 50 to 6,000 mm | Furnace and heat-exchanger shells, expansion-joint rings, gear and bearing blanks |
| Forged and contoured rings | Outside the ring-mill envelope | Valve seat rings, retaining rings, heavy sections |
| Forged flanges | To ASME B16.5 and B16.47 | Weld neck, blind, slip-on, lap joint, orifice and long weld neck |
| Forged shafts and spindles | To 14,000 mm turned length | Furnace rolls, fan and blower shafts, stirrer and mixer shafts |
| Discs, tube sheets and covers | To 5,000 mm machined | Heat exchangers, pressure-vessel covers, hubs and blanks |
| Round, flat and square bars | Per drawing | Machining stock for valve internals and bolting |
| Cylinders, sleeves and bushings | Bored to 1,600 by 10,000 mm | Hollow sections bored from solid forged blanks |
| Valve bodies, bonnets and stems | Per drawing | High-temperature valves, nozzles, manifolds |
Typical service for 321-type material
Published applications for the 321 family include aircraft exhaust manifolds, expansion joints, bellows, furnace parts, heating-element tubing, heat exchangers, woven and welded screens for high-temperature mineral processing, and spiral-welded tube for burner pipes and flues. In forged form this covers annealing and muffle furnace components, heat-exchanger tube sheets and flanges, high-temperature valve and nozzle bodies, and rings for expansion joints and ducting.
When another grade is the better answer
| Grade | Use it instead of 321 when |
|---|---|
| 304L | The requirement is intergranular corrosion resistance only, not high-temperature strength |
| 3CR12 | The environment is only mildly hot, to about 600 °C |
| 304H | The environment is only mildly hot, to about 800 °C |
| 310 | Service reaches about 1100 °C, too high for 321 or 321H |
| S30815, 253MA | Service reaches about 1150 °C |
| Duplex F51 and F55 | Warm chlorides, pitting or stress corrosion cracking dominate the duty |
All of these grades are forged here, so grade advice is not limited by what is in stock. Work is made to order from steel melted on site.
How a 321S51 forging is made here
The steel for a 321S51 forging is melted at this works. It is not bought in as billet. For a stabilised grade the titanium to carbon ratio decides whether the part resists sensitisation at all, and that ratio is set at the furnace. A shop that buys billet from a third party cannot set it.
| Step | Equipment |
|---|---|
| 1. Melt | 25 t electric arc furnace, 25 t and 50 t ladle furnaces, 30 t and 60 t vacuum oxygen decarburisation. Maximum heat size 60 t. |
| 2. Remelt, if specified | 3 t vacuum induction, 6 t vacuum arc, 3 t and 6 t protective-atmosphere electroslag |
| 3. Forge | 6,300 t, 4,000 t and 2,000 t hydraulic open-die presses, hammers from 5 t down to 750 kg |
| 4. Ring roll | Radial-axial mills at 6 m, 3 m and 1 m maximum outside diameter |
| 5. Heat treat | 14 furnaces, including three high-temperature car-bottom furnaces and two 15 m well furnaces |
| 6. Machine and test | Vertical lathes to 5,000 mm swing, CNC lathes, deep-hole drilling to 1,600 by 10,000 mm, in-house laboratory |
460 people work at the site, including 9 senior engineers, 32 intermediate engineers and 140 technicians. The works has been operating since 1997.
Testing, approvals and certification
The works holds CCS, BV, DNV, LR and NK classification society approvals and runs its own laboratory, so chemistry is verified at the furnace rather than taken from a supplier certificate. Traceability runs from the melt number through forging, heat treatment and machining to shipment.
| Test | Standard | Where |
|---|---|---|
| Chemical analysis, optical emission | ASTM E415 | In-house |
| Carbon and sulphur | ASTM E1019 | In-house |
| Positive material identification | Handheld XRF | In-house |
| Tensile | ASTM A370, ISO 6892 | In-house, 600 kN and 300 kN machines |
| Charpy V-notch impact | ASTM A370, to minus 60 °C | In-house |
| Ultrasonic testing | ASTM A388, EN 10228-3 | In-house |
| Magnetic particle | ASTM E709 | In-house |
| Grain size and metallography | ASTM E112 | In-house |
| Intergranular corrosion | ASTM A262 | Accredited third-party laboratory |
| Certification | EN 10204 3.1 standard, 3.2 on request | Witnessed by BV, DNV, LR, SGS, TUV or your inspector |
For a stabilised grade, ASTM A262 practice testing is the meaningful acceptance test, because it shows whether the stabilisation worked. Specify it at enquiry stage so it is scheduled before shipment rather than added afterwards.
Request a price for 321S51 forgings
A price comes back within two working days from a complete enquiry. Minimum order is 10 kg with no minimum piece count. Normal lead time is 20 to 60 days. Send the grade or specification, the dimensions or a drawing in PDF, DWG, DXF or STEP, the quantity, the delivery condition, the heat treatment and testing scope, and the certification level and destination.
Email sales@steelforgepieces.com Call or WhatsApp +86 189 2135 9659Frequently asked questions about 321S51
What is 321S51 steel?
A British Standard designation for a titanium-stabilised austenitic stainless steel of the 18Cr 10Ni type. It appears in BS 1501-3 for plate, BS 3059-2 for boiler and superheater tubes, and BS 1503 for forgings for pressure purposes. The BS 1501-3 composition is C 0.04 to 0.10 %, Cr 17.00 to 19.00 %, Ni 9.00 to 12.00 %, Ti 0.80 % max. AZoM's comparison table lists it against Type 321H, UNS S32109, EN 1.4878 and JIS SUS 321H.
What is the difference between 321S51 and 321S31?
Carbon content. In AZoM's table 321S31 is the older British designation for standard Type 321, UNS S32100, EN 1.4541. 321S51 corresponds to Type 321H, UNS S32109, EN 1.4878. The H variant carries higher carbon, which improves high-temperature strength and makes it the usual choice for high-temperature structural work.
Can 321S51 be hardened by heat treatment?
No. Grades in the 321 family cannot be hardened thermally. The treatments that apply are solution annealing at 950 to 1120 °C with rapid cooling, stabilising at 870 to 900 °C for one hour per 25 mm followed by air cooling, and stress relief at 700 °C for one to two hours.
What is the maximum service temperature?
Good oxidation resistance in intermittent service to 900 °C and continuous service to 925 °C. The family performs well between 425 and 900 °C, where unstabilised grades would sensitise. Above about 1100 °C use Type 310. Above about 1150 °C use S30815.
Is 321S51 resistant to hydrofluoric acid?
No, although that claim appears on many supplier pages. Annealed 321 has corrosion resistance equivalent to Type 304, is subject to pitting and crevice corrosion in warm chlorides, and is subject to stress corrosion cracking above about 60 °C. For hydrofluoric acid duty, evaluate a nickel-copper or nickel-molybdenum alloy instead.
Which filler metal is used to weld it?
Grade 347. Titanium does not transfer well across a high-temperature arc, so 321 is not used as a consumable. The niobium in 347 performs the same stabilisation task and does transfer. Weldability is good by all standard fusion methods and post-weld annealing is not required.
What size 321S51 forgings can you produce?
Seamless rolled rings to 6,000 mm outside diameter on the 6 m radial-axial mill, single forgings to 30 tonnes on 6,300 t, 4,000 t and 2,000 t presses, shafts to 14,000 mm turned length, and discs and tube sheets machined to 5,000 mm. Minimum order 10 kg, no minimum piece count, lead time 20 to 60 days.
What certification is supplied?
EN 10204 3.1 as standard. EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector on request. Ultrasonic testing to ASTM A388 or EN 10228-3. ASTM A262 intergranular corrosion testing is placed with an accredited third-party laboratory when specified.
Do you sell 321S51 from stock?
No. Jiangyin Jiangnan Metal is a manufacturer with its own melt shop, not a stockist or trading company. Every forging is made to order from a customer drawing or specification, from steel melted at the works, so pricing is quoted per enquiry rather than published as a list price.