ASTM A182 F348 Forgings (UNS S34800)
Niobium and tantalum stabilised austenitic stainless steel forgings with restricted cobalt and tantalum. Rolled rings, flanges, shafts, discs, sleeves, bars and tube sheets, forged to drawing in Jiangyin, China.
Grade summary
ASTM A182 Grade F348 (UNS S34800) is an 18Cr-8Ni austenitic stainless forging grade described in the standard as 18 chromium, 8 nickel modified with columbium. Niobium plus tantalum tie up carbon as stable carbides, which reduces the risk of chromium carbide precipitation at grain boundaries and the intergranular attack that follows it. The difference between F348 and the closely related F347 is chemistry control rather than strength: F348 carries tighter maximum limits on tantalum, 0.10 percent, and cobalt, 0.20 percent. Under ASTM A182/A182M, F348 forgings are accepted against 515 MPa (75 ksi) minimum tensile strength, 205 MPa (30 ksi) minimum yield strength, 30 percent minimum elongation and 50 percent minimum reduction of area. Jiangyin Jiangnan Metal Co., Ltd. forges F348 open-die parts and seamless rolled rings to customer drawings with EN 10204 3.1 or 3.2 certification.
- UNS number
- S34800
- Tensile, min
- 515 MPa
- Yield, min
- 205 MPa
- Cobalt limit
- 0.20% max
- Tantalum limit
- 0.10% max
- Size range
- 50 to 3000 mm
1. Grade description and selection
Grade 348 sits in the same family as Types 321 (UNS S32100) and 347 (UNS S34700). All three are stabilised austenitic stainless steels intended for equipment that spends service time in the chromium carbide precipitation range, where an unstabilised grade would sensitise. Types 347 and 348 use niobium, also written as columbium, together with tantalum as the stabilising addition. Type 321 uses titanium instead.
Type 348 is normally specified when the governing document calls for restricted tantalum and cobalt content. Cobalt activates under neutron flux, so reactor-adjacent hardware is often bought with a cobalt cap on the certificate. The restricted chemistry makes the grade usable for that kind of work, but it does not on its own make a forging nuclear grade. Approval still depends on the design code, the product specification, traceability, the quality programme, cleanliness, examination and documentation.
One further point on scope. F348 is stabilised, and it contains no molybdenum. It should therefore not be treated as a drop-in alternative to Type 316 in chloride service without a separate corrosion review.
2. Chemical composition
| Element | Composition, % | Function |
|---|---|---|
| Carbon, C | 0.08 max | Low carbon with stabilisation limits chromium carbide formation |
| Manganese, Mn | 2.00 max | Austenite stabiliser and deoxidiser |
| Phosphorus, P | 0.045 max | Residual, controlled for toughness |
| Sulfur, S | 0.030 max | Residual, controlled for hot workability |
| Silicon, Si | 1.00 max | Deoxidiser |
| Nickel, Ni | 9.00 to 13.00 | Austenite former |
| Chromium, Cr | 17.00 to 20.00 | Passive film and general corrosion resistance |
| Cobalt, Co | 0.20 max | Restricted. Main reason F348 is specified over F347 |
| Tantalum, Ta | 0.10 max | Restricted, separates 348 from 347 |
| Niobium plus tantalum, Nb+Ta | Stabilisation ratio tied to carbon content, commonly expressed as 10 x C minimum. Nominal value about 0.8 | Stabilising addition that fixes carbon |
In stabilised grades the Nb+Ta requirement is written as a function of carbon rather than a fixed band, so the minimum applying to your material test report depends on the actual heat carbon. Where restricted cobalt or tantalum is the reason F348 was selected, both values have to be reported on the mill certificate. A certificate of conformity does not replace a test report for that purpose.
F348 compared with F348H
| Grade | UNS | Carbon, % | Co / Ta, % max | Tensile / yield, min |
|---|---|---|---|---|
| F348 | S34800 | 0.08 max | 0.20 / 0.10 | 515 / 205 MPa |
| F348H | S34809 | 0.04 to 0.10 | 0.20 / 0.10 | 515 / 205 MPa |
3. Mechanical properties
Two different data sets circulate for this grade and mixing them up causes rejected orders. The first table below is what a forging is accepted against. The second is what annealed Type 348 typically measures, which is useful as design reference only.
3.1 ASTM A182/A182M acceptance requirements
| Property | Requirement |
|---|---|
| Tensile strength, min | 75 ksi (515 MPa) |
| Yield strength, min | 30 ksi (205 MPa) |
| Elongation in 2 in. (50 mm) or 4D, min | 30% |
| Reduction of area, min | 50% |
| Brinell hardness | Not specified by A182 for this grade |
3.2 Typical annealed properties, reference only
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 655 MPa | 95,000 psi |
| Yield strength, 0.2% offset | 275 MPa | 39,900 psi |
| Elongation at break in 50 mm | 45% | 45% |
| Charpy impact | 160 J | 118 ft-lb |
| Hardness, Brinell, converted from HRB | 147 HB | 147 HB |
| Hardness, Rockwell B | 85 HRB | 85 HRB |
Published sources differ slightly on typical figures, and density for example is quoted both as about 7.96 and about 8.0 g/cm3. For pressure or elevated temperature calculation, use code allowables rather than datasheet typicals.
3.3 Physical and thermal properties
| Property | Value |
|---|---|
| Density | About 7.96 to 8.0 g/cm3 (0.289 lb/in3) |
| Melting point | About 1427 C (2600 F) |
| Thermal conductivity | About 16.3 W/m.K |
| Mean coefficient of thermal expansion | 16.6 to 17.3 um/m.C, source dependent |
4. Forging, heat treatment, welding and machining
Hot working
Type 348 is hot worked between 1149 C and 1232 C (2100 to 2250 F) and should not be worked below 927 C (1700 F). After hot work the part is water quenched or fully annealed to restore corrosion resistance. On open-die forgings this matters more than it does on bar, because the last reduction and the cooling route decide whether the finished piece is genuinely in the solution annealed condition.
Heat treatment
Annealing is carried out at 1010 to 1093 C (1850 to 2000 F) followed by water quenching. The grade does not respond to hardening heat treatment. Strength above the annealed level comes only from cold reduction, so higher properties cannot be ordered by heat treating harder.
Welding
Fusion and resistance welding processes are suitable. Oxyacetylene welding is not preferred for this alloy. AWS E/ER348 is the matching filler metal. Weldability depends on the whole material, process, joint and service combination, so a qualified procedure covering filler lot, heat input, interpass temperature, shielding and cleaning matters more than the choice between TIG and MIG.
Machining
Type 348 is slightly tougher than Type 304 and work hardens in the way other austenitic grades do. Rigid workholding, sharp tools with positive geometry, adequate feed and good coolant supply keep the cutting edge below the work hardened layer. Dwelling or very slow feeds glaze the surface and shorten tool life. Allow for residual stress movement on forgings that are machined asymmetrically.
5. Equivalents and related specifications
The same chemistry is purchased under several designations depending on product form and region. Cross references commonly listed for grade 348 include UNS S34800, AISI 348, DIN and EN 1.4550, SAE 30348 under SAE J405, and the ASME twin specification SA-182. Product standards covering grade 348 in other forms include A240 for plate and sheet, A276 and A479 for bar, A312 and A376 for pipe, A403 for fittings, A336 for pressure part forgings, A213 and A249 for tube, and A358, plus the corresponding SA- versions. Because each standard controls a different product form and test regime, a grade name by itself is never a complete purchase description.
EN 1.4550 is listed as a cross reference to grade 348 and is chemically comparable as a niobium stabilised 18/10 austenitic steel. It does not by itself carry the restricted cobalt and tantalum limits that define F348. Where those limits are an engineering requirement, order to A182 F348 and state the limits on the purchase order.
6. F348 forging products
Everything below is forged to customer drawing or to a supplied size list.
Seamless rolled rings
Radial and axial rolled rings and ring blanks for reactor internals, turbine and gearbox work, rolled from solution treated F348 billet.
Forged flanges
Weld neck, slip-on, blind, threaded and special bore flanges, plus flange blanks for high temperature piping.
Shafts and spindles
Open-die forged shafts, eccentric shafts, spindles and crankshafts for compressors, generators and power transmission.
Discs and blanks
Upset forged discs and hubs, supplied rough machined or with sonic test allowance.
Sleeves, bushings, hollow bar
Forged and bored sleeves and bushings for subsea, deepwater and offshore production hardware.
Tube sheets
Forged tube sheets and tube plates, separator and heat exchanger components for refining and desalination duty.
Valve components
Forged valve bodies, blocks, seat rings, stems and bonnets for ball, gate, globe, check and plug valves.
Bars, pipe, nozzles
Forged round bar, forged pipe and tube, nozzle forgings, manifolds and forged rolls.
Service industries
F348 forgings go into nuclear related equipment, power generation, oil and gas production including subsea and deepwater systems, petroleum refining including polythionic acid service where stabilised grades are the usual answer, pulp and paper digesters and liquor tanks, seawater desalination, industrial air and gas compressors, food processing equipment and storage, pharmaceutical and biochemical plant, thermal oxidisers in waste treatment, shipbuilding and heavy machinery.
7. Manufacturing, testing and certification
| Item | Detail |
|---|---|
| Melting route | EAF plus VOD, with ESR available where the specification or cleanliness requirement calls for it |
| Process | Open-die forging, upsetting and drawing, seamless ring rolling |
| Size range | About 50 mm to 3000 mm outside dimension, single pieces from a few kilograms to multi-tonne |
| Delivery condition | Solution annealed at 1010 to 1093 C and water quenched, rough machined or finish machined to drawing |
| Ultrasonic testing | EN 10228-3, SEP 1921 or ASTM A388, acceptance class to order |
| Other examination | Liquid penetrant, dimensional report, hardness survey, positive material identification on request |
| Certification | EN 10204 3.1 mill certificate, or 3.2 with third party witness |
| Traceability | Heat number, full chemistry including Co and Ta, heat treatment charts, mechanical test results |
The same material is supplied under its other designations, AISI 348, UNS S34800, EN 1.4550 and Alloy 348, and as A182 F348H (UNS S34809) where elevated temperature creep strength is required.
8. Questions we are asked about F348
What is the difference between ASTM A182 F347 and F348?
Both are niobium and tantalum stabilised austenitic stainless forging grades in the same chromium nickel range. Grade 348 applies tighter maximum limits on tantalum, 0.10 percent, and cobalt, 0.20 percent. When a drawing calls out F348 instead of F347, that restriction is almost always the reason, so it should be verified on the certificate rather than assumed.
What are the minimum mechanical properties of A182 F348 forgings?
ASTM A182/A182M requires 75 ksi (515 MPa) minimum tensile strength, 30 ksi (205 MPa) minimum yield strength, 30 percent minimum elongation in 2 in. (50 mm) or 4D, and 50 percent minimum reduction of area. Annealed Type 348 typically measures around 655 MPa tensile and 275 MPa yield, well above the minima, but typical values are not acceptance criteria.
Is A182 F348 a nuclear grade material?
Not by itself. The restricted cobalt and tantalum limits make Type 348 suitable for specified nuclear related requirements, and that is the main reason the grade exists. Qualification for a nuclear application also depends on the design code, the product specification, material traceability, an approved quality programme, cleanliness, examination and documentation.
What heat treatment do F348 forgings receive?
Solution annealing at 1010 to 1093 C (1850 to 2000 F) followed by water quenching. The grade cannot be hardened by heat treatment, and only cold work raises strength above the annealed level. Hot working is done between 1149 C and 1232 C and should not continue below 927 C.
Which filler metal is used to weld A182 F348?
AWS E/ER348 is the matching filler. Fusion and resistance welding processes are suitable and oxyacetylene welding is not preferred. Use a qualified welding procedure for the product form, thickness and service, with control of cleaning, heat input and interpass temperature.
Is F348 equivalent to EN 1.4550?
1.4550 is commonly cross referenced to grade 348 and is chemically comparable as a niobium stabilised 18/10 austenitic steel. The cross reference does not automatically carry the restricted cobalt and tantalum maxima that define Type 348, so where those limits matter, order to A182 F348 and state them on the purchase order.
Can F348 replace Type 316 in chloride or seawater service?
That should not be assumed. Type 348 is stabilised against sensitisation but does not contain the molybdenum level of Type 316, so chloride pitting, crevice corrosion and stress corrosion cracking need separate evaluation against concentration, temperature, stress and oxygen level. Stabilisation addresses intergranular corrosion after thermal exposure, not every corrosion mechanism.
What should an F348 forging enquiry include?
The drawing or finished dimensions, quantity, the governing specification and edition, delivery condition, any restricted cobalt or tantalum values you need certified, the ultrasonic acceptance standard and class, machining allowance, certificate type and the required delivery date. Send it to sales@steelforgepieces.com or call +86-189-2135-9659.
9. Related stainless steel forging grades
Enquiries for A182 F348 forgings
Send a drawing or a size list and we will come back with forging weight, machining allowance, test scope and lead time.
sales@steelforgepieces.com +86-189-2135-9659
Chemistry and mechanical requirements on this page follow ASTM A182/A182M Grade F348 and F348H. Typical annealed properties, physical and thermal data, hot working, annealing, welding and cross reference information follow published grade 348 (UNS S34800) datasheets. Data is for guidance. Confirm every value against the current edition of the governing standard and against your project code before design or purchase.
Page reviewed , Jiangyin Jiangnan Metal Co., Ltd.