UNS S34709 (347H) Forgings to ASTM A182 F347H
Niobium stabilised austenitic stainless forgings for creep service above 550 °C. Rolled rings, flanges, shafts, discs and bars, open-die forged to drawing in Jiangyin, China.
UNS S34709 is the UNS number for 347H stainless steel, the high-carbon, niobium (columbium) stabilised version of 18Cr-10Ni austenitic stainless steel. In forged form it is listed as F347H in ASTM A182, the specification covering forged stainless piping components for pressure service.
Carbon is held at 0.04 to 0.10 %. Niobium locks that carbon up as stable niobium carbides before chromium can form chromium carbides, so the grade stays clear of sensitisation, while the raised carbon gives the coarse grain structure that creep and stress rupture strength above roughly 550 °C depends on.
Jiangyin Jiangnan Metal Co., Ltd. open-die forges UNS S34709 into seamless rolled rings, flanges, shafts, discs, sleeves, bushings, tube sheets and bars, delivered solution annealed with EN 10204 3.1 or 3.2 certification.
Chemical composition of UNS S34709 (F347H)
Composition limits applied to forgings under ASTM A182, identification symbol F347H, UNS S34709.
| Element | ASTM A182 F347H | Notes |
|---|---|---|
| Carbon, C | 0.04 to 0.10 | The carbon minimum is mandatory and is what makes this an H grade |
| Chromium, Cr | 17.00 to 20.00 | Tube specifications such as ASTM A213 TP347H narrow this to 17.00 to 19.00 |
| Nickel, Ni | 9.00 to 13.00 | |
| Manganese, Mn | 2.00 max | |
| Silicon, Si | 1.00 max | |
| Phosphorus, P | 0.045 max | |
| Sulfur, S | 0.030 max | |
| Niobium, Nb (Cb) | 8 x C to 1.00 (TP347H basis) | General 347H datasheets quote 0.32 to 1.00. Confirm the ratio required by the governing specification and its current edition |
| Iron, Fe | Balance, about 62.8 to 73.6 |
Composition data compiled from the ASTM A182 / A182M chemical requirements for F347H published by Ferrobend, the 347H (UNS S34709) grade datasheet published by AZoM, and the ASTM A213 TP347H niobium ratio published by XTD.
Mechanical properties
Two sets of figures circulate for this grade and they serve different purposes. Column A lists what the material has to meet to be accepted under ASTM A182 F347H. Column B lists typical published datasheet values for annealed 347H, which are useful for design reference. Note that the commonly quoted 480 MPa typical tensile figure sits below the 515 MPa ASTM acceptance minimum, so it cannot be used as an acceptance criterion on a purchase order.
| Property | A. ASTM A182 F347H minimum | B. Typical published value, 347H |
|---|---|---|
| Tensile strength | 515 MPa / 75 ksi min | 480 MPa / 69,600 psi |
| Yield strength, 0.2 % | 205 MPa / 30 ksi min | 205 MPa / 29,700 psi |
| Elongation, 2 in. (50 mm) or 4D | 30 % min | 29 % |
| Reduction of area | 50 % min | n/a |
| Hardness, Brinell | Not specified in A182 for F347H | 187 HB |
| Elastic modulus | n/a | 190 to 210 GPa (27,557 to 30,458 ksi) |
| Poisson's ratio | n/a | 0.27 to 0.30 |
| Stress rupture, 750 °C, 100,000 h | n/a | 38 to 39 MPa (5,510 to 5,660 psi) |
| Density | n/a | 7.7 to 8.03 g/cm³ (0.278 to 0.290 lb/in³) |
For solution annealed TP347H tube, ASTM A213 calls for 515 MPa tensile and 205 MPa yield with 35 % minimum elongation after a solution anneal at 1040 °C (1900 °F) minimum. That is a useful cross check when one project specification covers both forgings and tubing.
Why 347H rather than 347
Three things separate the H grade from standard 347, and they work together.
- Coarse grain is mandatory. The carbon minimum plus a high temperature solution anneal produce ASTM grain size No. 7 or coarser, which resists creep deformation and stress rupture under sustained load above 550 °C.
- Higher ASME allowable stresses. ASME Section I and Section VIII Division 1 assign higher allowable stress values to 347H than to 347 above roughly 550 °C, which lets the designer use a thinner wall for the same duty.
- Stabilisation and raised carbon at the same time. Unstabilised H grades such as 304H and 316H get the coarse grain but stay prone to sensitisation. The niobium in 347H holds off chromium carbide precipitation during fabrication while the carbon still delivers the creep performance.
Equivalent grades
| Standard | Designation |
|---|---|
| UNS, USA | S34709 |
| AISI / ASTM | 347H, A182 F347H for forgings, A213 and A312 TP347H for tube and pipe |
| EN / DIN | 1.4961 (1.4550 covers the base niobium stabilised composition) |
| ISO | X6CrNiNb18-10 |
| JIS, Japan | SUS347H, SUS347HTB for boiler tube under JIS G3463 |
| GB, China | 07Cr18Ni11Nb, old code S34779, and 06Cr18Ni11Nb in GB/T 13296 |
| GOST, Russia | 08Kh18N12B |
| SAE | 30347H |
Product standards listing 347H or S34709 include ASTM A182, A213, A240, A249, A271, A312, A336, A376, A403, A430, A479, A813 and A814, together with EN 10216-5 and EN 10217-7.
Forging, heat treatment, welding and machining
Hot working
Forging, upsetting and other hot work operations run at 1149 to 1232 °C (2100 to 2250 °F). The material is annealed and water quenched after hot work.
Solution annealing
The published annealing range is 1010 to 1193 °C (1850 to 2000 °F) followed by a water quench. For H-grade elevated temperature service, ASTM A213 sets a 1040 °C (1900 °F) minimum, and 1065 °C minimum is the safer figure to specify for reaching the required coarse grain. 347H does not respond to hardening heat treatment. Hardness and strength can only be raised by cold work.
Welding
347H welds by most fusion and resistance methods. Oxyacetylene welding is not recommended for this grade.
Machining
Machining is tougher than grade 304 because the alloy work hardens quickly. Run slow speeds with constant positive feeds, keep the setup rigid and the tooling sharp, and avoid dwelling in the cut.
Cold working
The grade is tough and ductile, and takes stamping, blanking, spinning and drawing readily.
UNS S34709 forged products
All items are open-die forged or ring rolled to customer drawing.
| Product form | Typical service |
|---|---|
| Seamless rolled rings, forged rings | Chemical processing, food processing equipment and storage, turbines, gearboxes |
| Forged flanges, tube sheets, forged tubes and pipes | Pressure vessels, air receivers, shell and tube heat exchangers, HRSG modules |
| Shafts, spindles, eccentric shafts, crankshafts, gears | Power transmission, gas compressors, turbines |
| Discs, disks, sleeves, bushings | Offshore and onshore oil production, subsea and deepwater systems, industrial air compressors, power and nitrogen generators |
| Valve bodies, stems, seat rings, valve blocks | Ball, gate, globe, check and plug valves, strainers |
| Nozzles, manifolds, forging rolls, custom blocks | Columns and towers, tanks, silos, preheaters, recuperators, process modules |
Where UNS S34709 is used
347H gets selected wherever an austenitic stainless has to hold load at red heat without sensitising. Documented application areas include:
- Power station boilers. Superheater and reheater components in supercritical and ultra-supercritical units, where the higher allowable stresses permit thinner walls than standard 347.
- Petroleum refining. Heater coils and radiant and convection section components in atmospheric and vacuum distillation and catalytic reforming furnaces running continuously at 600 to 800 °C, plus fluid catalytic cracking units and polythionic acid service.
- Heat recovery steam generators in combined cycle plants subject to rapid thermal transients.
- Hydrocarbon processing transfer lines between reactors and fractionators in delayed coking and visbreaking units, where carburisation resistance matters.
- High temperature pressure vessels to ASME Section VIII in sulfur recovery and thermal oxidation units.
- Chemical, pharmaceutical and food processing equipment, waste heat recovery and recuperators.
Manufacturing route, testing and certification
- Melting. EAF plus VOD. ESR remelt available where the specification or the customer calls for it.
- Delivery standard. ASTM A182 F347H. Other product standards quoted on request.
- Heat treatment. Solution annealed and water quenched. No ageing treatment, since the grade is not precipitation hardenable.
- Ultrasonic testing. EN 10228-3, SEP 1921 or ASTM A388, acceptance class to customer specification.
- Certification. EN 10204 3.1, or 3.2 with third party witness such as TUV, BV, LR, DNV or SGS.
- Supplementary testing on request. Grain size to ASTM E112, intergranular corrosion to ASTM A262, PMI, impact testing, hardness survey.
Request a quotation
UNS S34709 forgings are made to order, so price follows the drawing, the finished weight, the quantity, the heat treatment condition and the certification level. Send the drawing or the finished dimensions, the governing specification and its edition, the quantity and the certification level required, and we will come back with a weight estimate, price and lead time. If you have the application and operating temperature but no drawing yet, send those instead and we will advise whether 347H, 321H, 304H or a nickel alloy suits the duty better.
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Frequently asked questions
What is UNS S34709?
Is UNS S34709 the same as 310H?
What is the difference between 347 and 347H?
What are the minimum mechanical properties of ASTM A182 F347H forgings?
Can UNS S34709 be hardened by heat treatment?
What is the solution annealing temperature for 347H?
At what temperature is 347H hot worked?
What are the equivalent grades of UNS S34709?
Which forged products are available in UNS S34709?
Is 347H difficult to machine?
How is UNS S34709 quoted?
Related stainless forging grades
Other stabilised and high temperature stainless grades we forge: A182 F347, AISI 347H, A182 F321, AISI 330, 904L, A182 F44, A182 F51, A182 F55, Incoloy 800H, Inconel 625.
Page revised by the technical sales department, Jiangyin Jiangnan Metal Co., Ltd. Values on this page are compiled from ASTM A182 / A182M F347H requirements, ASTM A213 TP347H and published 347H (UNS S34709) grade datasheets. They are given for reference. Verify against the current edition of the governing specification and against the mill certificate supplied with your order.