Unifit Fastener is a trusted manufacturer, stockist and exporter of Stainless Steel 347 / 347H fasteners especially designed for the high temperature and corrosive environment of the world. The chromium-nickel stainless steel of grade 347 is an austenitic type of steel which is stabilised with niobium and tantalum (columbium) to prevent the precipitation of chromium-carbides that cause intergranular corrosion after welding. The 347H variant has a controlled higher carbon range (0.04-0.10%) to increase creep and stress-rupture strength for extended use at temperatures from 800°F to 1500°F (427-816°C). All Unifit fasteners, including hex bolts, stud bolts and socket screws, hex nuts, plain washers, spring washers and threaded rods, are manufactured from mill traceable raw material, precision cold formed and/or machined and packaged with EN 10204 3.1 documentation. Ready stock, tight dimensional control and global logistics help you avoid downtime and hit on-time delivery, whether you are specifying fasteners for a heat exchanger in a refinery, a power-plant superheater or a petrochemical reactor.
Request a QuoteStainless Steel 347/347H fasteners belong to the stabilised austenitic family. The deliberate addition of columbium (Nb + Ta) gives them a decisive advantage over standard 304 and 304L grades in applications where components are repeatedly heated into the carbide-precipitation range. This makes the grade a default choice for chemical, oil-and-gas and thermal-power assemblies that must remain leak-tight and corrosion-free across thousands of thermal cycles.
| Parameter | Specification |
|---|---|
| Grades | SS 347, SS 347H |
| UNS No. | S34700 (347) / S34709 (347H) |
| Werkstoff Nr. | 1.4550 (347) / 1.4961 (347H) |
| Governing Standards | ASTM A193 / A194, ASME SA193 / SA194, DIN, EN, JIS, BS, ISO |
| Size Range | M3 – M100 | 3/16" – 4" | custom sizes |
| Length | 3 mm – 200 mm and above (made to order) |
| Thread Type | UNC, UNF, BSW, BSF, Metric coarse & fine, or as required |
| Product Forms | Bolts, screws, nuts, washers, studs, threaded rods |
| Surface / Coating | Self-colour, passivated, PTFE, zinc, black oxide, xylan (on request) |
| Inspection | EN 10204 3.1 / 3.2 mill test certificate |
| Grade | C | Mn | Si | P | S | Cr | Nb (Cb) | Ni | Fe |
|---|---|---|---|---|---|---|---|---|---|
| 347 | 0.08 max | 2.0 max | 1.0 max | 0.045 max | 0.030 max | 17.0–20.0 | 10×C–1.10 | 9.0–13.0 | Bal. |
| 347H | 0.04–0.10 | 2.0 max | 1.0 max | 0.045 max | 0.030 max | 17.0–19.0 | 8×C–1.10 | 9.0–13.0 | Bal. |
Note: Columbium is added at a ratio pegged to carbon content, which is what gives 347/347H its signature resistance to carbide precipitation.
| Density | Melting Point | Tensile Strength | Yield Strength (0.2%) | Elongation |
|---|---|---|---|---|
| 8.0 g/cm³ | 1454 °C (2650 °F) | 515 MPa (75,000 psi) min | 205 MPa (30,000 psi) min | 35% min |
| Standard | Werkstoff Nr. | UNS | JIS | GOST | EN |
|---|---|---|---|---|---|
| SS 347 | 1.4550 | S34700 | SUS 347 | 08Ch18N12B | X6CrNiNb18-10 |
| SS 347H | 1.4961 | S34709 | SUS 347H | — | X6CrNiNb18-12 |
| Criterion | SS 347 | SS 347H |
|---|---|---|
| Carbon content | 0.08% max | 0.04–0.10% (controlled higher) |
| Primary strength | General corrosion resistance | Creep & stress-rupture strength |
| Best service window | Ambient to moderate heat | Sustained 800–1500°F (427–816°C) |
| Grain size control | Standard | Coarser, specified for high-temp creep |
| Typical use | Chemical & general process fasteners | Superheaters, reformers, high-temp bolting |
Quick rule of thumb: Choose 347 for corrosion-driven service and 347H when your bolting must hold clamp load at red-heat temperatures for years.
The stabilised chemistry of 347/347H makes it the go-to fastener grade wherever heat, pressure and aggressive media meet. Typical sectors include:
| Industry | Typical Use |
|---|---|
| Oil & gas | wellheads, pipelines and offshore structures |
| Petrochemical & refineries | reactors, columns and heat exchangers |
| Power generation | boilers, superheaters and turbine assemblies |
| Chemical processing | reactors, tanks and pressure vessels |
| Pulp & paper | plants and digesters |
| Food & pharmaceutical | processing equipment |
| Aerospace | exhaust / high-temperature systems |
| Desalination, sugar mills and fertiliser plants | heat, pressure and aggressive media assemblies |
Every Unifit 347/347H fastener passes through a controlled production route — wire drawing, cold heading or CNC machining, thread rolling, solution annealing, passivation, inspection and packing. Quality is verified through a combination of destructive and non-destructive methods:
Manufactured and inspected to ASTM A193 / A194, ASME SA193 / SA194, DIN, EN, JIS, BS and ISO. Material dispatched with EN 10204 3.1 test reports; third-party inspection (Lloyd's, BV, DNV, SGS) available on request.
Pricing depends on grade, size, quantity, thread type and coating. The reference figures below are indicative FOB values — request a formal quote for your exact specification.
| Product | Indicative Price (per pc / per kg)* |
|---|---|
| SS 347/347H Hex Bolts | from USD 6.50 / pc • USD 2.0–10.0 / kg |
| SS 347/347H Hex Nuts | from USD 1.30 / pc |
| SS 347/347H Machine Bolts | from USD 5.60 / pc |
| SS 347/347H Allen (Socket) Bolts | from USD 5.25 / pc |
| SS 347/347H Stud Bolts & Washers | on request |
*Indicative only. Live pricing varies with nickel/LME movement, size and order volume. Contact us for a firm quotation.
Because most orders travel through multiple handling points before reaching site, we protect every consignment with export-grade packing: wooden boxes, pallets, carton boxes, shrink-wrapping and wooden crates — labelled and documented for hassle-free customs clearance. We regularly export across the Middle East, Europe, North America, Africa, Southeast Asia and Oceania.
Both are niobium-stabilised austenitic stainless steels. The key difference is carbon: 347H holds a controlled higher carbon range (0.04–0.10%), which improves creep and stress-rupture strength for sustained high-temperature service. Grade 347 is preferred where corrosion resistance is the priority rather than long-term strength at red-heat temperatures.
Niobium (with tantalum) preferentially combines with carbon to form stable niobium carbides. This prevents chromium from tying up as chromium carbide at grain boundaries during welding or high-temperature exposure, so the steel resists intergranular corrosion — a failure mode that affects non-stabilised grades like 304.
SS 347H is designed for continuous service roughly between 800°F and 1500°F (427–816°C), with good oxidation resistance up to about 1500°F. This makes it a common choice for superheaters, reformers and other hot bolting applications.
Our fasteners are manufactured to ASTM A193/A194, ASME SA193/SA194, and international standards including DIN, EN, JIS, BS and ISO. Every order can be supplied with EN 10204 3.1 mill test certificates and, if required, third-party inspection.
We supply M3 to M100 and 3/16" to 4" in bolts, nuts, washers, studs, screws and threaded rods, in lengths from 3 mm upward. Custom sizes, threads and coatings are made to order.
Yes. Standard supply includes EN 10204 3.1 documentation with heat traceability. We also perform PMI, chemical, mechanical, IGC and NDT testing, and can arrange 3.2 / third-party certification on request.
In the fully annealed austenitic condition they are essentially non-magnetic. Cold working (such as thread rolling) can induce slight magnetism, which is normal and does not affect grade compliance.
Send us your size list and drawing — get a same-day quote, ready-stock availability and a test-certificate sample from the Unifit Fastener team.
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