Stainless steel / UNS S34709
347H is the controlled high-carbon version of 347 for elevated-temperature pressure service, offering higher creep strength while keeping niobium stabilisation.
- UNS S34709
- Spec ASTM A240
- Density 7.96 g/cm³
Also known as / equivalents
| System | Designation |
|---|---|
| UNS | S34709 |
| Also known as | AISI 347H |
Chemical composition
| Element | Min % | Max % |
|---|---|---|
| C | 0.04 | 0.10 |
| Mn | — | 2.00 |
| P | — | 0.045 |
| S | — | 0.030 |
| Si | — | 0.75 |
| Cr | 17.0 | 19.0 |
| Ni | 9.0 | 13.0 |
| Nb | 8×C | 1.00 |
| Fe | Bal. | — |
Mechanical properties
| Property | Value |
|---|---|
| Tensile strength (min) | 515 MPa (74.7 ksi) |
| Yield strength, 0.2% offset (min) | 205 MPa (29.7 ksi) |
| Elongation in 50 mm (min) | 40 % |
| Hardness | 201 HB max |
Physical properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.96 g/cm³ | 0.288 lb/in³ |
| Magnetic response | Non-magnetic when annealed; may become slightly magnetic after cold work | — |
Available forms & specifications
| Form | Specification | Size range |
|---|---|---|
| Sheets, plates & coils | ASTM A240 / ASME SA240 | 0.3 mm – 6 mm |
| Seamless & welded pipe | ASTM A312 / ASME SA312 | 1/8" – 24" NB |
| Tubes | ASTM A213, A249, A269 | 1/8" – 24" NB |
| Bars & rods | ASTM A276, A479 | 3 mm – 500 mm |
| Flanges & forgings | ASTM A182 / ASME SA182 | 1/2" – 48" NB (larger on request) |
| Buttweld fittings | ASTM A403 / ASME SA403 | 1/2" – 48" NB |
| Fasteners | ASTM A193 / A194, F593 / F594 | M3 – M56 |
Corrosion & temperature resistance
Corrosion resistance rises with chromium, molybdenum and nitrogen: 304 handles general atmospheric and food-contact service, 316/317 add resistance to chlorides and pitting, 904L handles strong reducing acids, and stabilised 321/347 resist intergranular attack after welding or high-temperature exposure.
Applications
SS 347H: Superheater and reheater tubes, refinery piping. Process piping, tanks and vessels, heat exchangers, food, dairy and pharmaceutical equipment, architectural work and general engineering.
SS 347H vs SS 347
| SS 347H | SS 347 | |
|---|---|---|
| UNS | S34709 | S34700 |
| Key property | High-temperature niobium-stabilised grade | Niobium-stabilised |
| Typical use | Superheater and reheater tubes, refinery piping | Aircraft exhaust, refinery and boiler parts |
| Cr (wt %) | 17.0–19.0 | 17.0–19.0 |
| Ni (wt %) | 9.0–13.0 | 9.0–13.0 |
| Mo (wt %) | — | — |
| C (wt %) | 0.04–0.10 | ≤ 0.08 |
| Tensile / yield (min, MPa) | 515 / 205 | 515 / 205 |
Frequently asked questions
What is the UNS number of SS 347H?
SS 347H is designated UNS S34709.
What is SS 347H used for?
High-temperature niobium-stabilised grade. Typical uses: superheater and reheater tubes, refinery piping.
Is SS 347H magnetic?
Non-magnetic when annealed; may become slightly magnetic after cold work.
In which forms can I buy SS 347H from Rajkamal Metals?
Coils & Strips, Sheets & Plates, Pipes & Tubes, Round Bars & Rods, Structural Sections, Flanges, Buttweld Fittings, Socket Weld & Threaded Fittings, Fasteners, Ferrule / Instrumentation Fittings, Dairy Fittings, Dish Ends, SS Tanks, Custom Orders. Sizes as per standard; other sizes on request.
Do you supply a Mill Test Certificate with SS 347H?
Yes. Actual values are given in the Mill Test Certificate (EN 10204 3.1) supplied with each order.
What is the difference between SS 347H and SS 347?
SS 347H: high-temperature niobium-stabilised grade. SS 347: niobium-stabilised. See the comparison table on this page.
Last updated: 30 October 2026. Grade names identify the supply range; designations are not engineering equivalents. Availability, make, origin and documentation are confirmed at quotation.
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