Data completeness: partial. Last verified 19 August 2026.
Designations
| Common name | 347 |
| UNS | S34700 |
| EN number | 1.4550 |
| Class | Austenitic stainless steel |
| Specified by | ASTM A240/A240M, EN 10088-2 |
347 is the niobium-stabilised counterpart to titanium-stabilised 321. Same idea, different carbide former, and the practical difference is in welding: niobium survives transfer across the arc where titanium largely does not, so 347 has a matching filler and 321 usually does not. That single fact decides most choices between them.
Properties, with what each one rests on
| Property | Value | Unit | Condition | Evidence | Source | Retrieved |
|---|---|---|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 220 | MPa | cold rolled coil and sheet, 20 °C | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Tensile strength Rm, minimum | 520 | MPa | cold rolled; datasheet gives a 520–720 range | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Elongation A, minimum | 40 | % | cold rolled; A and A80 both 40 | E3 | EN 10088-2 via Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| PREN | 18 | — | from typical composition, not from a heat | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Density | 7.9 | g/cm³ | 20 °C | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Modulus of elasticity | 200 | GPa | 20 °C | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Thermal conductivity | 15 | W/(m·K) | 20 °C | E3 | Outokumpu Core range datasheet — standard austenitic and ferritic stainless steels | 2026-08-20 |
| Elevated temperature strength | not established | — | — | — | the Core datasheet carries no elevated temperature table for this grade | — |
| Niobium content and the Nb:C ratio required for stabilisation | not established | — | — | — | set by the standard, which is paywalled | — |
| Composition limits | not established | — | — | — | ASTM A240 is paywalled; the datasheet gives typical values, which are not limits | — |
7 sourced values, 3 gaps named. Publishing the gaps is more useful than filling them from an aggregator that does not say where its numbers came from. The routes to filling them are the standard itself, a mill datasheet, or a mill certificate for your actual heat — which supersedes both at E5.
Where the numbers come from
PREN. 17.5% Cr, no molybdenum, no nitrogen gives 17.5 in the datasheet’s own formula, printed as 18. One point above 321 and level with 304 — a rounding difference, not a material one.
Why we do not just copy an aggregator. Because then this page would be a worse copy of MatWeb with no way for you to tell which rows to trust, and the one thing we have that MatWeb does not is the evidence column. Our coverage and its limits.
What 347 is usually chosen for
Welded pressure and high-temperature work where a matching stabilised filler is needed. Niobium transfers across the arc, so a 347 weld is stabilised too; that is why the grade dominates in power plant piping, superheater components and refinery service, and why ASME work tends to specify it over 321 for welded construction.
And what it is usually rejected for
Cost and hot cracking. Niobium is dearer than titanium and 347 is less widely stocked, so where the part is not welded, 321 usually wins on price and availability. Niobium-stabilised weld metal is also more prone to hot cracking than titanium-stabilised base material, which puts more weight on procedure qualification than a drawing note can carry.
The number to be more careful with than any of the above is the difference between a specified minimum and a typical value — a floor the standard guarantees, versus what a supplier’s production usually does. The full version, and the most expensive routine mistake in material data.
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What this page does not cover
- No elevated temperature values, which is the service most 347 is bought for.
- The niobium content and the stabilisation ratio are not established here.
- The ASTM plate minima are not established here.
- Fatigue, creep, fracture toughness and chloride stress corrosion cracking.
- The distinction between 347 and 347H, which is a carbon range set by the standard.
- Weld procedure guidance. The hot cracking tendency noted above is not sourced on this page and is not a design input.
Generated from data/materials/347.yaml. Regenerate rather than editing this file by hand — edits here are lost on the next build.