SS347 is an austenitic stainless steel like 304 with niobium added. Niobium ties up carbon so the steel keeps its corrosion resistance after welding and in service at about 425–850 °C. It is used for high-temperature pipes, exhaust and heater parts, and welding filler, and is often preferred to SS321 where welds must be strong.
Quick facts
- Type
- Niobium-stabilised austenitic stainless steel
- Key addition
- Niobium, at least 10 × carbon, max about 1%
- Service temperature
- Good up to about 800–850 °C
- Corrosion
- Similar to 304
- Magnetic
- No (annealed)
- Weldability
- Good
Equivalent grades
| Standard | Grade |
|---|---|
| AISI / ASTM | 347 |
| EN | 1.4550 (X6CrNiNb18-10) |
| UNS | S34700 |
| JIS | SUS347 |
Equivalents are close, not identical. Name the grade and standard on the drawing.
Typical chemical composition
| Element | % |
|---|---|
| Carbon (C) | 0.08 max |
| Chromium (Cr) | About 17–19 |
| Nickel (Ni) | About 9–13 |
| Niobium (Nb) | 10 × C min, about 1 max |
Values are typical. The exact limits depend on the standard and supplier; ask for the mill test certificate when it matters.
SS347 or SS321?
| SS347 | SS321 | |
|---|---|---|
| Stabiliser | Niobium | Titanium |
| Loses stabiliser in welding | Less | More (titanium oxidises) |
| Typical use | Welded high-temperature parts | Exhausts, bellows |
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Questions
- Why add niobium to stainless steel?
- Niobium bonds with carbon first, so chromium carbides do not form when the steel is heated, keeping welds and hot parts corrosion resistant.
- What is 347H?
- A higher-carbon version for better strength at high temperature, used in boiler and refinery pressure parts.
- Is SS347 magnetic?
- Not when annealed; it can become slightly magnetic after heavy cold work.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 23 October 2026.