347 Stainless Steel
An austenitic stainless steel stabilized with niobium
Typical values for the temper in the title
347 is an 18/8 austenitic stainless steel with added niobium. The niobium bonds with carbon before chromium can, preventing chromium carbides from forming at grain boundaries. Annealed, its tensile strength is 515–620 MPa.
Niobium does not burn off in the arc like titanium, so 347 is easier to weld, and ER347 filler is also used to weld 321. It is used in hot equipment, aircraft exhaust systems and the petrochemical industry.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 515–620 MPa | |
| Yield strength Rp0.2 | 205–310 MPa | |
| Elongation A | 40% | |
| Hardness | 160–190 HB | |
| Modulus of elasticity E | 200 GPa | |
| Density ρ | 7.96 g/cm³ | |
| Machinability | 42% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Cr chromium | 17.0–19.0 | the protective layer |
| Ni nickel | 9.0–13.0 | austenitic structure |
| Nb niobium | min 10×C, up to 1.00 | ties up carbon and prevents sensitization |
| C carbon | max 0.08 | |
| Mn manganese | max 2.00 | |
| Si silicon | max 0.75 | |
| Fe iron | balance |
Ranges per ASTM A240 (plate and sheet). Other product standards, and different editions of the standard, vary slightly. For purchasing, rely on the standard in the order.
Conditions and heat treatment
Like all austenitic stainless, it is not hardened by heat treatment. The normal delivery condition is annealed.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed | the normal condition: soft, ductile, most corrosion resistant | most applications |
| Cold worked (¼H to full hard) | much higher strength, slightly magnetic | strong springs, sheet and strip |
| Not hardenable by heat treatment | — | austenitic stainless strengthens only by cold work |
Applications
- Exhaust systems and manifolds
- Expansion joints
- Equipment working between 425 and 815 °C
- Heat exchangers and furnaces
- Aerospace engine components
Fabrication
Welding
Welds well, usually with ER347 filler.
Sensitization
In the range of about 425–815 °C, ordinary stainless forms chromium carbides at grain boundaries and becomes vulnerable to intergranular corrosion. Stabilization prevents this, so it suits prolonged service in that range.
Machining
Similar to 304: gummy and work hardening. Sharp tools and a steady feed.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 321 | 515–620 / 205–310 MPa | Excellent — Ti Stabilized | stabilized with titanium, more available · material page |
| 304 / 304L | 515–620 / 205–310 MPa | Good — ER308L | for room temperature, cheaper · material page |
| 310 / 310S | 515–620 / 205–310 MPa | Good — ER310 | for higher heat · material page |
Common mistakes
Using ordinary 304 for prolonged hot service
In the 425–815 °C range it becomes sensitive to intergranular corrosion. For such service, a stabilized grade or an H grade.
Assuming 304L is enough for hot service
304L solves the welding problem, but in prolonged heat it may also become sensitized, and its hot strength is lower.
Ordering without stating a condition
Products for hot service may require a stabilizing treatment or a specific condition. The drawing and standard are binding.
Equivalents, standards and supply
| EN | 1.4550 |
|---|---|
| DIN | X6CrNiNb18-10 |
| JIS | SUS347 |
| Standards | ASTM A240 / EN 10088-2 |
| Forms | plate · pipe |
| Producers | Outokumpu · Aperam · ThyssenKrupp · Valbruna |
Learn more
Values are typical and for comparison only. For design, rely on the standard and on the mill certificate. Sources: ASTM A240, ASTM A276 and EN 10088 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026