347 Stainless Steel
347 stainless steel is a stabilized austenitic grade designed for welded parts and high-temperature exposure. It uses niobium (Nb) to help reduce the risk of intergranular corrosion after welding or long heat cycles.
In practice, 347 is often selected when a project needs 304-like fabrication with better stability at heat. For long continuous service above about 600°C, many engineers move to 347H for stronger creep resistance.
Stabilization
Niobium (Nb)
Helps protect welded zones during high-temperature exposure.
Typical heat limit
Up to ~870°C
Continuous service depends on design and environment.
Common equivalents
SUS347 / 1.4550
Confirm by your governing standard and product form.
Magnetism
Non-magnetic (annealed)
Slight magnetism may appear after cold work.
347 is widely used in industries that run hot equipment and welded assemblies. It is often chosen for parts that see repeated heating and cooling, where standard grades may lose corrosion stability near welds.
- Refinery and petrochemical: hot piping, manifolds, reformer-related parts
- Heat exchangers and boilers: tubes, headers, and hot-side components
- Thermal processing: furnace parts, covers, expansion joints
- Power generation: exhaust components and hot gas handling
- Chemical equipment: tanks and dryers in moderate-temperature acid service
Equivalents help cross-check drawings and certificates. For purchasing, always write the order to the target standard and product form.
| System | Designation | Note |
|---|---|---|
| ASTM / AISI | 347 | Common U.S. grade name |
| JIS | SUS347 | Japanese designation |
| UNS | S34700 | Common ID used on MTC |
| EN | 1.4550 | European equivalent often specified in projects |
| DIN / ISO style | X6CrNiNb18-10 | Format used in technical documents |
| GOST / GB | 08Х18Н12Б / 06Cr18Ni11Nb | Regional equivalents seen in some markets |
- Weld stability: niobium stabilization helps reduce sensitization risk after welding.
- Heat resistance: strong oxidation and scaling resistance in elevated temperature service.
- Thermal cycling: performs well under repeated heating and cooling.
- Fabrication: commonly formed and welded with standard shop practices.
The values below follow common limits used in 347 specifications. Always confirm the delivered chemistry on the Mill Test Certificate.
| Element | Typical limit / range | Role |
|---|---|---|
| C | ≤ 0.08% | Controls weld behavior and sensitization risk |
| Cr | 17.0–19.0% | Base corrosion and oxidation resistance |
| Ni | 9.0–13.0% | Toughness and austenitic structure stability |
| Nb + Ta | 10×C min to 1.0% max | Stabilizes carbon to support weld and heat stability |
| Mn / Si | Mn ≤ 2.0%, Si ≤ 1.0% | Supports processing and deoxidation control |
| P / S | P ≤ 0.045%, S ≤ 0.03% | Impurity control for quality consistency |
| Fe | Balance | Base metal |
Properties vary by thickness and product form. For design, use code tables and your governing specification.
| Property | Typical value | Note |
|---|---|---|
| Tensile strength | ≥ 520 MPa | Common reference for sheet/plate |
| Yield strength (0.2%) | ≥ 205 MPa | Annealed reference |
| Elongation | ≥ 40% | Supports forming and fabrication |
| Hardness (HRB) | ≤ 95 | Reference value; confirm by your standard |
347 is designed for hot service where weld stability matters. The stabilized chemistry helps reduce intergranular corrosion risk after welding or exposure in the sensitization temperature range.
- Oxidation resistance: suitable for continuous service up to about 870°C in many conditions.
- Intergranular corrosion control: improved stability after welding and heat exposure.
- When to consider 347H: for continuous service above ~600°C where stronger creep resistance is needed.
347 is available in many industrial forms. Supply depends on tolerance, finish, testing, and project documentation. If you share your standard and size list, LYH Steel can advise a workable supply route.
| Form | Typical size range | Notes |
|---|---|---|
| Sheet (cold rolled) | Thickness 0.3–6.0 mm, width 1000–2000 mm | Common for fabrication and cladding |
| Plate (hot rolled) | Thickness 3–100 mm, width 1000–2000 mm | Pressure parts and heavy equipment |
| Cold-rolled coil | Thickness 0.3–6.0 mm, width 1000–2000 mm | Slitting and cut-to-length available |
| Hot-rolled coil | Thickness 3–14 mm, width 1000–2000 mm | Thicker coils for industrial use |
| Strip | Width 7–600 mm, thickness 0.3–10 mm | Parts, clamps, and formed items |
| Seamless pipe | OD ≤ 610 mm, WT 1–100 mm | Specify NDT and hydrotest if required |
| Welded pipe | OD 6–3000 mm, WT 1–100 mm | Good option for large diameter projects |
| Round bar | Dia 1–200 mm, length 100–12000 mm | Machining and hot-duty components |
| Flat bar / angle / channel / H beam | Flat 20–800 mm; Angle 20–250 mm; Channel 50–400 mm; H 100–1000 mm | For frames and structural support |
347 is generally easy to form and weld. In many shop conditions, it does not require preheating. Post-weld heat treatment is not needed in most standard fabrication, but follow your project code if it is a pressure part.
- Welding: common methods such as TIG, MIG, and SMAW are widely used.
- Forming: good ductility; plan for work hardening on heavy forming.
- Machining: similar to 304/321; use sharp tooling and stable feeds.
- Finishing: compatible with pickling, passivation, and polishing when specified.
Both grades share the same stabilized chemistry. The main difference is carbon content, which impacts strength at high temperature.
| Topic | 347 | 347H |
|---|---|---|
| Carbon limit | ≤ 0.08% | 0.04–0.10% |
| High-temperature strength | Good | Excellent |
| Creep resistance | Moderate | Superior |
| Typical temperature limit | ≤ 870°C | ≤ 925°C |
| Common use | General hot service, welded parts | Pressure parts, superheaters, refinery equipment |
Use these internal tools to confirm equivalents, estimate weight, and plan tolerances before you issue an RFQ.
Why is 347 stainless steel used for welded parts?
347 is stabilized with niobium. This helps reduce carbide issues after welding and improves resistance to intergranular corrosion in heat-affected zones.
Can 347 replace 304 in most applications?
In many cases, yes. 347 often performs similarly to 304 in general corrosion, but it provides better stability for welded and high-temperature duty.
What is the difference between 321 and 347?
Both are stabilized grades. 321 uses titanium, while 347 uses niobium. 347 is often selected when long heat exposure is a key risk.
Why is 347H popular for high-temperature service?
347H has higher carbon content, which supports stronger creep resistance and better long-term strength in continuous service above about 600°C.
Is 347 stainless steel magnetic?
In the annealed condition, it is generally non-magnetic. Cold work can introduce slight magnetism.