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Nb-stabilized austenitic stainless steel for high-temperature service up to 870°C. AISI 347 / UNS S34700 / EN 1.4550. Cold-rolled sheets, hot-rolled plates, and coils — factory direct from China.
Nb-stabilized austenitic grade for high-temperature applications
347 stainless steel (UNS S34700, EN 1.4550) is an austenitic chromium-nickel stainless steel stabilized with niobium (columbium) and tantalum. The addition of niobium — typically 10× the carbon content — prevents chromium carbide precipitation at grain boundaries during welding or exposure to 425–870°C, a phenomenon known as sensitization.
This stabilization makes 347 the preferred alternative to 321 in many high-temperature applications, offering better overall corrosion resistance and weldability. It is generally not recommended for cryogenic service (use 304/304L instead).
Continuous service up to 870°C (1600°F). Intermittent service up to 925°C.
Nb stabilization prevents weld decay. No sensitization after welding in 425–870°C range.
Fusion welding excellent. No post-weld annealing required. ER347 / E347 recommended filler metals.
Heat exchangers, boiler tubes, refinery equipment, aircraft exhaust systems, chemical processing.
Generally non-magnetic in annealed condition. May become slightly magnetic after cold working or welding.
UNS S34700 · EN 1.4550 · JIS SUS 347 · GB 0Cr18Ni11Nb · W.Nr. 1.4550
Cross-reference across major international standards
| Standard | Grade / Designation | Notes |
|---|---|---|
| ASTM / AISI | 347 | Base grade |
| UNS (Unified Numbering System) | S34700 | UNS designation |
| AMS (Aerospace) | AMS 5512, AMS 5646 | Sheet, bar & forging |
| EN (Europe) | X6CrNiNb18-10 | EN 10088-1 / EN 1.4550 |
| WERKSTOFF (Germany) | 1.4550 | Werkstoff Number |
| JIS (Japan) | SUS 347 | Japanese Industrial Standard |
| GB (China) | 0Cr18Ni11Nb (old) / 06Cr18Ni11Nb (new) | GB/T 4237 |
| GOST (Russia) | 08Kh18N12B | GOST 5632 |
| BS (UK) | 347S31 | BS 970 Part 1 |
| AFNOR (France) | Z6CNNb18-10 | NF A35-574 |
| ISO | X6CrNiNb18-10 | ISO 15510 |
Source: ASTM A240 / ASME SA-240 · EN 10088-1 · JIS G4303 · GB/T 4237 · ASM Handbook Vol.1
Per ASTM A240 / ASME SA-240 specification
| Element | 347 (S34700) | 347H (S34709) | Notes |
|---|---|---|---|
| Carbon (C) | ≤ 0.08% | 0.04 – 0.10% | 347H has higher C for creep strength |
| Chromium (Cr) | 17.0 – 19.0% | 17.0 – 19.0% | Corrosion resistance |
| Nickel (Ni) | 9.0 – 13.0% | 9.0 – 13.0% | Austenite stabilizer |
| Niobium (Nb) | ≥ 10×C, ≤1.00% | ≥ 8×C, ≤1.00% | Stabilization element |
| Manganese (Mn) | ≤ 2.00% | ≤ 2.00% | |
| Silicon (Si) | ≤ 0.75% | ≤ 0.75% | |
| Phosphorus (P) | ≤ 0.045% | ≤ 0.045% | |
| Sulfur (S) | ≤ 0.030% | ≤ 0.030% | |
| Tantalum (Ta) | Part of Nb content (Ta+Nb ≤ 1.00%) | Present with Nb | |
Room-temperature properties in annealed condition (ASTM A240)
| Property | Value |
|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa (75 ksi) |
| Yield Strength (Rp0.2) | ≥ 205 MPa (30 ksi) |
| Elongation (A50mm) | ≥ 35% |
| Hardness (Brinell) | ≤ 201 HB |
| Hardness (Rockwell B) | ≤ 92 HRB |
| Property | Value |
|---|---|
| Density | 7.96 g/cm³ (0.288 lb/in³) |
| Melting Point | 1400–1450°C (2550–2640°F) |
| Thermal Conductivity (100°C) | 16.3 W/m·K |
| Thermal Expansion (0–100°C) | 16.0 × 10⁻ /K |
| Specific Heat Capacity | 500 J/kg·K |
| Electrical Resistivity | 0.73 µΩ·m |
| Modulus of Elasticity | 200 GPa (29 × 10 psi) |
Source: ASTM A240 · ASME SA-240 · ASM Handbook Volume 1 · EN 10088-1
347 is an austenitic stainless steel — proper heat treatment is critical
| Process | Temperature | Purpose | Notes |
|---|---|---|---|
| Solution Annealing | 980–1150°C (1800–2100°F), rapid cooling (water quench for thin sections) | Dissolve carbides, restore corrosion resistance after welding | Standard mill practice. Do NOT air cool heavy sections. |
| Stress Relieving | 850–900°C (1560–1650°F), followed by slow cooling | Reduce residual stresses from cold working or welding | Less effective than solution annealing for carbide dissolution. |
| Stabilization Annealing | 870–900°C (1600–1650°F), 1–4 hours, air cool | Ensure Nb(C,N) precipitation before exposure to sensitization range | Performed before service in 425–870°C range. Prevents subsequent sensitization. |
| ❌ Quenching & Tempering | NOT APPLICABLE — 347 is austenitic, not martensitic. No phase transformation on cooling. | ||
| ❌ Age Hardening | NOT APPLICABLE — 347 is not a precipitation-hardening grade. Use 17-4PH for age-hardenable stainless. | ||
Source: ASM Handbook, Volume 4: Heat Treating · ASTM A240 · NACE MR0175
Side-by-side comparison to help you select the right grade
| Property | 347 (S34700) | 321 (S32100) | 304 (S30400) | 316L (S31603) | 310S (S31008) | 17-4PH (S17400) |
|---|---|---|---|---|---|---|
| Max Service Temp | 870°C (continuous) | 870°C | 870°C (intermittent only) | 870°C (intermittent) | 1150°C | 300°C (max use) |
| Stabilization | Nb (Niobium) | Ti (Titanium) | None (L grade: low C) | None (low C) | None | Precipitation hardening |
| Weldability | Excellent | Good (Ti can cause slag issues) | Excellent (use 308L filler) | Excellent (use 316L filler) | Good | Good (requires preheat) |
| Intergranular Corrosion After Welding | ✅ Resistant (Nb stabilized) | ✅ Resistant (Ti stabilized) | ❌ Sensitizes (unless 304L) | ✅ Resistant (low C) | ✅ Resistant | ✅ Resistant |
| Pitting Corrosion (PREN) | ~18–20 | ~18–20 | ~18–20 | ~24–26 | ~25 | ~16 |
| Magnetic | Generally No* | Generally No* | No | No | No | Yes (magnetic in aged condition) |
| Relative Price | $$$ | $$$ | $ | $$ | $$$$ | $$$$ |
| Best Application | High-temp + welding (425–870°C) | High-temp + welding (lower cost than 347) | General purpose, indoor, non-high-temp | Marine, chemical, chloride environment | Extreme high-temp (furnace parts) | High-strength structural, not high-temp |
*May become slightly magnetic after heavy cold working or welding.
Not sure which stainless steel grade fits your application? Follow this decision flow.
Sheets, plates, and coils — custom cut to your specifications
Thickness: 3–150mm · Width: 1000–2500mm · ASME SA240
Nb-stabilized plate for pressure vessels and heat exchangers. High-temperature service up to 870°C. Mill edge or slit edge. MTC included.
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Thickness: 0.05–8.0mm · Surface: 2B/BA/No.4/8K · AISI 347
Precision cold-rolled sheets with excellent surface finish. Ideal for fabricated components, heat shields, and welded assemblies. Custom cut to size.
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Thickness: 0.03–8.0mm · ID: 508/610mm · Slitting available
Coils for heat exchanger tubing, welded pipe production, and chemical tank fabrication. Tight thickness tolerance. DIN/EN/ASTM standards.
View Specifications →15+ years of experience supplying stainless steel to 60+ countries
100% mill test certificate (MTC) per EN 10204 3.1/3.2. Third-party inspection (SGS/TÜV/BV) available at buyer's request.
Standard sizes ex-stock. Custom orders: 7–20 days. Expedited production available for urgent projects.
Dimension, surface, PMI (positive material identification), and packaging inspection before every shipment.
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Answers to the most common questions from buyers and engineers
Both are stabilized austenitic grades for high-temperature service. 321 uses titanium (Ti) as the stabilizing element, while 347 uses niobium (Nb/columbium). Key differences:
Continuous service: up to 870°C (1600°F). Intermittent service: up to 925°C (1700°F). Below 425°C, 304/304L is usually more economical. Above 925°C, consider 310S/310H.
The key advantage of 347 is that it resists sensitization in the 425–870°C range, which is the exact temperature range where unstabilized grades (304/304H) would lose corrosion resistance after welding.
347 is generally non-magnetic in the annealed (solution-treated) condition. However:
347 can be used at cryogenic temperatures (it retains toughness down to liquid nitrogen temperatures, −196°C), but 304/304L is more commonly specified for cryogenic service because:
For welding 347 base metal:
Important: If welding 347 to 304/316, you can use ER309L (austenitic, high Cr/Ni) as a barrier layer to avoid dilution issues, then cap with ER347. Always consult your welding procedure specification (WPS).
347H (UNS S34709) is the high-carbon version of 347:
Huaxiao can supply both grades. Specify "347H" in your inquiry if your design requires higher creep strength or compliance with ASME boiler code.
Visual identification is unreliable. Use one of these methods:
Huaxiao provides MTC with every shipment. PMI testing before shipment is available on request.
Approximate relative price (base: 304 = 1.0x):
Prices fluctuate with nickel market. Contact Huaxiao for current FOB China pricing. We offer volume discounts for orders above 5 tons.
Yes. Huaxiao can arrange EN 10204 3.2 certification (inspection by third-party agency such as TÜV, SGS, BV, or DNV) on request. This is commonly required for:
Note: 3.2 certification incurs additional cost and lead time (typically +7–10 days). Please specify this requirement when requesting a quote.
Huaxiao's MOQ depends on product form:
For trial orders or small projects, contact us — we maintain a stock of common sizes and may be able to accommodate lower quantities.
Indicative FOB China pricing — contact us for firm quote
| Product Form | Size Range | Indicative Price (FOB China) | Lead Time |
|---|---|---|---|
| Cold Rolled Sheet (2B) | 0.5–3.0mm × 1219mm | $3,800 – $4,600 / ton | Ex-stock / 7 days |
| Hot Rolled Plate | 6–50mm × 1500–2500mm | $3,500 – $4,200 / ton | Ex-stock / 10 days |
| Cold Rolled Coil | 0.3–3.0mm × 1219mm | $3,900 – $4,700 / ton | Ex-stock / 7 days |
| 347H (high carbon) | All forms | + 8–15% vs standard 347 | 10–20 days |
Specify your grade (347/347H), dimensions, quantity, and destination port. Our technical team will respond with firm pricing and lead time.
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