STAINLESS STEEL 347 AND 347H — TECHNICAL DATASHEET AND METALLURGICAL REPORT
Stainless Steel 347 (UNS S30400 / W.Nr. 1.4550) is a stabilized, chromium-nickel austenitic stainless steel developed to solve the localized degradation issues associated with standard 18-8 class stainless steels. By incorporating niobium (columbium) and tantalum as strong carbide-forming agents, this material maintains metallurgical stability and corrosion resistance after exposure to temperatures within the sensitizing range.
The high-carbon variant, Grade 347H (UNS S30709 / W.Nr. 1.4940 / W.Nr. 1.4961), is formulated with a higher carbon range to optimize creep-rupture properties and high-temperature mechanical strength, making it suitable for long-term pressure vessel and structural installations.
■ Global Classifications and Standard Specifications
The equivalent specifications of Grade 347 and 347H across different international standard bodies represent a unified family of stabilized high-temperature alloys, supporting a comprehensive wrought, cast, and welding-consumable supply matrix.
| Standard Body | Grade 347 (UNS S34700) Equivalent | Grade 347H (UNS S34709) Equivalent |
|---|---|---|
| Werkstoff Number (W.Nr.) | 1.4550 | 1.4940 (sheet/strip) / 1.4961 (forgings) |
| European Norm (EN) | X6CrNiNb18-10 | X6CrNiNb18-12 |
| Japanese Industrial Standards (JIS) | SUS 347 | SUS 347H |
| British Standards (BS) | 347S31 / 347S17 | 347S17 |
| Chinese National Standard (GB) | 06Cr18Ni11Nb | 1Cr18Ni11Nb |
| Russian GOST | 08Kh18N12B | — |
| ASTM / ASME Casting Standards | CF8C | CF8C |
■ Chemical Composition and Stabilization Limits
The thermodynamic stabilization of Grade 347 relies on the addition of niobium and tantalum. Niobium forms highly stable niobium carbides (NbC) at higher temperatures than chromium carbides, effectively tieing up interstitial carbon within the grain interiors and preventing boundary passivity depletion.
| Element | ASTM A240 UNS S34700 (347 Flat-Rolled) % | ASTM A240 UNS S34709 (347H Flat-Rolled) % | ASTM A182 UNS S34700 (F347 Forgings) % | ASTM A182 UNS S34709 (F347H Forgings) % |
|---|---|---|---|---|
| Carbon (C) | ≤ 0.08 | 0.04 − 0.10 | ≤ 0.08 | 0.04 − 0.10 |
| Chromium (Cr) | 17.00 − 19.00 | 17.00 − 19.00 | 17.00 Extracted − 19.00 | 17.00 − 20.00 |
| Nickel (Ni) | 9.00 − 13.00 | 9.00 − 13.00 | 9.00 − 13.00 | 9.00 − 13.00 |
| Niobium + Tantalum (Nb+Ta) | 10 × C min / 1.00 max | 8 × C min / 1.00 max | 10 × C min / 1.10 max | 8 × C min / 1.10 max |
| Manganese (Mn) max | 2.00 | 2.00 | 2.00 | 2.00 |
| Silicon (Si) max | 0.75 | 0.75 | 1.00 | 1.00 |
| Phosphorus (P) max | 0.045 | 0.045 | 0.045 | 0.045 |
| Sulfur (S) max | 0.030 | 0.030 | 0.030 | 0.030 |
| Iron (Fe) | Balance | Balance | Balance | Balance |
■ Proprietary Datasheet Download
For principal piping specialists, boiler design engineers, and procurement inspectors requiring finite element stress boundaries, dynamic scaling rates, and multi-lot mill validation records, the unified datasheet must be accessed.
Alloy 347 / 347H — Complete Technical Yield & Structural Capacity Datasheet
Contains empirical data for stress simulations, international regulatory compliance audits, and ASTM A262 Practice E validation logs. Corporate credentials required.
⬇ DOWNLOAD DATASHEET■ Physical, Thermal, and Electromagnetic Properties
Owing to its stable face-centered cubic matrix, Grade 347 exhibits low thermal conductivity (about 30% that of plain carbon steels) and high thermal expansion rates, which introduces unique thermal strain profiles under high thermal loads.
| Property Parameter | Metric Unit (SI) | Imperial Unit (US Customary) |
|---|---|---|
| Density (at 20°C) | 7.96 g/cm³ | 0.288 lb/in³ |
| Melting Range Limits | 1398°C − 1446°C | 2550°F − 2635°F |
| Specific Heat Capacity (0−100°C) | 500 J/kg·K | 0.120 Btu/lb·°F |
| Electrical Resistivity (at 20°C) | 72 μΩ·cm | 28.4 μΩ·in |
| Modulus of Elasticity (Tension, 20°C) | 193 GPa | 28.0 × 10⁶ psi |
| Modulus of Elasticity (Tension, 400°C) | 172 GPa | 24.9 × 10⁶ psi |
| Modulus of Elasticity (Torsion, 20°C) | 77 GPa | 11.2 × 10³ ksi |
| Poisson's Ratio | 0.27 − 0.30 | 0.27 − 0.30 |
| Thermal Conductivity (at 20°C) | 15.0 W/m·K | 104 Btu·in/hr·ft²·°F |
| Mean Coeff. of Linear Thermal Expansion (20−100°C) | 16.0 × 10⁻⁶ K⁻¹ | 8.9 × 10⁻⁶ /°F |
| Mean Coeff. of Linear Thermal Expansion (20−500°C) | 18.0 × 10⁻⁶ K⁻¹ | 10.0 × 10⁻⁶ /°F |
| Relative Magnetic Permeability (Annealed) | ≤ 1.02 at H = 200 Oe | ≤ 1.02 at H = 200 Oe |
■ Ambient Mechanical Property Requirements
The minimum mechanical boundaries at room temperature vary by product form, standard code, and processing conditions.
| Product Standard / Form | Yield Strength Rp0.2 | Tensile Strength Rm | Min. Elongation (A₅) | Hardness Limits |
|---|---|---|---|---|
| ASTM A240 UNS S34700 (Plate/Sheet) | ≥ 205 MPa (≥ 30 ksi) | ≥ 515 MPa (≥ 75 ksi) | ≥ 40% | ≤ 201 HBW / ≤ 95 HRB |
| EN 10088-2 W.Nr. 1.4550 (Hot-rolled plate) | ≥ 200 MPa | 500 − 700 MPa | ≥ 40% | ≤ 201 HBW |
| EN 10088-2 W.Nr. 1.4550 (Bars & Profiles) | ≥ 205 MPa | 510 − 740 MPa | ≥ 40% | — |
| ASTM A182 UNS S34709 (Forged F347H) | ≥ 205 MPa (≥ 30 ksi) | ≥ 515 MPa (≥ 75 ksi) | ≥ 30% | ≤ 187 HBW (RA ≥ 50%) |
■ Short-Time High-Temperature Tensile Data
| Operating Temperature | Typical Tensile Strength (UTS) | Typical 0.2% Yield Strength | Typical Elongation (at Break) |
|---|---|---|---|
| 20°C (68°F) | 643 MPa (93.3 ksi) | 252 MPa (36.5 ksi) | 50% |
| 537.8°C (1000°F) | 438 MPa (63.5 ksi) | 189 MPa (27.4 ksi) | 45% |
| 815.6°C (1500°F) | 182 MPa (26.4 ksi) | 128 MPa (18.6 ksi) | — |
■ Creep and ASME Allowable Stress Envelope
The high-carbon content and mandatory coarse grain parameters of Grade 347H limit dislocation movement under continuous thermal load. The resulting strength gap between standard 347 and F347H forged components is tracked below:
| Design Temperature | SA182 F347 Allowable Stress | SA182 F347H Allowable Stress | High-Temperature Performance Margin |
|---|---|---|---|
| 538°C (1000°F) | 13.5 ksi (93.1 MPa) | 14.2 ksi (97.9 MPa) | F347H is ≈ 5% stronger |
| 593°C (1100°F) | 10.1 ksi (69.6 MPa) | 13.2 ksi (91.0 MPa) | F347H is ≈ 30% stronger |
| 649°C (1200°F) | 6.4 ksi (44.1 MPa) | 10.5 ksi (72.4 MPa) | F347H is ≈ 64% stronger |
| 704°C (1300°F) | 3.5 ksi (24.1 MPa) | 6.5 ksi (44.8 MPa) | F347H is ≈ 85% stronger |
| 760°C (1400°F) | 1.8 ksi (12.4 MPa) | 3.8 ksi (26.2 MPa) | F347H is ≈ 110% stronger |
| 816°C (1500°F) | 0.9 ksi (6.2 MPa) | 1.9 ksi (13.1 MPa) | F347H is ≈ 111% stronger |
■ AWS ER347 Welding Consumable Specifications
Welding must be performed using matching solid wire or shielded electrodes containing stabilized niobium additions to prevent corrosion boundary decay.
| Parameter Type | AWS A5.9 ER347 Requirement % | Typical ER347 Wrought Deposit Output |
|---|---|---|
| Carbon (C) | ≤ 0.08 | 0.04 − 0.05 |
| Chromium (Cr) | 19.0 − 21.5 | 19.6 − 20.0 |
| Nickel (Ni) | 9.0 − 11.0 | 9.0 − 10.7 |
| Niobium (Nb) | 10 × C min / 1.00 max | 0.60 − 0.86 |
| As-Welded Tensile Strength | — | 607 − 627 MPa (88 − 91 ksi) |
| As-Welded Yield Strength | — | 393 − 407 MPa (57 − 59 ksi) |
| As-Welded Elongation | — | 35 − 42% |
■ Metallurgical Engineering Controls and Structural Recommendations
- Material Selection Guidelines: Standard Grade 347 should be restricted to configurations operating up to 538°C (1000°F) where intergranular corrosion boundaries are the primary criteria. Above this point, high-carbon Grade 347H must be requested to capitalize on structural creep limitations.
- Chromium Carbide Prevention Verification: Stabilized lots must undergo quality assurance screening per ASTM A262. Practice A (Oxalic Acid Etch) isolates step morphologies for immediate release. Suspect ditch patterns must be validated via Practice E (Strauss Test), requiring a continuous 15-hour boil in copper-copper sulfate-sulfuric acid followed by a 180° mandrel bend check to confirm a zero-crack boundary.
- Pitting Limitations: Due to the absolute lack of molybdenum, Grade 347 exhibits a limited PREN profile (17.0 – 19.0). Do not specify this material for continuous high-chloride aqueous streams or reducing environments like active sulfuric acid lines due to rapid localized pitting threat risks.
- Solidification Micro-Fissuring Prevention: Fully austenitic weld pools exhibit an intrinsic susceptibility to hot cracking due to low segregation limits for sulfur and phosphorus impurities. Weld pool chemistry must be balanced using stringer passes and a maximum interpass limit of 120°C (248°F) to ensure the weld deposits solidify with a small volume of delta ferrite, strictly targeted within a Ferrite Number (FN) range of 5 to 13.