Excellent High-Temperature Resistance of 347 Stainless Steel
347 stainless steel is a niobium-stabilized austenitic stainless steel that offers excellent resistance to intergranular corrosion, superior high-temperature strength, and good weldability. It is particularly well-suited for cyclic thermal applications and environments where exposure to carbide precipitation is a concern.
This article will introduce the chemical composition, mechanical properties and typical application scenarios of 347 to help you select suitable high-temperature alloy materials in industries such as heat treatment, petrochemicals, power and aviation.
What is 347 Stainless Steel?
347 (UNS S34700) is a stabilized austenitic stainless steel containing chromium and nickel, with niobium (Nb) added to improve resistance to sensitization (carbide precipitation at grain boundaries). It is commonly used in applications involving repeated heating and cooling in the 427–899°C range.
Compared to conventional 304 and 321, 347 is more stable in high temperature environments and is particularly suitable for structures that do not require annealing after welding.
347 Equivalent Grades
| Standard / System | Equivalent Designation |
| UNS | S34700 |
| ASTM / ASME | A240, A312, A479, A182 |
| EN / DIN | 1.4550 (X6CrNiNb18-10) |
| JIS | SUS 347 |
| ISO | X6CrNiNb18-10 |
347 Chemical Composition
| Element | Content (%) |
| Chromium (Cr) | 17.0 – 19.0 |
| Nickel (Ni) | 9.0 – 13.0 |
| Niobium (Nb) | ≥ 10 × C and ≤ 1.0 |
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Iron (Fe) | Balance |
347 Mechanical Properties
| Property | Typical Value |
| Tensile Strength | ≥ 515 MPa |
| Yield Strength | ≥ 205 MPa |
| Elongation | ≥ 35% |
| Hardness (HBW) | ≤ 217 |
347 Physical Properties
| Property | Value |
| Density | 7.9 g/cm³ |
| Melting Point | 1398–1446 °C |
| Thermal Conductivity | ~16.3 W/m·K |
| Electrical Resistivity | ~0.75 µΩ·m |
| Modulus of Elasticity | ~193 GPa |
| Service Temperature | Up to ~870 °C |
Applications of 347 Stainless Steel
- Heat Exchangers: Tubes and headers for high-temperature fluids.
- Furnace Parts: Burners, radiant tubes, and thermocouple sheaths.
- Welded Pressure Vessels: For nitric acid and high-temperature chemical processes.
- Aerospace Exhaust Systems: Good creep strength and thermal fatigue resistance.
- Petrochemical Processing Equipment: Handles corrosive and hot atmospheres.
- Power Plant Equipment: Boilers, reheaters, and superheaters.
Advantages of 347
- Excellent resistance to intergranular corrosion after welding.
- Good oxidation and creep resistance at high temperatures.
- Stable during thermal cycling, making it ideal for furnace environments.
- No post-weld heat treatment required for most fabrication.
- Similar forming and machining characteristics to 304.
Limitations of 347
- Lower resistance to chloride pitting and crevice corrosion compared to 316.
- Higher cost than 304 due to niobium addition.
- Not suitable for extremely aggressive reducing acids (e.g., sulfuric acid).
- Limited availability in some formats compared to standard grades.
347 vs Other Stainless Steels
| Feature | 304 | 321 | 347 |
| Stabilizing Element | None | Titanium | Niobium |
| Welded Corrosion Resistance | Low | Good | Excellent |
| High Temp Strength | Good | Very Good | Excellent |
| Chloride Resistance | Moderate | Moderate | Moderate |
| Cost | Low | Medium | Medium–High |
Summary
347 stainless steel is a reliable material for high-temperature applications, offering enhanced weldability and thermal stability due to niobium stabilization. It is particularly useful in pressure vessels, exhaust systems, and process piping where resistance to intergranular attack and thermal fatigue is critical.
MT.BOLTS supplies fasteners, pipes, plates, and components made from 347 stainless steel. For technical assistance or to request a quotation, please contact our engineering team or visit our website.
