What is the Difference Between 321H and 347H Stainless Steel?
Nov 10, 2025
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If you are searching for high-temperature stainless steel alloys for industrial applications, understanding the difference between 321H and 347H stainless steel is crucial. Both are austenitic stainless steels stabilized with titanium (321H) or niobium (347H), designed to resist sensitization during welding and provide excellent high-temperature strength, but their chemical composition, corrosion resistance, and performance characteristics differ.
GNEE can supply high-quality 321H and 347H stainless steel plates, sheets, and pipes, with custom sizes, thickness, and surface finishes to meet your industrial requirements.
What are the international equivalents?
321H ≈ EN 1.4878, UNS S32109
347H ≈ EN 1.4958, UNS S34709
Key Differences Between 321H and 347H
| Property | 321H Stainless Steel | 347H Stainless Steel |
|---|---|---|
| Base Alloy Type | Austenitic | Austenitic |
| Stabilizing Element | Titanium (Ti) | Niobium (Nb) |
| Carbon Content | 0.04–0.10% (higher than 321) | 0.04–0.10% (high carbon) |
| Temperature Resistance | Up to 900°C (1700°F) | Up to 950°C (1740°F) |
| Corrosion Resistance | Excellent in general and high-temperature environments | Excellent in oxidizing environments and against intergranular corrosion |
| Applications | Aircraft, chemical reactors, heat exchangers, gas turbines | Boilers, pressure vessels, high-temperature piping, aerospace components |
Chemical Composition (Typical)
| Element | 321H (%) | 347H (%) |
|---|---|---|
| C | 0.08–0.10 | 0.08–0.10 |
| Cr | 17–19 | 17–19 |
| Ni | 9–13 | 9–13 |
| Ti/Nb | Ti 5×C min | Nb 10×C min |
| Mn | ≤2 | ≤2 |
| Si | ≤1 | ≤1 |
| P | ≤0.045 | ≤0.045 |
| S | ≤0.03 | ≤0.03 |
Mechanical Properties
| Property | 321H | 347H |
|---|---|---|
| Tensile Strength | 520–750 MPa | 520–750 MPa |
| Yield Strength | 205–310 MPa | 205–310 MPa |
| Elongation | 40–50% | 40–50% |
| Hardness (HRB) | 70–95 | 70–95 |
Applications:
321H stainless steel, with titanium stabilizer, prevents chromium carbide precipitation and sensitization during welding. Suitable for furnace components, petrochemical plants, and high-temperature piping up to 450–950°C.
347H stainless steel, with niobium stabilizer, the high-carbon version offers excellent resistance to intergranular corrosion. Suitable for superheaters, heat exchangers, and boiler tubes exposed to high-temperature steam and corrosive environments.
Can 321H and 347H be used interchangeably?
Not always. While both are stabilized austenitic steels, 347H provides slightly better creep and stress rupture properties at very high temperatures. Select 321H for general high-temperature corrosion resistance, 347H for long-term steam exposure or stress-critical applications.
Can 321H replace 347H for high-temperature applications?
321H can be used in many high-temperature applications, but for steam boilers or superheaters with temperatures above 600°C, 347H is recommended for better long-term creep resistance.
The choice between 321H and 347H depends on your specific high-temperature application, stress requirements, and environmental conditions. 321H is ideal for general high-temperature corrosion resistant applications, while 347H is better suited for applications requiring high stress and long-term high-temperature operation. Partnering with a reliable supplier like GNEE ensures access to certified materials, consistent quality, and tailored solutions.
GNEE Supply: GNEE offers a wide range of 321H and 347H stainless steel products in various sizes and specifications,processed into various practical product forms, including plates, coils, tubes, bars, and wires, fully compliant with ASTM, EN, and UNS standards. Custom cutting, polishing, and delivery options are available to meet diverse industrial needs.
FAQ
Q: Can these stainless steels be welded?
Yes, both 321H and 347H are easy to weld, and stabilizers prevent sensitization during welding.
Q: Can GNEE provide custom sizes and finishes?
Yes. GNEE offers plates, sheets, and coils in various thicknesses (0.3–14mm), widths, and finishes (including 2B, No.4, BA), and provides on-demand cutting services.
Q: What certifications are available?
All GNEE products come with ISO, SGS, and factory test certificates (MTC) covering chemical composition and mechanical properties.
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