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AISI 347H UNS S34709 stainless steel is a high-carbon, niobium-stabilized austenitic stainless steel developed for high-temperature service, welded pressure equipment and industrial components exposed to the chromium carbide precipitation temperature range. Compared with 304 and 304L stainless steel, 347H stainless steel offers better stability after welding or prolonged heat exposure because niobium helps reduce chromium carbide precipitation at grain boundaries. It is widely used for boilers, heat exchangers, refinery equipment, petrochemical plants, furnace parts, exhaust manifolds, pressure vessels and high-temperature welded components.
Xi'an Dongmeng Group Co., Ltd. supplies ASTM A240 / ASME SA240 347H stainless steel and UNS S34709 stainless steel in plate, sheet, coil, strip, pipe, tube, bar and customized processed forms. 347H is the high-carbon version of 347 stainless steel, designed to improve high-temperature creep and stress-rupture strength; industry references commonly describe Type 347H as containing controlled carbon, typically 0.04–0.10%, for better high-temperature performance.
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WHAT IS AISI 347H?
AISI 347H is the high-carbon version of 347 stainless steel (UNS S34709).
It is stabilized with niobium (Nb), which prevents chromium carbide precipitation and improves resistance to intergranular corrosion after welding.
Key definition:
347H = High carbon + stabilized stainless steel
UNS S34709 = international material number
EN 1.4980 = European equivalent
👉 Designed for long-term high-temperature service above 550°C
AISI 347H stainless steel is based on the 18Cr-10Ni austenitic stainless steel system and is stabilized with niobium, also known as columbium. The niobium addition combines with carbon to form stable niobium carbides, reducing the formation of chromium carbides during welding or high-temperature exposure. This helps maintain corrosion resistance around welded and heat-affected zones.
The "H" grade indicates higher carbon control compared with standard 347 stainless steel. Higher carbon improves creep strength and stress-rupture strength at elevated temperatures, making UNS S34709 stainless steel a common choice for thermal equipment, refinery units, boilers, heat exchangers and high-temperature pressure components.
347 / 347H stainless steels are often used in the 800–1500°F / 427–816°C range, where resistance to intergranular corrosion after thermal exposure is important.
Core Advantages
1. High-temperature Strength
347H has controlled higher carbon content compared with 347, which improves creep and stress-rupture strength at elevated temperatures.
2. Niobium Stabilization
Niobium stabilization helps resist carbide precipitation during welding or prolonged high-temperature exposure, improving intergranular corrosion resistance.
3. Suitable for Welded High-temperature Components
347H is commonly used in welded components that later operate in elevated-temperature environments, such as refinery equipment, pressure vessels and heat exchanger parts.
4. Better Heat Service than 304 / 304L
Compared with standard 304 or 304L stainless steel, 347H is more suitable for thermal cycling and high-temperature service where stabilization and creep strength are required.
5. Multiple Product Forms
Plate, sheet, coil, strip, pipe, tube, bar and custom processed parts can be supplied for project-based procurement.
6. Custom Processing and Inspection
Cutting, slitting, beveling, polishing, marking, PMI, mechanical testing, MTC 3.1 and third-party inspection can be arranged according to order requirements.
Chemical Composition (Typical)
| Element | % |
|---|---|
| C | 0.04 – 0.10 |
| Mn | ≤ 2.0 |
| Si | ≤ 1.0 |
| P | ≤ 0.045 |
| S | ≤ 0.03 |
| Cr | 17.0 – 19.0 |
| Ni | 9.0 – 13.0 |
| Nb + Ta | ≥ 10 × C (~0.5%) |
| Fe | Balance |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | ≥ 515 MPa |
| Yield Strength (0.2% offset) | ≥ 205 MPa |
| Elongation | ≥ 40% |
| Hardness | ≤ 95 HRB |
| Maximum Service Temperature | ~900°C |
Physical Properties
| Property | Typical Value / Description |
|---|---|
| Density | Approx. 7.9–8.0 g/cm³ |
| Structure | Austenitic stainless steel |
| Magnetic Property | Generally non-magnetic in annealed condition |
| Heat Resistance | Suitable for selected elevated-temperature service |
| Oxidation Resistance | Good oxidation resistance under proper service conditions |
| Creep Strength | Improved compared with standard 347 due to higher carbon control |
| Welded Corrosion Resistance | Improved by niobium stabilization |
AZoM notes that 347H can be hot worked, cold worked, stamped, blanked, spun and drawn, and gives annealing temperature guidance of 1010–1193°C / 1850–2000°F followed by water quenching.
High Temperature Performance Analysis
347H stainless steel is specifically selected when long-term heat exposure, thermal cycling or pressure service requires higher creep strength than standard 304 or 304L stainless steel. The controlled carbon range improves stress-rupture performance, while niobium stabilization reduces the risk of chromium carbide precipitation.
Suitable High-temperature Uses
Boiler components
Furnace parts
Heat exchanger tubes and plates
Refinery equipment
Petrochemical process units
High-temperature welded assemblies
Exhaust manifolds
Thermal expansion components
Selection Logic
Choose 347H when the application requires:
High-temperature strength
Better creep resistance
Welded component stability
Resistance to intergranular corrosion after heat exposure
Better thermal service performance than 304 / 304L
Specifications (Metric & Imperial)
| Item | Available Range |
|---|---|
| Product | AISI 347H UNS S34709 Stainless Steel |
| Grade | AISI 347H / UNS S34709 / EN 1.4961 |
| Material Type | High Carbon Niobium-Stabilized Austenitic Stainless Steel |
| Standards | ASTM A240 / ASME SA240 / ASTM A312 / ASTM A213 / ASTM A269 / EN 10088 |
| Forms | Plate, Sheet, Coil, Strip, Pipe, Tube, Bar, Forging, Custom Parts |
| Thickness | Sheet / Plate / Strip: customized according to order |
| OD / WT | Pipe / Tube: customized according to project requirement |
| Surface | No.1, 2B, BA, Pickled, Polished, No.4, HL |
| Processing | Cutting, slitting, beveling, welding preparation, forming, marking |
| Heat Treatment | Solution annealed / annealed according to standard and order |
| Certificate | MTC 3.1 / EN 10204 3.1 / 3.2 / Third-party inspection |
| Packing | Wooden case, pallet, bundle, waterproof wrapping, seaworthy packing |
Available Product Forms
| Product Form | Typical Use |
|---|---|
| 347H Stainless Steel Plate | Pressure vessels, boiler parts, heat-resistant structures |
| 347H Stainless Steel Sheet | Heat shields, furnace panels, thermal equipment |
| 347H Stainless Steel Coil | Re-rolling, fabrication, heat-resistant components |
| 347H Stainless Steel Strip | Gaskets, expansion joints, exhaust components |
| 347H Stainless Steel Pipe | High-temperature piping, refinery systems, boiler piping |
| 347H Stainless Steel Tube | Heat exchangers, furnace tubes, thermal equipment |
| 347H Stainless Steel Bar | Machined components, fasteners, shafts, supports |
| 347H Custom Parts | Welded assemblies, furnace fittings, petrochemical parts |
Project Case – Petrochemical Plant
Client Country: South Korea
Industry: Petrochemical Processing
Material Supplied:
347H Stainless Steel Pipe
Specification:
OD 168mm × SCH40
Requirement:
Long-term service at 700°C
Resistance to creep deformation
Welded structure stability
Our Solution:
Provided stabilized 347H seamless pipes
Controlled grain structure per ASTM A213
Full PMI + UT inspection
Result:
Improved service life of high-temperature piping system by over 30%.
Export Experience
Exported to 60+ countries
Widely used in petrochemical & energy industries
Stable supply for EPC engineering projects
Why 347H Is Used in High Temperature Service
347H contains niobium (Nb) which:
Stabilizes carbon at high temperatures
Prevents chromium carbide formation
Improves creep rupture strength
Enhances long-term thermal stability
👉 This makes it superior to 304H and 321H in high-temperature environments.
High Temperature Performance
Continuous service: up to 850°C
Oxidation resistance: excellent
Creep resistance: high
Weld performance: stable after heat exposure
347 vs 347H
| Item | 347 Stainless Steel | 347H Stainless Steel |
|---|---|---|
| UNS Number | S34700 | S34709 |
| Carbon Content | Standard carbon level | Controlled higher carbon, usually 0.04–0.10% |
| Stabilization | Nb / Ta stabilized | Nb / Ta stabilized |
| Main Advantage | Intergranular corrosion resistance after welding | Higher high-temperature creep and stress-rupture strength |
| Typical Use | General stabilized stainless steel applications | High-temperature pressure and thermal service |
| Cost | Usually lower | Usually higher |
| Best For | Welded components and general heat exposure | Boilers, heat exchangers, refinery and petrochemical equipment |
👉 Conclusion:
347H is preferred for long-term high-temperature and pressure applications.
347H Stainless Steel vs 321 Stainless Steel
| Item | 347H Stainless Steel | 321 Stainless Steel |
|---|---|---|
| Stabilizing Element | Niobium / Columbium | Titanium |
| High-temperature Strength | Better due to higher carbon control | Good |
| Welded Intergranular Corrosion Resistance | Good | Good |
| Typical Application | Boiler, refinery, heat exchanger, pressure equipment | Exhaust systems, heat shields, expansion joints |
| Service Focus | High-temperature strength and creep resistance | Heat exposure and stabilized corrosion resistance |
| Selection Logic | Choose 347H for higher temperature strength | Choose 321 for general Ti-stabilized heat service |
347H Stainless Steel vs 304H Stainless Steel
| Item | 347H Stainless Steel | 304H Stainless Steel |
|---|---|---|
| Stabilization | Nb / Ta stabilized | Not stabilized |
| Carbon Level | Controlled high carbon | Controlled high carbon |
| Intergranular Corrosion Resistance | Better after welding / heat exposure | Lower than stabilized grades |
| High-temperature Strength | Good | Good |
| Typical Use | Refinery, boiler, heat exchanger, petrochemical | General high-temperature pressure equipment |
| Best Advantage | Stabilized + high-temperature strength | Cost-effective high-temperature 18-8 stainless steel |
Standards & Compliance
AISI 347H complies with:
ASTM A240 / A312 / A213
ASME SA240
UNS S34709
EN 1.4980
Widely recognized in boiler, refinery, and power generation industries.
Manufacturing Capability
10+ years stainless steel export experience
Hot & cold rolling production lines
Precision tube & plate processing
OEM fabrication for industrial systems
Products Key Features
High-carbon version for enhanced high-temperature strength
Niobium-stabilized to prevent intergranular corrosion
Excellent creep and stress rupture resistance
Superior oxidation and thermal fatigue performance
Good weldability in heavy-section components
Reliable for long-term service at 538–900°C
Products Applications
Boiler and Power Plant Equipment
Used for boiler components, superheater parts, reheater sections, high-temperature supports and thermal power equipment.
Heat Exchangers
Used for heat exchanger plates, tubes, baffles, shells, fins and thermal processing components.
Refinery and Petrochemical Equipment
Used for refinery process units, catalytic cracking equipment, high-temperature piping, reactor internals and welded components.
Furnace and Heat Treatment Systems
Used for furnace parts, heat shields, baskets, trays, radiant tubes, supports and high-temperature fixtures.
Aerospace and Exhaust Systems
347 stainless steel is used in high-temperature aeronautical and exhaust-related applications such as exhaust stacks, manifolds and engine-related components.
Chemical Processing
Used in chemical equipment, welded tanks, high-temperature process vessels and corrosion-resistant fabricated parts.
Expansion Joints and Gaskets
347H strip and sheet can be used for high-temperature expansion joints, flexible connectors, gaskets and heat-resistant sealing components.
Corrosion Resistance Analysis
347H stainless steel has general corrosion resistance similar to 304 stainless steel, but its main advantage is improved resistance to intergranular corrosion after welding or prolonged exposure to the carbide precipitation range.
| Environment | 347H Stainless Steel Suitability |
|---|---|
| General atmospheric environment | Good |
| Welded high-temperature components | Excellent |
| Boiler and heat exchanger service | Good |
| Refinery and petrochemical equipment | Good |
| Oxidizing environments | Good in selected conditions |
| Marine chloride environment | Limited; consider 316L / 2205 |
| Strong reducing acid | Not recommended without corrosion evaluation |
| Severe chloride pitting environment | Consider 904L / 2205 / 2507 |
347 stainless steel is known for resistance to intergranular corrosion after exposure to the chromium carbide precipitation range, typically 800–1500°F / 427–816°C.
Inspection & Quality Assurance
Xi'an Dongmeng Group Co., Ltd. provides strict inspection for AISI 347H UNS S34709 stainless steel before shipment.
| Inspection Item | Description |
|---|---|
| Raw Material Verification | Grade, heat number, batch number and standard verification |
| Chemical Composition | C, Cr, Ni, Nb/Ta, Mn, Si, P, S verification |
| PMI Test | Positive material identification before shipment |
| Mechanical Test | Tensile strength, yield strength, elongation and hardness |
| Dimensional Inspection | Thickness, width, length, OD, wall thickness or diameter according to product form |
| Surface Inspection | Scratches, dents, pits, scale, stains and surface defects |
| Heat Treatment Check | Annealed / solution annealed condition confirmation |
| NDT Inspection | UT / PT / RT available according to product and requirement |
| Intergranular Corrosion Test | Available according to project requirement |
| MTC | EN 10204 3.1 / 3.2 available |
| Third-party Inspection | SGS, BV, TUV, Lloyd's or customer-appointed inspection accepted |
Packaging & Shipping
Plate / sheet packed on wooden pallet or metal pallet
Coil packed eye-to-wall or eye-to-sky with waterproof wrapping
Pipe and tube bundled with end caps and steel strips
Bar packed in bundles or wooden cases
Waterproof paper and plastic film protection
Edge and surface protection for precision products
Clear labels with grade, heat number, size and quantity
Export seaworthy packing
Container loading photos available
Shipping by sea, railway or air freight according to order volume
Why Choose Xi'an Dongmeng Group Co., Ltd.
Special Stainless Steel Grade Supply
347H / UNS S34709 stainless steel products can be supplied in plate, sheet, coil, strip, pipe, tube and bar forms.
High-temperature Application Support
Material selection can be matched with boiler, heat exchanger, refinery, petrochemical and furnace equipment requirements.
Custom Processing Service
Cutting, slitting, beveling, polishing, forming, marking and packing can be arranged according to customer drawings.
Strict Material Verification
PMI, chemical composition, mechanical properties, heat number tracking and MTC 3.1 are available.
Export Project Experience
Seaworthy packing, third-party inspection, certificate documents and global delivery support for international industrial projects.
Looking for AISI 347H UNS S34709 stainless steel price, datasheet or MTC sample? Contact us today for a fast quotation.
Our address
Room 4107, Runfeng Building, Sanqiao New Street, Weiyang District, Xi'an City, Shaanxi Province
Phone Number
+86 15769214734
FAQ
1. What is AISI 347H stainless steel?
AISI 347H is a high-carbon, niobium-stabilized austenitic stainless steel designed for high-temperature service and welded components.
2. What is UNS S34709?
UNS S34709 is the UNS designation for 347H stainless steel.
3. What is the difference between 347 and 347H stainless steel?
347H has a controlled higher carbon range, usually 0.04–0.10%, which improves high-temperature creep and stress-rupture strength compared with standard 347.
4. Is 347H stainless steel heat resistant?
Yes. 347H stainless steel is used for boilers, heat exchangers, refinery equipment, petrochemical plants and other high-temperature industrial applications.
5. What is the stabilizing element in 347H?
347H is stabilized with niobium, also known as columbium, often with tantalum included in the Nb + Ta requirement.
6. Can 347H stainless steel be welded?
Yes. 347H stainless steel has good weldability, but suitable filler material and welding procedure should be selected for high-temperature or pressure equipment.
7. Is 347H better than 321 stainless steel?
347H is often selected when higher high-temperature strength and creep resistance are required. 321 is titanium-stabilized and is commonly used for general heat-resistant components.
8. Can you supply 347H stainless steel pipe?
Yes. 347H stainless steel pipe and tube can be supplied according to ASTM A312, ASTM A213 or project-specific requirements.
9. Can you provide MTC 3.1?
Yes. EN 10204 3.1 material test certificate can be supplied with shipment. Third-party inspection can also be arranged.
10. What information should I provide for quotation?
Please provide product form, grade, standard, size, thickness or OD/wall thickness, quantity, surface, processing requirement, destination port and certificate requirement.
AISI 347H (UNS S34709) is a niobium-stabilized high-carbon austenitic stainless steel designed for excellent creep resistance, high-temperature strength, and long-term stability in boilers, heat exchangers, and petrochemical systems.
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