Stainless Steel, Austenitic
321H Stainless Steel (S32109) Fittings and Flanges
A higher carbon modification of stainless steel 321 which provides greater strength at elevated temperatures.
321H is able to withstand higher temperatures than type 321, due to its elevated carbon levels. While 321H displays the same welding and forming characteristics of type 321, the metal cannot be hardened by heat treatment.
It is utilized in situations where type 321 cannot withstand the high temperatures. Type 321H displays better resistance against creep than both 321 and 304 stainless steels.
321H also shows resistance against acid corrosion in a variety of environments. Lower temperatures provide better resistance, but the metal is able to withstand up to a 10% acid solution, that has been diluted, at elevated temperatures. However, the metal shows very little resistance against chlorine or sulfuric solutions at any given temperature.
Given their similar composition and characteristics, it is possible for stainless steels 321 and 321H to become dually certified.
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Related Specifications
- 321H
- X8CrNiTi18-10（W.-Nr. 1.487）
- S32109
- EN 1.4541 (X6CrNiTi18‑10)
- 07Cr19Ni11Ti
Properties
Chemical Composition
S32109 Fittings
ASTM A182
| Chemical Element | % Present |
| Carbon (C) | 0.04 - 0.10 |
| Chromium (Cr) | 17.00 - 19.00 |
| Nickel (Ni) | 9.00 - 12.00 |
| Manganese (Mn) | 0.00 - 2.00 |
| Phosphorous (P) | 0.00 - 0.04 |
| Sulphur (S) | 0.00 - 0.03 |
| Silicon (Si) | 0.00 - 1.00 |
| Titanium (Ti) | 0.00 - 0.60 |
| Iron (Fe) | Balance |
Mechanical Properties
Fittings and Flanges
ASTM A182
| Mechanical Property | Value |
| Proof Stress | 205 Min MPa |
| Tensile Strength | 515 Min MPa |
| Elongation A50 mm | 30 Min % |
Applications of 321H Stainless Steel
321H stainless steel is specifically designed for high-temperature service, offering excellent strength, stability, and oxidation resistance in elevated-temperature environments. Its high carbon content enhances creep strength, making it suitable for long-term exposure to heat.
Below are the primary application areas:
1. High-Temperature Piping and Tubing
Superheater and reheater tubes
Boiler tubes for power generation
Heat exchanger tubing
High-temperature steam and process piping
2. Furnace and Thermal Processing Equipment
Furnace components
Heating elements and heat shields
Thermal oxidizer parts
Radiant tubes and combustion chambers
3. Petrochemical and Refining Industry
Hydrocarbon processing equipment
Reactor vessels and transfer piping
Catalytic cracking units
High-temperature chemical processing systems
4. Exhaust and Emission Control Systems
Industrial exhaust manifolds
Thermal processing ducts
Flue gas handling components
5. Aerospace and Industrial Applications
High-temperature structural components
Gas turbine parts (non-critical areas)
Supports and brackets used in thermal environments
Summary
321H stainless steel is widely used in high-temperature, high-stress, and oxidizing environments, especially where long-term structural integrity is required. Its combination of creep resistance, oxidation resistance, and titanium stabilization makes it an ideal choice for demanding industrial applications.
Characteristics of 321H Stainless Steel
321H stainless steel is a high-carbon, titanium-stabilized austenitic stainless steel engineered for excellent performance in high-temperature environments. It offers a combination of superior creep strength, thermal stability, and resistance to intergranular corrosion, making it ideal for long-term elevated-temperature service.
1. High Carbon for Improved Creep Strength
The increased carbon content (compared to 321) significantly enhances
creep resistance and high-temperature strength.Suitable for continuous service in temperatures up to 900°C (1650°F).
2. Titanium Stabilization
Titanium forms stable carbides, preventing chromium carbide precipitation.
Provides excellent resistance to intergranular corrosion, especially after welding or prolonged heating.
3. Excellent Heat and Oxidation Resistance
Withstands oxidizing atmospheres at elevated temperatures.
Maintains mechanical integrity during long-term exposure to heat.
4. Good Mechanical Properties
Retains strength and toughness across a wide temperature range.
Exhibits reliable performance under thermal stress and cyclic heating.
5. Good Formability and Weldability
Readily welded using standard methods, with minimized risk of sensitization.
Can be hot- and cold-worked with appropriate techniques.
6. Corrosion Resistance
Good resistance to general atmospheric and mild chemical corrosion.
More stable in high-temperature environments compared to non-stabilized grades like 304H.
Summary
321H stainless steel combines high-temperature strength, excellent oxidation resistance, and titanium stabilization to deliver reliable performance in demanding applications such as furnace components, petrochemical processing systems, and high-temperature piping.
Additional Information
Fabrication
Fabrication of 321H Stainless Steel
321H stainless steel is a high-carbon, titanium-stabilized austenitic stainless steel that offers good fabricability using conventional forming, machining, and welding techniques. Its enhanced high-temperature strength and resistance to carbide precipitation make it suitable for manufacturing components used in elevated-temperature environments.
1. Forming
Hot Forming:
Preferred temperature range: 1150–900°C (2100–1650°F).
Heavy forming should be performed at the upper end of the range to maintain ductility.
Components should be water-quenched or rapidly cooled after hot forming to ensure maximum corrosion resistance.
Cold Forming:
Good cold formability due to its austenitic structure.
Material may work-harden during cold deformation, so intermediate annealing is recommended for complex shapes.
Suitable for bending, drawing, and rolling operations.
2. Machining
Similar machining characteristics to other austenitic grades.
Exhibits work hardening, so tools must be sharp and rigid.
Use carbide tools, adequate lubrication, and controlled cutting speeds for best results.
3. Welding
Excellent weldability using common methods such as TIG, MIG, and SMAW.
Titanium stabilization minimizes the risk of intergranular corrosion after welding.
For optimal performance, low-carbon filler metals (e.g., 347 or 321) may be used.
4. Post-Fabrication Heat Treatment
After severe forming or welding, stabilizing annealing may be performed to restore corrosion resistance.
Typical annealing temperature: 950–1120°C (1740–2050°F).
Rapid cooling is essential to maintain the stabilized structure.
5. Surface Finishing
Pickling, passivation, or mechanical polishing is recommended to remove scale and improve corrosion resistance, especially after hot forming or welding.
Summary
321H stainless steel is highly workable in both hot and cold conditions and supports reliable machining and welding. Its titanium stabilization and high carbon content make it well suited for fabricating high-temperature components used in furnaces, petrochemical systems, and thermal processing equipment.
Weldability
Weldability of 321H Stainless Steel
321H stainless steel offers excellent weldability due to its austenitic structure and titanium stabilization, which helps prevent carbide precipitation and intergranular corrosion during and after welding. It is well suited for welded structures that operate in high-temperature environments.
1. General Weldability
Can be welded using all standard fusion welding techniques, including:
TIG (GTAW)
MIG (GMAW)
SMAW (Shielded Metal Arc Welding)
FCAW (Flux-Cored Arc Welding)
Welds typically maintain good toughness and corrosion resistance.
2. Titanium Stabilization Benefits
Titanium binds to carbon, preventing chromium carbide formation.
This reduces the risk of sensitization and intergranular corrosion, especially after prolonged high-temperature exposure.
Makes 321H superior to non-stabilized grades like 304H in welded high-temperature applications.
3. Filler Metal Recommendations
Suitable filler metals include:
ER321 (matching stabilized filler)
ER347 (niobium-stabilized filler with similar corrosion performance)
For thick sections or demanding high-temperature service, stabilized fillers are preferred to ensure long-term stability.
4. Heat Input and Preparation
Moderate heat input is recommended to avoid excessive grain growth.
Joint areas should be clean and free of contaminants such as oil, paint, and moisture.
Preheat is generally not required.
5. Post-Weld Heat Treatment (PWHT)
Typically not required for most applications.
For critical high-temperature service, stabilizing annealing may be performed at 950–1120°C (1740–2050°F) to enhance corrosion resistance.
Rapid cooling is recommended after annealing.
6. Welding Considerations
The alloy work-hardens, so distortion control and proper fixturing are important.
Use appropriate shielding gas (e.g., argon or argon/helium mix for TIG/MIG).
Avoid excessive heat that may reduce mechanical properties.
Summary
321H stainless steel demonstrates excellent weldability, supported by titanium stabilization that protects against intergranular corrosion and maintains high-temperature performance. With proper filler metals and controlled welding parameters, it delivers strong, reliable welds for furnaces, petrochemical systems, boilers, and high-temperature piping.
Machinability
Machinability of 321H Stainless Steel
321H stainless steel, an austenitic grade stabilized with titanium and containing higher carbon, has moderate machinability similar to other high-alloy austenitic stainless steels. Its excellent toughness and work-hardening tendency make it more challenging to machine than carbon steel or ferritic stainless steels, but good results can be achieved with proper tooling and techniques.
Key Machinability Characteristics
1. Tendency to Work-Harden
321H work-hardens rapidly during machining.
Cutting tools must maintain constant feed rates to avoid rubbing, which increases hardness and tool wear.
2. Requires Sharp, Rigid Cutting Tools
Carbide tooling is recommended for optimal performance.
High-speed steel (HSS) tools can be used at slower speeds.
3. Lower Cutting Speeds Needed
Use reduced cutting speeds compared with carbon steels to minimize heat buildup.
Higher heat generation can reduce tool life and affect surface finish.
4. Good Surface Finish with Proper Techniques
Produces a clean, smooth finish when correct feeds, speeds, and lubrication are used.
Use sulfurized cutting oils or high-performance coolants for best results.
5. Chip Formation
Chips tend to be tough and stringy.
Chip breakers or positive rake inserts help maintain control and improve safety.
Recommended Machining Practices
Use rigid machine setups to reduce vibration.
Maintain steady, heavy feeds to prevent work-hardening.
Apply adequate coolant to reduce heat and tool wear.
Prefer carbide inserts with positive rake angles.
Avoid dwell or pauses during cutting to prevent hard spots.
Summary
While 321H stainless steel is not as easy to machine as free-machining or ferritic grades, it can be machined successfully with proper tooling, controlled cutting parameters, and sufficient cooling. Its machinability is comparable to 304/316 grades but slightly reduced due to higher carbon content.
Corrosion Resistance
Corrosion Resistance of 321H Stainless Steel
321H stainless steel is a high-carbon, titanium-stabilized austenitic stainless steel designed to provide enhanced corrosion resistance, especially in high-temperature environments. Its stability at elevated temperatures and resistance to intergranular corrosion make it ideal for demanding applications.
1. General Corrosion Resistance
Offers good resistance to oxidation and general atmospheric corrosion.
Performs well in mild chemical environments and industrial atmospheres.
2. High-Temperature Corrosion Resistance
Titanium stabilization prevents sensitization during prolonged exposure to temperatures above 500°C (932°F).
Maintains corrosion resistance in welded and heat-treated components.
3. Resistance to Intergranular Corrosion
Titanium combines with carbon to form stable carbides, preventing the formation of chromium carbides at grain boundaries.
Ensures excellent resistance to intergranular corrosion (IGC) even after high-temperature exposure.
4. Oxidation and Scaling
Resists oxidation at temperatures up to approximately 870°C (1600°F) in continuous service and 925°C (1700°F) for intermittent exposure.
Forms a stable chromium oxide layer that protects the steel from further high-temperature corrosion.
5. Limitations
Like other austenitic stainless steels, 321H can be susceptible to pitting and crevice corrosion in chloride-rich environments.
Not suitable for extremely aggressive chemical environments without additional protection.
6. Applications Related to Corrosion Resistance
Exhaust systems, furnace parts, and heat exchangers exposed to high temperatures
Chemical and petrochemical equipment
Aircraft and automotive components requiring resistance to high-temperature oxidation
Industrial piping and tanks in elevated-temperature service
Summary
321H stainless steel provides excellent corrosion resistance, particularly at elevated temperatures, due to titanium stabilization and austenitic structure. Its combination of high-temperature performance, intergranular corrosion resistance, and general corrosion resistance makes it ideal for chemical, industrial, and high-temperature applications.
Cold Working
Cold Working of 321H Stainless Steel
321H stainless steel is a titanium-stabilized austenitic stainless steel with good ductility, which allows effective cold working. Cold working increases strength through work hardening while maintaining corrosion resistance.
1. Common Cold Working Processes
Bending and Forming: Can be bent into complex shapes for structural and decorative applications.
Rolling: Suitable for sheet, strip, and coil production.
Deep Drawing: Can produce sinks, trays, and other complex components.
Stamping and Punching: Used in industrial and architectural applications.
2. Work Hardening
Cold working significantly increases tensile and yield strength.
The material has a high work-hardening rate, which improves durability but can reduce ductility if overworked.
Intermediate annealing is recommended for extensive deformation to restore ductility.
3. Fabrication Considerations
Use gradual deformation to avoid cracking or excessive stress.
Sharp tooling and proper lubrication are essential for good surface finish and reduced tool wear.
Cold-worked components may require stress relief for critical applications.
4. Applications Related to Cold Working
Furnace components and high-temperature equipment
Sheet metal parts in chemical and petrochemical industries
Decorative panels and architectural trims
Industrial and mechanical components requiring high strength
Summary
321H stainless steel exhibits excellent cold working characteristics, allowing bending, rolling, stamping, and deep drawing. Cold working enhances strength while maintaining corrosion resistance, making 321H suitable for high-temperature, industrial, and architectural applications.
Heat Treatment
Heat Treatment of 321H Stainless Steel
321H stainless steel is a titanium-stabilized austenitic stainless steel with high carbon content. It is primarily strengthened through cold working and has excellent high-temperature stability. Conventional hardening heat treatments are not effective for increasing strength, but heat treatment is used for annealing, stress relief, and restoration of ductility.
1. Annealing
Purpose: Restore ductility, relieve stress, and improve corrosion resistance after cold working or welding.
Typical temperature: 950–1120°C (1740–2050°F) for austenitizing.
Cooling method: Rapid cooling (air or water quench) to retain the stabilized austenitic structure.
2. Stress Relief
Applied to relieve internal stresses from welding, cold working, or forming.
Temperature range: 450–650°C (840–1200°F).
Reduces the risk of distortion or cracking in fabricated components.
3. Stabilization
Titanium forms stable carbides, preventing chromium carbide precipitation during high-temperature exposure.
Unlike 321, 321H has higher carbon, so stabilization ensures resistance to intergranular corrosion in welded or heated components.
4. Effects of Heat Treatment
Restores ductility in heavily cold-worked parts.
Reduces hardness caused by work hardening.
Does not significantly increase strength through quenching or tempering.
5. Applications Related to Heat Treatment
Welded high-temperature piping and tubing
Furnace and heat exchanger components
Petrochemical equipment exposed to thermal cycles
Components requiring stress relief for dimensional stability
Summary
Heat treatment of 321H stainless steel is used primarily for annealing and stress relief, maintaining ductility, corrosion resistance, and dimensional stability in high-temperature applications. It does not respond to conventional hardening but is essential for long-term reliability in furnaces, boilers, petrochemical systems, and heat-resistant components.
Heat Resistance
Heat Resistance of 321H Stainless Steel
321H stainless steel is a titanium-stabilized, high-carbon austenitic stainless steel designed for excellent performance in high-temperature environments. Its chemical composition and stabilization make it ideal for components exposed to prolonged elevated temperatures, where creep resistance, oxidation resistance, and mechanical integrity are critical.
1. Continuous Service Temperature
Suitable for continuous service up to approximately 900°C (1650°F) in oxidizing atmospheres.
Maintains mechanical strength and corrosion resistance at elevated temperatures.
2. Intermittent Exposure
Can withstand intermittent exposures up to 950°C (1740°F) without significant scaling or oxidation.
Ideal for components exposed to thermal cycling or fluctuating high temperatures.
3. Oxidation Resistance
Forms a stable chromium oxide layer on the surface, protecting against scaling.
Titanium stabilization enhances resistance to carbide precipitation, preserving corrosion resistance at high temperatures.
4. Creep Strength
High carbon content in 321H increases creep resistance compared to standard 321 stainless steel.
Suitable for long-term service under mechanical stress at elevated temperatures.
5. Applications Related to Heat Resistance
Furnace components, radiant tubes, and heat exchangers
High-temperature piping in petrochemical and power generation industries
Superheater and reheater tubes in boilers
Thermal processing equipment, including ducts and exhaust systems
Summary
321H stainless steel provides excellent heat resistance, maintaining strength, oxidation resistance, and dimensional stability up to 900°C (1650°F) for continuous service. Its titanium stabilization and high-carbon content make it ideal for high-temperature applications such as furnaces, boilers, petrochemical equipment, and thermal processing components.
Hot Working
Hot Working of 321H Stainless Steel
321H stainless steel is a titanium-stabilized, high-carbon austenitic stainless steel with excellent hot working characteristics. Hot working allows the material to be shaped at elevated temperatures while maintaining ductility and minimizing work hardening.
1. Hot Working Temperature
Suitable hot working range: 1150–900°C (2100–1650°F).
Proper temperature control is essential to prevent grain growth and maintain mechanical properties.
2. Hot Working Processes
Hot Rolling: Produces sheets, plates, and strips with precise thickness.
Forging: Forms structural components and heavy parts for high-temperature service.
Extrusion: Allows production of rods, tubes, and profiles.
Hot Pressing and Forming: Enables shaping of complex geometries with reduced risk of cracking.
3. Advantages of Hot Working
Reduces work hardening compared to cold working.
Improves ductility and toughness in the finished component.
Facilitates the production of large, complex, or thick sections that are difficult to form cold.
4. Post-Hot Working Treatments
Annealing may be performed to restore uniform mechanical properties and relieve residual stresses.
Pickling or passivation improves corrosion resistance after hot working.
5. Applications Related to Hot Working
Furnace components, heat exchangers, and high-temperature piping
Structural and industrial parts in petrochemical or power generation equipment
Automotive exhaust and high-temperature duct components
Summary
321H stainless steel exhibits excellent hot working performance, allowing rolling, forging, extrusion, and complex forming at 1150–900°C. Hot working reduces work hardening, enhances ductility, and enables the production of large or intricate parts for high-temperature industrial and thermal applications.
