In today’s industrial world, stainless steels play a vital role in manufacturing, energy, marine, and chemical sectors. Among the many grades, 329 stainless steel has gained increasing attention for its exceptional balance of strength and corrosion resistance. It is one of the duplex stainless steels, combining the qualities of both austenitic and ferritic microstructures. This unique composition allows it to perform effectively in demanding environments where ordinary stainless steels may fail.
In this article, we’ll dive into what 329 stainless steel is, its composition, key characteristics, mechanical properties, and major industrial uses. As a global supplier of high-quality stainless steels, SAKYSTEEL provides insights into why this alloy is becoming a preferred choice for engineers and manufacturers worldwide.
329 stainless steel, also known as UNS S32900, is a duplex stainless steel consisting of roughly equal amounts of ferrite and austenite. This balanced microstructure provides a combination of high tensile strength, excellent resistance to chloride stress corrosion cracking, and superior resistance to pitting and crevice corrosion compared to standard austenitic grades like 304 or 316.
It was originally developed for use in marine and chemical process industries, where corrosion caused by chlorides, acids, and seawater is a constant challenge. Thanks to its duplex structure, 329 stainless steel offers both mechanical durability and corrosion performance, making it suitable for aggressive and high-pressure environments.
The typical chemical composition of 329 stainless steel includes:
Chromium (Cr): 23–28%
Nickel (Ni): 2.5–5%
Molybdenum (Mo): up to 1.5%
Manganese (Mn): ≤1.0%
Silicon (Si): ≤1.0%
Carbon (C): ≤0.08%
Nitrogen (N): ≤0.2%
This composition gives the alloy high chromium and moderate nickel content, which together stabilize the duplex microstructure and enhance resistance to corrosion. The addition of molybdenum further improves resistance to localized corrosion such as pitting and crevice attack, particularly in chloride-bearing solutions.
329 stainless steel’s duplex nature results in a two-phase microstructure:
Ferrite (α) contributes to strength and resistance to stress corrosion cracking.
Austenite (γ) contributes to toughness and ductility.
The microstructure is typically maintained through controlled heat treatment during production. The dual-phase structure offers twice the yield strength of 300-series stainless steels, while still retaining adequate elongation and formability.
At high temperatures, care must be taken to avoid sigma phase formation, which can reduce toughness and corrosion resistance. Hence, controlled processing and annealing are crucial for maintaining optimal properties.
329 stainless steel exhibits a superior balance of mechanical strength and ductility. Typical mechanical values (in annealed condition) are:
Tensile strength: ≥ 620 MPa
Yield strength (0.2% offset): ≥ 450 MPa
Elongation: ≥ 25%
Hardness (HB): ≤ 250
This combination of high yield and tensile strength makes 329 an excellent material for load-bearing and structural applications where corrosion resistance is equally critical.
One of the standout advantages of 329 stainless steel is its exceptional corrosion resistance. It performs well in both oxidizing and reducing environments, especially where chloride exposure is a concern. Key corrosion characteristics include:
Resistance to Chloride Stress Corrosion Cracking: Its ferritic phase makes it much more resistant than austenitic grades like 316L.
Excellent Pitting Resistance: Due to high chromium and molybdenum content, it withstands pitting in seawater and chemical processing environments.
Good Resistance to Sulfide Stress Cracking: Making it suitable for oil and gas environments containing hydrogen sulfide (H₂S).
Resistance to Intergranular Corrosion: Proper heat treatment prevents carbide precipitation and ensures long-term corrosion stability.
For these reasons, 329 stainless steel is often preferred in marine structures, desalination plants, and offshore oil platforms.
Although 329 stainless steel is stronger than most austenitic stainless steels, it can still be machined, welded, and formed using proper techniques:
Machining: Requires powerful equipment and sharp tools due to its high strength. Slow speeds and rigid setups are recommended.
Welding: Can be welded by common processes such as TIG, MIG, and SMAW. However, control of heat input and interpass temperature is essential to maintain phase balance.
Forming: Due to its higher strength, forming may require more force compared with 304 or 316, but cold-forming operations remain feasible.
After fabrication, solution annealing is often performed to restore corrosion resistance and toughness.
The unique combination of strength, corrosion resistance, and fatigue performance makes 329 stainless steel suitable for a wide range of industrial applications:
Used in seawater pipelines, propeller shafts, and heat exchangers, 329 resists corrosion in saltwater and brine environments.
Resistant to aggressive chemicals, acids, and chlorides, making it ideal for chemical storage tanks, heat exchangers, and evaporators.
Commonly used in tubing, valves, pumps, and fittings for offshore drilling and sour-gas service environments requiring NACE MR0175 compliance.
Applied in boiler feedwater systems and condensers that require high resistance to corrosion and scaling.
Used in digesters, bleach washers, and heat recovery systems, where chloride and acid exposure is high.
Ideal for desalination equipment, pumps, and filters because of its resistance to chloride ions and salt corrosion.
When compared with standard grades, 329 stainless steel clearly demonstrates its superior balance of mechanical and corrosion properties:
Versus 304: Much higher strength and chloride resistance.
Versus 316: Better pitting and stress corrosion resistance.
Versus 2205 (UNS S31803): Slightly lower molybdenum content, but good performance in medium chloride conditions at lower cost.
This balance makes 329 a cost-effective choice where both strength and corrosion resistance are critical, but super duplex grades (like 2507) may be over-specified or cost-prohibitive.
Heat treatment is crucial in controlling phase balance and mechanical performance:
Solution Annealing: Typically at 1050–1120°C, followed by rapid cooling to retain duplex structure.
Stress Relief: Usually performed below 300°C to avoid precipitation.
Careful control of heat cycles helps prevent formation of harmful intermetallic phases. Proper annealing ensures the final structure provides maximum corrosion resistance and toughness.
Reputable suppliers like SAKYSTEEL provide full traceability and certification with every batch of 329 stainless steel, ensuring compliance with international standards such as:
ASTM A182 / A240 / A276
EN 10088-3
ASME SA182 / SA240
NACE MR0175 / ISO 15156
Customers receive mill test certificates (EN 10204 3.1 or 3.2) showing mechanical, chemical, and nondestructive testing data. With advanced inspection and strict quality control, SAKYSTEEL ensures consistent product reliability across every delivery.
329 stainless steel is supplied in various product forms to meet different engineering needs:
Round Bars / Rods
Plates and Sheets
Pipes and Tubes (Seamless or Welded)
Forged Flanges and Fittings
Wire and Welding Filler Rods
Manufacturers and end-users can choose the most appropriate form depending on application requirements and fabrication processes.
Key benefits that make 329 stainless steel a smart material choice include:
Excellent corrosion resistance in marine and chloride environments.
High tensile and yield strength compared to 300-series steels.
Superior resistance to stress corrosion cracking and sulfide attack.
Good weldability and formability with proper heat control.
Long service life and reduced maintenance costs.
These advantages translate directly into improved performance and durability, ensuring long-term reliability in challenging operating conditions.
Using 329 stainless steel can also reduce lifecycle costs. Its long service life minimizes replacement frequency, while its strength allows for thinner wall sections, reducing overall material consumption.
Furthermore, stainless steel is 100% recyclable, aligning with modern sustainability goals. Many industries now prefer duplex grades like 329 for both technical and environmental reasons, offering an excellent balance between performance, cost, and sustainability.
With years of export experience and strong technical background, SAKYSTEEL supplies high-quality 329 stainless steel bars, plates, and tubes to global clients in the oil, gas, marine, and chemical sectors.
Our materials are:
Produced under strict metallurgical control.
Tested for corrosion, mechanical strength, and microstructure.
Delivered with complete documentation and inspection certificates.
Whether you need precision-cut plates or custom-machined bars, our team ensures fast delivery, competitive pricing, and reliable quality.
329 stainless steel stands as one of the most reliable materials for corrosive and high-stress environments. Its duplex structure, combining strength and corrosion resistance, makes it a versatile and efficient choice across multiple industries.
As global industries move toward higher performance standards and sustainability, materials like 329 will continue to gain popularity.
When selecting a trusted supplier, SAKYSTEEL remains committed to delivering the best quality stainless steel materials, backed by certification, technical expertise, and a strong reputation in the international market.
If you are looking for a dependable source of 329 stainless steel round bars, sheets, or pipes, contact SAKYSTEEL today to learn how we can support your next project with premium materials and professional service.