STAINLESS STEEL GRADE
SUS 439L Stainless Steel
SUS 439 is a low-carbon, titanium-stabilized ferritic stainless steel containing approximately 17–19% chromium. It combines good corrosion resistance, oxidation resistance, weldability, formability, and thermal-fatigue performance.
Compared with SUS 409L, its higher chromium content provides better resistance to atmospheric corrosion and exhaust condensates. Compared with austenitic grades such as SUS 304, SUS 439 is magnetic, contains little or no deliberately added nickel, and has lower thermal expansion.
These characteristics make SUS 439 suitable for automotive exhaust systems, heat exchangers, hot-water tanks, appliance components, kitchen equipment, and fabricated parts exposed to moderate corrosion and repeated temperature changes.
MATERIAL INTRODUCTION
SUS 439L Stainless Steel Overview
SUS 439 belongs to the ferritic stainless steel family. Its ferritic crystal structure makes the material magnetic and gives it lower thermal expansion and higher thermal conductivity than common austenitic grades.
Titanium stabilization helps control chromium-carbide formation during welding and elevated-temperature exposure. This improves resistance to weld-related sensitization and supports the production of welded tubes, tanks, exhaust parts, and fabricated assemblies.
Type 439 is broadly associated with UNS S43035 and EN 1.4510, although equivalent designations may have different composition limits, mechanical requirements, testing methods, and certification rules.
SUS 439L Equivalent Grades
SUS 439 is a titanium-stabilized ferritic stainless steel broadly associated with Type 439, UNS S43035, and EN 1.4510. These designations describe comparable materials intended for applications requiring corrosion resistance, weldability, and thermal-cycling performance.
| Standard or System | Equivalent Designation |
|---|---|
| JIS | SUS 439 |
| AISI | Type 439 |
| ASTM / UNS | Type 439 / S43035 |
| EN Material Number | 1.4510 |
| EN Steel Name | X3CrTi17 |
Designation note: “SUS 439L” is sometimes used informally to emphasize low carbon content, but the recognized JIS designation is generally SUS 439. Equivalent grades are broadly comparable rather than automatically interchangeable. Chemical limits, stabilization requirements, mechanical properties, dimensions, testing, and certification can vary by specification and product form.
Key Characteristics of SUS 439L
SUS 439 is a low-carbon, titanium-stabilized ferritic stainless steel designed to combine corrosion resistance, weldability, formability, and dependable performance under repeated temperature changes. It is commonly selected for automotive exhaust components, heat exchangers, hot-water tanks, appliances, and welded tubing.
Titanium-Stabilized Composition
Titanium binds carbon and nitrogen, helping reduce sensitization and preserve corrosion resistance around properly fabricated welded areas.
Good General Corrosion Resistance
Its approximately 17–19% chromium content provides better general corrosion resistance than lower-chromium ferritic grades such as SUS 409L.
Good Oxidation Resistance
SUS 439 offers useful resistance to oxidation and scaling in compatible elevated-temperature applications, including selected exhaust and heating components.
Strong Thermal-Cycling Performance
Its relatively low thermal expansion helps reduce thermal stress during repeated heating and cooling, supporting exhaust-system and heat-related applications.
Good Weldability
The stabilized composition makes SUS 439 suitable for welded tubing, tanks, heat exchangers, and fabricated assemblies when appropriate ferritic stainless steel procedures are used.
Good Formability
The grade can be bent, roll-formed, stamped, drawn, and formed into tubing and complex components. Formability depends on thickness, condition, tooling, and forming direction.
Efficient Heat Transfer
SUS 439 generally provides higher thermal conductivity than common austenitic stainless steels, supporting selected heat exchangers, burners, and thermally cycled components.
Lower Thermal Expansion
Its ferritic structure expands less than austenitic grades such as SUS 304, helping improve dimensional stability during temperature changes.
Naturally Magnetic
SUS 439 has a ferritic microstructure and is magnetic in both annealed and cold-worked conditions.
Nickel-Efficient Material
Because the grade does not depend on the high nickel content used in austenitic stainless steels, it can offer stable alloy costs for compatible applications.
Designation note: The recognized JIS designation is generally SUS 439. “SUS 439L” may be used informally to emphasize its low-carbon composition. Final material selection should be based on the applicable specification, service environment, product form, and material test certificate.
SUS 439LChemical Composition
SUS 439 is a low-carbon ferritic stainless steel containing approximately 17–19% chromium. Titanium stabilizes carbon and nitrogen, helping improve weldability and resistance to sensitization during fabrication and elevated-temperature service.
| Element | Minimum | Maximum |
|---|---|---|
| Carbon (C) | — | 0.030% |
| Silicon (Si) | — | 1.00% |
| Manganese (Mn) | — | 1.00% |
| Phosphorus (P) | — | 0.040% |
| Sulfur (S) | — | 0.030% |
| Chromium (Cr) | 17.00% | 19.00% |
| Nickel (Ni) | — | 0.50% |
| Nitrogen (N) | — | 0.030% |
| Aluminum (Al) | — | 0.150% |
| Titanium (Ti) | 0.20 + 4(C + N) | 0.75% |
| Iron (Fe) | Balance | Balance |
Values are common reference limits for Type 439 / UNS S43035 and may differ from specific JIS, ASTM, EN, mill, or product-form requirements. Titanium is controlled by a stabilization formula based on carbon and nitrogen content. Use the governing material specification and mill test certificate for procurement and compliance. The recognized JIS designation is generally SUS 439; “SUS 439L” is sometimes used informally to emphasize its low-carbon composition.
SUS 439L Mechanical Properties
Annealed SUS 439 provides moderate strength and useful ductility for automotive exhaust components, heat exchangers, hot-water tanks, appliance parts, welded tubing, and other fabricated products exposed to repeated temperature changes.
| Mechanical Property | Requirement | Unit |
|---|---|---|
| 0.2% Proof Strength | ≥205 | MPa (N/mm²) |
| Tensile Strength | ≥415 | MPa (N/mm²) |
| Elongation | ≥22 | % |
| Rockwell Hardness | ≤89 | HRB |
These are common reference values for annealed flat products. Mechanical requirements vary according to the governing JIS, ASTM, or EN standard, product form, thickness, heat treatment, processing condition, and test direction. Confirm final requirements using the applicable specification and material test certificate. The recognized JIS designation is generally SUS 439; “SUS 439L” may be used informally to emphasize its low-carbon composition.
Physical Properties of SUS 439L
SUS 439 has higher thermal conductivity and lower thermal expansion than common austenitic stainless steels. These properties support dimensional stability, heat transfer, and thermal-fatigue performance in automotive exhaust systems, heat exchangers, hot-water tanks, and heating components.
| Physical Property | Reference Value | Unit |
|---|---|---|
| Density | Approx. 7.7 | g/cm³ |
| Elastic Modulus | Approx. 200–220 | GPa |
| Thermal Conductivity | Approx. 25–26 | W/m·K |
| Specific Heat Capacity | Approx. 460 | J/kg·K |
| Mean Thermal Expansion | Approx. 10–11 | µm/m·K |
| Electrical Resistivity | Approx. 0.60 | µΩ·m |
| Magnetic Response | Magnetic | — |
Values are approximate room-temperature references and may vary with composition, product form, processing condition, temperature, and testing method. Use the applicable material standard and supplier documentation for engineering calculations. The recognized JIS designation is generally SUS 439; “SUS 439L” may be used informally to emphasize its low-carbon composition.
SUS 439 vs. SUS 409L
SUS 439 and SUS 409L are stabilized ferritic stainless steels commonly evaluated for automotive exhaust and thermally cycled components. SUS 439 contains more chromium and generally provides better corrosion resistance, oxidation resistance, and surface appearance, while SUS 409L is frequently selected for cost-sensitive functional exhaust components.
| Feature | SUS 439 | SUS 409L |
|---|---|---|
| Stainless Steel Family | Ferritic stainless steel | Ferritic stainless steel |
| Chromium Content | Approximately 17–19% | Approximately 10.5–11.75% |
| Carbon Content | Maximum approximately 0.030% | Maximum approximately 0.030% |
| Stabilization | Primarily titanium-stabilized | Titanium-stabilized |
| General Corrosion Resistance | Better than SUS 409L in many mild atmospheric, condensate, and aqueous environments | Moderate; better than carbon steel, but surface staining may occur |
| Oxidation Resistance | Generally better because of its higher chromium content | Suitable for many standard automotive exhaust applications |
| Thermal-Cycling Performance | Good dimensional stability and resistance to repeated temperature changes | Good thermal-fatigue performance for cost-sensitive exhaust parts |
| Weldability | Good when suitable ferritic stainless steel procedures are used | Good when suitable ferritic stainless steel procedures are used |
| Surface Appearance | Better suited to applications requiring improved appearance and staining resistance | Usually selected where functional performance is more important than appearance |
| Magnetic Response | Magnetic | Magnetic |
| Typical Applications | Exhaust components, heat exchangers, hot-water tanks, appliance parts, burners, and welded tubing | Exhaust pipes, mufflers, catalytic-converter shells, heat shields, and industrial exhaust components |
| Common Selection Reason | Higher corrosion and oxidation resistance for more demanding ferritic stainless steel applications | Lower-cost functional performance for compatible exhaust and thermal applications |
Neither grade is automatically suitable for seawater, severe chloride exposure, strong acids, or highly corrosive chemical-processing environments. Final selection should consider temperature, condensate chemistry, chloride exposure, fabrication, required appearance, service life, governing specification, and material test certificate.
Corrosion and Oxidation Resistance of SUS 439L
SUS 439 combines approximately 17–19% chromium with a stabilized ferritic structure. It generally provides better corrosion and oxidation resistance than SUS 409L and is suitable for automotive exhaust systems, heat exchangers, hot-water tanks, appliance components, and other fabricated parts exposed to mild corrosion and repeated temperature changes.
General Corrosion Resistance
Chromium forms a passive oxide layer that protects the underlying metal in compatible atmospheric and aqueous environments. Titanium stabilization helps preserve corrosion resistance around properly fabricated welded areas.
- Better general corrosion resistance than SUS 409L
- Good performance in many indoor and mildly corrosive environments
- Suitable for selected hot-water and condensate applications
- Useful where improved staining resistance is required
Oxidation and Thermal-Cycling Resistance
SUS 439 provides useful resistance to oxidation and scaling in compatible elevated-temperature environments. Its relatively low thermal expansion helps reduce stress during repeated heating and cooling.
- Good resistance to repeated thermal cycling
- Suitable for selected automotive exhaust components
- Lower thermal expansion than austenitic stainless steels
- Useful dimensional stability at changing temperatures
Commonly Suitable Environments
SUS 439 is frequently evaluated where moderate corrosion resistance, welded fabrication, heat transfer, and thermal stability are required.
- Automotive exhaust and condensate exposure
- Hot-water tanks and compatible water systems
- Heat-exchanger tubing and fabricated components
- Kitchen and household appliance components
- Burners, heat shields, and industrial thermal parts
Important Service Limitations
SUS 439 is not a substitute for higher-alloy stainless steel in every environment. Suitability depends on chloride concentration, acidity, temperature, drainage, surface condition, and required service life.
- Continuous seawater or saltwater immersion
- High-chloride or stagnant-water conditions
- Hydrochloric acid and strong reducing acids
- Highly corrosive chemical-processing environments
- Poorly drained crevices and concentrated deposits
Maintaining Corrosion Resistance
Appropriate fabrication, cleaning, component design, and maintenance help preserve the protective surface and extend service life.
- Avoid contamination from carbon-steel tools and grinding dust
- Control welding heat input and use suitable shielding
- Remove weld residues and fabrication contamination
- Prevent trapped moisture and stagnant condensate
- Select cleaning chemicals compatible with ferritic stainless steel
Selecting the Correct Grade
When SUS 439 cannot provide sufficient resistance, another grade should be evaluated according to the actual operating environment.
- Consider SUS 304 for broader general corrosion resistance
- Consider SUS 316L for improved chloride resistance
- Consider duplex or higher-alloy grades for severe environments
- Confirm suitability through testing when conditions are uncertain
Selection note: Oxidation resistance at elevated temperature does not automatically indicate resistance to aqueous corrosion, chlorides, or strong chemicals. Confirm the actual temperature, exposure duration, gas composition, condensate chemistry, fabrication condition, loading, and maintenance requirements before specifying SUS 439. Final selection should follow the governing standard and material test certificate.
SUS 439 Stainless Steel Applications
Automotive Exhaust Systems
Common applications include exhaust pipes, mufflers, resonators, catalytic-converter shells, manifolds, and related components.
Heat Exchangers
Its thermal conductivity, corrosion resistance, and weldability support selected heat-exchanger tubing and fabricated components.
Hot-Water Tanks
Type 439 is used for selected welded hot-water tanks and tubing applications. ASTM specifically notes TP439 for hot-water tank service. ASTM A268/A268M
Kitchen and Household Appliances
Applications include appliance panels, oven components, burners, housings, and internal components exposed to compatible temperatures and corrosion conditions.
Commercial Food Equipment
SUS 439 may be used for equipment panels, cabinets, counters, tubing, and fabricated parts when its corrosion resistance meets the operating and cleaning conditions.
Industrial Thermal Components
Selected applications include burner parts, furnace components, exhaust ducts, enclosures, heat shields, and equipment exposed to repeated temperature changes.
faq
Stainless Steel SUS 439L Material FAQ
Yes. SUS 439 has a ferritic microstructure and is magnetic.
It depends on the application. SUS 439 is generally better suited to welded components and thermal cycling, while SUS 430 is widely used for decorative and indoor appliance components.
SUS 439 generally provides better corrosion and oxidation resistance because of its higher chromium content. SUS 409L may remain more economical for less demanding exhaust applications.
Not automatically. SUS 304 generally provides better overall corrosion resistance and ductility. SUS 439 offers lower thermal expansion, useful thermal conductivity, magnetic behavior, and potentially lower alloy cost.
It is generally not recommended for continuous seawater immersion or severe chloride exposure. SUS 316L, duplex stainless steel, or a higher-alloy material may be required.
Major uses include automotive exhaust components, welded hot-water tanks, heat exchangers, appliance components, tubing, and thermally cycled fabricated parts.
SUS 439 is officially characterized as a titanium-stabilized 17% chromium ferritic grade with improved corrosion resistance, formability, and weldability compared with unstabilized ferritic grades. Its ferritic structure also makes it magnetic and prevents hardening through conventional heat treatment. Outokumpu, Nippon Steel
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