404 Stainless Steel: Properties and Key Applications
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Table Of Content
Table Of Content
404 Stainless Steel is classified as an austenitic stainless steel, primarily known for its high chromium and nickel content, which imparts excellent corrosion resistance and good mechanical properties. The primary alloying elements in 404 stainless steel include chromium (Cr), nickel (Ni), and molybdenum (Mo), with the following approximate composition:
| Element | Percentage Range (%) |
|---|---|
| Chromium (Cr) | 18.0 - 20.0 |
| Nickel (Ni) | 8.0 - 10.0 |
| Molybdenum (Mo) | 0.5 - 1.0 |
| Carbon (C) | ≤ 0.03 |
| Manganese (Mn) | 2.0 - 3.0 |
| Silicon (Si) | ≤ 1.0 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.03 |
The inherent properties of 404 stainless steel include excellent weldability, good formability, and resistance to oxidation and corrosion. Its unique microstructure allows it to maintain strength and toughness at elevated temperatures, making it suitable for various applications in industries such as automotive, aerospace, and chemical processing.
Advantages and Limitations
Advantages:
- Corrosion Resistance: 404 stainless steel exhibits excellent resistance to a wide range of corrosive environments, including atmospheric conditions and many chemicals.
- Weldability: This grade can be easily welded using standard techniques, making it versatile for fabrication.
- Mechanical Properties: It offers a good balance of strength and ductility, which is essential for structural applications.
Limitations:
- Cost: The alloying elements can make 404 stainless steel more expensive than carbon steels.
- Work Hardening: While it can be formed, excessive cold working can lead to work hardening, which may complicate further processing.
Historically, 404 stainless steel has been significant in applications requiring both strength and corrosion resistance, positioning it as a reliable choice in various engineering sectors.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S40400 | USA | Closest equivalent to AISI 404 |
| AISI/SAE | 404 | USA | Minor compositional differences to be aware of |
| ASTM | A240 | USA | Standard specification for stainless steel plates |
| EN | 1.4002 | Europe | Similar properties but may differ in mechanical performance |
| JIS | SUS 404 | Japan | Comparable but may have different processing standards |
The differences between equivalent grades often lie in the specific composition and mechanical properties, which can affect performance in particular applications. For instance, while both AISI 404 and EN 1.4002 may offer similar corrosion resistance, their tensile strength and ductility can vary, influencing their suitability for specific engineering tasks.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| Cr (Chromium) | 18.0 - 20.0 |
| Ni (Nickel) | 8.0 - 10.0 |
| Mo (Molybdenum) | 0.5 - 1.0 |
| C (Carbon) | ≤ 0.03 |
| Mn (Manganese) | 2.0 - 3.0 |
| Si (Silicon) | ≤ 1.0 |
| P (Phosphorus) | ≤ 0.045 |
| S (Sulfur) | ≤ 0.03 |
The primary role of chromium in 404 stainless steel is to enhance corrosion resistance and improve hardness. Nickel contributes to the steel's toughness and ductility, while molybdenum increases resistance to pitting and crevice corrosion, particularly in chloride environments.
Mechanical Properties
| Property | Condition/Temper | Test Temperature | Typical Value/Range (Metric - SI Units) | Typical Value/Range (Imperial Units) | Reference Standard for Test Method |
|---|---|---|---|---|---|
| Tensile Strength | Annealed | Room Temp | 520 - 750 MPa | 75 - 109 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Annealed | Room Temp | 210 - 310 MPa | 30 - 45 ksi | ASTM E8 |
| Elongation | Annealed | Room Temp | 40 - 50% | 40 - 50% | ASTM E8 |
| Hardness | Annealed | Room Temp | 160 - 220 HB | 90 - 100 HRB | ASTM E10 |
| Impact Strength | Annealed | -20°C | 40 J | 30 ft-lbf | ASTM E23 |
The combination of these mechanical properties makes 404 stainless steel suitable for applications requiring high strength and ductility, such as structural components in buildings and machinery. Its ability to withstand significant loads while maintaining integrity under stress is crucial for safety and performance.
Physical Properties
| Property | Condition/Temperature | Value (Metric - SI Units) | Value (Imperial Units) |
|---|---|---|---|
| Density | Room Temp | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting Point | - | 1400 - 1450 °C | 2550 - 2642 °F |
| Thermal Conductivity | Room Temp | 16 W/m·K | 9.3 BTU·in/ft²·h·°F |
| Specific Heat Capacity | Room Temp | 500 J/kg·K | 0.12 BTU/lb·°F |
| Electrical Resistivity | Room Temp | 0.73 µΩ·m | 0.00000073 Ω·in |
| Coefficient of Thermal Expansion | 20 - 100 °C | 16.5 x 10⁻⁶ /K | 9.2 x 10⁻⁶ /°F |
The density and melting point of 404 stainless steel indicate its robustness, making it suitable for high-temperature applications. The thermal conductivity and specific heat capacity are essential for applications involving heat exchange, while the electrical resistivity is relevant in electrical applications.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3.5% | 25°C/77°F | Good | Risk of pitting |
| Sulfuric Acid | 10% | 20°C/68°F | Fair | Susceptible to SCC |
| Acetic Acid | 5% | 25°C/77°F | Good | Resistant to localized corrosion |
| Atmospheric Conditions | - | - | Excellent | Performs well in humid environments |
404 stainless steel exhibits excellent resistance to atmospheric corrosion and good resistance to many acids and chlorides. However, it is susceptible to stress corrosion cracking (SCC) in certain environments, particularly in the presence of chlorides. Compared to 304 stainless steel, which offers similar corrosion resistance but with better performance in acidic environments, 404 may be preferred in applications where chloride exposure is a concern.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 800 °C | 1472 °F | Suitable for high-temperature applications |
| Max Intermittent Service Temp | 900 °C | 1652 °F | Can withstand short-term exposure |
| Scaling Temperature | 1000 °C | 1832 °F | Risk of oxidation beyond this limit |
At elevated temperatures, 404 stainless steel maintains its strength and oxidation resistance, making it suitable for applications in high-temperature environments. However, prolonged exposure above 800 °C can lead to scaling and degradation of mechanical properties.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER404 | Argon | Good for thin sections |
| MIG | ER404 | Argon/CO2 | Suitable for thicker sections |
| Stick | E404 | - | Not commonly used |
404 stainless steel is highly weldable using various methods, including TIG and MIG welding. Preheating may be necessary for thicker sections to avoid cracking. Post-weld heat treatment can enhance the mechanical properties of the weld.
Machinability
| Machining Parameter | [404 Stainless Steel] | [AISI 1212] | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 60% | 100% | More difficult to machine than carbon steels |
| Typical Cutting Speed (Turning) | 30 m/min | 50 m/min | Use carbide tools for best results |
Machining 404 stainless steel can be challenging due to its work-hardening characteristics. Utilizing appropriate tooling and cutting speeds is essential for efficient machining.
Formability
404 stainless steel can be formed through both cold and hot processes. Cold forming may lead to work hardening, while hot forming allows for better ductility. The minimum bend radius should be considered during fabrication to avoid cracking.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 1000 - 1100 °C / 1832 - 2012 °F | 1 - 2 hours | Air cool | Relieve stresses, improve ductility |
| Solution Treatment | 1050 - 1150 °C / 1922 - 2102 °F | 30 minutes | Water quench | Enhance corrosion resistance |
Heat treatment processes such as annealing and solution treatment are critical for optimizing the microstructure of 404 stainless steel, enhancing its mechanical properties and corrosion resistance.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection (Brief) |
|---|---|---|---|
| Automotive | Exhaust systems | Corrosion resistance, high-temperature strength | Durability in harsh environments |
| Chemical Processing | Storage tanks | Corrosion resistance, weldability | Safety and reliability in chemical handling |
| Aerospace | Structural components | Strength-to-weight ratio, oxidation resistance | Performance under extreme conditions |
Other applications include:
* - Food processing equipment
* - Marine environments
* - Architectural structures
404 stainless steel is chosen for these applications due to its excellent balance of strength, corrosion resistance, and ease of fabrication, ensuring long-lasting performance in demanding environments.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | 404 Stainless Steel | 304 Stainless Steel | 316 Stainless Steel | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High strength | Moderate strength | High strength | 404 offers better strength than 304 but less than 316 |
| Key Corrosion Aspect | Good in mild environments | Excellent in many environments | Superior in chloride environments | 316 is preferred for marine applications |
| Weldability | Excellent | Excellent | Good | All grades are weldable, but 316 may require more care |
| Machinability | Moderate | Good | Fair | 404 is harder to machine than 304 |
| Formability | Good | Excellent | Good | 404 is less formable than 304 |
| Approx. Relative Cost | Moderate | Lower | Higher | 404 is cost-effective for specific applications |
| Typical Availability | Moderate | High | High | 304 and 316 are more commonly stocked |
When selecting 404 stainless steel, considerations include cost-effectiveness, availability, and specific application requirements. Its unique properties make it suitable for niche applications, particularly where a balance of strength and corrosion resistance is critical. Additionally, safety factors and environmental conditions should be assessed to ensure optimal performance and longevity in service.