317 Stainless Steel: Properties and Key Applications
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Table Of Content
Table Of Content
317 Stainless Steel is classified as an austenitic stainless steel, notable for its high corrosion resistance and excellent mechanical properties. This grade is primarily alloyed with chromium (Cr), nickel (Ni), and molybdenum (Mo), which significantly enhance its resistance to pitting and crevice corrosion, particularly in chloride environments. The presence of molybdenum is particularly beneficial, as it improves the steel's performance in acidic conditions and increases its overall strength.
Comprehensive Overview
317 Stainless Steel is recognized for its superior resistance to corrosion compared to other stainless steel grades, making it a preferred choice in various applications, especially in chemical processing and marine environments. Its unique composition, which typically includes around 18% chromium, 14% nickel, and 3% molybdenum, contributes to its excellent mechanical properties, including high tensile strength and ductility.
Advantages:
- Corrosion Resistance: Exceptional resistance to a wide range of corrosive environments, including chlorides and sulfuric acid.
- High Strength: Retains strength at elevated temperatures, making it suitable for high-stress applications.
- Versatility: Can be used in various applications, from food processing to chemical manufacturing.
Limitations:
- Cost: Generally more expensive than lower-grade stainless steels due to its alloying elements.
- Workability: While it has good formability, it can be more challenging to machine compared to lower alloy steels.
Historically, 317 Stainless Steel has been utilized in industries where corrosion resistance is critical, such as in the production of chemical equipment, marine applications, and in the food industry. Its market position remains strong due to its unique properties, making it a common choice for engineers and designers.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S31700 | USA | Closest equivalent to AISI 317L |
| AISI/SAE | 317 | USA | Similar to 317L but with higher carbon content |
| ASTM | A240 | USA | Standard specification for chromium and chromium-nickel stainless steel plate, sheet, and strip for pressure vessels and general applications |
| EN | 1.4449 | Europe | Equivalent to 317 with minor compositional differences |
| JIS | SUS317 | Japan | Similar properties to AISI 317 |
| ISO | 1.4449 | International | Closest equivalent to AISI 317 |
The differences between equivalent grades can affect performance, particularly in terms of corrosion resistance and mechanical properties. For instance, 317L has a lower carbon content, which enhances its weldability and reduces the risk of carbide precipitation during welding.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| Cr (Chromium) | 18.0 - 20.0 |
| Ni (Nickel) | 12.0 - 15.0 |
| Mo (Molybdenum) | 2.5 - 3.0 |
| C (Carbon) | 0.08 max |
| Mn (Manganese) | 2.0 max |
| Si (Silicon) | 1.0 max |
| P (Phosphorus) | 0.045 max |
| S (Sulfur) | 0.030 max |
The primary role of chromium is to enhance corrosion resistance, while nickel contributes to toughness and ductility. Molybdenum further improves resistance to pitting and crevice corrosion, especially in chloride environments. Carbon, although present in small amounts, can affect weldability and corrosion resistance.
Mechanical Properties
| Property | Condition/Temper | Typical Value/Range (Metric - SI Units) | Typical Value/Range (Imperial Units) | Reference Standard for Test Method |
|---|---|---|---|---|
| Tensile Strength | Annealed | 515 - 690 MPa | 75 - 100 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Annealed | 205 - 310 MPa | 30 - 45 ksi | ASTM E8 |
| Elongation | Annealed | 40% - 50% | 40% - 50% | ASTM E8 |
| Reduction of Area | Annealed | 60% - 70% | 60% - 70% | ASTM E8 |
| Hardness (Rockwell B) | Annealed | 85 - 95 HRB | 85 - 95 HRB | ASTM E18 |
| Impact Strength (Charpy V-notch) | -40°C | 40 J | 30 ft-lbf | ASTM E23 |
The combination of high tensile and yield strength, along with good elongation, makes 317 Stainless Steel suitable for applications requiring structural integrity under mechanical loading. Its impact strength at low temperatures also indicates its reliability in cold environments.
Physical Properties
| Property | Condition/Temperature | Value (Metric - SI Units) | Value (Imperial Units) |
|---|---|---|---|
| Density | Room Temperature | 8.0 g/cm³ | 0.289 lb/in³ |
| Melting Point | - | 1400 - 1450 °C | 2550 - 2642 °F |
| Thermal Conductivity | Room Temperature | 16.2 W/m·K | 112 BTU·in/(hr·ft²·°F) |
| Specific Heat Capacity | Room Temperature | 500 J/kg·K | 0.12 BTU/lb·°F |
| Electrical Resistivity | Room Temperature | 0.72 µΩ·m | 0.0000013 Ω·in |
| Coefficient of Thermal Expansion | 20 - 100 °C | 16.0 x 10⁻⁶ /K | 8.9 x 10⁻⁶ /°F |
| Magnetic Permeability | Room Temperature | Non-magnetic | Non-magnetic |
The density and melting point indicate that 317 Stainless Steel can withstand high temperatures without losing structural integrity. Its thermal conductivity and specific heat capacity are important for applications involving heat exchange, while its non-magnetic nature makes it suitable for electronic and medical applications.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-10% | 20-60°C / 68-140°F | Excellent | Risk of pitting |
| Sulfuric Acid | 10-30% | 20-40°C / 68-104°F | Good | Moderate resistance |
| Hydrochloric Acid | 5-20% | 20-50°C / 68-122°F | Fair | Susceptible to localized corrosion |
| Acetic Acid | 5-20% | 20-60°C / 68-140°F | Good | Risk of stress corrosion cracking |
| Sea Water | - | Ambient | Excellent | Highly resistant |
317 Stainless Steel exhibits excellent resistance to a variety of corrosive agents, particularly in marine environments. Its performance in chloride-rich conditions is superior to many other stainless steels, such as 304 and 316 grades, which are more susceptible to pitting and crevice corrosion. However, it is important to note that while it performs well in sulfuric and acetic acids, it can be vulnerable to localized corrosion in hydrochloric acid.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 925 °C | 1700 °F | Suitable for high-temperature applications |
| Max Intermittent Service Temp | 1035 °C | 1900 °F | Can withstand short-term exposure |
| Scaling Temperature | 800 °C | 1470 °F | Risk of scaling above this temperature |
| Creep Strength considerations begin around | 600 °C | 1112 °F | Creep resistance decreases at high temps |
At elevated temperatures, 317 Stainless Steel maintains its strength and oxidation resistance, making it suitable for high-temperature applications. However, prolonged exposure to temperatures above 800 °C can lead to scaling, which may affect its surface properties and corrosion resistance.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER317 or ER317L | Argon | Good for thin sections |
| MIG | ER317 or ER317L | Argon + CO2 mix | Suitable for thicker sections |
| SMAW | E317 | - | Requires preheat |
317 Stainless Steel is generally considered to have good weldability, although preheating may be necessary to avoid cracking. Post-weld heat treatment can enhance the corrosion resistance of welded joints. Care should be taken to select appropriate filler metals to match the base material's properties.
Machinability
| Machining Parameter | 317 Stainless Steel | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 40 | 100 | Requires slower cutting speeds |
| Typical Cutting Speed (Turning) | 20 m/min | 60 m/min | Use carbide tools for best results |
317 Stainless Steel has a lower machinability index compared to free-machining steels like AISI 1212. Optimal conditions include using sharp tools and slower cutting speeds to minimize work hardening.
Formability
317 Stainless Steel exhibits good formability, allowing for cold and hot forming processes. However, due to its work-hardening characteristics, careful control of bending radii and forming speeds is essential to avoid cracking.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 1040 - 1120 °C / 1900 - 2050 °F | 1-2 hours | Air or water | Relieve stresses, improve ductility |
| Solution Treatment | 1000 - 1100 °C / 1830 - 2010 °F | 30 minutes | Water | Dissolve carbides, enhance corrosion resistance |
During heat treatment, 317 Stainless Steel undergoes metallurgical transformations that improve its microstructure and properties. Annealing helps relieve internal stresses, while solution treatment enhances corrosion resistance by dissolving carbides.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection (Brief) |
|---|---|---|---|
| Chemical Processing | Reactors and storage tanks | High corrosion resistance, strength | Essential for handling aggressive chemicals |
| Marine Engineering | Ship components | Excellent resistance to seawater | Prevents corrosion in marine environments |
| Food and Beverage | Processing equipment | Non-reactive, easy to clean | Meets hygiene standards |
| Pharmaceutical | Equipment and piping | Corrosion resistance, cleanliness | Critical for sterile environments |
Other applications include:
- Oil and gas industry components
- Heat exchangers
- Pulp and paper manufacturing
317 Stainless Steel is chosen for these applications due to its exceptional resistance to corrosion and ability to maintain structural integrity under challenging conditions.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | 317 Stainless Steel | 316 Stainless Steel | 304 Stainless Steel | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High tensile strength | Moderate tensile strength | Moderate tensile strength | 317 offers better performance in corrosive environments |
| Key Corrosion Aspect | Excellent in chlorides | Good in chlorides | Fair in chlorides | 317 is superior in chloride resistance |
| Weldability | Good | Excellent | Good | 316 is often preferred for welding |
| Machinability | Moderate | Moderate | High | 304 is easier to machine |
| Formability | Good | Good | Excellent | 304 has better formability |
| Approx. Relative Cost | Higher | Moderate | Lower | 317 is more expensive due to alloying elements |
| Typical Availability | Moderate | High | Very High | 304 is the most commonly available |
When selecting 317 Stainless Steel, considerations include its cost-effectiveness relative to performance, availability, and specific application requirements. While it may be more expensive than other grades, its superior corrosion resistance can lead to longer service life and reduced maintenance costs in harsh environments.
In summary, 317 Stainless Steel is a versatile and high-performance material suitable for a wide range of applications, particularly where corrosion resistance is paramount. Its unique properties make it a valuable choice for engineers and designers in various industries.