316LVM Stainless Steel: Properties and Key Applications
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Table Of Content
316LVM stainless steel is a specialized variant of the 316L grade, classified as an austenitic stainless steel. This low-carbon steel is primarily alloyed with chromium (16-18%), nickel (10-14%), and molybdenum (2-3%), which enhance its corrosion resistance and mechanical properties. The "VM" designation indicates that it is a vacuum melted version, which significantly reduces the presence of impurities and enhances the overall quality of the steel.
Comprehensive Overview
316LVM stainless steel is renowned for its exceptional corrosion resistance, particularly in harsh environments. Its low carbon content minimizes the risk of carbide precipitation during welding, making it suitable for applications requiring high weld integrity. The primary characteristics of 316LVM include excellent ductility, high tensile strength, and good formability, which make it a preferred choice in various industries, especially in biomedical applications.
Advantages:
- Corrosion Resistance: Outstanding resistance to pitting and crevice corrosion, especially in chloride environments.
- Biocompatibility: Its vacuum melting process results in a cleaner steel, making it suitable for medical implants and devices.
- Weldability: Excellent weldability without the need for post-weld heat treatment.
Limitations:
- Cost: Higher production costs due to the vacuum melting process.
- Strength Limitations: While strong, it may not be suitable for applications requiring higher strength alloys.
Historically, 316LVM has found significant use in the medical field, particularly for surgical implants and devices, due to its biocompatibility and corrosion resistance. Its market position is strong, particularly in specialized applications where purity and performance are paramount.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S31673 | USA | Closest equivalent to 316L with lower carbon content |
| AISI/SAE | 316L | USA | Commonly used designation for 316L stainless steel |
| ASTM | A240/A240M | USA | Standard specification for stainless steel sheet and plate |
| EN | 1.4404 | Europe | Equivalent grade in European standards |
| JIS | SUS316L | Japan | Japanese equivalent with similar properties |
| ISO | 316L | International | International standard designation |
The differences between these grades often lie in the specific composition and processing methods, which can affect performance in specific applications. For instance, while 316LVM is designed for high purity, standard 316L may contain more impurities due to less stringent manufacturing processes.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| Cr (Chromium) | 16.0 - 18.0 |
| Ni (Nickel) | 10.0 - 14.0 |
| Mo (Molybdenum) | 2.0 - 3.0 |
| C (Carbon) | ≤ 0.03 |
| Mn (Manganese) | ≤ 2.0 |
| Si (Silicon) | ≤ 1.0 |
| P (Phosphorus) | ≤ 0.045 |
| S (Sulfur) | ≤ 0.03 |
The key alloying elements in 316LVM stainless steel play crucial roles:
- Chromium: Enhances corrosion resistance and contributes to the formation of a passive oxide layer.
- Nickel: Improves toughness and ductility, particularly at low temperatures.
- Molybdenum: Increases resistance to pitting corrosion, especially in chloride environments.
Mechanical Properties
| Property | Condition/Temper | Typical Value/Range (Metric) | Typical Value/Range (Imperial) | Reference Standard for Test Method |
|---|---|---|---|---|
| Tensile Strength | Annealed | 480 - 620 MPa | 70 - 90 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Annealed | 170 - 310 MPa | 25 - 45 ksi | ASTM E8 |
| Elongation | Annealed | 40 - 50% | 40 - 50% | ASTM E8 |
| Hardness (Rockwell B) | Annealed | 70 - 90 HRB | 70 - 90 HRB | ASTM E18 |
| Impact Strength (Charpy) | -20°C | 40 J | 30 ft-lbf | ASTM E23 |
The mechanical properties of 316LVM stainless steel make it suitable for applications requiring high strength and ductility. Its tensile strength and yield strength provide excellent structural integrity, while its elongation indicates good formability, making it ideal for complex shapes and components.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | Room Temperature | 8.0 g/cm³ | 0.289 lb/in³ |
| Melting Point | - | 1375 - 1400 °C | 2500 - 2550 °F |
| Thermal Conductivity | Room Temperature | 16 W/m·K | 9.3 BTU·in/h·ft²·°F |
| Specific Heat Capacity | Room Temperature | 500 J/kg·K | 0.12 BTU/lb·°F |
| Electrical Resistivity | Room Temperature | 0.72 µΩ·m | 0.72 µΩ·in |
| Coefficient of Thermal Expansion | 20 - 100 °C | 16.0 x 10⁻⁶/K | 8.9 x 10⁻⁶/°F |
The density and melting point of 316LVM indicate its robustness, while the thermal conductivity and specific heat capacity suggest its suitability for applications involving heat transfer. The electrical resistivity is relatively low, making it a good conductor, which is beneficial in certain electronic applications.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-10 | 20-60 / 68-140 | Excellent | Risk of pitting corrosion |
| Sulfuric Acid | 10-30 | 20-60 / 68-140 | Good | Susceptible to SCC |
| Hydrochloric Acid | 5-10 | 20-60 / 68-140 | Fair | Not recommended |
| Sea Water | - | Ambient | Excellent | Highly resistant |
316LVM stainless steel exhibits exceptional resistance to a variety of corrosive environments, particularly in chloride-rich conditions, which is critical for marine and chemical processing applications. However, it is susceptible to stress corrosion cracking (SCC) in environments containing chlorides, particularly at elevated temperatures.
When compared to other stainless steels, such as 304 and 316, 316LVM offers superior resistance to pitting and crevice corrosion, making it the preferred choice in highly corrosive environments. Its vacuum melting process further enhances its resistance by minimizing impurities that can lead to localized corrosion.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 870 °C | 1600 °F | Suitable for high-temperature applications |
| Max Intermittent Service Temp | 925 °C | 1700 °F | Short-term exposure only |
| Scaling Temperature | 800 °C | 1470 °F | Risk of oxidation beyond this limit |
At elevated temperatures, 316LVM maintains its mechanical properties and corrosion resistance, making it suitable for high-temperature applications. However, prolonged exposure to temperatures above 870 °C can lead to oxidation and scaling, which may compromise its integrity.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER316L | Argon | Excellent for thin sections |
| MIG | ER316L | Argon + CO2 | Good for thicker sections |
| SMAW | E316L | - | Suitable for field welding |
316LVM stainless steel is highly weldable, with minimal risk of cracking. Pre- and post-weld heat treatments are generally not required, which simplifies the fabrication process. However, care must be taken to avoid overheating during welding, which can lead to changes in microstructure.
Machinability
| Machining Parameter | 316LVM | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 50 | 100 | Requires slower cutting speeds |
| Typical Cutting Speed (Turning) | 30-50 m/min | 80-120 m/min | Use carbide tools for best results |
Machining 316LVM can be challenging due to its toughness and work hardening characteristics. Optimal conditions include using sharp tools and slower cutting speeds to prevent excessive heat buildup and tool wear.
Formability
316LVM exhibits good formability, allowing for cold and hot working processes. However, due to its work-hardening nature, careful consideration must be given to bend radii and forming techniques to avoid cracking.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Solution Annealing | 1000 - 1100 °C / 1830 - 2010 °F | 30 minutes | Air or Water | Dissolves carbides, enhances corrosion resistance |
| Stress Relief | 300 - 500 °C / 570 - 930 °F | 1 hour | Air | Reduces residual stresses |
Heat treatment processes such as solution annealing are critical for optimizing the microstructure of 316LVM, enhancing its corrosion resistance and mechanical properties. The process dissolves carbides that may form during welding or fabrication, ensuring a uniform structure.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Medical | Surgical implants | Biocompatibility, corrosion resistance | Essential for patient safety and longevity |
| Marine | Boat fittings | Corrosion resistance, strength | Exposure to harsh environments |
| Chemical | Process equipment | High-temperature resistance, corrosion resistance | Durability in aggressive chemicals |
| Food Processing | Food handling equipment | Cleanliness, corrosion resistance | Compliance with hygiene standards |
Other applications include:
- Aerospace components
- Pharmaceutical equipment
- Oil and gas industry components
316LVM is chosen for these applications due to its unique combination of mechanical properties, corrosion resistance, and biocompatibility, making it ideal for environments where reliability and safety are paramount.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | 316LVM | 304 | 316 | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High Strength | Moderate Strength | High Strength | 316LVM offers superior strength and ductility |
| Key Corrosion Aspect | Excellent | Good | Excellent | 316LVM excels in chloride environments |
| Weldability | Excellent | Good | Good | 316LVM requires no post-weld treatment |
| Machinability | Moderate | Good | Moderate | 316LVM is tougher to machine than 304 |
| Formability | Good | Excellent | Good | 316LVM has good formability but requires care |
| Approx. Relative Cost | High | Moderate | Moderate | 316LVM is more expensive due to processing |
| Typical Availability | Moderate | High | High | 316LVM may be less readily available than 304 |
When selecting 316LVM stainless steel, considerations include its cost-effectiveness, availability, and specific application requirements. Its unique properties make it suitable for specialized applications, particularly in the medical and marine industries. The trade-offs in terms of cost and machinability must be balanced against the performance benefits it offers in critical environments.
In summary, 316LVM stainless steel stands out for its superior corrosion resistance, mechanical properties, and biocompatibility, making it an essential material in various high-performance applications.