316LN Stainless Steel: Properties and Key Applications

316LN stainless steel is a low-carbon, nitrogen-enhanced version of the 316 stainless steel grade, classified as an austenitic stainless steel. It is primarily composed of iron, chromium, nickel, and molybdenum, with the addition of nitrogen to enhance its mechanical properties. The typical composition of 316LN includes approximately 16-18% chromium, 10-14% nickel, and 2-3% molybdenum, with nitrogen levels around 0.1-0.2%. This unique combination of alloying elements contributes to its excellent corrosion resistance, high strength, and good weldability.

Characteristics and Properties

316LN stainless steel is known for its superior resistance to pitting and crevice corrosion, especially in chloride environments. Its low carbon content minimizes the risk of carbide precipitation during welding, making it suitable for applications requiring high strength and corrosion resistance. The addition of nitrogen improves tensile strength and yield strength, making it a preferred choice in demanding applications.

Advantages (Pros):
- Excellent corrosion resistance, particularly in marine and chemical environments.
- High strength and toughness at elevated temperatures.
- Good weldability and formability.
- Low risk of sensitization due to low carbon content.

Limitations (Cons):
- Higher cost compared to standard stainless steels.
- Not as readily available as more common grades like 304 or 316.
- Limited resistance to certain reducing acids.

Historically, 316LN has been significant in industries such as petrochemical, marine, and pharmaceutical, where its corrosion resistance and mechanical properties are critical.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S31653	USA	Closest equivalent to 316L with enhanced nitrogen content.
AISI/SAE	316LN	USA	Low carbon variant of 316 with improved strength.
ASTM	A240/A240M	USA	Standard specification for chromium and chromium-nickel stainless steel plates.
EN	1.4406	Europe	Equivalent to 316LN with similar properties.
JIS	SUS316LN	Japan	Japanese standard equivalent with minor compositional differences.

The differences between 316LN and its equivalents often lie in the nitrogen content and specific mechanical properties, which can affect performance in certain applications. For instance, while 316L is known for its excellent weldability, 316LN offers enhanced strength, making it more suitable for high-stress environments.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Fe (Iron)	Balance
Cr (Chromium)	16.0 - 18.0
Ni (Nickel)	10.0 - 14.0
Mo (Molybdenum)	2.0 - 3.0
N (Nitrogen)	0.1 - 0.2
C (Carbon)	≤ 0.03

The primary role of chromium is to enhance corrosion resistance, while nickel improves toughness and ductility. Molybdenum provides additional resistance to pitting and crevice corrosion, particularly in chloride environments. Nitrogen enhances strength and improves resistance to stress corrosion cracking.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	Reference Standard for Test Method
Tensile Strength	Annealed	520 - 720 MPa	75 - 104 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
Hardness (Rockwell B)	Annealed	70 - 90 HRB	70 - 90 HRB	ASTM E18
Impact Strength	-20°C	40 J	29.5 ft-lbf	ASTM E23

The combination of high tensile and yield strength, along with good elongation, makes 316LN suitable for applications requiring structural integrity under mechanical loading. Its impact strength at low temperatures ensures performance in cryogenic environments.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temperature	8.0 g/cm³	0.289 lb/in³
Melting Point/Range	-	1375 - 1400 °C	2500 - 2550 °F
Thermal Conductivity	Room Temperature	16 W/m·K	92 BTU·in/ft²·h·°F
Specific Heat Capacity	Room Temperature	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	Room Temperature	0.72 µΩ·m	0.00000072 Ω·m
Coefficient of Thermal Expansion	20 - 100 °C	16.0 x 10⁻⁶ /K	8.9 x 10⁻⁶ /°F

The density and melting point indicate that 316LN can withstand high-temperature applications, while its thermal conductivity and specific heat capacity make it suitable for heat exchangers. The low electrical resistivity is beneficial in applications requiring electrical conductivity.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-10%	20-60°C / 68-140°F	Excellent	Risk of pitting corrosion.
Sulfuric Acid	10-20%	20-50°C / 68-122°F	Good	Limited resistance, especially at higher temperatures.
Hydrochloric Acid	5-10%	20-40°C / 68-104°F	Fair	Not recommended for prolonged exposure.
Sea Water	-	Ambient	Excellent	Highly resistant to marine environments.

316LN exhibits excellent resistance to a variety of corrosive agents, particularly in marine environments where chlorides are prevalent. However, it is less resistant to strong acids like hydrochloric acid, where alternative materials may be more suitable. Compared to 304 and 316 stainless steels, 316LN offers superior resistance to pitting and stress corrosion cracking, making it a preferred choice in aggressive environments.

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	870 °C	1600 °F	Can withstand short-term exposure to higher temperatures.
Scaling Temperature	800 °C	1470 °F	Risk of oxidation above this temperature.
Creep Strength considerations	600 °C	1112 °F	Creep resistance begins to decline above this temperature.

316LN maintains its strength and corrosion resistance at elevated temperatures, making it suitable for applications such as heat exchangers and pressure vessels. However, care must be taken to avoid oxidation and scaling at high temperatures.

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 + 2% CO2	Good for thicker sections.
SMAW	E316L	-	Suitable for field applications.

316LN is highly weldable, with the recommended filler metals ensuring compatibility and maintaining corrosion resistance. Pre- and post-weld heat treatments are often not necessary due to its low carbon content, reducing the risk of sensitization.

Machinability

Machining Parameter	316LN	AISI 1212	Notes/Tips
Relative Machinability Index	45%	100%	316LN is more challenging to machine.
Typical Cutting Speed (Turning)	25-30 m/min	50-60 m/min	Use carbide tools for best results.

Machining 316LN requires careful consideration of cutting speeds and tooling due to its work-hardening characteristics. Carbide tools are recommended to achieve optimal results.

Formability

316LN exhibits good formability, allowing for cold and hot forming processes. However, it is important to note that excessive cold working can lead to increased hardness and reduced ductility. Recommended bend radii should be adhered to in order to prevent cracking during forming operations.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Solution Annealing	1000 - 1100 °C / 1832 - 2012 °F	30 minutes	Air or Water	Dissolve carbides, improve corrosion resistance.
Stress Relief	400 - 600 °C / 752 - 1112 °F	1 hour	Air	Reduce residual stresses.

During heat treatment, 316LN undergoes metallurgical transformations that enhance its microstructure, improving its mechanical properties and corrosion resistance. Solution annealing is particularly effective in restoring ductility after cold working.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Marine	Shipbuilding	Corrosion resistance, strength	Exposure to seawater.
Chemical	Process piping	Corrosion resistance, weldability	Handling aggressive chemicals.
Pharmaceutical	Equipment fabrication	Cleanliness, corrosion resistance	Compliance with sanitary standards.
Oil & Gas	Offshore platforms	Strength, toughness, corrosion resistance	Harsh environmental conditions.

Other applications include:
* Food processing equipment
* Heat exchangers
* Pressure vessels
* Valves and fittings

316LN is chosen for these applications due to its excellent corrosion resistance and mechanical properties, which are critical in environments where hygiene and structural integrity are paramount.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	316LN	304	321	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate strength	High strength	316LN offers better corrosion resistance than 304.
Key Corrosion Aspect	Excellent	Good	Good	316LN is superior in chloride environments.
Weldability	Good	Excellent	Good	316LN requires careful welding practices.
Machinability	Moderate	Good	Moderate	316LN is harder to machine than 304.
Formability	Good	Excellent	Good	316LN has slightly reduced formability.
Approx. Relative Cost	Higher	Lower	Higher	Cost considerations may affect selection.
Typical Availability	Moderate	High	Moderate	304 is more commonly available.

When selecting 316LN, considerations include cost-effectiveness, availability, and specific application requirements. Its unique properties make it suitable for niche applications where performance is critical, despite its higher cost compared to more common grades like 304. Additionally, its low magnetic permeability makes it suitable for applications in sensitive environments.

In conclusion, 316LN stainless steel is a versatile and high-performance material that excels in demanding environments, offering a balance of strength, corrosion resistance, and fabricability. Its unique properties make it a preferred choice in various industries, ensuring reliability and longevity in applications where failure is not an option.