320 Stainless Steel: Properties and Key Applications

320 Stainless Steel is classified as an austenitic stainless steel, primarily composed of iron, chromium, and nickel, with a low carbon content. This specific grade typically contains around 18% chromium and 8% nickel, which contribute significantly to its corrosion resistance and mechanical properties. The low carbon content enhances its weldability and reduces the risk of carbide precipitation during welding, making it suitable for various applications in industries where high corrosion resistance and formability are essential.

Comprehensive Overview

320 Stainless Steel is known for its excellent resistance to oxidation and corrosion, particularly in high-temperature environments. Its austenitic structure provides good ductility and toughness, making it a preferred choice for applications that require both strength and flexibility. The primary alloying elements, chromium and nickel, play crucial roles in enhancing the steel's resistance to corrosive environments, while the low carbon content minimizes the risk of intergranular corrosion.

Advantages:
- Corrosion Resistance: Exceptional resistance to a wide range of corrosive environments, including acidic and alkaline conditions.
- High-Temperature Stability: Maintains strength and oxidation resistance at elevated temperatures.
- Weldability: Low carbon content allows for easy welding without significant risk of weld decay.

Limitations:
- Cost: Generally more expensive than carbon steels due to alloying elements.
- Work Hardening: Can become hard and brittle when subjected to extensive cold working, which may require careful handling during fabrication.

Historically, 320 Stainless Steel has been utilized in various applications, particularly in the food processing, chemical, and petrochemical industries, where its unique properties are highly valued. Its market position is strong, with a consistent demand for its use in environments that challenge other materials.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S32000	USA	Closest equivalent to AISI 304 with minor compositional differences.
AISI/SAE	320	USA	Similar to 316 but with different alloying elements.
ASTM	A240	USA	Standard specification for stainless steel plates.
EN	1.4301	Europe	Equivalent to AISI 304, but with different mechanical properties.
JIS	SUS 304	Japan	Closely related, with similar corrosion resistance.

The subtle differences between these grades can significantly affect performance in specific applications. For instance, while 320 and 304 stainless steels share many properties, 320's enhanced resistance to certain corrosive agents makes it more suitable for specific environments.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Fe (Iron)	Balance
Cr (Chromium)	18.0 - 20.0
Ni (Nickel)	8.0 - 10.0
C (Carbon)	≤ 0.08
Mn (Manganese)	2.0 - 2.5
Si (Silicon)	≤ 1.0

The primary alloying elements in 320 Stainless Steel include chromium, which enhances corrosion resistance and oxidation stability, and nickel, which contributes to its toughness and ductility. The low carbon content is crucial for maintaining the steel's weldability and preventing carbide precipitation, which can lead to intergranular corrosion.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	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	Annealed	160 - 190 HB	90 - 100 HB	ASTM E10
Impact Strength	-40°C	40 J	30 ft-lbf	ASTM E23

The mechanical properties of 320 Stainless Steel make it suitable for applications requiring high strength and ductility. Its tensile strength and yield strength indicate its ability to withstand significant loads, while its elongation percentage reflects its capacity for deformation without fracture, making it ideal for structural applications.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	-	7.93 g/cm³	0.286 lb/in³
Melting Point/Range	-	1400 - 1450 °C	2552 - 2642 °F
Thermal Conductivity	20°C	16 W/m·K	92 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	20°C	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	20°C	0.73 µΩ·m	0.0000013 Ω·in

The density of 320 Stainless Steel indicates its substantial mass, which contributes to its strength. Its thermal conductivity is moderate, making it suitable for applications where heat transfer is necessary but not excessive. The specific heat capacity is relatively high, allowing it to absorb and retain heat, which is beneficial in high-temperature applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-10	20-60 / 68-140	Good	Risk of pitting corrosion.
Sulfuric Acid	10-30	20-50 / 68-122	Fair	Susceptible to stress corrosion cracking.
Acetic Acid	5-20	20-60 / 68-140	Good	Generally resistant.
Alkaline Solutions	5-30	20-60 / 68-140	Excellent	Very resistant.

320 Stainless Steel exhibits excellent resistance to a variety of corrosive environments, particularly in alkaline solutions and organic acids. However, it is susceptible to pitting corrosion in chloride environments and stress corrosion cracking in sulfuric acid. Compared to 316 stainless steel, which has molybdenum added for enhanced pitting resistance, 320 may not perform as well in chloride-rich environments but offers better resistance in alkaline conditions.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	800	1472	Suitable for high-temperature applications.
Max Intermittent Service Temp	900	1652	Can withstand short-term exposure to higher temperatures.
Scaling Temperature	1000	1832	Begins to oxidize significantly above this temperature.

At elevated temperatures, 320 Stainless Steel maintains its strength and oxidation resistance, making it suitable for applications in high-temperature environments. However, prolonged exposure to temperatures above 800 °C (1472 °F) can lead to oxidation and scaling, which may compromise its structural integrity.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER308L	Argon	Excellent for thin sections.
MIG	ER308L	Argon + CO2	Good for thicker sections.
Stick	E308L	-	Suitable for outdoor applications.

320 Stainless Steel is highly weldable due to its low carbon content, which minimizes the risk of carbide precipitation during welding. Pre-heat treatment is generally not required, but post-weld heat treatment may be beneficial to relieve stresses and improve corrosion resistance.

Machinability

Machining Parameter	320 Stainless Steel	AISI 1212	Notes/Tips
Relative Machinability Index	40	100	More challenging to machine.
Typical Cutting Speed (Turning)	25 m/min	50 m/min	Use carbide tools for best results.

Machining 320 Stainless Steel can be more challenging compared to carbon steels due to its work hardening characteristics. It is advisable to use high-speed steel or carbide tools and to maintain adequate cutting speeds and coolant application to prevent overheating.

Formability

320 Stainless Steel exhibits good formability, allowing for cold and hot forming processes. However, it is essential to consider the work hardening effect during cold forming, which may require additional force and can lead to reduced ductility. The minimum bend radius should be carefully calculated to avoid cracking.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	1000 - 1100 / 1832 - 2012	1 - 2 hours	Air	Relieve stresses and improve ductility.
Solution Treatment	1000 - 1100 / 1832 - 2012	30 minutes	Water	Dissolve carbides and improve corrosion resistance.

Heat treatment processes such as annealing and solution treatment are critical for optimizing the microstructure of 320 Stainless Steel. These treatments enhance ductility and corrosion resistance by dissolving carbides and relieving internal stresses.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Food Processing	Equipment and piping	Corrosion resistance, ease of cleaning	Hygiene and durability
Chemical Processing	Reactors and storage tanks	High-temperature stability, corrosion resistance	Safety and longevity
Oil and Gas	Pipeline components	Strength, weldability, and corrosion resistance	Reliability in harsh environments

Other applications include:
- Pharmaceutical equipment
- Marine environments
- Architectural structures

The selection of 320 Stainless Steel for these applications is primarily due to its excellent corrosion resistance and mechanical properties, which ensure safety and longevity in demanding environments.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	320 Stainless Steel	AISI 316 Stainless Steel	AISI 304 Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High tensile strength	Excellent corrosion resistance	Good ductility	320 offers a balance of strength and corrosion resistance.
Key Corrosion Aspect	Good in alkaline solutions	Best in chloride environments	Moderate resistance	316 is superior in chloride environments.
Weldability	Excellent	Good	Good	All grades are weldable, but 320 has an edge due to low carbon.
Machinability	Moderate	Good	Excellent	320 is harder to machine than 304 and 316.
Approx. Relative Cost	Moderate	Higher	Lower	320 is generally more cost-effective than 316.
Typical Availability	Moderate	High	High	304 is the most commonly available stainless steel.

When selecting 320 Stainless Steel, considerations include its cost-effectiveness, availability, and specific performance requirements in corrosive environments. Its unique properties make it suitable for niche applications where other grades may not perform as well. Additionally, safety considerations in high-stress environments must be taken into account, ensuring that the selected material meets all regulatory and performance standards.