307 Stainless Steel: Properties and Key Applications

307 stainless steel is classified as an austenitic stainless steel, notable for its high chromium and nickel content, which enhances its corrosion resistance and mechanical properties. This grade is primarily alloyed with approximately 18% chromium and 8% nickel, along with small amounts of manganese, silicon, and carbon. The presence of these elements contributes to its excellent ductility, formability, and resistance to oxidation and corrosion.

Comprehensive Overview

307 stainless steel is recognized for its versatility and is often utilized in environments where corrosion resistance is critical. Its austenitic structure provides superior toughness and strength at both elevated and cryogenic temperatures. The alloy's high chromium content offers excellent resistance to oxidation and corrosion, making it suitable for various applications, including food processing, chemical handling, and marine environments.

Advantages:
- Corrosion Resistance: Exceptional resistance to a wide range of corrosive environments, including acidic and alkaline solutions.
- Ductility and Formability: High ductility allows for easy fabrication and forming into complex shapes.
- Weldability: Good weldability makes it suitable for various fabrication processes.

Limitations:
- Cost: Higher alloy content can lead to increased material costs compared to lower-grade steels.
- Work Hardening: The material can work-harden quickly, which may complicate machining processes.
- Magnetic Properties: Generally non-magnetic, but may become slightly magnetic when cold worked.

Historically, 307 stainless steel has been a reliable choice for applications requiring both strength and corrosion resistance, maintaining a strong market position due to its favorable properties.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S30700	USA	Closest equivalent to AISI 304, with minor compositional differences.
AISI/SAE	307	USA	Similar to 304 but with higher sulfur content for improved machinability.
ASTM	A240	USA	Standard specification for chromium and chromium-nickel stainless steel plate, sheet, and strip.
EN	1.4305	Europe	Equivalent grade with slightly different mechanical properties.
JIS	SUS 307	Japan	Japanese standard with similar corrosion resistance characteristics.

The differences between 307 and its equivalents, such as AISI 304, primarily lie in the sulfur content, which enhances machinability but may slightly affect corrosion resistance. Understanding these nuances is crucial for selecting the appropriate grade for specific applications.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Cr (Chromium)	18.0 - 20.0
Ni (Nickel)	8.0 - 10.0
Mn (Manganese)	2.0 max
Si (Silicon)	1.0 max
C (Carbon)	0.08 max
P (Phosphorus)	0.045 max
S (Sulfur)	0.03 - 0.10

The primary alloying elements in 307 stainless steel include chromium, which provides corrosion resistance; nickel, which enhances toughness and ductility; and sulfur, which improves machinability. The balance of these elements contributes to the overall performance of the steel in various applications.

Mechanical Properties

Property	Condition/Temper	Test Temperature	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	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 (Rockwell B)	Annealed	Room Temp	70 - 90 HRB	70 - 90 HRB	ASTM E18
Impact Strength	Charpy V-notch	-20°C	40 J	29.5 ft-lbf	ASTM E23

The mechanical properties of 307 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 to deform without fracture, making it ideal for structural applications.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.93 g/cm³	0.286 lb/in³
Melting Point/Range	-	1400 - 1450 °C	2552 - 2642 °F
Thermal Conductivity	Room Temp	16.2 W/m·K	112 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	Room Temp	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	Room Temp	0.72 µΩ·m	0.00000072 Ω·m
Coefficient of Thermal Expansion	20 - 100 °C	16.0 x 10⁻⁶/K	8.89 x 10⁻⁶/°F

Key physical properties such as density and melting point are crucial for applications involving high temperatures or structural integrity. The thermal conductivity indicates its ability to dissipate heat, which is important in applications where thermal management is critical.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C)	Resistance Rating	Notes
Chlorides	3-10	20-60	Good	Risk of pitting corrosion.
Sulfuric Acid	10-30	20-40	Fair	Susceptible to SCC.
Hydrochloric Acid	5-20	20-60	Poor	Not recommended.
Sea Water	-	Ambient	Excellent	Excellent resistance.

307 stainless steel exhibits good resistance to a variety of corrosive environments, particularly in chloride-rich conditions. However, it is susceptible to stress corrosion cracking (SCC) in the presence of chlorides and should be used with caution in such environments. Compared to 304 stainless steel, 307 offers improved machinability but may have slightly reduced corrosion resistance in certain acidic environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	870	1600	Suitable for high-temperature applications.
Max Intermittent Service Temp	925	1700	Can withstand short-term exposure to higher temperatures.
Scaling Temperature	600	1112	Risk of scaling above this temperature.

307 stainless steel maintains its mechanical properties at elevated temperatures, making it suitable for applications involving heat exposure. However, prolonged exposure to temperatures above 600 °C can lead to scaling and degradation of the material.

Fabrication Properties

Weldability

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

307 stainless steel is known for its good weldability, particularly with TIG and MIG processes. Pre-heat and post-weld heat treatment may be necessary to avoid cracking and ensure optimal mechanical properties. Careful selection of filler metals is crucial to maintain corrosion resistance.

Machinability

Machining Parameter	[307 Stainless Steel]	AISI 1212	Notes/Tips
Relative Machinability Index	60%	100%	Requires sharp tools and coolant.
Typical Cutting Speed (Turning)	30-50 m/min	80-100 m/min	Lower speeds recommended.

307 stainless steel has moderate machinability, which can be improved with the use of appropriate cutting tools and techniques. The work hardening tendency can pose challenges, necessitating careful control of machining parameters.

Formability

307 stainless steel exhibits excellent formability, allowing for cold and hot forming processes. It can be easily bent and shaped into complex geometries, making it suitable for various fabrication applications. However, care must be taken to avoid excessive work hardening during cold forming.

Heat Treatment

Treatment Process	Temperature Range (°C)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	1010 - 1120	1-2 hours	Air or Water	Relieve stresses, improve ductility.
Solution Treatment	1000 - 1100	30 minutes	Rapid Cooling	Enhance corrosion resistance.

Heat treatment processes such as annealing and solution treatment are essential for optimizing the microstructure and properties of 307 stainless steel. These treatments enhance ductility and corrosion resistance, making the material more suitable for demanding applications.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Food Processing	Equipment and containers	Corrosion resistance, ease of cleaning	Hygiene and durability
Chemical Industry	Storage tanks	High strength, corrosion resistance	Safety and longevity
Marine	Boat fittings	Excellent resistance to seawater	Durability in harsh environments
Pharmaceutical	Processing equipment	Non-reactive, easy to sterilize	Compliance with standards

307 stainless steel is widely used in industries where corrosion resistance and hygiene are paramount. Its properties make it an ideal choice for food processing equipment, chemical storage tanks, and marine applications.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	307 Stainless Steel	AISI 304	AISI 316	Brief Pro/Con or Trade-off Note
Key Mechanical Property	Moderate Strength	High Strength	High Strength	316 offers better corrosion resistance.
Key Corrosion Aspect	Good in many environments	Good in many environments	Excellent in chlorides	316 is preferred for marine applications.
Weldability	Good	Excellent	Good	304 is often easier to weld.
Machinability	Moderate	Good	Moderate	304 is easier to machine.
Formability	Excellent	Excellent	Good	All grades are formable but vary in ease.
Approx. Relative Cost	Moderate	Moderate	Higher	316 is more expensive due to molybdenum.
Typical Availability	Common	Very Common	Common	304 is the most widely available.

When selecting 307 stainless steel, considerations such as cost, availability, and specific application requirements are crucial. While it offers a good balance of properties, alternatives like AISI 304 and AISI 316 may be more suitable depending on the specific environmental conditions and mechanical demands. Understanding these trade-offs can guide engineers and designers in making informed material choices for their projects.