402 Stainless Steel: Properties and Key Applications

402 stainless steel is classified as an austenitic stainless steel, primarily known for its high chromium and nickel content. This grade is characterized by its excellent corrosion resistance, good formability, and high strength, making it suitable for a variety of applications in industries such as automotive, aerospace, and food processing. The primary alloying elements in 402 stainless steel include chromium (Cr), nickel (Ni), and iron (Fe), with chromium being the most significant for enhancing corrosion resistance and nickel contributing to its toughness and ductility.

Comprehensive Overview

The most significant characteristics of 402 stainless steel include its high resistance to oxidation and corrosion, particularly in mildly corrosive environments. It also exhibits good mechanical properties, including strength and ductility, which are essential for structural applications. However, it is important to note that while 402 stainless steel offers many advantages, it also has limitations. For instance, it may not perform as well in highly acidic or chloride-rich environments compared to other stainless steel grades, such as 304 or 316.

Advantages:
- Excellent corrosion resistance in mild environments
- Good mechanical properties, including strength and ductility
- High-temperature resistance

Limitations:
- Reduced performance in highly acidic or chloride-rich environments
- Lower weldability compared to some other stainless steel grades

Historically, 402 stainless steel has been used in applications where a combination of strength and corrosion resistance is required, such as in the manufacturing of automotive components and industrial equipment. Its market position is strong, particularly in sectors that prioritize durability and resistance to wear.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S40200	USA	Closest equivalent to AISI 402
AISI/SAE	402	USA	Minor compositional differences to be aware of
ASTM	A240	USA	Standard specification for stainless steel plates
EN	1.4006	Europe	Equivalent grade in European standards
JIS	SUS 402	Japan	Similar properties with slight variations

The table above highlights the various standards and designations associated with 402 stainless steel. Notably, while grades like AISI 304 and 316 are more commonly used, 402 offers specific advantages in certain applications, particularly where moderate corrosion resistance is sufficient.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Cr (Chromium)	11.5 - 13.5
Ni (Nickel)	0.5 - 2.0
Fe (Iron)	Balance
C (Carbon)	0.03 max
Mn (Manganese)	1.0 max
Si (Silicon)	1.0 max

The primary role of chromium in 402 stainless steel is to enhance its corrosion resistance, while nickel contributes to its toughness and ductility. The low carbon content helps prevent carbide precipitation, which can lead to intergranular corrosion. Manganese and silicon are included to improve the steel's overall strength and workability.

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	205 - 310 MPa	30 - 45 ksi	ASTM E8
Elongation	Annealed	Room Temp	40 - 50%	40 - 50%	ASTM E8
Hardness (Rockwell B)	Annealed	Room Temp	80 - 90 HRB	80 - 90 HRB	ASTM E18
Impact Strength	Annealed	-20°C (-4°F)	40 J	29.5 ft-lbf	ASTM E23

The mechanical properties of 402 stainless steel make it suitable for applications requiring good strength and ductility. Its tensile strength and yield strength indicate that it can withstand significant loads, while its elongation percentage shows that it can be deformed without breaking, which is crucial for forming processes.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.8 g/cm³	0.282 lb/in³
Melting Point	-	1400 - 1450 °C	2552 - 2642 °F
Thermal Conductivity	Room Temp	25 W/m·K	14.5 BTU·in/h·ft²·°F
Specific Heat Capacity	Room Temp	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	Room Temp	0.73 µΩ·m	0.00000073 Ω·m
Coefficient of Thermal Expansion	Room Temp	16.5 x 10⁻⁶/K	9.2 x 10⁻⁶/°F

The density and melting point of 402 stainless steel indicate its robustness, while its thermal conductivity and specific heat capacity are important for applications involving heat transfer. The electrical resistivity is relatively low, making it suitable for certain electrical applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3 - 10	20 - 60 / 68 - 140	Fair	Risk of pitting corrosion
Sulfuric Acid	10 - 30	20 - 40 / 68 - 104	Poor	Not recommended
Acetic Acid	5 - 20	20 - 60 / 68 - 140	Good	Moderate resistance
Atmospheric	-	-	Excellent	Good resistance

402 stainless steel exhibits good resistance to atmospheric corrosion and moderate resistance to certain acids. However, it is susceptible to pitting corrosion in chloride environments, which is a critical consideration for applications in coastal or marine environments. Compared to grades like 304 and 316, 402's performance in highly corrosive environments is notably inferior, particularly in chloride-rich conditions.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	800 °C	1472 °F	Suitable for high temps
Max Intermittent Service Temp	900 °C	1652 °F	Short-term exposure
Scaling Temperature	1000 °C	1832 °F	Risk of oxidation

At elevated temperatures, 402 stainless steel maintains its strength and oxidation resistance, making it suitable for applications involving heat. However, prolonged exposure to temperatures above 800 °C can lead to scaling, which may compromise its structural integrity.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER 308L	Argon	Preheat recommended
MIG	ER 308L	Argon + CO2 mix	Post-weld heat treatment may be necessary

402 stainless steel can be welded using standard techniques, but preheating and post-weld heat treatment are recommended to minimize the risk of cracking. The choice of filler metal is crucial to ensure compatibility and maintain corrosion resistance.

Machinability

Machining Parameter	402 Stainless Steel	AISI 1212	Notes/Tips
Relative Machinability Index	40	100	Requires slower cutting speeds
Typical Cutting Speed (Turning)	30 m/min	80 m/min	Use carbide tools for best results

Machining 402 stainless steel can be challenging due to its toughness. Optimal conditions include using carbide tools and slower cutting speeds to prevent tool wear.

Formability

402 stainless steel exhibits good formability, making it suitable for cold and hot forming processes. However, it is essential to consider work hardening, which can affect the material's ductility during forming operations.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	1050 - 1150 °C / 1922 - 2102 °F	1 - 2 hours	Air or water	Improve ductility and reduce hardness

Heat treatment processes such as annealing are crucial for enhancing the ductility and reducing the hardness of 402 stainless steel. During annealing, the microstructure transforms, leading to improved mechanical properties.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Automotive	Exhaust systems	Corrosion resistance, high-temperature strength	Durability and performance
Aerospace	Engine components	High strength, heat resistance	Safety and reliability
Food Processing	Equipment and fixtures	Corrosion resistance, ease of cleaning	Hygiene and compliance

Other applications include:
- Chemical processing equipment
- Marine hardware
- Architectural applications

402 stainless steel is chosen for applications requiring a balance of strength and corrosion resistance, particularly in environments where exposure to moisture or mild corrosive agents is expected.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	402 Stainless Steel	AISI 304 Stainless Steel	AISI 316 Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	Moderate strength	High strength	High strength	402 is less strong than 304 and 316
Key Corrosion Aspect	Fair in chlorides	Good in chlorides	Excellent in chlorides	316 offers superior corrosion resistance
Weldability	Moderate	Good	Good	402 requires more care in welding
Machinability	Moderate	Good	Moderate	304 is easier to machine
Formability	Good	Excellent	Good	304 has superior formability
Approx. Relative Cost	Moderate	Moderate	Higher	402 is cost-effective for specific applications
Typical Availability	Moderate	High	High	304 and 316 are more commonly available

When selecting 402 stainless steel, considerations include its cost-effectiveness, availability, and specific performance requirements. While it may not be as widely used as 304 or 316, it offers unique advantages in certain applications, particularly where moderate corrosion resistance and good mechanical properties are required. Safety and magnetic properties are also essential factors, especially in industries where non-magnetic materials are preferred.

In summary, 402 stainless steel is a versatile material that balances strength, corrosion resistance, and cost, making it suitable for a variety of engineering applications.