405 Stainless Steel: Properties and Key Applications

405 stainless steel is classified as a martensitic stainless steel, known for its high strength and moderate corrosion resistance. This grade contains significant amounts of chromium (12-14%) and nickel (1-2%), with carbon content typically around 0.05-0.15%. The presence of chromium provides oxidation resistance, while nickel enhances toughness and ductility. The low carbon content helps in maintaining corrosion resistance while allowing for hardening through heat treatment.

Comprehensive Overview

405 stainless steel is primarily utilized in applications requiring high strength and moderate corrosion resistance. Its martensitic structure allows it to be hardened through heat treatment, making it suitable for components that endure mechanical stress. The steel exhibits good weldability and can be easily machined, which adds to its versatility in various engineering applications.

Advantages:
- High Strength: The ability to harden through heat treatment allows for enhanced mechanical properties.
- Moderate Corrosion Resistance: Suitable for environments where exposure to moisture and mild corrosive agents occurs.
- Good Fabricability: Can be welded and machined effectively, making it adaptable for various manufacturing processes.

Limitations:
- Lower Corrosion Resistance Compared to Austenitic Grades: While it performs well in certain environments, it is not as resistant to aggressive corrosive agents as austenitic stainless steels.
- Susceptibility to Stress Corrosion Cracking: In certain conditions, particularly in chloride environments, it may be prone to stress corrosion cracking.

Historically, 405 stainless steel has been used in applications such as automotive exhaust systems, heat exchangers, and various industrial components, reflecting its balance of strength and corrosion resistance.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S40500	USA	Closest equivalent to AISI 405
AISI/SAE	405	USA	Commonly used designation
ASTM	A240/A240M	USA	Standard specification for stainless steel plates
EN	1.4002	Europe	Minor compositional differences to be aware of
JIS	SUS405	Japan	Similar properties, but may vary in specific applications

The differences between equivalent grades often lie in their specific alloying elements and mechanical properties, which can affect performance in specific applications. For instance, while both 405 and 1.4002 may offer similar corrosion resistance, the latter may have slightly different mechanical properties due to variations in nickel content.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.05 - 0.15
Cr (Chromium)	12.0 - 14.0
Ni (Nickel)	1.0 - 2.0
Mn (Manganese)	0.5 - 1.0
Si (Silicon)	0.5 max
P (Phosphorus)	0.04 max
S (Sulfur)	0.03 max

The primary role of chromium in 405 stainless steel is to enhance corrosion resistance and oxidation resistance. Nickel contributes to improved toughness and ductility, while manganese aids in deoxidation and improves hardenability. The low carbon content is crucial for maintaining corrosion resistance and allows for effective hardening through heat treatment.

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	550 - 750 MPa	80 - 110 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	Room Temp	300 - 450 MPa	44 - 65 ksi	ASTM E8
Elongation	Annealed	Room Temp	20 - 30%	20 - 30%	ASTM E8
Hardness (Rockwell B)	Annealed	Room Temp	80 - 90	80 - 90	ASTM E18
Impact Strength	Annealed	-20 °C	30 - 50 J	22 - 37 ft-lbf	ASTM E23

The combination of high tensile and yield strength makes 405 stainless steel suitable for applications that require structural integrity under mechanical loading. Its elongation values indicate good ductility, allowing for deformation without fracture, which is essential in dynamic applications.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.75 g/cm³	0.28 lb/in³
Melting Point/Range	-	1400 - 1450 °C	2552 - 2642 °F
Thermal Conductivity	Room Temp	25 W/m·K	14.5 BTU·in/(hr·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	16.0 x 10⁻⁶/K	8.9 x 10⁻⁶/°F

The density of 405 stainless steel contributes to its weight and strength characteristics, while its melting point indicates suitability for high-temperature applications. The thermal conductivity and specific heat capacity are important for applications involving heat transfer, such as heat exchangers.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-5	25 °C / 77 °F	Fair	Risk of pitting
Sulfuric Acid	10	25 °C / 77 °F	Poor	Not recommended
Acetic Acid	5	25 °C / 77 °F	Good	Moderate resistance
Sea Water	-	25 °C / 77 °F	Fair	Susceptible to localized corrosion

405 stainless steel exhibits moderate resistance to corrosion in various environments. It performs reasonably well in mildly corrosive conditions, such as acetic acid and sea water, but is susceptible to pitting and stress corrosion cracking in chloride-rich environments. Compared to austenitic grades like 304 or 316, 405 has lower overall corrosion resistance, particularly in aggressive environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	650 °C	1202 °F	Suitable for high-temperature applications
Max Intermittent Service Temp	700 °C	1292 °F	Short-term exposure only
Scaling Temperature	800 °C	1472 °F	Risk of oxidation above this temperature
Creep Strength considerations begin around	500 °C	932 °F	Creep resistance decreases significantly

At elevated temperatures, 405 stainless steel maintains its strength but may experience oxidation. The maximum continuous service temperature indicates its suitability for high-temperature applications, while the scaling temperature highlights the risk of oxidation at extreme conditions.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER 405	Argon	Good results with proper technique
MIG	ER 308L	Argon/CO2	Suitable for thicker sections
Stick	E 308L	-	Preheat recommended

405 stainless steel is generally considered weldable, but preheating is recommended to minimize the risk of cracking. Post-weld heat treatment can enhance the properties of the weldment, ensuring integrity and performance.

Machinability

Machining Parameter	405 Stainless Steel	AISI 1212	Notes/Tips
Relative Machinability Index	60	100	Moderate machinability
Typical Cutting Speed (Turning)	30 m/min	50 m/min	Use carbide tools for best results

405 stainless steel has moderate machinability, requiring appropriate tooling and cutting speeds to achieve optimal results. Carbide tools are recommended for effective machining.

Formability

405 stainless steel can be formed through both cold and hot processes. Cold forming is feasible but may require higher forces due to its strength. The material exhibits work hardening, which can affect bend radii and forming limits.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	800 - 900 °C / 1472 - 1652 °F	1 - 2 hours	Air or water	Relieve stresses, improve ductility
Hardening	1000 - 1100 °C / 1832 - 2012 °F	30 minutes	Oil or air	Increase hardness and strength

During heat treatment, 405 stainless steel undergoes metallurgical transformations that enhance its mechanical properties. Annealing relieves internal stresses and improves ductility, while hardening significantly increases strength.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Automotive	Exhaust systems	High strength, moderate corrosion resistance	Durability under thermal stress
Oil & Gas	Valve components	High strength, weldability	Reliability in harsh environments
Aerospace	Engine components	High strength, heat resistance	Performance at elevated temperatures

Other applications include:
* - Heat exchangers
* - Industrial machinery components
* - Fasteners and fittings

The selection of 405 stainless steel for these applications is primarily due to its balance of strength, corrosion resistance, and fabricability, making it suitable for components that experience mechanical stress and exposure to various environments.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	405 Stainless Steel	AISI 304 Stainless Steel	AISI 316 Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate strength	Moderate strength	405 offers superior strength
Key Corrosion Aspect	Moderate resistance	Good resistance	Excellent resistance	405 is less resistant than 304/316
Weldability	Good	Excellent	Excellent	405 requires more care in welding
Machinability	Moderate	Good	Moderate	405 is less machinable than 304
Formability	Moderate	Good	Good	405 is less formable than 304
Approx. Relative Cost	Moderate	Moderate	Higher	405 is often more cost-effective
Typical Availability	Common	Very common	Common	405 is widely available

When selecting 405 stainless steel, considerations include its cost-effectiveness, availability, and suitability for specific applications. While it may not offer the same level of corrosion resistance as austenitic grades, its high strength and moderate resistance make it a viable choice for many engineering applications. Additionally, its weldability and machinability enhance its versatility in manufacturing processes.

In conclusion, 405 stainless steel is a valuable material in various industries, balancing strength, corrosion resistance, and fabricability. Understanding its properties and applications can guide engineers and designers in making informed material choices for their projects.