407 Stainless Steel: Properties and Key Applications

407 stainless steel is classified as a martensitic stainless steel, known for its high strength and moderate corrosion resistance. This grade is primarily alloyed with chromium (12-14%) and nickel (1-2%), which contribute to its unique properties. The presence of chromium enhances its corrosion resistance, while nickel improves toughness and ductility.

Comprehensive Overview

407 stainless steel is characterized by its excellent mechanical properties, including high tensile strength and hardness, making it suitable for applications requiring durability and wear resistance. It is often used in environments where moderate corrosion resistance is sufficient, such as in the food processing and chemical industries.

Advantages:
- High Strength: 407 stainless steel exhibits superior strength compared to many other stainless steel grades, making it ideal for structural applications.
- Good Wear Resistance: Its hardness allows it to withstand abrasive conditions, extending the lifespan of components made from this material.
- Moderate Corrosion Resistance: While not as corrosion-resistant as austenitic grades, it performs well in mildly corrosive environments.

Limitations:
- Lower Ductility: Compared to austenitic stainless steels, 407 has lower ductility, which can limit its formability.
- Susceptibility to Stress Corrosion Cracking: In certain environments, particularly those containing chlorides, it may be prone to stress corrosion cracking.

Historically, 407 stainless steel has been utilized in various applications due to its balance of strength and corrosion resistance, positioning it as a reliable choice in the manufacturing sector.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S40700	USA	Closest equivalent to AISI 410 with minor compositional differences.
AISI/SAE	407	USA	Similar to 410 but with slightly different properties.
ASTM	A240	USA	Standard specification for chromium and chromium-nickel stainless steel plate, sheet, and strip.
EN	1.4006	Europe	Equivalent to AISI 410, with similar properties.
JIS	SUS 410	Japan	Comparable to AISI 410, used in similar applications.

The differences between these equivalent grades often lie in their specific alloying elements and mechanical properties, which can affect performance in particular applications. For instance, while both 407 and 410 stainless steels are martensitic, 410 typically has a higher carbon content, which can enhance hardness but may reduce ductility.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Cr (Chromium)	12.0 - 14.0
Ni (Nickel)	1.0 - 2.0
C (Carbon)	0.08 max
Mn (Manganese)	1.0 max
Si (Silicon)	1.0 max
P (Phosphorus)	0.04 max
S (Sulfur)	0.03 max

Chromium is the primary alloying element that provides corrosion resistance, while nickel enhances toughness and ductility. Carbon contributes to hardness and strength, making it a critical element in martensitic stainless steels.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Annealed	620 - 750 MPa	90 - 109 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	450 - 550 MPa	65 - 80 ksi	ASTM E8
Elongation	Annealed	15 - 25%	15 - 25%	ASTM E8
Hardness (Rockwell C)	Annealed	25 - 35 HRC	25 - 35 HRC	ASTM E18
Impact Strength (Charpy)	-20°C	30 J	22 ft-lbf	ASTM E23

The combination of high tensile and yield strength makes 407 stainless steel suitable for applications that require structural integrity under load. Its hardness provides wear resistance, while the elongation percentage indicates reasonable ductility for forming processes.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	-	7.75 g/cm³	0.28 lb/in³
Melting Point/Range	-	1450 - 1510 °C	2642 - 2750 °F
Thermal Conductivity	20°C	25 W/m·K	14.5 BTU·in/h·ft²·°F
Specific Heat Capacity	20°C	500 J/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	20°C	0.73 µΩ·m	0.00000073 Ω·m
Coefficient of Thermal Expansion	20-100°C	16.5 x 10⁻⁶ /K	9.2 x 10⁻⁶ /°F

The density of 407 stainless steel indicates a relatively heavy material, which contributes to its strength. The thermal conductivity and specific heat capacity suggest that it can handle thermal stresses well, making it suitable for applications involving heat exposure.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	0 - 5	20 - 60 / 68 - 140	Fair	Risk of pitting corrosion.
Acids (HCl)	0 - 10	20 - 40 / 68 - 104	Poor	Not recommended for use.
Alkalis	0 - 5	20 - 60 / 68 - 140	Good	Moderate resistance.
Atmospheric	-	-	Good	Performs well in mild environments.

407 stainless steel exhibits moderate resistance to various corrosive agents, particularly in atmospheric conditions. However, it is less effective in acidic environments, which can lead to significant degradation. Compared to austenitic grades like 304 or 316, 407's corrosion resistance is limited, particularly in chloride-rich environments where pitting is a concern.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Suitable for high-temperature applications.
Max Intermittent Service Temp	425 °C	797 °F	Can withstand short-term exposure to higher temperatures.
Scaling Temperature	600 °C	1112 °F	Risk of oxidation above this temperature.

At elevated temperatures, 407 stainless steel maintains its strength but may experience oxidation if exposed to air. Its performance in high-temperature applications is generally good, but care must be taken to avoid prolonged exposure to temperatures exceeding its scaling limit.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER 410	Argon	Preheat recommended to avoid cracking.
MIG	ER 410	Argon + CO2	Suitable for thin sections.

407 stainless steel can be welded using standard techniques, but preheating is often recommended to minimize the risk of cracking. Post-weld heat treatment may also be necessary to relieve stresses and improve ductility.

Machinability

Machining Parameter	[407 Stainless Steel]	Benchmark Steel (AISI 1212)	Notes/Tips
Relative Machinability Index	60%	100%	Requires slower cutting speeds.
Typical Cutting Speed	30 m/min	60 m/min	Use carbide tools for best results.

Machinability is moderate; while 407 can be machined effectively, it requires specific tooling and slower speeds compared to more machinable steels like AISI 1212.

Formability

407 stainless steel is less formable than austenitic grades due to its martensitic structure. Cold forming is possible but may lead to work hardening, necessitating careful control of bending radii and forming processes.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	800 - 900 / 1472 - 1652	1 - 2 hours	Air	Improve ductility and reduce hardness.
Hardening	1000 - 1100 / 1832 - 2012	30 - 60 minutes	Oil or Air	Increase hardness and strength.

Heat treatment processes significantly affect the microstructure of 407 stainless steel, enhancing its hardness and strength while also allowing for adjustments in ductility through annealing.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Food Processing	Cutlery and kitchen tools	High strength, moderate corrosion resistance	Durability and ease of cleaning.
Chemical Industry	Pump components	Wear resistance, strength	Longevity in harsh environments.
Automotive	Exhaust systems	High-temperature strength	Performance under thermal stress.

Other applications include:
- Medical instruments: Due to its strength and corrosion resistance.
- Oil and gas: Components that require durability in corrosive environments.

407 stainless steel is chosen for these applications due to its balance of strength, wear resistance, and moderate corrosion resistance, making it suitable for demanding environments.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	407 Stainless Steel	AISI 410 Stainless Steel	AISI 304 Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate strength	Good ductility	407 is stronger but less ductile.
Key Corrosion Aspect	Moderate resistance	Moderate resistance	Excellent resistance	304 is superior in corrosive environments.
Weldability	Moderate	Good	Excellent	407 requires more care in welding.
Machinability	Moderate	Good	Excellent	407 is harder to machine than 304.
Formability	Limited	Moderate	Excellent	304 is easier to form due to its ductility.
Approx. Relative Cost	Moderate	Moderate	Higher	304 generally costs more due to alloy content.
Typical Availability	Common	Common	Very common	304 is widely available due to its popularity.

When selecting 407 stainless steel, considerations include its mechanical properties, corrosion resistance, and suitability for specific applications. While it offers advantages in strength and wear resistance, its limitations in ductility and corrosion resistance compared to austenitic grades like 304 should be carefully evaluated based on the intended use.

In summary, 407 stainless steel is a versatile material that finds its place in various industries due to its unique combination of properties. Understanding its characteristics, advantages, and limitations is essential for making informed decisions in material selection.