422 Stainless Steel: Properties and Key Applications

422 stainless steel is a martensitic stainless steel known for its high strength and moderate corrosion resistance. It is classified as a martensitic stainless steel due to its high carbon content and the presence of chromium, which contributes to its hardness and strength. The primary alloying elements in 422 stainless steel include chromium (12-14%), nickel (1-2%), and carbon (0.15-0.25%). These elements significantly influence the steel's properties, making it suitable for various applications where strength and wear resistance are critical.

Comprehensive Overview

422 stainless steel is recognized for its excellent mechanical properties, particularly its high tensile strength and hardness. It is often used in applications that require materials to withstand high stress and wear, such as in the manufacturing of turbine blades, valve components, and other high-performance parts. The steel's martensitic structure allows it to be hardened through heat treatment, enhancing its strength and wear resistance.

Advantages:
- High Strength: 422 stainless steel exhibits superior tensile strength, making it ideal for high-stress applications.
- Good Wear Resistance: The hardness of this steel grade provides excellent wear resistance, prolonging the lifespan of components.
- Moderate Corrosion Resistance: While not as corrosion-resistant as austenitic stainless steels, 422 offers decent resistance to oxidation and corrosion in certain environments.

Limitations:
- Lower Toughness: Compared to austenitic grades, 422 stainless steel has lower toughness, which may limit its use in applications requiring high impact resistance.
- Weldability Issues: The high carbon content can lead to challenges in welding, necessitating careful selection of filler materials and techniques.

Historically, 422 stainless steel has been utilized in various industries, including aerospace and automotive, due to its unique balance of strength and corrosion resistance. Its market position is well-established, particularly in applications where high performance is essential.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S42200	USA	Closest equivalent to AISI 420 with minor compositional differences.
AISI/SAE	422	USA	Similar to 420 but with higher carbon content for improved hardness.
ASTM	A276	USA	Standard specification for stainless steel bars and shapes.
EN	1.4002	Europe	Equivalent grade in European standards.
JIS	SUS 420J2	Japan	Similar properties but with slight differences in composition.

The differences between these equivalent grades can affect selection based on specific performance requirements. For instance, while AISI 420 and 422 are similar, the higher carbon content in 422 enhances its hardness but may reduce its toughness.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.15 - 0.25
Cr (Chromium)	12.0 - 14.0
Ni (Nickel)	1.0 - 2.0
Mn (Manganese)	1.0 max
Si (Silicon)	1.0 max
P (Phosphorus)	0.04 max
S (Sulfur)	0.03 max

The primary role of chromium in 422 stainless steel is to enhance corrosion resistance and improve hardness. Nickel contributes to toughness and ductility, while carbon increases hardness and strength 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	620 - 750 MPa	90 - 110 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	Room Temp	450 - 600 MPa	65 - 87 ksi	ASTM E8
Elongation	Annealed	Room Temp	10 - 15%	10 - 15%	ASTM E8
Hardness (Rockwell C)	Annealed	Room Temp	30 - 40 HRC	30 - 40 HRC	ASTM E18
Impact Strength	Charpy V-notch	-20 °C	30 - 50 J	22 - 37 ft-lbf	ASTM E23

The combination of high tensile and yield strength makes 422 stainless steel suitable for applications requiring significant mechanical loading. Its hardness provides wear resistance, while the moderate elongation indicates that it can withstand some deformation before failure.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.75 g/cm³	0.28 lb/in³
Melting Point	-	1450 - 1510 °C	2642 - 2750 °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	0.72 µΩ·m	0.72 µΩ·in
Coefficient of Thermal Expansion	Room Temp	16.5 x 10⁻⁶/K	9.2 x 10⁻⁶/°F

The density and melting point of 422 stainless steel indicate its robustness, making it suitable for high-temperature applications. The thermal conductivity is moderate, which is beneficial for applications where heat dissipation is necessary.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C)	Resistance Rating	Notes
Chlorides	3-5%	20-60 °C	Fair	Risk of pitting corrosion.
Sulfuric Acid	10-20%	20-40 °C	Poor	Not recommended for high concentrations.
Acetic Acid	5-10%	20-50 °C	Good	Moderate resistance.
Sea Water	-	Ambient	Fair	Susceptible to localized corrosion.

422 stainless steel exhibits moderate resistance to various corrosive environments. It performs well in mildly corrosive conditions but is susceptible to pitting in chloride-rich environments. Compared to austenitic grades like 304 or 316, 422 has lower corrosion resistance, making it less suitable for marine applications.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	600 °C	1112 °F	Suitable for high-temperature applications.
Max Intermittent Service Temp	650 °C	1202 °F	Can withstand short-term exposure to higher temperatures.
Scaling Temperature	800 °C	1472 °F	Risk of oxidation at elevated temperatures.

At elevated temperatures, 422 stainless steel maintains its strength but may experience oxidation. It is essential to consider the environment and potential scaling when using this steel grade in high-temperature applications.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER420	Argon	Preheat recommended.
MIG	ER420	Argon + CO2	Post-weld heat treatment may be necessary.

Welding 422 stainless steel can be challenging due to its high carbon content, which can lead to cracking. Preheating and post-weld heat treatment are often recommended to mitigate these issues.

Machinability

Machining Parameter	422 Stainless Steel	AISI 1212	Notes/Tips
Relative Machinability Index	50	100	Requires slower speeds and more robust tooling.
Typical Cutting Speed (Turning)	30 m/min	60 m/min	Use carbide tools for best results.

Machining 422 stainless steel requires careful consideration of cutting speeds and tooling due to its hardness. Carbide tools are recommended for effective machining.

Formability

422 stainless steel has limited formability due to its martensitic structure. Cold forming is possible but may lead to work hardening, requiring careful control of the bending radius to avoid cracking.

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	Reduce hardness, improve ductility.
Hardening	1000 - 1100 °C / 1832 - 2012 °F	30 minutes	Oil or air	Increase hardness and strength.

Heat treatment processes significantly affect the microstructure of 422 stainless steel, enhancing its hardness and strength while potentially reducing ductility.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Aerospace	Turbine components	High strength, wear resistance	Critical for performance and safety.
Automotive	Valve components	Corrosion resistance, strength	Essential for durability under stress.
Oil and Gas	Pump shafts	High strength, toughness	Required for high-pressure environments.
Medical	Surgical instruments	Corrosion resistance, hardness	Ensures longevity and reliability.

Other applications include:
- Marine hardware: where moderate corrosion resistance is needed.
- Industrial machinery: components that require high wear resistance.

422 stainless steel is chosen for these applications due to its unique combination of strength, hardness, and moderate corrosion resistance, making it suitable for demanding environments.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	422 Stainless Steel	AISI 304	AISI 316	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate	Moderate	422 offers superior strength but lower toughness.
Key Corrosion Aspect	Moderate resistance	Good	Excellent	422 is less resistant to corrosion than austenitic grades.
Weldability	Challenging	Good	Good	422 requires careful welding practices.
Machinability	Moderate	Good	Good	422 is harder to machine than austenitic grades.
Formability	Limited	Good	Good	422 has lower formability due to its structure.
Approx. Relative Cost	Moderate	Moderate	Higher	Cost can vary based on market conditions.
Typical Availability	Moderate	High	High	422 may be less commonly stocked than 304 or 316.

When selecting 422 stainless steel, considerations include its mechanical properties, corrosion resistance, and fabrication challenges. It is essential to weigh these factors against the specific requirements of the application to ensure optimal performance and longevity. The cost-effectiveness of 422 stainless steel makes it an attractive option for applications where high strength is paramount, but its limitations in corrosion resistance and weldability must be carefully managed.