CA6NM Stainless Steel: Properties and Key Applications

CA6NM Stainless Steel (Casting) is a high-performance stainless steel grade primarily classified as a martensitic stainless steel. This grade is notable for its excellent mechanical properties, corrosion resistance, and ability to withstand high temperatures, making it suitable for various demanding applications, particularly in the oil and gas industry, as well as in power generation.

Comprehensive Overview

CA6NM is characterized by its unique composition, which includes significant amounts of chromium and nickel, along with molybdenum and nitrogen. These alloying elements contribute to its strength, toughness, and resistance to corrosion. The presence of nitrogen enhances the steel's mechanical properties, particularly its yield strength and toughness, while chromium provides excellent oxidation resistance.

The primary characteristics of CA6NM include:

• High Strength: CA6NM exhibits superior tensile and yield strength compared to many other stainless steels, making it ideal for structural applications.
• Corrosion Resistance: It offers good resistance to a variety of corrosive environments, including seawater and acidic conditions.
• Heat Resistance: This grade can maintain its mechanical properties at elevated temperatures, making it suitable for high-temperature applications.

Advantages and Limitations

Advantages (Pros)	Limitations (Cons)
Excellent mechanical properties	More expensive than standard carbon steels
Good corrosion resistance	Limited formability compared to austenitic grades
High-temperature performance	Susceptible to stress corrosion cracking in certain environments

Historically, CA6NM has been used in critical applications such as pump and valve components in the oil and gas sector due to its reliability and performance under harsh conditions. Its market position is strong, particularly in industries requiring high-performance materials.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S41500	USA	Closest equivalent to AISI 410 with enhanced properties
ASTM	A743/A744	USA	Specification for castings of stainless steel
EN	1.4006	Europe	Similar to CA6NM but with minor compositional differences
JIS	SUS 410	Japan	Equivalent with variations in mechanical properties

The differences between CA6NM and its equivalents often lie in the specific percentages of alloying elements, which can affect performance in particular applications. For instance, while both CA6NM and SUS 410 are martensitic, CA6NM's enhanced nitrogen content provides improved toughness and strength.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.05 - 0.15
Cr (Chromium)	12.0 - 14.0
Ni (Nickel)	2.0 - 4.0
Mo (Molybdenum)	0.5 - 1.5
N (Nitrogen)	0.1 - 0.25
Mn (Manganese)	0.5 - 1.0
Si (Silicon)	0.5 - 1.0
P (Phosphorus)	≤ 0.04
S (Sulfur)	≤ 0.03

The key alloying elements in CA6NM play crucial roles in its properties:

• Chromium: Enhances corrosion resistance and contributes to the formation of a protective oxide layer.
• Nickel: Improves toughness and ductility, particularly at low temperatures.
• Molybdenum: Increases resistance to pitting and crevice corrosion, especially in chloride environments.
• Nitrogen: Enhances strength and toughness, improving overall mechanical performance.

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 - 109 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	Room Temp	450 - 600 MPa	65 - 87 ksi	ASTM E8
Elongation	Annealed	Room Temp	20 - 30%	20 - 30%	ASTM E8
Hardness (Rockwell C)	Annealed	Room Temp	30 - 35 HRC	30 - 35 HRC	ASTM E18
Impact Strength	Charpy (at -40°C)	-40°C	40 - 60 J	30 - 44 ft-lbf	ASTM E23

The mechanical properties of CA6NM make it particularly suitable for applications that require high strength and toughness, such as in the construction of pressure vessels and piping systems. Its ability to withstand significant mechanical loads while maintaining structural integrity is a key advantage in demanding environments.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.75 g/cm³	0.28 lb/in³
Melting Point/Range	-	1450 - 1500 °C	2642 - 2732 °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	0.74 µΩ·m	0.74 µΩ·in
Coefficient of Thermal Expansion	20 - 100 °C	16.5 x 10⁻⁶/K	9.2 x 10⁻⁶/°F

The density and melting point of CA6NM indicate its suitability for high-temperature applications, while its thermal conductivity and specific heat capacity are important for applications involving heat transfer. The electrical resistivity is relevant for applications where electrical conductivity is a consideration.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3.5%	25°C/77°F	Good	Risk of pitting
Sulfuric Acid	10%	20°C/68°F	Fair	Susceptible to localized corrosion
Hydrochloric Acid	5%	25°C/77°F	Poor	Not recommended
Seawater	-	Ambient	Excellent	Good overall resistance

CA6NM exhibits good resistance to various corrosive environments, particularly in seawater and moderate acidic conditions. However, it is susceptible to pitting corrosion in chloride-rich environments and localized corrosion in strong acids like hydrochloric acid. Compared to other stainless steel grades, such as AISI 316, CA6NM may offer better performance in high-stress applications but may not be as resistant to certain corrosive agents.

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	Short-term exposure
Scaling Temperature	700 °C	1292 °F	Risk of oxidation beyond this limit
Creep Strength Considerations	550 °C	1022 °F	Creep resistance begins to decline

CA6NM maintains its mechanical properties at elevated temperatures, making it suitable for applications such as turbine components and heat exchangers. However, prolonged exposure to temperatures above 600 °C can lead to oxidation and scaling, which may compromise its integrity.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER410	Argon	Preheat recommended
MIG	ER410	Argon + CO2 mix	Post-weld heat treatment advised
SMAW	E410	-	Care needed to avoid cracking

CA6NM is generally weldable, but care must be taken to avoid cracking, particularly in thicker sections. Preheating and post-weld heat treatment can help mitigate these risks. The choice of filler metal is crucial to ensure compatibility and maintain corrosion resistance.

Machinability

Machining Parameter	CA6NM	AISI 1212	Notes/Tips
Relative Machinability Index	60%	100%	More difficult to machine than mild steels
Typical Cutting Speed	30 m/min	50 m/min	Use carbide tools for best results

CA6NM presents challenges in machining due to its hardness and strength. Utilizing appropriate tooling and cutting speeds can enhance machinability, but operators should be prepared for increased tool wear.

Formability

CA6NM exhibits limited formability compared to austenitic stainless steels. Cold forming is possible, but significant work hardening can occur, necessitating careful control of bending radii and forming processes. Hot forming is more feasible but requires precise temperature control to avoid compromising material properties.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	1000 - 1100 °C / 1832 - 2012 °F	1 - 2 hours	Air or water	Relieve stresses, improve ductility
Hardening	950 - 1050 °C / 1742 - 1922 °F	1 hour	Oil or air	Increase hardness and strength
Tempering	500 - 700 °C / 932 - 1292 °F	1 hour	Air	Reduce brittleness, improve toughness

Heat treatment processes significantly affect the microstructure and properties of CA6NM. Annealing can enhance ductility, while hardening increases strength. Tempering is essential to balance hardness and toughness, particularly in applications where impact resistance is critical.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Oil and Gas	Pump components	High strength, corrosion resistance	Reliability under harsh conditions
Power Generation	Turbine blades	High-temperature performance	Durability and efficiency
Marine	Valve bodies	Resistance to seawater corrosion	Longevity in marine environments

Other applications include:

• Chemical Processing: Components exposed to corrosive chemicals.
• Aerospace: Parts requiring high strength-to-weight ratios.
• Mining: Equipment subjected to abrasive conditions.

CA6NM is chosen for these applications due to its combination of strength, toughness, and corrosion resistance, which are critical in environments where failure is not an option.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	CA6NM	AISI 316	AISI 410	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate strength	Moderate strength	CA6NM offers superior strength
Key Corrosion Aspect	Good resistance	Excellent resistance	Fair resistance	CA6NM is less resistant to chlorides
Weldability	Moderate	Good	Fair	CA6NM requires careful welding practices
Machinability	Moderate	Good	Excellent	CA6NM is harder to machine
Formability	Limited	Good	Moderate	CA6NM is less formable than austenitic grades
Approx. Relative Cost	Higher	Moderate	Lower	CA6NM is more expensive due to alloying elements
Typical Availability	Moderate	High	High	CA6NM may be less readily available

When selecting CA6NM, considerations include its cost-effectiveness, availability, and suitability for specific applications. While it may be more expensive than standard carbon steels, its performance in critical applications often justifies the investment. Additionally, its magnetic properties are minimal, making it suitable for applications where magnetic interference is a concern.

In summary, CA6NM stainless steel is a versatile and high-performance material that excels in demanding environments, making it a preferred choice for various industrial applications. Its unique combination of mechanical and corrosion-resistant properties ensures reliability and longevity in service.