A286 Stainless Steel: Properties and Key Applications

A286 Stainless Steel, also known as Alloy 660, is an austenitic stainless steel primarily characterized by its high strength and excellent oxidation resistance at elevated temperatures. This alloy is notable for its composition, which includes significant amounts of nickel and chromium, along with smaller quantities of molybdenum and titanium. These alloying elements contribute to its unique properties, making it suitable for various high-temperature applications.

Comprehensive Overview

A286 is classified as an austenitic stainless steel, which means it has a face-centered cubic crystal structure that provides excellent ductility and toughness. The primary alloying elements in A286 include:

• Nickel (Ni): Enhances corrosion resistance and improves high-temperature strength.
• Chromium (Cr): Increases oxidation resistance and contributes to the overall corrosion resistance.
• Molybdenum (Mo): Improves resistance to pitting and crevice corrosion.
• Titanium (Ti): Stabilizes the structure and helps prevent carbide precipitation during welding.

The significant characteristics of A286 include:

• High Strength: Retains strength at elevated temperatures, making it ideal for aerospace and industrial applications.
• Corrosion Resistance: Offers good resistance to a variety of corrosive environments.
• Good Fabricability: Can be easily welded and formed.

Advantages (Pros):
- Excellent high-temperature strength.
- Good oxidation resistance.
- Versatile for various applications, including aerospace and chemical processing.

Limitations (Cons):
- More expensive than some other stainless steels.
- Lower resistance to certain types of corrosion compared to other alloys, such as duplex stainless steels.

Historically, A286 has been widely used in the aerospace industry for components like turbine engines and exhaust systems due to its ability to withstand extreme conditions.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S66286	USA	Closest equivalent to AISI 316 but with higher strength at elevated temperatures.
AISI/SAE	660	USA	Commonly referred to as Alloy 660.
ASTM	A453	USA	Specification for high-temperature bolting materials.
EN	1.4980	Europe	Similar properties but may have slight compositional differences.
JIS	SUS 660	Japan	Equivalent grade with minor differences in composition.

The differences between these grades often lie in the specific alloying elements and their concentrations, which can affect properties like corrosion resistance and mechanical performance. For instance, while A286 and AISI 316 both offer good corrosion resistance, A286 is specifically designed for high-temperature applications, making it more suitable for aerospace uses.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Carbon (C)	0.08 max
Manganese (Mn)	1.0 max
Silicon (Si)	1.0 max
Chromium (Cr)	14.0 - 17.0
Nickel (Ni)	24.0 - 27.0
Molybdenum (Mo)	1.0 - 2.0
Titanium (Ti)	0.5 - 1.0
Iron (Fe)	Balance

The primary role of key alloying elements in A286 includes:

• Nickel: Enhances the alloy's ability to withstand high temperatures and improves its overall toughness.
• Chromium: Provides excellent oxidation resistance, crucial for applications exposed to high temperatures.
• Molybdenum: Increases resistance to localized corrosion, particularly in chloride environments.
• Titanium: Stabilizes the microstructure, especially during welding, preventing the formation of carbides.

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	310 - 450 MPa	45 - 65 ksi	ASTM E8
Elongation	Annealed	Room Temp	30% - 40%	30% - 40%	ASTM E8
Hardness (Rockwell B)	Annealed	Room Temp	85 - 95 HRB	85 - 95 HRB	ASTM E18
Impact Strength (Charpy V-notch)	Annealed	-196 °C	30 J	22 ft-lbf	ASTM E23

The combination of these mechanical properties makes A286 suitable for applications requiring high strength and toughness at elevated temperatures, such as in gas turbines and aerospace components. Its ability to maintain structural integrity under mechanical loading is critical in these demanding environments.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.93 g/cm³	0.286 lb/in³
Melting Point/Range	-	1370 - 1425 °C	2500 - 2600 °F
Thermal Conductivity	Room Temp	15.1 W/m·K	87.5 BTU·in/h·ft²·°F
Specific Heat Capacity	Room Temp	500 J/kg·K	0.119 BTU/lb·°F
Electrical Resistivity	Room Temp	0.72 µΩ·m	0.00000072 Ω·m
Coefficient of Thermal Expansion	20 - 100 °C	16.0 x 10⁻⁶/K	8.9 x 10⁻⁶/°F

The practical significance of A286's physical properties includes:

• Density: Its relatively high density contributes to its strength and durability, making it suitable for heavy-duty applications.
• Thermal Conductivity: Moderate thermal conductivity allows for effective heat dissipation in high-temperature environments.
• Coefficient of Thermal Expansion: This property is crucial for applications where temperature fluctuations occur, as it helps to minimize thermal stresses.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-10	20-60 / 68-140	Good	Risk of pitting corrosion.
Sulfuric Acid	10-30	20-60 / 68-140	Fair	Susceptible to stress corrosion cracking.
Nitric Acid	10-50	20-60 / 68-140	Excellent	Highly resistant.
Sea Water	-	20-60 / 68-140	Good	Risk of localized corrosion.

A286 exhibits good resistance to many corrosive environments, including atmospheric conditions, fresh water, and certain acids. However, it is susceptible to pitting and stress corrosion cracking in chloride-rich environments, which is a critical consideration for applications in marine or chemical processing industries.

When compared to other stainless steels, such as AISI 316 and duplex stainless steels, A286 offers superior high-temperature performance but may not match the corrosion resistance of duplex grades in certain aggressive environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	700 °C	1292 °F	Suitable for long-term exposure.
Max Intermittent Service Temp	800 °C	1472 °F	Short-term exposure only.
Scaling Temperature	900 °C	1652 °F	Risk of oxidation above this temp.
Creep Strength Considerations	600 °C	1112 °F	Creep resistance begins to decline.

A286 maintains its strength and oxidation resistance at elevated temperatures, making it suitable for applications such as gas turbine components and heat exchangers. However, care must be taken to avoid prolonged exposure to temperatures above 700 °C, where oxidation can become significant.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ER660 (A286)	Argon	Preheat may be required.
MIG	ER660 (A286)	Argon + 2-5% CO₂	Good fusion characteristics.
Stick	E660 (A286)	-	Suitable for field repairs.

A286 is generally considered to have good weldability, although preheating and post-weld heat treatment may be necessary to avoid cracking. The use of appropriate filler metals is crucial to maintain the desired mechanical properties in the weld zone.

Machinability

Machining Parameter	A286	AISI 1212	Notes/Tips
Relative Machinability Index	50%	100%	Requires slower speeds.
Typical Cutting Speed (Turning)	25 m/min	50 m/min	Use carbide tools.

A286 has moderate machinability, requiring slower cutting speeds and specialized tooling to achieve optimal results. The use of carbide tools is recommended to enhance performance and tool life.

Formability

A286 exhibits good formability, allowing for cold and hot forming processes. However, due to its strength, it may require higher forces compared to lower-strength alloys. The alloy's work hardening characteristics should be considered during forming operations to avoid excessive strain.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Solution Annealing	1040 - 1150 / 1900 - 2100	1 hour	Air or water	Dissolves carbides, improves ductility.
Aging	700 - 800 / 1292 - 1472	4 hours	Air	Increases strength through precipitation hardening.

The heat treatment processes for A286 involve solution annealing to dissolve carbides and aging to enhance strength. These treatments significantly affect the microstructure, 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)
Aerospace	Gas turbine components	High strength, oxidation resistance	Required for high-temperature performance.
Chemical Processing	Heat exchangers	Corrosion resistance, high-temperature stability	Essential for durability in harsh environments.
Oil and Gas	Wellhead components	Strength, toughness	Critical for safety and reliability.
Automotive	Exhaust systems	High-temperature strength, corrosion resistance	Necessary for performance and longevity.

Other applications include:

• Marine environments: Components exposed to seawater.
• Power generation: Parts in steam and gas turbines.
• Nuclear reactors: Structural components requiring high strength and corrosion resistance.

A286 is chosen for these applications due to its ability to withstand extreme conditions while maintaining structural integrity.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	A286	AISI 316	Duplex Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Good corrosion resistance	Excellent corrosion resistance	A286 excels in high-temperature applications.
Key Corrosion Aspect	Good in many environments	Excellent in chloride environments	Superior in aggressive environments	A286 may not perform as well in chloride-rich environments.
Weldability	Good	Excellent	Moderate	A286 requires careful welding practices.
Machinability	Moderate	Good	Moderate	A286 requires slower speeds and specialized tooling.
Formability	Good	Excellent	Moderate	A286 may require more force to form.
Approx. Relative Cost	Higher	Moderate	Higher	Cost considerations may influence selection.
Typical Availability	Moderate	High	Moderate	Availability can vary by region.

When selecting A286, considerations include its cost-effectiveness for high-temperature applications, availability in the market, and its performance in specific environments. While it may be more expensive than other stainless steels, its unique properties justify its use in critical applications.

In summary, A286 stainless steel is a versatile and high-performance alloy suitable for demanding applications, particularly in aerospace and chemical processing industries. Its combination of high strength, oxidation resistance, and good fabricability makes it a preferred choice for engineers and designers.