Maraging Steel: Properties and Key Applications

Maraging steel is a high-strength, low-carbon steel alloy known for its exceptional toughness and strength, achieved through a unique aging process. Classified as a low-carbon alloy steel, maraging steel typically contains significant amounts of nickel (around 15-25%), along with cobalt, molybdenum, and titanium as primary alloying elements. This composition contributes to its distinctive properties, including high tensile strength, excellent ductility, and good weldability.

Comprehensive Overview

Maraging steel is primarily characterized by its low carbon content, which allows for a high degree of toughness and ductility. The aging process, which involves heating the steel to a specific temperature and then cooling it, precipitates intermetallic compounds that enhance its mechanical properties. The most significant characteristics of maraging steel include:

• High Strength: Maraging steels can achieve tensile strengths exceeding 2000 MPa (290 ksi) after aging.
• Good Ductility: Despite their high strength, these steels maintain good elongation properties, making them suitable for complex shapes and applications.
• Excellent Weldability: The low carbon content minimizes the risk of cracking during welding processes.

Advantages and Limitations

Advantages	Limitations
Exceptional strength-to-weight ratio	Limited corrosion resistance compared to stainless steels
Good machinability and weldability	Higher cost due to alloying elements
Excellent dimensional stability	Requires precise heat treatment for optimal properties

Maraging steel has a unique position in the market, often used in aerospace, tooling, and high-performance applications due to its historical significance in the development of advanced materials. Its ability to maintain strength at elevated temperatures and resist deformation under load makes it a preferred choice for critical components.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S66500	USA	Closest equivalent to AISI 300M
AISI/SAE	AISI 250	USA	Commonly used in aerospace applications
ASTM	ASTM A588	USA	Similar properties, but with different corrosion resistance
EN	EN 1.2709	Europe	European equivalent with minor compositional differences
JIS	JIS G 4404	Japan	Japanese standard with similar applications

The subtle differences between these grades can significantly impact performance. For instance, while AISI 250 and UNS S66500 are often considered equivalent, the specific heat treatment processes and resultant microstructures can lead to variations in toughness and strength.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Ni (Nickel)	15 - 25
Co (Cobalt)	4 - 10
Mo (Molybdenum)	3 - 5
Ti (Titanium)	0.2 - 1.0
Al (Aluminum)	0.01 - 0.1
C (Carbon)	< 0.03

Nickel is the primary alloying element, providing strength and toughness. Cobalt enhances hardness and resistance to softening at elevated temperatures. Molybdenum contributes to strength and hardenability, while titanium helps in grain refinement and stabilization of the microstructure.

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	1400 - 2000 MPa	203 - 290 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	Room Temp	1200 - 1800 MPa	174 - 261 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	Quenched & Tempered	-40°C	50 - 100 J	37 - 74 ft-lbf	ASTM E23

The combination of high tensile and yield strength, along with good ductility, makes maraging steel suitable for applications requiring high mechanical loading and structural integrity, such as aerospace components and tooling.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	-	7.85 g/cm³	0.284 lb/in³
Melting Point/Range	-	1425 - 1450 °C	2600 - 2642 °F
Thermal Conductivity	20 °C	25 W/m·K	17.3 BTU·in/h·ft²·°F
Specific Heat Capacity	20 °C	460 J/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	20 °C	0.7 µΩ·m	0.7 µΩ·in

The density of maraging steel contributes to its strength-to-weight ratio, making it ideal for aerospace applications. The thermal conductivity is moderate, which is beneficial in applications where heat dissipation is required.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C)	Resistance Rating	Notes
Chlorides	3-5	25	Fair	Risk of pitting
Sulfuric Acid	10-20	25	Poor	Not recommended
Sea Water	-	25	Fair	Moderate resistance

Maraging steel exhibits limited corrosion resistance compared to stainless steels. It is susceptible to pitting and stress corrosion cracking in chloride environments. In contrast, stainless steels, such as 316L, offer superior resistance to corrosive agents, making them more suitable for marine applications.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	300	572	Suitable for high-temperature applications
Max Intermittent Service Temp	400	752	Can withstand short-term exposure
Scaling Temperature	600	1112	Risk of oxidation beyond this limit

At elevated temperatures, maraging steel maintains its strength but can experience oxidation. Careful consideration of service temperatures is crucial to avoid degradation of mechanical properties.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ERNiCrMo-3	Argon	Good results with preheat
MIG	ERNiCrMo-3	Argon/CO2	Requires post-weld heat treatment

Maraging steel is generally weldable, but preheating is recommended to minimize the risk of cracking. Post-weld heat treatment can help restore mechanical properties.

Machinability

Machining Parameter	Maraging Steel	AISI 1212	Notes/Tips
Relative Machinability Index	60	100	Requires carbide tooling
Typical Cutting Speed (Turning)	50 m/min	100 m/min	Adjust for tool wear

Maraging steel has good machinability, but it requires specialized tooling due to its hardness.

Formability

Maraging steel can be cold and hot formed, but its work hardening characteristics necessitate careful control of the forming process. The bend radii should be larger than those for conventional steels to avoid cracking.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Solution Annealing	820 - 850 / 1508 - 1562	1 - 2 hours	Air	Dissolve precipitates
Aging	480 - 500 / 896 - 932	4 - 8 hours	Air	Increase strength and hardness

The heat treatment process is critical for achieving the desired mechanical properties. Solution annealing dissolves precipitates, while aging enhances strength through precipitation hardening.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Aerospace	Aircraft landing gear	High strength, toughness, and fatigue resistance	Critical load-bearing components
Tooling	Molds for injection molding	Dimensional stability and wear resistance	Precision applications requiring durability
Defense	Missile components	High strength-to-weight ratio	Performance under extreme conditions

Other applications include:

• High-performance automotive components
• Sports equipment (e.g., golf clubs, bicycle frames)
• Medical devices (e.g., surgical instruments)

Maraging steel is chosen for these applications due to its unique combination of strength, toughness, and resistance to deformation under load.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	Maraging Steel	AISI 4140	304 Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate	Moderate	Maraging steel offers superior strength
Key Corrosion Aspect	Fair	Good	Excellent	Maraging steel is less corrosion-resistant
Weldability	Good	Fair	Excellent	Maraging steel requires careful welding techniques
Machinability	Moderate	Good	Excellent	Maraging steel requires specialized tooling
Formability	Moderate	Good	Excellent	Maraging steel is less formable than stainless steel
Approx. Relative Cost	High	Moderate	Moderate	Cost considerations may limit use
Typical Availability	Moderate	High	High	Availability can affect project timelines

When selecting maraging steel, considerations include cost-effectiveness, availability, and specific application requirements. Its unique properties make it suitable for niche applications, particularly in aerospace and defense, where performance is critical.

In summary, maraging steel is a high-performance material with unique properties that make it suitable for demanding applications. Its combination of strength, toughness, and machinability, along with careful consideration of fabrication processes, allows for its effective use in various industries.