Maraging 350 Steel: Properties and Key Applications

Maraging 350 Steel (C350) is a high-strength, low-carbon steel known for its exceptional mechanical properties and unique metallurgical characteristics. Classified as a maraging steel, it primarily consists of iron with significant additions of nickel (up to 18%), cobalt, and molybdenum. These alloying elements enhance its strength, toughness, and resistance to deformation, making it suitable for demanding applications in various industries.

Comprehensive Overview

Maraging 350 Steel is particularly noted for its ability to achieve high strength levels through a process known as aging, which involves heat treatment that precipitates intermetallic compounds. This steel grade exhibits a yield strength of approximately 2,400 MPa (348,000 psi) and a tensile strength of around 2,500 MPa (362,500 psi), making it one of the strongest steels available. Its low carbon content minimizes the risk of brittleness, while the nickel content contributes to its toughness and ductility.

Advantages:
- High Strength-to-Weight Ratio: Ideal for applications where weight savings are critical.
- Excellent Ductility and Toughness: Allows for complex shapes and forms without cracking.
- Good Weldability: Can be welded using standard techniques, although preheating is often recommended.

Limitations:
- Cost: Generally more expensive than conventional steels due to alloying elements and processing.
- Corrosion Resistance: While it has decent resistance, it is not as corrosion-resistant as stainless steels.
- Heat Treatment Sensitivity: Requires precise control during heat treatment to achieve desired properties.

Historically, maraging steels have been used in aerospace, tooling, and high-performance applications, establishing a strong market position due to their unique properties.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S35000	USA	Closest equivalent to AISI 300M
AISI/SAE	350	USA	High-performance maraging steel
ASTM	A203	USA	Used for pressure vessels
EN	1.6350	Europe	Similar properties to C350
JIS	SCMN 350	Japan	Minor compositional differences

The table above outlines various standards and equivalent designations for Maraging 350 Steel. Notably, while these grades may exhibit similar mechanical properties, subtle differences in composition can affect performance, particularly in specific applications such as aerospace or tooling.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
Fe (Iron)	Balance
Ni (Nickel)	15.0 - 18.0
Co (Cobalt)	4.0 - 5.0
Mo (Molybdenum)	3.0 - 4.0
Ti (Titanium)	0.1 - 0.3
C (Carbon)	0.03 max

The primary alloying elements in Maraging 350 Steel play crucial roles in defining its properties:
- Nickel: Enhances toughness and strength, contributing to the steel's overall ductility.
- Cobalt: Improves hardenability and strength at elevated temperatures.
- Molybdenum: Increases strength and resistance to softening during heat treatment.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Quenched & Tempered	2,500 MPa	362,500 psi	ASTM E8
Yield Strength (0.2% offset)	Quenched & Tempered	2,400 MPa	348,000 psi	ASTM E8
Elongation	Quenched & Tempered	10%	10%	ASTM E8
Reduction of Area	Quenched & Tempered	50%	50%	ASTM E8
Hardness (Rockwell C)	Quenched & Tempered	40 - 45 HRC	40 - 45 HRC	ASTM E18
Impact Strength (Charpy)	-40°C	50 J	37 ft-lbf	ASTM E23

The mechanical properties of Maraging 350 Steel make it particularly suitable for applications requiring high strength and toughness. Its high yield and tensile strength allow it to withstand significant mechanical loads, while its elongation and reduction of area indicate good ductility, making it ideal for complex shapes and forms.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	Room Temperature	8.0 g/cm³	0.289 lb/in³
Melting Point/Range	-	1,400 - 1,500 °C	2,552 - 2,732 °F
Thermal Conductivity	Room Temperature	20 W/m·K	13.1 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	Room Temperature	460 J/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	Room Temperature	0.7 µΩ·m	0.0000013 Ω·in

The physical properties of Maraging 350 Steel, such as its density and thermal conductivity, are significant for applications where weight and heat dissipation are critical. Its relatively high melting point allows it to maintain structural integrity at elevated temperatures.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-5%	25°C/77°F	Fair	Risk of pitting corrosion
Sulfuric Acid	10%	25°C/77°F	Poor	Not recommended
Sea Water	-	25°C/77°F	Good	Moderate resistance

Maraging 350 Steel exhibits moderate resistance to corrosion, particularly in chloride environments, where it can be susceptible to pitting. Compared to stainless steels, it does not perform as well in acidic conditions, making it less suitable for applications in highly corrosive environments.

When compared to other steel grades, such as 304 stainless steel, Maraging 350 Steel may offer superior mechanical properties but at the expense of corrosion resistance. This trade-off is crucial when selecting materials for specific applications.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	300 °C	572 °F	Suitable for high-temperature applications
Max Intermittent Service Temp	400 °C	752 °F	Short-term exposure only
Scaling Temperature	600 °C	1,112 °F	Risk of oxidation at this temperature

Maraging 350 Steel maintains its strength and toughness at elevated temperatures, making it suitable for applications that experience thermal cycling. However, prolonged exposure to temperatures above 300 °C can lead to oxidation and degradation of mechanical properties.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
TIG	ERNiCrMo-3	Argon	Preheat recommended
MIG	ERNiCrMo-3	Argon/CO2	Post-weld heat treatment advised

Maraging 350 Steel is generally weldable using standard processes such as TIG and MIG. However, preheating is often recommended to prevent cracking, and post-weld heat treatment is essential to restore the desired mechanical properties.

Machinability

Machining Parameter	Maraging 350 Steel	AISI 1212	Notes/Tips
Relative Machinability Index	50	100	Requires carbide tooling
Typical Cutting Speed (Turning)	30 m/min	60 m/min	Use coolant to reduce heat

Maraging 350 Steel has moderate machinability, requiring carbide tools and appropriate cutting speeds to achieve optimal results. Careful attention to cooling is necessary to prevent work hardening.

Formability

Maraging 350 Steel exhibits good formability, allowing for cold and hot forming processes. However, due to its high strength, larger bend radii are recommended to avoid cracking during forming operations.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Solution Treatment	820 - 850 °C / 1,508 - 1,562 °F	1 - 2 hours	Air or Oil	Dissolve precipitates
Aging	480 - 500 °C / 896 - 932 °F	4 - 8 hours	Air	Precipitation hardening

The heat treatment processes for Maraging 350 Steel involve solution treatment followed by aging. These processes lead to a fine distribution of intermetallic compounds, significantly enhancing the material's strength and toughness.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Aerospace	Aircraft components	High strength, low weight	Critical for performance
Tooling	Molds and dies	Toughness, wear resistance	Durability in harsh conditions
Automotive	High-performance parts	Strength, ductility	Safety and performance

Other applications include:
- Sports Equipment: Used in high-performance gear due to its strength-to-weight ratio.
- Military: Components in defense systems where reliability is paramount.

Maraging 350 Steel is chosen for applications requiring exceptional strength and toughness, particularly where weight savings are essential, such as in aerospace and high-performance automotive components.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	Maraging 350 Steel	AISI 4340 Steel	304 Stainless Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Good toughness	Moderate strength	C350 excels in strength
Key Corrosion Aspect	Fair	Poor	Excellent	C350 less suitable for corrosive environments
Weldability	Good	Fair	Excellent	C350 requires pre/post treatment
Machinability	Moderate	Good	Excellent	C350 needs carbide tooling
Formability	Good	Fair	Excellent	C350 requires larger bend radii
Approx. Relative Cost	High	Moderate	Moderate	C350 is more expensive
Typical Availability	Moderate	High	High	C350 less common

When selecting Maraging 350 Steel, considerations include its high cost and moderate availability compared to more common grades like AISI 4340 or 304 stainless steel. However, its unique properties make it invaluable for applications where performance is critical.

In summary, Maraging 350 Steel stands out for its exceptional mechanical properties, making it a preferred choice in high-performance applications. Its unique combination of strength, toughness, and weldability, along with its specific heat treatment requirements, positions it as a material of choice for engineers and designers in demanding industries.