25CrMo4 Steel: Properties and Key Applications
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Table Of Content
25CrMo4 Steel is a medium-carbon alloy steel that falls under the category of low-alloy steels. It is primarily characterized by its chromium and molybdenum content, which enhances its strength, hardenability, and resistance to wear and fatigue. The steel is often used in applications requiring high strength and toughness, particularly in the automotive and aerospace industries.
Comprehensive Overview
25CrMo4 is classified as a medium-carbon alloy steel, specifically designed for high-strength applications. Its primary alloying elements are chromium (Cr) and molybdenum (Mo), which significantly influence its mechanical properties. The addition of chromium improves hardenability and corrosion resistance, while molybdenum enhances strength and toughness, especially at elevated temperatures.
The most significant characteristics of 25CrMo4 include:
- High Strength: The alloying elements contribute to a tensile strength that can reach up to 1,000 MPa (145 ksi) in the quenched and tempered condition.
- Good Toughness: It maintains toughness even at lower temperatures, making it suitable for dynamic loading applications.
- Excellent Wear Resistance: The steel exhibits good wear resistance, which is beneficial in applications involving friction and abrasion.
Advantages and Limitations
Advantages:
- High strength-to-weight ratio, making it ideal for structural applications.
- Good weldability and machinability, allowing for versatile fabrication methods.
- Enhanced fatigue resistance, suitable for components subjected to cyclic loading.
Limitations:
- Moderate corrosion resistance compared to stainless steels, necessitating protective coatings in corrosive environments.
- Requires careful heat treatment to achieve desired mechanical properties, which can complicate processing.
Historically, 25CrMo4 has been widely used in the manufacturing of components such as gears, shafts, and pressure vessels, establishing its reputation as a reliable material in engineering applications.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | G41300 | USA | Closest equivalent to 25CrMo4 |
| AISI/SAE | 4130 | USA | Minor compositional differences |
| EN | 1.7218 | Europe | Commonly used in Europe |
| DIN | 25CrMo4 | Germany | Standard designation in Germany |
| JIS | SCM420 | Japan | Similar properties, but different applications |
| GB | 30CrMo | China | Comparable, but with different mechanical properties |
| ISO | 25CrMo4 | International | International standard designation |
The differences between these equivalent grades can affect selection based on specific application requirements. For instance, while AISI 4130 and 25CrMo4 are similar in composition, 25CrMo4 may offer better hardenability due to its higher chromium content, making it preferable for certain high-strength applications.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| C (Carbon) | 0.24 - 0.29 |
| Cr (Chromium) | 0.90 - 1.20 |
| Mo (Molybdenum) | 0.15 - 0.30 |
| Mn (Manganese) | 0.40 - 0.70 |
| Si (Silicon) | 0.15 - 0.40 |
| P (Phosphorus) | ≤ 0.025 |
| S (Sulfur) | ≤ 0.025 |
The primary role of the key alloying elements in 25CrMo4 is as follows:
- Chromium: Enhances hardenability and corrosion resistance, contributing to the steel's overall strength.
- Molybdenum: Improves high-temperature strength and toughness, making the steel suitable for demanding applications.
- Carbon: Increases hardness and strength, but must be balanced to avoid brittleness.
Mechanical Properties
| Property | Condition/Temper | Test Temperature | Typical Value/Range (Metric) | Typical Value/Range (Imperial) | Reference Standard for Test Method |
|---|---|---|---|---|---|
| Tensile Strength | Quenched & Tempered | Room Temp | 800 - 1,000 MPa | 1160 - 145 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Quenched & Tempered | Room Temp | 600 - 850 MPa | 87 - 123 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | Room Temp | 15 - 20% | 15 - 20% | ASTM E8 |
| Hardness (HB) | Quenched & Tempered | Room Temp | 250 - 300 HB | 250 - 300 HB | ASTM E10 |
| Impact Strength (Charpy) | Quenched & Tempered | -20°C (-4°F) | 30 - 50 J | 22 - 37 ft-lbf | ASTM E23 |
The mechanical properties of 25CrMo4 make it suitable for applications that require high strength and toughness, such as in the automotive and aerospace sectors. Its ability to withstand high stress and fatigue makes it ideal for components like gears and shafts.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | Room Temp | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting Point | - | 1,500 °C | 2,732 °F |
| Thermal Conductivity | Room Temp | 45 W/m·K | 31 BTU·in/h·ft²·°F |
| Specific Heat Capacity | Room Temp | 460 J/kg·K | 0.11 BTU/lb·°F |
| Electrical Resistivity | Room Temp | 0.000001 Ω·m | 0.000001 Ω·in |
| Coefficient of Thermal Expansion | Room Temp | 12 × 10⁻⁶/K | 6.67 × 10⁻⁶/°F |
The practical significance of these physical properties includes:
- Density: Affects weight considerations in structural applications, where reducing weight without compromising strength is crucial.
- Thermal Conductivity: Important in applications where heat dissipation is necessary, such as in engine components.
- Melting Point: Indicates the steel's ability to withstand high temperatures, relevant for applications involving heat exposure.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Atmospheric | Varies | Ambient | Fair | Risk of rusting without protection |
| Chlorides | Varies | Ambient | Poor | Susceptible to pitting corrosion |
| Acids | Varies | Ambient | Fair | Requires protective coatings |
| Alkalis | Varies | Ambient | Good | Generally resistant |
| Organics | Varies | Ambient | Good | Generally resistant |
25CrMo4 exhibits moderate corrosion resistance, particularly in atmospheric conditions and environments with chlorides. It is susceptible to pitting corrosion in chloride-rich environments, which can be a significant concern in marine applications. Compared to stainless steels, such as 316L, which offer excellent corrosion resistance, 25CrMo4 may require protective coatings or treatments to enhance its durability in corrosive environments.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 400 °C | 752 °F | Suitable for prolonged exposure |
| Max Intermittent Service Temp | 500 °C | 932 °F | Short-term exposure |
| Scaling Temperature | 600 °C | 1,112 °F | Risk of oxidation beyond this temp |
| Creep Strength considerations begin around | 400 °C | 752 °F | Significant reduction in strength |
At elevated temperatures, 25CrMo4 maintains its strength and toughness, making it suitable for applications in high-temperature environments. However, oxidation can become a concern at temperatures above 600 °C (1,112 °F), necessitating protective measures.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| MIG | ER70S-6 | Argon + CO2 mix | Good results with proper technique |
| TIG | ER70S-2 | Argon | Excellent control and finish |
| Stick | E7018 | - | Requires preheat for best results |
25CrMo4 is generally considered weldable, but preheating is recommended to prevent cracking. Post-weld heat treatment can further enhance the mechanical properties of the welds. Common defects include porosity and undercutting, which can be minimized with proper technique.
Machinability
| Machining Parameter | 25CrMo4 | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 60 | 100 | Moderate machinability |
| Typical Cutting Speed | 30 m/min | 50 m/min | Adjust for tool wear |
The machinability of 25CrMo4 is moderate, requiring appropriate tooling and cutting speeds to achieve optimal results. Tool wear can be a concern, and using high-speed steel or carbide tools is recommended for better performance.
Formability
25CrMo4 exhibits good formability, allowing for both cold and hot forming processes. However, it is essential to consider work hardening effects during cold forming, which can increase the material's strength but may also lead to cracking if not managed properly. Bend radii should be calculated based on the thickness of the material to avoid failure.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 600 - 650 °C / 1,112 - 1,202 °F | 1 - 2 hours | Air or water | Softening, improved machinability |
| Quenching | 850 - 900 °C / 1,562 - 1,652 °F | 30 minutes | Oil or water | Hardening, increased strength |
| Tempering | 400 - 600 °C / 752 - 1,112 °F | 1 hour | Air | Reducing brittleness, improving toughness |
The heat treatment processes significantly affect the microstructure and properties of 25CrMo4. Quenching increases hardness, while tempering balances strength and toughness, making it suitable for high-stress applications.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Automotive | Gears | High strength, toughness | Essential for durability under load |
| Aerospace | Aircraft components | Lightweight, high strength | Critical for performance and safety |
| Oil & Gas | Drill pipes | Wear resistance, toughness | Necessary for harsh environments |
| Machinery | Shafts | Fatigue resistance, strength | Vital for operational reliability |
- Other applications include:
- Pressure vessels
- Structural components in construction
- High-performance fasteners
25CrMo4 is chosen for these applications due to its excellent mechanical properties, which ensure reliability and performance under demanding conditions.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | 25CrMo4 | AISI 4130 | 30CrMo | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High strength | Moderate strength | High toughness | 25CrMo4 offers better hardenability |
| Key Corrosion Aspect | Moderate | Poor | Fair | 25CrMo4 is better than AISI 4130 but less than stainless steels |
| Weldability | Good | Excellent | Fair | 25CrMo4 requires preheating |
| Machinability | Moderate | Good | Moderate | 25CrMo4 is less machinable than AISI 4130 |
| Formability | Good | Fair | Good | 25CrMo4 has better formability than AISI 4130 |
| Approx. Relative Cost | Moderate | Low | Moderate | Cost can vary based on market conditions |
| Typical Availability | Common | Common | Less common | 25CrMo4 is widely available in Europe |
When selecting 25CrMo4, considerations should include the specific mechanical and corrosion properties required for the application, as well as the availability and cost of the material. Its balance of strength, toughness, and weldability makes it a versatile choice for many engineering applications.
In conclusion, 25CrMo4 steel is a robust material that offers a combination of high strength, toughness, and good machinability, making it suitable for a wide range of applications in demanding environments. Its unique properties and performance characteristics make it a valuable choice for engineers and designers in various industries.