SUJ2 Steel: Properties and Key Applications in Bearings
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Table Of Content
Table Of Content
SUJ2 steel, also known as JIS Bearing Steel, is a high-carbon chromium alloy steel primarily used in the manufacture of rolling bearings. Classified as a medium-carbon alloy steel, SUJ2 is characterized by its excellent hardness, wear resistance, and fatigue strength, making it ideal for applications requiring high performance under mechanical stress.
Comprehensive Overview
SUJ2 steel is primarily composed of carbon (C), chromium (Cr), and other alloying elements that enhance its mechanical properties. The typical chemical composition includes approximately 1.0% carbon and 1.5% chromium, which contribute significantly to its hardness and wear resistance. The presence of chromium not only improves corrosion resistance but also enhances the steel's ability to withstand high temperatures.
The most significant characteristics of SUJ2 steel include:
- High Hardness: Achievable hardness levels can reach up to 64 HRC after appropriate heat treatment.
- Excellent Wear Resistance: The combination of high carbon and chromium content provides exceptional wear resistance, making it suitable for high-load applications.
- Good Fatigue Strength: SUJ2 exhibits high fatigue strength, which is crucial for components subjected to cyclic loading.
Advantages:
- Superior wear resistance and hardness.
- Good dimensional stability during heat treatment.
- High fatigue strength, making it suitable for dynamic applications.
Limitations:
- Limited corrosion resistance compared to stainless steels.
- Difficult to machine due to high hardness.
- Requires careful heat treatment to achieve desired properties.
Historically, SUJ2 has been widely used in the automotive and aerospace industries for components such as bearings, gears, and shafts. Its market position remains strong due to its reliability and performance in critical applications.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | G52100 | USA | Closest equivalent to SUJ2 |
| AISI/SAE | 52100 | USA | Minor compositional differences |
| ASTM | A295 | USA | Specification for bearing steels |
| EN | 100Cr6 | Europe | Similar properties, often used interchangeably |
| DIN | 100Cr6 | Germany | Equivalent to SUJ2 with slight variations |
| JIS | SUJ2 | Japan | Standard designation for bearing steel |
| GB | GCr15 | China | Comparable grade with similar applications |
| ISO | 100Cr6 | International | Global standard equivalent |
The differences between these grades can affect performance in specific applications. For instance, while G52100 and SUJ2 are often considered equivalent, variations in heat treatment processes can lead to differences in hardness and wear resistance.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| C (Carbon) | 0.95 - 1.05 |
| Cr (Chromium) | 1.30 - 1.65 |
| Mn (Manganese) | 0.30 - 0.50 |
| Si (Silicon) | 0.15 - 0.40 |
| P (Phosphorus) | ≤ 0.025 |
| S (Sulfur) | ≤ 0.025 |
The primary role of the key alloying elements in SUJ2 steel includes:
- Carbon (C): Increases hardness and strength through the formation of carbides during heat treatment.
- Chromium (Cr): Enhances wear resistance and improves hardenability, allowing for deeper hardening during heat treatment.
- Manganese (Mn): Improves toughness and helps in deoxidizing the steel during production.
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 | 1,700 - 2,100 MPa | 247 - 304 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Quenched & Tempered | 1,500 - 1,800 MPa | 218 - 261 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | 10 - 12% | 10 - 12% | ASTM E8 |
| Hardness (HRC) | Quenched & Tempered | 58 - 64 HRC | 58 - 64 HRC | ASTM E18 |
| Impact Strength (Charpy) | Room Temperature | 20 - 30 J | 15 - 22 ft-lbf | ASTM E23 |
The combination of these mechanical properties makes SUJ2 steel suitable for applications that require high strength and wear resistance, such as bearings and gears, where fatigue and wear are critical considerations.
Physical Properties
| Property | Condition/Temperature | Value (Metric - SI Units) | Value (Imperial Units) |
|---|---|---|---|
| Density | Room Temperature | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting Point | - | 1,450 - 1,500 °C | 2,642 - 2,732 °F |
| Thermal Conductivity | Room Temperature | 25 W/m·K | 14.5 BTU·in/(h·ft²·°F) |
| Specific Heat Capacity | Room Temperature | 0.46 J/g·K | 0.11 BTU/lb·°F |
| Coefficient of Thermal Expansion | Room Temperature | 11.5 x 10⁻⁶ /°C | 6.36 x 10⁻⁶ /°F |
The practical significance of SUJ2's physical properties includes:
- Density: Affects the weight and balance of components, crucial in applications like automotive and aerospace.
- Thermal Conductivity: Important for heat dissipation in high-speed bearings.
- Coefficient of Thermal Expansion: Impacts dimensional stability under varying temperature conditions, critical for precision applications.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Water | - | Ambient | Fair | Susceptible to rust |
| Acids | Low | Ambient | Poor | Risk of pitting |
| Chlorides | High | Ambient | Poor | Risk of stress corrosion |
| Alkaline Solutions | Low | Ambient | Fair | Moderate resistance |
SUJ2 steel exhibits limited corrosion resistance, particularly in acidic and chloride-rich environments. It is susceptible to rusting when exposed to moisture, making protective coatings or surface treatments necessary for outdoor applications. Compared to stainless steels like AISI 440C, which offer superior corrosion resistance, SUJ2 is less suitable for environments where corrosion is a significant concern.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 200 | 392 | Suitable for high-speed applications |
| Max Intermittent Service Temp | 250 | 482 | Short-term exposure only |
| Scaling Temperature | 300 | 572 | Risk of oxidation beyond this temp |
| Creep Strength considerations | 400 | 752 | Begins to degrade at elevated temps |
At elevated temperatures, SUJ2 steel maintains its hardness and strength up to a certain limit, beyond which it may experience oxidation and loss of mechanical properties. This makes it suitable for applications where components may experience high temperatures intermittently but not continuously.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| MIG | ER70S-6 | Argon + CO2 | Preheat recommended |
| TIG | ER80S-D2 | Argon | Requires post-weld heat treatment |
| SMAW | E7018 | - | Not recommended for thick sections |
SUJ2 steel is generally not recommended for welding due to its high carbon content, which can lead to cracking. Preheating and post-weld heat treatment are essential to minimize these risks. The choice of filler metal is critical to ensure compatibility and maintain mechanical properties.
Machinability
| Machining Parameter | SUJ2 Steel | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 60 | 100 | SUJ2 is more challenging to machine |
| Typical Cutting Speed (Turning) | 30 m/min | 60 m/min | Use carbide tools for best results |
Machining SUJ2 steel can be challenging due to its hardness. Optimal conditions include using high-speed steel or carbide tools and ensuring proper cooling to prevent tool wear.
Formability
SUJ2 steel exhibits limited formability due to its high hardness and strength. Cold forming is possible but may lead to work hardening, requiring careful control of bending radii and forming processes. Hot forming is more feasible but requires precise temperature control to avoid degradation of properties.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 700 - 800 / 1,292 - 1,472 | 1 - 2 hours | Air or Furnace | Reduce hardness, improve machinability |
| Quenching | 800 - 850 / 1,472 - 1,562 | 30 minutes | Oil or Water | Achieve high hardness |
| Tempering | 150 - 200 / 302 - 392 | 1 hour | Air | Reduce brittleness, improve toughness |
During heat treatment, SUJ2 undergoes significant metallurgical transformations. Quenching transforms the microstructure to martensite, providing high hardness, while tempering reduces brittleness and enhances toughness, making the steel suitable for dynamic applications.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Automotive | Wheel bearings | High hardness, wear resistance | Essential for durability under load |
| Aerospace | Engine components | Fatigue strength, dimensional stability | Critical for safety and performance |
| Industrial | Gear shafts | High tensile strength, impact resistance | Necessary for reliability in machinery |
Other applications include:
- Precision instruments
- High-speed spindles
- Roller bearings
SUJ2 is chosen for these applications due to its superior hardness and wear resistance, which are critical for components subjected to high stress and fatigue.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | SUJ2 Steel | AISI 440C | D2 Tool Steel | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High hardness | Excellent corrosion resistance | High wear resistance | SUJ2 is less corrosion-resistant |
| Key Corrosion Aspect | Fair | Excellent | Fair | SUJ2 requires protective coatings |
| Weldability | Poor | Fair | Poor | All grades require careful handling |
| Machinability | Challenging | Moderate | Moderate | SUJ2 is harder to machine |
| Formability | Limited | Good | Limited | SUJ2 is less formable |
| Approx. Relative Cost | Moderate | Higher | Moderate | Cost varies by market demand |
| Typical Availability | Common | Common | Less common | SUJ2 is widely available |
When selecting SUJ2 steel, considerations include its mechanical properties, cost-effectiveness, and availability. While it excels in hardness and wear resistance, its limitations in corrosion resistance and machinability must be weighed against the specific application requirements. Additionally, safety considerations in high-stress environments necessitate careful evaluation of its performance characteristics.
