S390 Steel (Bohler HSS): Properties and Key Applications
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Table Of Content
Table Of Content
S390 Steel, also known as Bohler HSS, is a high-speed steel (HSS) grade renowned for its exceptional hardness, wear resistance, and ability to maintain cutting performance at elevated temperatures. Classified as a tool steel, S390 is primarily used in applications requiring high wear resistance and toughness. The steel's composition includes significant amounts of tungsten, molybdenum, and vanadium, which contribute to its unique properties.
Comprehensive Overview
S390 Steel is classified as a high-speed steel, specifically designed for cutting tools and applications that demand high hardness and wear resistance. The primary alloying elements in S390 include tungsten (W), molybdenum (Mo), and vanadium (V), which enhance its hardness and toughness. The presence of carbon (C) is also crucial, as it forms carbides that contribute to the steel's hardness.
The most significant characteristics of S390 Steel include:
- High Hardness: Achievable hardness levels can reach up to 67 HRC, making it suitable for demanding cutting applications.
- Excellent Wear Resistance: The carbide structure provides outstanding wear resistance, prolonging tool life.
- Good Toughness: Despite its hardness, S390 maintains a level of toughness that prevents chipping and cracking during use.
Advantages:
- Exceptional performance in high-speed cutting applications.
- Retains sharpness longer than many other tool steels.
- Versatile for various machining processes.
Limitations:
- More expensive than conventional tool steels.
- Requires careful heat treatment to achieve optimal properties.
- Can be challenging to machine due to its hardness.
Historically, S390 has been significant in the manufacturing of cutting tools, particularly in industries such as automotive and aerospace, where precision and durability are paramount.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | T11302 | USA | Closest equivalent to Bohler S390 |
| AISI/SAE | M2 | USA | Minor compositional differences |
| DIN | 1.3343 | Germany | Similar properties, but different heat treatment |
| JIS | SKH51 | Japan | Comparable performance in cutting applications |
| ISO | 4957 | International | Standard for high-speed steels |
The subtle differences between these grades can affect performance in specific applications. For instance, while M2 is a common alternative, it may not achieve the same hardness as S390 under identical heat treatment conditions.
Key Properties
Chemical Composition
| Element (Symbol) | Percentage Range (%) |
|---|---|
| Carbon (C) | 1.40 - 1.60 |
| Molybdenum (Mo) | 4.00 - 5.00 |
| Tungsten (W) | 9.00 - 10.00 |
| Vanadium (V) | 2.00 - 3.00 |
| Chromium (Cr) | 3.00 - 4.00 |
| Iron (Fe) | Balance |
The primary role of tungsten and molybdenum in S390 Steel is to enhance hardness and wear resistance, while vanadium contributes to the formation of fine carbides, improving toughness and stability during high-temperature applications.
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 | 2000 - 2200 MPa | 290 - 320 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Quenched & Tempered | Room Temp | 1800 - 2000 MPa | 261 - 290 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | Room Temp | 2 - 5% | 2 - 5% | ASTM E8 |
| Hardness | Quenched & Tempered | Room Temp | 64 - 67 HRC | 64 - 67 HRC | ASTM E18 |
| Impact Strength | Quenched & Tempered | -20 °C | 20 - 30 J | 15 - 22 ft-lbf | ASTM E23 |
The combination of high tensile and yield strength, along with excellent hardness, makes S390 Steel suitable for applications involving high mechanical loads and wear resistance, such as cutting tools and dies.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | Room Temp | 8.0 g/cm³ | 0.289 lb/in³ |
| Melting Point | - | 1400 - 1450 °C | 2552 - 2642 °F |
| Thermal Conductivity | Room Temp | 25 W/m·K | 17.3 BTU·in/h·ft²·°F |
| Specific Heat Capacity | Room Temp | 460 J/kg·K | 0.11 BTU/lb·°F |
The density and melting point of S390 Steel indicate its robustness, while its thermal conductivity is essential for applications involving heat generation during cutting processes. The specific heat capacity is also crucial for understanding thermal management in high-speed machining.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-5% | 20 - 60 | Fair | Risk of pitting |
| Sulfuric Acid | 10% | 25 | Poor | Not recommended |
| Sodium Hydroxide | 5% | 25 | Good | Moderate resistance |
S390 Steel exhibits fair resistance to chlorides but is susceptible to pitting corrosion in aggressive environments. Compared to other high-speed steels like M2 and SKH51, S390's corrosion resistance is generally lower, making it less suitable for applications in highly corrosive environments.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 600 | 1112 | Suitable for high-speed cutting |
| Max Intermittent Service Temp | 650 | 1202 | Short-term exposure only |
| Scaling Temperature | 700 | 1292 | Risk of oxidation beyond this temp |
At elevated temperatures, S390 Steel maintains its hardness and wear resistance, making it ideal for high-speed cutting applications. However, prolonged exposure to temperatures above 650 °C can lead to oxidation and degradation of properties.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER80S-D2 | Argon | Preheat recommended |
| MIG | ER70S-6 | Argon/CO2 | Post-weld heat treatment |
S390 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 mitigate these risks.
Machinability
| Machining Parameter | [S390 Steel] | [AISI 1212] | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 30 | 100 | S390 is significantly harder |
| Typical Cutting Speed (Turning) | 20 m/min | 60 m/min | Use carbide tools for S390 |
Machining S390 Steel requires specialized tooling and conditions due to its hardness. Carbide tools are recommended for effective machining.
Formability
S390 Steel is not typically known for its formability due to its high hardness. Cold forming is challenging, while hot forming may be feasible with proper temperature control. Work hardening can occur, necessitating careful management of bend radii.
Heat Treatment
| Treatment Process | Temperature Range (°C) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 800 - 850 | 1 - 2 hours | Air | Reduce hardness, improve machinability |
| Hardening | 1200 - 1250 | 30 - 60 minutes | Oil | Achieve maximum hardness |
| Tempering | 550 - 600 | 1 hour | Air | Reduce brittleness, improve toughness |
The heat treatment processes significantly influence the microstructure of S390 Steel, enhancing its hardness and toughness through the formation of fine carbides.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Aerospace | Cutting tools for turbine manufacturing | High hardness, wear resistance | Extended tool life |
| Automotive | Dies for stamping operations | Toughness, resistance to wear | Durability under stress |
| Metalworking | High-speed drills | Retention of sharpness, heat resistance | Efficiency in cutting |
Other applications include:
-
- Molds for injection molding
-
- Saws and blades for metal cutting
-
- Tooling for machining operations
S390 Steel is chosen for these applications due to its ability to maintain performance under high-stress conditions, ensuring longevity and efficiency.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | [S390 Steel] | [M2] | [SKH51] | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High hardness | Moderate | High hardness | S390 offers superior wear resistance |
| Key Corrosion Aspect | Fair | Good | Fair | M2 has better corrosion resistance |
| Weldability | Poor | Fair | Fair | S390 is challenging to weld |
| Machinability | Low | Moderate | High | M2 is easier to machine |
| Approx. Relative Cost | High | Moderate | Moderate | S390 is more expensive |
| Typical Availability | Moderate | High | High | M2 and SKH51 are more common |
When selecting S390 Steel, considerations include its cost-effectiveness, availability, and specific application requirements. While it offers exceptional performance in high-speed cutting, its higher cost and lower machinability compared to alternatives like M2 can be limiting factors. Additionally, safety considerations in handling and machining are paramount due to the steel's hardness and potential for tool wear.
In summary, S390 Steel is a premium choice for high-performance cutting tools, offering a unique combination of hardness, wear resistance, and toughness, making it suitable for demanding industrial applications.
