S690QL Steel: Properties and Key Applications
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Table Of Content
Table Of Content
STE 690 Steel (S690QL) is a high-strength structural steel grade classified under the EN 10025-6 standard. It is primarily a quenched and tempered steel, known for its excellent mechanical properties and weldability. The main alloying elements in S690QL include carbon, manganese, silicon, and small amounts of chromium, molybdenum, and vanadium. These elements contribute significantly to the steel's strength, toughness, and overall performance in demanding applications.
Comprehensive Overview
S690QL is characterized by its high yield strength, typically around 690 MPa, which allows for thinner sections in structural applications without compromising strength. This property is particularly advantageous in industries such as construction, where weight reduction can lead to cost savings in materials and transportation. The steel also exhibits good impact toughness, making it suitable for low-temperature applications.
Advantages of S690QL:
- High Strength-to-Weight Ratio: Enables the design of lighter structures.
- Good Weldability: Suitable for various welding processes, which simplifies fabrication.
- Excellent Toughness: Maintains performance in low-temperature environments.
Limitations of S690QL:
- Cost: Higher than standard structural steels due to alloying elements and processing.
- Brittleness at Low Temperatures: While it has good toughness, care must be taken in extremely low temperatures.
- Limited Availability: Not as commonly stocked as lower-grade steels.
Historically, S690QL has gained traction in sectors requiring high-performance materials, such as heavy machinery, offshore structures, and high-rise buildings, due to its ability to withstand significant loads while minimizing material usage.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S690QL | International | Closest equivalent to ASTM A572 Grade 65 |
| ASTM | A572 Grade 65 | USA | Minor compositional differences to be aware of |
| EN | S690QL | Europe | Standard for high-strength structural steel |
| DIN | 1.8928 | Germany | Equivalent designation in German standards |
| JIS | - | Japan | No direct equivalent but similar grades exist |
The differences between S690QL and its equivalents often lie in the specific alloying elements and mechanical properties, which can affect performance in particular applications. For example, while ASTM A572 Grade 65 offers similar strength, it may not provide the same toughness at low temperatures.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| C (Carbon) | 0.12 - 0.20 |
| Mn (Manganese) | 1.00 - 1.60 |
| Si (Silicon) | 0.10 - 0.50 |
| Cr (Chromium) | 0.20 - 0.50 |
| Mo (Molybdenum) | 0.10 - 0.30 |
| V (Vanadium) | 0.02 - 0.10 |
| P (Phosphorus) | ≤ 0.025 |
| S (Sulfur) | ≤ 0.015 |
The primary alloying elements in S690QL play crucial roles:
- Carbon (C): Increases strength and hardness but can reduce ductility.
- Manganese (Mn): Enhances hardenability and toughness.
- Chromium (Cr): Improves corrosion resistance and strength at elevated temperatures.
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 | 690 - 770 MPa | 100 - 112 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Quenched & Tempered | Room Temp | ≥ 690 MPa | ≥ 100 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | Room Temp | ≥ 20% | ≥ 20% | ASTM E8 |
| Reduction of Area | Quenched & Tempered | Room Temp | ≥ 50% | ≥ 50% | ASTM E8 |
| Hardness (Brinell) | Quenched & Tempered | Room Temp | 200 - 250 HB | 200 - 250 HB | ASTM E10 |
| Impact Strength | Quenched & Tempered | -40°C (-40°F) | ≥ 27 J | ≥ 20 ft-lbf | ASTM E23 |
The combination of high tensile and yield strength, along with good elongation, makes S690QL suitable for applications requiring high mechanical loading and structural integrity. Its impact strength at low temperatures ensures reliability in harsh environments.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | Room Temp | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting Point | - | 1420 - 1540 °C | 2590 - 2810 °F |
| Thermal Conductivity | Room Temp | 50 W/m·K | 34.5 BTU·in/(hr·ft²·°F) |
| Specific Heat Capacity | Room Temp | 0.46 kJ/kg·K | 0.11 BTU/lb·°F |
| Electrical Resistivity | Room Temp | 0.0000017 Ω·m | 0.0000017 Ω·in |
Key physical properties such as density and melting point are significant for applications where weight and thermal performance are critical. The thermal conductivity indicates how well the steel can dissipate heat, which is essential in applications involving high temperatures.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Atmospheric | - | - | Good | Susceptible to rust |
| Chlorides | 3-5 | 20-60 °C (68-140 °F) | Fair | Risk of pitting |
| Acids | 10-20 | 20-60 °C (68-140 °F) | Poor | Not recommended |
| Alkalis | 5-10 | 20-60 °C (68-140 °F) | Fair | Limited resistance |
S690QL exhibits good resistance to atmospheric corrosion but is susceptible to pitting in chloride environments. Compared to other high-strength steels like S355, S690QL offers improved performance in structural applications but may require protective coatings in aggressive environments.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 400 °C | 752 °F | Suitable for structural applications |
| Max Intermittent Service Temp | 500 °C | 932 °F | Short-term exposure only |
| Scaling Temperature | 600 °C | 1112 °F | Risk of oxidation beyond this temp |
| Creep Strength Considerations | 400 °C | 752 °F | Begins to degrade at this temp |
S690QL maintains its mechanical properties up to approximately 400 °C, making it suitable for applications involving elevated temperatures. However, care must be taken to avoid prolonged exposure to temperatures above its scaling limit, as this can lead to oxidation and loss of material integrity.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| MIG | ER70S-6 | Argon + CO2 | Good for thin sections |
| TIG | ER70S-2 | Argon | Excellent for precision work |
| SMAW | E7018 | - | Requires preheat |
S690QL is highly weldable, but preheating is recommended to avoid cracking. Post-weld heat treatment can enhance the toughness of the welds, especially in critical applications.
Machinability
| Machining Parameter | S690QL | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 60% | 100% | Requires high-speed tooling |
| Typical Cutting Speed | 20 m/min | 40 m/min | Adjust based on tooling |
S690QL has moderate machinability, requiring careful selection of cutting tools and speeds to achieve optimal results. The use of carbide tools is recommended for effective machining.
Formability
S690QL exhibits limited formability due to its high strength. Cold forming is possible but may require significant force, while hot forming can be performed at elevated temperatures to improve ductility. The minimum bend radius should be considered during fabrication to avoid cracking.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Quenching | 850-900 °C / 1562-1652 °F | 30-60 minutes | Water/Oil | Hardening |
| Tempering | 500-600 °C / 932-1112 °F | 1-2 hours | Air | Toughness improvement |
Heat treatment processes such as quenching and tempering significantly enhance the mechanical properties of S690QL. The quenching process increases hardness, while tempering reduces brittleness, resulting in a balanced material suitable for structural applications.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection (Brief) |
|---|---|---|---|
| Construction | High-rise buildings | High strength, good weldability | Reduces material weight |
| Heavy Machinery | Excavators | Toughness, impact resistance | Endures heavy loads |
| Offshore Structures | Oil rigs | Corrosion resistance, strength | Withstands harsh environments |
| Transportation | Bridges | High yield strength, low weight | Enhances structural efficiency |
Other applications include:
- Mining equipment
- Pressure vessels
- Shipbuilding
S690QL is chosen for these applications due to its ability to withstand extreme conditions while maintaining structural integrity, making it ideal for critical load-bearing components.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | S690QL | S355 | S700MC | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High Strength | Moderate Strength | Very High Strength | S690QL offers a balance of strength and toughness |
| Key Corrosion Aspect | Fair | Good | Fair | S690QL may require coatings in aggressive environments |
| Weldability | Good | Excellent | Moderate | S690QL needs preheating for optimal welds |
| Machinability | Moderate | Good | Poor | S690QL requires careful machining techniques |
| Formability | Limited | Good | Moderate | S690QL is less formable due to high strength |
| Approx. Relative Cost | High | Moderate | High | Cost considerations may affect selection |
| Typical Availability | Limited | Widely Available | Limited | Availability can impact project timelines |
When selecting S690QL, considerations include its cost-effectiveness relative to performance requirements, availability in the market, and specific application needs. Its high strength and toughness make it suitable for demanding environments, but potential buyers should weigh these benefits against the higher costs and limited availability compared to lower-grade steels.
In summary, S690QL is a versatile high-strength steel that excels in structural applications requiring durability and reliability. Its unique properties make it a preferred choice in industries where performance is critical, despite some limitations in cost and availability.
