S690QL Steel: Properties and Key Applications
شارك
Table Of Content
Table Of Content
S690QL steel is a high-strength, low-alloy structural steel known for its excellent mechanical properties and versatility in various engineering applications. Classified as a quenched and tempered steel, S690QL falls under the category of high yield strength steels, specifically designed to provide enhanced performance in demanding conditions. The primary alloying elements in S690QL include carbon (C), manganese (Mn), silicon (Si), and small amounts of chromium (Cr) and molybdenum (Mo). These elements contribute significantly to the steel's strength, toughness, and weldability.
Comprehensive Overview
S690QL is characterized by its high yield strength, typically around 690 MPa (100 ksi), which allows for thinner sections in structural applications without compromising load-bearing capacity. This property makes it particularly advantageous in industries such as construction, mining, and heavy machinery, where weight reduction is crucial. The steel exhibits excellent toughness and ductility, ensuring that it can withstand dynamic loads and impact forces.
Advantages:
- High Strength-to-Weight Ratio: Enables the design of lighter structures.
- Good Weldability: Suitable for various welding processes, facilitating fabrication.
- Excellent Toughness: Maintains performance in low-temperature environments.
Limitations:
- Cost: Higher than conventional mild steels due to alloying elements and processing.
- Corrosion Resistance: While it has decent resistance, it may require protective coatings in aggressive environments.
S690QL has gained popularity in the market due to its ability to meet stringent performance criteria while providing cost-effective solutions in structural applications. Its historical significance lies in its development to meet the increasing demands for high-performance materials in modern engineering.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S690QL | USA | Closest equivalent to EN 10025-6 |
| EN | S690QL | Europe | High yield strength structural steel |
| ASTM | A709 Grade 50QL | USA | Similar properties, used in bridge applications |
| DIN | 1.8928 | Germany | Equivalent grade with minor compositional differences |
| JIS | - | Japan | No direct equivalent, but similar grades exist |
The table above highlights various standards and equivalent grades for S690QL. Notably, while ASTM A709 Grade 50QL shares similar mechanical properties, it may differ in chemical composition, which could affect performance in specific applications. Understanding these nuances is crucial for material selection.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| C (Carbon) | 0.12 - 0.20 |
| Mn (Manganese) | 1.40 - 1.80 |
| Si (Silicon) | 0.10 - 0.50 |
| Cr (Chromium) | 0.30 - 0.50 |
| Mo (Molybdenum) | 0.10 - 0.15 |
| P (Phosphorus) | ≤ 0.025 |
| S (Sulfur) | ≤ 0.015 |
The primary alloying elements in S690QL play critical 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 |
|---|---|---|---|---|---|
| Yield Strength (0.2% offset) | Quenched & Tempered | Room Temp | 690 - 900 MPa | 100 - 130 ksi | ASTM E8 |
| Tensile Strength | Quenched & Tempered | Room Temp | 770 - 1100 MPa | 112 - 160 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | Room Temp | 14 - 20% | 14 - 20% | ASTM E8 |
| Hardness | Quenched & Tempered | Room Temp | 200 - 250 HB | 200 - 250 HB | ASTM E10 |
| Impact Strength | Quenched & Tempered | -20°C (-4°F) | ≥ 27 J | ≥ 20 ft-lbf | ASTM E23 |
The combination of high yield and tensile strength, along with good elongation, makes S690QL suitable for applications requiring high mechanical loading and structural integrity. Its impact strength at low temperatures ensures performance in harsh environments.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | - | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting Point | - | 1420 - 1460 °C | 2590 - 2660 °F |
| Thermal Conductivity | 20°C | 50 W/m·K | 34.5 BTU·in/h·ft²·°F |
| Specific Heat Capacity | 20°C | 0.49 kJ/kg·K | 0.12 BTU/lb·°F |
| Coefficient of Thermal Expansion | 20 - 100 °C | 12 x 10⁻⁶/K | 6.67 x 10⁻⁶/°F |
Key physical properties such as density and thermal conductivity are significant for applications where weight and heat dissipation are critical. The relatively high melting point indicates good performance under elevated temperatures.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-5 | 20-60 | Fair | Risk of pitting corrosion |
| Sulfuric Acid | 10-20 | 20-40 | Poor | Not recommended |
| Sea Water | - | 20-30 | Good | Requires protective coating |
| Alkalis | 5-10 | 20-60 | Fair | Moderate resistance |
S690QL exhibits moderate corrosion resistance, particularly in chloride environments, making it suitable for marine applications with appropriate protective measures. However, it is susceptible to pitting in high chloride concentrations and should not be used in acidic environments without protective coatings.
When compared to grades like S355 and S690, S690QL offers superior strength but may require more careful handling in corrosive environments. S355, while less strong, has better overall corrosion resistance.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 400 | 752 | Suitable for structural applications |
| Max Intermittent Service Temp | 500 | 932 | Short-term exposure only |
| Scaling Temperature | 600 | 1112 | Risk of oxidation beyond this point |
At elevated temperatures, S690QL maintains its strength but may begin to lose hardness and toughness. Oxidation can occur at temperatures above 600 °C, necessitating careful consideration in high-temperature applications.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| MIG | ER70S-6 | Argon + CO2 | Preheat recommended |
| TIG | ER70S-2 | Argon | Requires clean surfaces |
| Submerged Arc Welding (SAW) | - | Flux-cored wire | Good for thicker sections |
S690QL is generally considered weldable using standard processes, although preheating is recommended to avoid cracking. Post-weld heat treatment can enhance toughness and relieve residual stresses.
Machinability
| Machining Parameter | S690QL | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 60 | 100 | Requires high-speed tooling |
| Typical Cutting Speed (Turning) | 50-80 m/min | 100-150 m/min | Adjust based on tool wear |
Machinability is moderate; high-speed steel tools are recommended for effective machining. Careful attention to cutting speeds and feeds can optimize performance.
Formability
S690QL exhibits limited formability due to its high strength. Cold forming is possible, but hot forming is preferred to reduce the risk of cracking. The minimum bend radius should be carefully calculated to avoid failure.
Heat Treatment
| Treatment Process | Temperature Range (°C) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Quenching | 850 - 900 | 30 - 60 minutes | Water/Oil | Hardening |
| Tempering | 500 - 700 | 1 - 2 hours | Air | Toughness improvement |
Heat treatment processes significantly influence the microstructure of S690QL, enhancing its mechanical properties. Quenching increases hardness, while tempering improves ductility and toughness.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Construction | High-rise buildings | High yield strength, good weldability | Reduces structural weight |
| Mining | Excavators | Toughness, impact resistance | Endures harsh conditions |
| Heavy Machinery | Cranes | High tensile strength | Supports heavy loads |
| Offshore Structures | Oil rigs | Corrosion resistance, strength | Operates in marine environments |
Other applications include:
- Bridges: Utilizing high strength for reduced material use.
- Transport Equipment: Lightweight structures for efficiency.
S690QL is chosen for these applications due to its ability to meet stringent performance requirements while providing cost-effective solutions.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | S690QL | S355 | S700MC | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High Yield Strength | Moderate Yield Strength | Higher Yield Strength | S690QL offers a balance of strength and weldability |
| Key Corrosion Aspect | Fair Resistance | Good Resistance | Fair Resistance | S355 may be better for corrosive environments |
| Weldability | Good | Excellent | Fair | S690QL requires careful handling |
| Machinability | Moderate | Good | Moderate | S355 is easier to machine |
| Formability | Limited | Good | Moderate | S690QL is less formable |
| Approx. Relative Cost | Higher | Lower | Higher | Cost considerations vary by application |
| Typical Availability | Moderate | High | Moderate | S355 is widely available |
When selecting S690QL, considerations include cost-effectiveness, availability, and specific application requirements. While it offers superior strength, its higher cost and moderate machinability may influence decisions in favor of alternative grades in less demanding applications. Additionally, safety factors and potential for fatigue failure should be evaluated in design processes.
In summary, S690QL is a versatile high-strength steel that excels in demanding applications, offering a unique combination of strength, toughness, and weldability. Its properties make it a preferred choice in modern engineering, particularly where weight reduction and structural integrity are critical.
