S690QL is a high-yield strength structural steel (HSLA) known for its exceptional strength (minimum 690 MPa yield) and toughness, produced to the EN 10025-6 standard using a quench and temper heat treatment, allowing for lighter, more efficient designs in heavy-duty applications like cranes, bridges, and earthmoving equipment, with excellent weldability and formability despite needing careful handling due to its strength. Its name signifies "Structural" (S), "690 MPa" minimum yield, "Quenching" (Q), and "Low" temperature toughness (L).
Key Characteristics
High Strength: Minimum yield strength of 690 MPa (for thinner sections), enabling lighter structures and increased payload capacity.
Quenched & Tempered (Q+T): Heat treatment provides superior strength, toughness, and durability.
Excellent Toughness: Good impact strength even at low temperatures (indicated by 'L').
Good Weldability & Formability: Allows for complex fabrications when proper procedures are followed.
Composition (Typical Max Values)
Carbon (C): ~0.20%
Manganese (Mn): ~1.70%
Silicon (Si): ~0.80%
Chromium (Cr): ~1.50%
Molybdenum (Mo): ~0.70%
Nickel (Ni): ~2.0%
Grain Refiners: Contains V, Nb, Ti, Zr (min 0.015%) for fine grain structure.
Applications
Mobile cranes and lifting equipment
Bridges and heavy-duty construction
Earthmoving and mining machinery (dump trucks, drilling rigs)
Wind turbine towers
What does the "L" stand for in S690QL?
The "L" in the steel grade designation S690QL stands explicitly for "Low Temperature" service, as formally defined within the European material standard EN 10025-6.
Here are the precise technical details:
Official Meaning: It is a sub-grade designation specifying the guaranteed impact toughness at low temperatures. For S690QL, this means the Charpy V-notch impact test is performed at -40°C (-40°F).
Required Toughness: To meet the S690QL specification, the steel must achieve a minimum average impact energy of 27 Joules at the test temperature of -40°C.
Purpose: The "L" designation ensures the material maintains ductility and resists brittle fracture in harsh, sub-zero environments. This is critical for safety and structural integrity in applications like:
Offshore structures in cold seas
Cranes and lifting equipment in Arctic climates
Mining equipment in high-latitude regions
Any welded structure subject to dynamic loading in freezing conditions
Contrast with Base Grade: The standard S690Q (without the "L") is typically tested for impact toughness at 0°C (32°F). Therefore, S690QL is a more stringent, application-specific version of S690Q, guaranteeing performance where extreme cold is a design factor.
In summary, the "L" is a mandatory quality and testing marker for low-temperature toughness, not just a general descriptive term.
EN10025-6 S690Q quenched and tempered steel plate Chemical composition
| Grade | C % | Si % | Mn % | P % | S % | N % | B % | Cr % |
| S690Q | 0.200 | 0.800 | 1.700 | 0.025 | 0.015 | 0.015 | 0.005 | 1.500 |
| Cu % | Mo % | Nb % | Ni % | Ti % | V % | Zr % | ||
| 0.500 | 0.700 | 0.060 | 2.000 | 0.050 | 0.120 | 0.150 |
EN10025-6 S690Q quenched and tempered steel plate mechanical properties
| Grade | Thickness | Min Yield | Tensile | Elongation | Min Impact Energy | |
| S690Q | 8mm-50mm | Min 690Mpa | 770-940Mpa | 14% | -20 | Min 30J |
| 51mm-100mm | Min 650Mpa | 760-930Mpa | 14% | -20 | Min 30J | |
| 101mm-150mm | Min 630Mpa | 710-900Mpa | 14% | -20 | Min 30J |
1. What is S690QL steel?
S690QL is a high-strength, quenched and tempered structural steel grade with a minimum yield strength of 690 MPa, specifically optimized for low-temperature toughness down to -40°C.
2. What does the "L" stand for in S690QL?
The "L" stands for "Low temperature," indicating the steel is certified for enhanced impact toughness at temperatures as low as -40°C.
3. What are the typical applications of S690QL?
It is commonly used in extreme environments such as Arctic construction, offshore platforms, high-latitude mining equipment, and mobile cranes operating in freezing conditions.
4. How does S690QL differ from S690Q?
The key difference is that S690QL guarantees higher impact toughness at -40°C, while standard S690Q is typically tested at 0°C, making S690QL better suited for freezing climates.
5. What is the chemical composition of S690QL?
It is a low-alloy steel containing carbon, manganese, silicon, and micro-alloys like niobium, vanadium, and titanium, with strict control of phosphorus and sulfur to ensure weldability and toughness.
6. What welding procedures are required for S690QL?
Welding requires low-hydrogen electrodes, strict preheating (often 100-150°C), controlled heat input, and often post-weld stress relief to maintain toughness and prevent cracking.
7. Is S690QL corrosion resistant?
No, S690QL is not inherently corrosion-resistant. Like other high-strength structural steels, it requires protective coatings (e.g., painting or galvanizing) for use in corrosive environments.
8. What standards cover S690QL material?
It is primarily defined by the European standard EN 10025-6, with equivalent specifications in other systems (e.g., ASTM, ISO).
9. Can S690QL be machined easily?
Machining S690QL is challenging due to its high strength and hardness; it requires robust tooling, adequate cooling, and optimized cutting parameters to avoid excessive tool wear.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
