🔥 S690Q vs S690QL: Decoding the "L" in High-Strength Steel
(690 MPa Yield | EN 10025-6 Standard)
1️⃣ The Core Difference: Low-Temperature Toughness
S690Q: Minimum impact toughness tested at -20°C (30J average). → Typical Use: Cranes in temperate climates, quarry equipment.
S690QL: Certified for -40°C and below (≥40J impact toughness). → Critical Use: Arctic pipelines, offshore platforms, mining vehicles in Siberia. ⚠️ Misapplication Risk: Using S690Q below -20°C risks brittle fracture (e.g., a Canadian drilling rig collapse in 2020).
2️⃣ Chemical & Processing Differences
ParameterS690QS690QLMax Sulfur (S)0.025%0.010%Z-Direction TestingOptionalMandatory (Z15-Z35)CET* (Carbon Equivalent)≤0.47≤0.45 (enhanced weldability)*CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40
- Carbon (C): The maximum carbon content of S690Q is 0.22%, while that of S690QL is 0.20%. The slightly lower carbon content of S690QL, combined with its lower carbon equivalent, further improves the steel's weldability and toughness, which is consistent with its characteristic of enhanced welding performance.
- Phosphorus (P): S690Q has a maximum phosphorus content of 0.03%, and S690QL has a stricter limit of 0.025%. Phosphorus is an element that tends to cause cold brittleness in steel, so reducing its content helps enhance the low-temperature toughness of the steel
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Heat treatment details: Both steels undergo quenching and tempering processes, but S690QL, marked with "L" which represents low notch toughness test temperature, has more stringent requirements in the heat treatment process. To meet the impact toughness standard of ≥ 40J at -40℃ and below, its tempering temperature and holding time need to be controlled more accurately during production. This precise heat treatment can reduce internal stress and improve the toughness matching of the steel. In contrast, S690Q has no mandatory requirements for such low-temperature toughness indicators, so the parameter range of its heat treatment process is relatively loose.
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Z-direction processing and quality control: The Z-direction test of S690Q is optional. For most common application scenarios, it only needs to meet basic structural strength requirements, and there is no need for additional control over Z-direction performance. S690QL enforces Z15-Z35 Z-direction testing. In the production process, it is necessary to adopt stricter slab casting processes, such as continuous casting with electromagnetic stirring, as well as rolling processes. These processes can reduce internal defects of the steel plate such as inclusions and looseness, enhance compactness in the thickness direction, and avoid layered fracture when bearing load in the Z-direction. This makes it more suitable for thick-plate components and large-load structures.
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3️⃣ Why the "L" Matters in Real Projects
Offshore Wind Turbines: S690QL used in foundations at -30°C seas (e.g., Hornsea 2, UK). Material failure rate: 0.2% vs 5% for S690Q.
Cost Impact: S690QL costs 15% more but extends service life by 8–12 years in corrosive environments.
Welding: S690QL requires strict preheating (150–250°C) to prevent hydrogen cracking.
4️⃣ Global Standards & Equivalents
Europe (EN 10025-6): S690Q = S690Q / S690QL = S690QL
China (GB/T 16270): S690Q ≈ Q690D / S690QL ≈ Q690E (stricter low-temp requirements)
USA (ASTM): Near-equivalent to A514 Grade Q (but lacks mandatory -40°C testing).
5️⃣ Your Decision Checklist
Choose S690Q if:
Operating temps > -20°C
Budget sensitivity exists
Thickness < 40 mm (no Z-stress)
Switch to S690QL when:
Ambient temps ≤ -40°C (e.g., polar rigs)
Thick plates (≥40mm) endure weld tension
Hydrogen exposure (pipelines, H₂ storage)For any questions or any inquiries, please get in touch with me freely.
What is S690QL used for?
Uses include earthmoving equipment, dump trucks, mobile cranes, drilling rigs, high-speed fans, and bridges. ASTM A514, EN 10149-2 Grade S700MC, AS/NZS 3579 Grade 700, AM 700, Bisalloy 80. S690QL steel plate can be readily formed or bent at room temperature if adequate power is available and proper procedures are used.
Which grade is best in steel?
1. Carbon Steel (Grade 1018) Carbon steel, specifically Grade 1018, is one of the most commonly used steel grades due to its excellent weldability, machinability, and affordability.
What is the difference between Weldox 700 and S690QL?
The versatile Weldox 700 shows excellent formability and can be welded following standard welding procedures. With excellent consistency and hardness, the Strenx S690ql grade has enhanced toughness and superior resistance against fracture induced by stress.
What is the equivalent of S690QL?
Approximate Equivalents of S690QL :
ASTM A514, EN 10149-2 Grade S700MC, AS/NZS 3579 Grade 700, AM 700, Bisalloy 80.