1. **What is S690 grade steel?**
S690 grade steel is a **high-strength, quenched and tempered structural steel** defined by the European standard EN 10025-6. Its key characteristic is a specified **minimum yield strength of 690 MPa** (Megapascals). This high strength is achieved through a controlled process of heating (quenching) and reheating (tempering). S690 steel is designed for demanding applications where high strength-to-weight ratio is critical, such as heavy lifting equipment, crane booms, mining structures, advanced construction, and specialized transportation.
2. **What is the equivalent of S690 steel?**
There is no single perfect global equivalent for S690 steel due to differences in standards and specifications. However, steels with similar minimum yield strength (690 MPa) and processing (quenched and tempered) are often considered comparable in strength class. Common approximate equivalents include:
* **ASTM A514 / A514M (Grade T1):** A US specification for quenched and tempered high-yield-strength steel plate, widely used and similar in strength.
* **ASTM A517 / A517M (Grade Q):** Primarily for pressure vessels, but offers similar high yield strength.
* **JIS G3128 (SHY685):** A Japanese high-strength steel specification.
* **ISO 4950 (Grade 690E/690F):** International standard grades often referenced.
**Important Note:** While these steels share the 690 MPa yield strength class, exact chemical composition, impact toughness requirements, and allowable thicknesses can differ significantly. Always consult the specific standards and ensure the material meets the required properties for the application.
3. **What is the difference between S690Q and S690QL?**
The key difference lies in the **impact toughness requirements at low temperatures**, indicated by the suffix:
* **S690Q:** This grade requires Charpy V-notch impact testing at **-20°C**. It provides good toughness for many general high-strength applications.
* **S690QL:** This grade requires Charpy V-notch impact testing at the **lower temperature of -40°C** (signified by the "L"). This provides **enhanced low-temperature toughness**, making it suitable for applications exposed to colder environments, such as offshore structures, arctic equipment, or where higher safety margins against brittle fracture are required. The "QL" suffix signifies both Quenched & Tempered and the lower temperature impact test.
4. **How thick is S690 steel?**
S690 steel (both Q and QL grades) is produced primarily as **plate or flat products**. The standard EN 10025-6 defines thickness ranges for which the mechanical properties (like the 690 MPa yield strength) are guaranteed:
* For **S690Q (as rolled)**: Properties are typically guaranteed for thicknesses up to **30 mm**.
* For **S690Q (normalized or normalized rolled)**: Properties are typically guaranteed for thicknesses up to **50 mm**.
* For **S690QL (quenched and tempered)**: Properties are guaranteed for a wider range, typically from **3 mm up to 150 mm**. This is the most common form for achieving the high strength through the full thickness in thicker sections. Manufacturers can produce outside these ranges, but properties might differ, so specific consultation is needed for non-standard thicknesses.
5. **What is the spec of S690QL?**
The specification for S690QL steel is defined by the European standard **EN 10025-6:2019 - Hot rolled products of structural steels - Part 6: Technical delivery conditions for flat products of high yield strength structural steels in the quenched and tempered condition**. Key requirements include:
* **Delivery Condition:** Quenched and Tempered (Q+T).
* **Minimum Yield Strength (ReH):** 690 MPa (for nominal thicknesses ≤ 50 mm).
* **Minimum Tensile Strength (Rm):** 770 - 940 MPa (for nominal thicknesses ≤ 50 mm).
* **Minimum Elongation (A5):** Typically 14% (varies slightly with thickness and test direction).
* **Impact Toughness (Charpy V-notch):** Minimum average energy of 40 Joules at **-40°C** (the requirement defining the "L" suffix). Individual values must be ≥ 30 J.
* **Chemical Composition:** Strict limits on elements like Carbon (C), Manganese (Mn), Phosphorus (P), Sulfur (S), Silicon (Si), and alloying elements like Chromium (Cr), Nickel (Ni), Molybdenum (Mo), Boron (B), Vanadium (V), Niobium (Nb), Titanium (Ti) are specified to achieve the properties and weldability.
* **Mandatory Inspection:** Verification of tensile properties, impact properties at -40°C, and chemical composition is required.
