S690QL is a high strength quenched and tempered steel grade that complies to steel specification EN 10025. The designation S690QL refers to a minimum yield strength of 690 MPa.
The combination of good availability and pricing and high strength combined with ease of fabrication has made S690QL steel plate a popular grade for both mobile applications such as cranes and lifting equipment and fixed steel structures. The high strength nature of this steel means that structures can be designed lighter and for mobile application this means increase in payload and operational efficiency.
| Typical chemical composition of S690QL % Max | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
C |
SI |
Mn |
P |
S |
N |
B | Cr | Cu | Mo | Nb | Ni | Ti | V | Zr |
| 0.2 | 0.80 | 1.70 | 0.025 | 0.015 | 0.015 | 0.005 | 1.50 | 0.50 | 0.70 | 0.06 | 2.0 | 0.05 | 0.12 | 0.15 |
| Mechanical Properties of S690QL | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Designation | Mechanical Properties (ambient temperature) | ||||||||||
| Steel Name | Steel Number | Min. Yield Strength ReH MPa | Tensile Strength Rm MPa | Min. & elongation after fracture | |||||||
| Nominal thickness (mm) | Nominal thickness (mm) | ||||||||||
| >3 <50 | >50 <100 | >100 <150 | >3 <50 | >50 <100 | >100 <150 | ||||||
| S690QL | 1.8931 | 690 | 650 | 630 | 770/940 | 760/930 | 710/900 | 14 | |||
| V notch impact testing | |||||
|---|---|---|---|---|---|
|
Grade |
Sample Orientation |
at 0°C |
at -20°C |
at -40°C |
at -60°C |
| S690QL | Longitudinal | 50J | 40J | 30J | |
| S690QL | Transverse | 35J | 30J | 27J | |
What is the main difference between S690QL and the more common S355 steel?
The difference is profound. S690QL has roughly double the yield strength (690 MPa vs. 355 MPa). This allows designers to use thinner, lighter sections to carry the same load, or to greatly increase the load capacity of a similarly sized structure. S690QL is also quenched and tempered with guaranteed low-temperature toughness, whereas standard S355 is typically delivered as normalized or thermomechanically rolled with lower toughness specs.
Can S690QL be welded on-site, and what are the critical precautions?
Yes, but with rigorous controls. It is not like welding mild steel. Critical precautions include:
Procedure Qualification: A Welding Procedure Specification (WPS) qualified to a relevant standard (e.g., EN ISO 15614) is mandatory.
Pre-heat & Interpass Temperature: Strictly required to prevent hydrogen-induced cold cracking (HICC). Temperature depends on thickness and CEV.
Consumables: Must use matching high-strength, low-hydrogen electrodes or wires (e.g., classification matching 690 MPa strength).
Heat Input Control: Must stay within the qualified range to preserve the heat-affected zone (HAZ) properties.
Post-Weld Heat Treatment (PWHT): Often required for thick sections to relieve stresses and temper the HAZ.
How does S690QL compare to S890QL? When do you choose one over the other?
It is a trade-off between ultimate strength and fabricability/cost.
S890QL: Higher strength (890 MPa yield) for maximum weight saving. However, it generally has lower toughness, is more challenging to weld (higher CEV, stricter procedures), and is more expensive.
S690QL: The "sweet spot" for many applications. Offers massive weight savings over S355 with better overall weldability, toughness, and often better formability than S890QL at a lower cost.
Choice Driver: If the design is strength-limited and every kilogram saved is critical (e.g., a crane boom tip), S890QL may be chosen. If the design involves complex welding, high dynamic loads, or cost sensitivity, S690QL is often the preferred, more pragmatic solution.
What are the common subgrades of S690QL and what do they mean?
Subgrades define the impact test temperature:
S690QL: The base grade. The test temperature (often -40°C or -60°C) and energy must be agreed upon at the time of ordering.
S690QL1: A specific, common subgrade that explicitly guarantees a minimum of 40 Joules impact energy at -40°C for all thicknesses. This provides a clear, high-toughness specification.
Is S690QL corrosion resistant?
No. S690QL is not a weathering or stainless steel. Its corrosion resistance is similar to that of ordinary carbon steel. For corrosive environments (e.g., offshore), it must be protected by painting systems, galvanizing, or metal spraying. Using it in an unpainted condition will lead to rust