What Is S690QL Steel?
S690QL is a quenched and tempered high-strength structural steel grade defined in EN 10025-6, the European standard for flat products of high yield strength structural steels in the quenched and tempered condition. In the designation: S means structural steel, 690 is the minimum yield strength in MPa, Q denotes the quenched and tempered delivery condition, and L means low-temperature impact toughness of at least 30 J at −40 °C.
With a minimum yield strength of 690 MPa, S690QL delivers significantly higher performance than conventional carbon structural steels, while also offering reliable forming characteristics, good weldability and excellent impact toughness at sub-zero temperatures.
Mechanical Properties
Commonly quoted mechanical values for S690QL are:
| Thickness (mm) | Min. yield strength (MPa) | Tensile strength (MPa) | Min. impact energy |
|---|---|---|---|
| 3 ≤ t ≤ 50 | 690 | 770 – 940 | 30 J at −40 °C |
| 50 < t ≤ 100 | 650 | 760 – 930 | 30 J at −40 °C |
| 100 < t ≤ 150 | 630 | 710 – 900 | 30 J at −40 °C |
The L designation is what makes the grade suitable for cold-climate and dynamically loaded structures: the guaranteed −40 °C impact toughness prevents brittle fracture in demanding service.
Chemical Composition
Table 2 lists the typical maximum composition values for S690QL. This controlled alloy composition supports strength, toughness and weldability while maintaining stable performance after quenching and tempering.
| Element (max, %) | Content |
|---|---|
| Carbon (C) | 0.20 |
| Manganese (Mn) | 1.70 |
| Silicon (Si) | 0.80 |
| Chromium (Cr) | 1.50 |
| Nickel (Ni) | 2.00 |
| Molybdenum (Mo) | 0.70 |
| Phosphorus (P) | 0.02 |
| Sulfur (S) | 0.01 |
Forming Characteristics
S690QL can be bent and formed using appropriately rated forming equipment. Recommended minimum bend radii are:
Transverse to rolling direction: minimum 2 × plate thickness
Longitudinal to rolling direction: minimum 3 × plate thickness
Hot forming above 600 °C is not recommended, because exposure to higher temperatures can adversely affect the mechanical properties. If forming is carried out beyond this threshold, re-quenching and tempering may be required to restore the performance characteristics.
Welding Guidelines
S690QL is weldable with standard arc processes used for quenched and tempered steels. Consumables should be selected to match the strength level, and the welding procedure should be qualified for the plate thickness and joint configuration. Preheat, interpass temperature and heat input must be controlled: excessive heat input can soften the heat-affected zone and reduce the strength of the joint.
Typical Applications
Mining equipment and wear structures
Agricultural machinery frames and components
Construction machinery and heavy-duty chassis
Dumper bodies and load-bearing platforms
Lifting equipment and crane structures
Jaw crushers and heavy industrial assemblies
Frequently Asked Questions
What does the Q in S690QL mean?
Q denotes the quenched and tempered delivery condition, which is the source of the high strength and toughness balance of the grade.
What does the L in S690QL mean?
L means impact toughness is verified at low temperature: at least 30 J at −40 °C.
What is the minimum yield strength of S690QL?
690 MPa for thicknesses up to 50 mm, 650 MPa for 50–100 mm and 630 MPa for 100–150 mm.
Can S690QL be hot formed?
Hot forming above 600 °C is not recommended because it can impair the mechanical properties; re-quenching and tempering would be required to restore them.
Is S690QL weldable?
Yes, with qualified procedures for quenched and tempered steels, including matched consumables and controlled preheat and heat input.
Where is S690QL commonly used?
In mining equipment, agricultural and construction machinery, dumper bodies, cranes, lifting equipment and heavy industrial assemblies where weight reduction and structural efficiency are critical.
