What Is S690Q Steel?
S690Q is a high-yield-strength structural steel grade defined by EN 10025-6, supplied in the quenched and tempered condition. In the designation, S stands for structural steel, 690 is the minimum yield strength in MPa for thicknesses under 50 mm, and Q indicates the quenched and tempered delivery condition. The steel is fine-grained and weldable, and it is used where very heavy loads and weight savings drive the design, such as high-rise buildings, bridges, crane booms and mining equipment.
S690Q, S690QL and S690QL1: Impact Toughness Tiers
The three variants differ in guaranteed Charpy impact performance:
| Grade | Minimum yield (MPa, t ≤ 50 mm) | Impact requirement (30 J avg) |
|---|---|---|
| S690Q | 690 | −20 °C |
| S690QL | 690 | −40 °C |
| S690QL1 | 690 | −60 °C |
S690Q suits temperate-climate cranes and quarry equipment; S690QL is specified for arctic pipelines, offshore platforms and mining vehicles in cold regions; S690QL1 covers the most demanding low-temperature duties.
Mechanical and Processing Characteristics
The combination of 690 MPa minimum yield and good toughness allows heavier loads, thinner sections and lighter structures compared with conventional structural steel. The high strength-to-weight ratio reduces material consumption and fabrication cost per tonne of load capacity, and the steel resists wind and seismic lateral forces well. The grade welds with qualified procedures: low-hydrogen consumables, controlled heat input and, for thicker sections, preheat and post-weld heat treatment as required by the design code. Cutting is normally by plasma or laser with preheat where needed.
Manufacturing Route
S690Q plate is produced through controlled steelmaking with tight composition and impurity control (particularly phosphorus and sulfur) for cleanliness, followed by controlled rolling to optimise the microstructure and quench and temper heat treatment to develop the final strength-toughness balance. The tempering step relieves internal stress and enhances toughness, and the quench and temper cycle is what makes the 690 MPa yield tier achievable in plate form.
Typical Applications
Typical applications include heavy machinery components for hoisting and mining equipment such as excavators and loaders; bridge main girders and piers; load-bearing columns and beams in high-rise buildings and large stadiums; offshore platforms and submarine pipeline components in marine engineering; hull structures and decks in shipbuilding; and oil storage tanks and refining equipment in the petrochemical industry. In every case the grade is selected for load capacity, weight efficiency or both.
Frequently Asked Questions
What is the difference between S690QL and S690Q?
S690Q guarantees 30 J average impact energy at −20 °C; S690QL guarantees the same energy at −40 °C, and S690QL1 at −60 °C. The low-temperature variants are specified for cold-climate and offshore service.
What is S690 grade steel?
S690 is a high-yield, fine-grain structural steel supplied quenched and tempered, used in structures that must withstand very heavy loads or where weight savings are important.
What are the equivalent grades of S690 steel?
Commonly cited equivalents include ASTM A709 Grade 100, ISO E690, and national designations such as E690T (France) and TStE690V (Germany). Equivalents should be verified against the project specification.
What material group does S690 belong to?
S690 belongs to the quenched and tempered fine-grain structural steel group of EN 10025-6, with good bending and welding properties within the limits of its high strength.
Is S690Q weldable?
Yes, with qualified welding procedures: low-hydrogen consumables, controlled heat input and, for thicker sections, preheat and post-weld heat treatment per the governing code.
What thickness range is available?
S690Q plate is commonly supplied from about 6 mm to 100 mm, with thicker plates available subject to mill capability and the governing edition of EN 10025-6.
