1. What Are S690QL Steel Plates?
S690QL is a high-yield fine-grain structural steel supplied in the quenched and tempered condition and defined in EN 10025-6. The designation S690 refers to the minimum yield strength of 690 MPa; Q indicates the quenched and tempered delivery condition; and L guarantees impact toughness of 30 J at -40 °C. The quench and temper treatment produces a fine-grain martensitic-tempered microstructure that combines very high strength with good toughness and adequate formability. S690QL is therefore used for load-bearing components in construction, heavy equipment, cranes, bridges and transportation where weight saving is a design priority.
2. Exceptional Strength and Durability
The minimum yield strength of 690 MPa is roughly twice that of conventional structural steel S355 and nearly three times that of mild steel S235. The tensile strength range is 770–940 MPa. This allows designers to reduce section thickness while keeping the same load capacity, which lowers the weight of the structure and the quantity of material to be transported, handled and welded. The high toughness at -40 °C also makes the grade suitable for components exposed to cold climates and dynamic loads, such as crane booms, mining equipment and offshore structures.
3. Weldability and Fabrication
S690QL welds successfully when the procedures are properly controlled. The key parameters are heat input, preheat and interpass temperature, which must be limited to protect the strength and toughness of the heat-affected zone. Consumables are selected with matching or slightly under-matching strength, and the welding procedure must be qualified before production. The plate can also be formed by bending and machining, with allowance for the higher strength: bending of thick plates with small radii may require preheating and larger bend radii than mild steel. Despite the higher material price, the reduced section sizes and lower fabrication quantities often make S690QL competitive on a per-project basis.
4. Abrasion and Wear Resistance
The high hardness of the quenched and tempered structure gives S690QL good resistance to impact and sliding abrasion, which makes it suitable for heavy wear applications such as construction equipment, mining machinery and material handling components. In abrasive service, the combination of high hardness and good toughness is important: hardness resists surface wear while toughness prevents cracking under impact loading. Where severe abrasion is the dominant mechanism, dedicated wear-resistant grades may still be a better choice, but S690QL offers a practical balance of strength, toughness and wear behaviour for combined loading cases.
5. Weight Reduction and Life-Cycle Cost
Because less material is needed for a given load, S690QL structures are lighter, which reduces foundation loads, transport cost and installation effort. The longer service life and reduced maintenance of high-strength components further improve the life-cycle economics. For cranes and lifting equipment the lower dead weight directly increases the useful payload. The initial material cost is higher than for conventional grades, so the economic case should be evaluated per project, but in heavy-load applications the weight and maintenance savings usually justify the premium.
Frequently Asked Questions
What is the difference between S690Q and S690QL? Both are quenched and tempered grades of EN 10025-6 with the same strength. They differ in the guaranteed impact test temperature: S690Q guarantees 30 J at -20 °C, while S690QL guarantees 30 J at -40 °C for more demanding cold-climate and offshore service.
What does the designation S690QL mean? S690 is the minimum yield strength in MPa, Q is the quenched and tempered delivery condition, and L guarantees Charpy impact energy of 30 J at -40 °C.
What is the tensile strength of S690QL? The tensile range is 770–940 MPa, in line with EN 10025-6 for the S690 strength class.
Is S690QL easy to weld? It welds reliably with qualified procedures: controlled heat input and interpass temperature, suitable consumables and, for thicker sections, preheating. The procedure must be validated before production welding.
What thicknesses are available? S690QL plate is commonly available from 8 mm to 100 mm, with widths up to about 3200 mm and lengths up to about 12200 mm, depending on the mill and the plate combination.
Where is S690QL used? Typical uses are cranes and lifting equipment, mobile machinery, bridges, offshore structures, mining equipment and heavily loaded building components where weight savings and high load capacity are required.
