S690QL1 is a high-strength, quenched and tempered structural steel specified in the European standard EN 10025-6. It is known for a minimum yield strength of 690 MPa, excellent low-temperature impact resistance, and good weldability when the correct procedure is followed. The grade is designed for demanding applications in construction, mining, and heavy machinery, and it is a common choice for cranes, excavators, and pressure-bearing components.
Chemical Composition
The chemical composition of S690QL1 is controlled to balance strength, toughness, and weldability. Maximum limits include carbon of 0.20 percent, silicon of 0.80 percent, manganese of 1.70 percent, nickel of 2.0 percent, chromium of 1.5 percent, molybdenum of 0.7 percent, copper of 0.5 percent, and boron of 0.005 percent. Phosphorus is limited to 0.020 percent and sulfur to 0.010 percent, while microalloying elements such as vanadium, niobium, and titanium are each limited to 0.12, 0.06, and 0.05 percent. The maximum carbon equivalent CEV is 0.83 percent, which signals that welding must be carefully controlled.
Mechanical Properties
The mechanical properties of S690QL1 depend on plate thickness. For thicknesses of 3 to 50 mm, the tensile strength is 770 to 940 MPa and the minimum yield strength is 690 MPa. For 50 to 100 mm the tensile strength is 760 to 930 MPa and the minimum yield strength is 650 MPa, and for 100 to 150 mm the tensile strength is 710 to 900 MPa with a minimum yield strength of 630 MPa. Minimum elongation is 14 percent, and Charpy impact values are 60 J at 0 deg C, 50 J at -20 deg C, 40 J at -40 deg C, and 30 J at -60 deg C, giving the grade outstanding low-temperature toughness.
Weldability Requirements
S690QL1 is weldable, but it must be welded with a qualified procedure. Low-hydrogen consumables are essential, and electrodes should be stored and baked according to the manufacturer instructions. Preheat is generally required to avoid hydrogen cracking, and the interpass temperature must be controlled to keep the heat-affected zone properties within acceptable limits. Heat input should be kept within the range approved by the welding procedure specification, and for highly restrained joints or thick sections higher preheat is applied. Post-weld heat treatment is not normally required and may be undesirable for quenched and tempered steels, because it can reduce the strength developed by quenching and tempering.
Typical Applications
Beams, columns, and structural frameworks where weight reduction and high load capacity are critical
Chassis, trailer frames, and platforms for heavy transport vehicles, increasing payload capacity
Crane booms, jibs, and lifting arms for mobile and offshore cranes
Dumper bodies, jaw crushers, quarry screens, and excavator buckets in mining and agriculture
Military vehicle components that require robustness and durability
Frequently Asked Questions
Is S690QL1 weldable? Yes, S690QL1 is weldable, but it requires a qualified procedure with low-hydrogen consumables, controlled preheat, and interpass temperature control.
What standard covers S690QL1? S690QL1 is specified in EN 10025-6, the European standard for high yield strength structural steels in the quenched and tempered condition.
What is the yield strength of S690QL1? The minimum yield strength is 690 MPa for thickness up to 50 mm, decreasing to 650 MPa and 630 MPa for thicker plates.
What heat treatment does S690QL1 receive? It is quenched and tempered, which creates a fine-grained microstructure with balanced strength and toughness.
Does S690QL1 have good low-temperature toughness? Yes, it guarantees Charpy impact values down to -60 deg C, with 30 J minimum at that temperature.
Is post-weld heat treatment required for S690QL1? Not normally; PWHT is usually avoided for quenched and tempered steels because it can reduce the strength obtained from the heat treatment.