S960QL is an ultra-high-strength quenched and tempered structural steel defined by the European standard EN 10025-6. With a minimum yield strength of 960 MPa and a tensile strength of 980 to 1150 MPa, it belongs to the family of ultra-high-strength steels designed to reduce structural weight while maintaining superior load-bearing capacity. The material is produced through a controlled quenching and tempering process, which gives it excellent toughness even at low temperatures.
Chemical Composition
The chemical composition of S960QL is optimized for strength and weldability. Maximum limits include carbon of 0.20 percent, silicon of 0.80 percent, manganese of 1.70 percent, and nickel of 2.0 percent, with chromium up to 1.50 percent and molybdenum up to 0.70 percent. Phosphorus is limited to 0.020 percent, sulfur to 0.010 percent, and boron to 0.0050 percent, with microalloying elements such as niobium, titanium, and vanadium controlled at 0.06, 0.05, and 0.12 percent respectively. The low carbon equivalent supports welding and forming in complex fabrications.
Mechanical Properties
For thickness from 4.0 to 53.0 mm, the minimum yield strength is 960 MPa and the tensile strength is 980 to 1150 MPa, with a minimum elongation of 12 percent. For thickness from 53.1 to 120.0 mm, the minimum yield strength is 850 MPa and the tensile strength is 900 to 1100 MPa, with a minimum elongation of 10 percent. The material guarantees Charpy impact energy of at least 40 J at -40 deg C, and some variants perform well at -60 deg C. The maximum carbon equivalent is 0.38 CET for thin sections and 0.41 CET for thick sections.
Welding and Fabrication
Welding is the most critical processing step for S960QL, because excessive heat input can soften the heat-affected zone and reduce the joint strength. Low-hydrogen filler materials are required, and under-matched fillers with lower strength than the base metal are often used to improve joint toughness and reduce the risk of cracking. Laser cutting is preferred for high precision and minimal thermal distortion, while plasma and oxy-fuel cutting are used for thicker plates. Thermal cut edges should be ground to remove defects before bending. Because of the high hardness, a bend radius of about 1.5 to 2.5 times the plate thickness is recommended, and stress-relieving at high temperature is generally avoided because it can impair the quenched and tempered properties.
Typical Applications
Crane booms, lifting arms, and mobile crane components where high strength-to-weight ratio allows longer reach and higher payloads
Chassis for heavy trucks, trailer frames, and specialized railway wagons
Excavators, dump trucks, and mining shovels in earthmoving and mining
Offshore structures and components that must resist fatigue and extreme environments
High-rise building members and transportation equipment where lightweight design is critical
Frequently Asked Questions
What is S960QL steel? It is an ultra-high-strength quenched and tempered structural steel to EN 10025-6 with a minimum yield strength of 960 MPa.
What is the tensile strength of S960QL? The tensile strength is 980 to 1150 MPa for thickness up to 53 mm, decreasing for thicker plates.
Does S960QL have good low-temperature toughness? Yes, it guarantees at least 40 J impact energy at -40 deg C, with some variants rated at -60 deg C.
How is S960QL welded? With low-hydrogen fillers, controlled heat input, and often under-matched consumables to protect joint toughness.
What is the bend radius for S960QL? general guideline is 1.5 to 2.5 times the plate thickness, depending on the direction of bending.
Where is S960QL used? In cranes, heavy transport, mining equipment, offshore structures, and high-rise building members.