S960Q is a quenched and tempered fine-grain structural steel supplied to EN 10025-6, with a minimum yield strength of 960 MPa for plate thicknesses up to 50 mm. The grade belongs to the ultra-high-strength family of structural steels and is used where weight reduction is critical, such as mobile cranes, heavy transport, mining machinery, and long-span structures. This article explains the properties, processing, and typical uses of S960Q.
Designation and Standard
The designation S960Q is read as follows: S indicates structural steel, 960 indicates the minimum yield strength in MPa, and Q indicates that the steel is delivered in the quenched and tempered condition. The governing product standard is EN 10025-6, which covers hot-rolled flat and long products of high-yield-strength structural steels in the quenched and tempered condition. The grade is supplied with a mill test certificate that verifies chemical composition, mechanical properties, and impact performance.
Chemical Composition
The composition is controlled within maximum limits that secure hardenability and toughness after quenching and tempering: carbon 0.20 percent, silicon 0.80 percent, manganese 1.70 percent, phosphorus 0.025 percent, sulfur 0.015 percent, nitrogen 0.015 percent, boron 0.005 percent, chromium 1.50 percent, copper 0.50 percent, molybdenum 0.70 percent, niobium 0.06 percent, nickel 2.0 percent, titanium 0.05 percent, vanadium 0.12 percent, and zirconium 0.15 percent. The low carbon content and the combination of nickel, chromium, and molybdenum provide the required strength after heat treatment while keeping the material weldable.
Mechanical Properties
For plates of 3 to 50 mm thickness, the minimum yield strength is 960 MPa and the tensile strength range is 980 to 1150 MPa, with a minimum elongation of 10 percent. For plates over 50 mm up to 100 mm, the minimum yield strength is 910 MPa and the tensile strength range is 920 to 1000 MPa. For plates over 100 mm up to 150 mm, the minimum yield strength is 860 MPa and the tensile strength range is 870 to 980 MPa. The minimum impact energy is 30 J at minus 20 degrees C for the standard grade.
Fabrication and Processing
S960Q is commonly cut by laser, plasma, or waterjet, with laser preferred for precision work and waterjet used where thermal distortion must be avoided. Welding requires strict heat input control to prevent softening of the heat-affected zone, with typical preheat temperatures of 125 to 200 degrees C for thicker sections and low-hydrogen consumables to avoid cold cracking. Cold forming is possible but requires higher force than conventional structural steel, larger bending radii, and allowance for springback. Post-weld heat treatment is generally not recommended because excessive heat can reduce the strength of the quenched and tempered structure.
Typical Applications
The grade is used in mobile crane booms and telescopic arms, where weight reduction increases lifting capacity and reach. It appears in heavy-duty truck chassis, trailers, and dump bodies that maximize payload and fuel efficiency, and in mining equipment such as excavator buckets and structural frames exposed to impact and abrasion. Long-span bridges, slender structural columns, and support structures for wind energy equipment also use the grade where high strength-to-weight ratio and low-temperature toughness are required.
Frequently Asked Questions
Is S960Q a quenched and tempered steel?
Yes, S960Q is delivered in the quenched and tempered condition, which is indicated by the letter Q in the designation.
What is the tensile strength range of S960Q?
For plates of 3 to 50 mm thickness, the tensile strength range is 980 to 1150 MPa, with lower ranges applying to thicker plates.
Can S960Q be welded?
Yes, but welding requires strict heat input control, preheat of 125 to 200 degrees C for thicker sections, and low-hydrogen consumables to prevent cold cracking and loss of strength.
What is the typical hardness of S960Q?
The typical Brinell hardness is in the range of 280 to 340 HBW, reflecting the high strength of the quenched and tempered structure.
Does S960Q require post-weld heat treatment?
Post-weld heat treatment is generally not recommended, because temperatures near or above the tempering temperature can reduce the strength of the quenched and tempered material.
What is the maximum thickness available for S960Q plate?
S960Q plate is commonly available up to about 150 mm thickness, with the yield and tensile requirements decreasing in the thicker ranges.