S960Q is a quenched and tempered structural steel with a specified minimum yield strength of 960 MPa. It is standardised in EN 10025-6, the part of the hot-rolled structural steel series that covers flat products of high yield strength in the quenched and tempered condition. The suffix letter Q defines the impact test temperature: Q for minus 20 degC, QL for minus 40 degC and QL1 for minus 60 degC. Chinese producers offer the equivalent strength level in the GB/T 16270 series, where grades such as Q960C, Q960D and Q960E carry impact requirements at progressively lower temperatures.
Property Basis
| Property | Requirement (thickness up to 50 mm) | Test method |
|---|---|---|
| Yield strength ReH, minimum | 960 MPa | ISO 6892-1 |
| Tensile strength Rm | 980-1150 MPa | ISO 6892-1 |
| Elongation A, minimum | 10 % | ISO 6892-1 |
| Impact energy at minus 20 degC, minimum | 27 J Charpy V | ISO 148-1 |
Minimum yield strength falls as thickness increases, so the drawing must state the thickness at which the requirement applies. The very high strength is reached by water quenching and tempering a microalloyed, low-carbon chemistry with a controlled carbon equivalent, which keeps toughness and weldability workable at a strength level roughly 2.7 times that of ordinary structural plate.
Application Cases in Construction Machinery
Mobile crane booms and outrigger beams, where every kilogram removed from the structure increases the payload that can be lifted at the same radius.
Concrete pump booms and placing arms, where stiffness and low weight govern reach.
Excavator and wheel loader arms, buckets linkages and quick couplers subjected to combined bending and impact.
Aerial work platforms, telehandlers and scissor lift chassis parts.
Mining truck bodies and dump body liners, where a thinner plate reduces dead weight and lets the payload increase.
Offshore and heavy lifting frames, spreader beams and crane hooks blocks.
Design Consequences
Using S960Q instead of a 355 MPa structural steel allows a weight reduction of roughly 25-35 % in a stiffness-critical or strength-critical member, but it changes the design method. Fatigue becomes the governing limit rather than static yield, so welded details must be classified carefully and stress concentrations reduced. Buckling of thin high-strength sections must be checked separately, since stiffness does not rise with yield strength. Where stiffness rather than strength drives the section size, the weight saving is smaller and a lower grade may be the better commercial choice.
Fabrication and Welding Practice
Cut by plasma, laser or waterjet to avoid a thermally hardened edge. Welding requires a procedure qualified to ISO 15614-1 and consumables matched to the parent metal strength, with low-hydrogen practice and controlled heat input; typical preheat is 100-150 degC depending on thickness and carbon equivalent, and interpass temperature is capped to protect toughness. The heat-affected zone softens slightly even with good practice, so welds should be placed away from peak stress regions. Cold forming is possible with generous radii and allowance for springback; hot forming is not permitted because it destroys the quenched and tempered condition.
Frequently Asked Questions
Q: What does the Q in S960Q mean?
A: It states the Charpy impact test temperature of minus 20 degC, with a minimum absorbed energy of 27 J; QL and QL1 designate minus 40 degC and minus 60 degC respectively.
Q: Which standard covers S960Q plate?
A: EN 10025-6 for quenched and tempered high yield strength flat products. Comparable strength grades in the GB/T 16270 series cover Q960C, Q960D and Q960E with increasingly severe impact requirements.
Q: How much weight can be saved compared with S355 plate?
A: In strength-governed members the reduction is typically 25-35 %. In stiffness-governed members the saving is smaller, because stiffness depends on elastic modulus, which is the same for every steel grade.
Q: Can S960Q be welded in a normal fabrication shop?
A: It can, provided the shop works to a qualified procedure to ISO 15614-1 with low-hydrogen consumables, documented preheat, controlled heat input and a cap on interpass temperature.
Q: Is hot forming allowed?
A: No. Heating above the tempering range destroys the quenched and tempered structure and the strength guarantee; cold forming with adequate radii is the accepted route.
Q: How is the plate tested before delivery?
A: Tensile testing to ISO 6892-1, Charpy impact testing to ISO 148-1 and dimensional checks per EN 10029, documented on an EN 10204 type 3.1 certificate for each heat.
