Q960E and Q690E are both Chinese high-strength structural steels with an E-class impact guarantee at -40 C, yet the 270 MPa gap between their minimum yield strengths places them on two different engineering tracks. Q690E is the mainstream workhorse of heavy fabrication, produced in large tonnage by many mills in either thermo-mechanically controlled rolled or quenched and tempered condition. Q960E is an ultra-high-strength quenched and tempered plate that only a limited number of integrated steelmakers can deliver with consistent properties. This guide compares the two grades on standards, chemistry, mechanical properties, thickness capability, welding practice, cost and application fit.
Grade Designation and Governing Standards
In the GB system, Q denotes minimum yield strength, the number is that strength in MPa, and the trailing letter defines the Charpy test temperature: B is +20 C, C is 0 C, D is -20 C and E is -40 C. Q690E therefore guarantees at least 690 MPa yield with E-class low-temperature toughness, while Q960E guarantees at least 960 MPa yield in the same toughness class. The difference between them is strength and metallurgical difficulty rather than toughness.
Q690E is normally ordered to GB/T 1591-2018 when delivered as thermo-mechanically controlled rolled plate, or to GB/T 16270-2009 when quenched and tempered plate in the Q690 class is required. Q960E lies outside the scope of GB/T 1591 and is produced to GB/T 28909-2012, the Chinese standard for ultra-high-strength structural steel. For export projects the closest European equivalents are EN 10025-6 grades S690QL and S960QL respectively. On the ASTM side, quenched and tempered alloy plate to ASTM A514 covers the 690 MPa class, while the 960 MPa class is normally specified through EN 10025-6 or a project specification.
Chemistry and Steelmaking Route
Q690E is a low-alloy microalloyed steel: carbon is normally capped near 0.18 percent and the carbon equivalent is held at about 0.45 to 0.49 percent, which is what allows both the thermo-mechanical route and conventional quenching and tempering to reach the required strength. Thermo-mechanically controlled rolled versions rely on controlled rolling plus accelerated cooling with niobium, vanadium and titanium additions, while quenched and tempered versions add a reheating, quenching and tempering sequence. Secondary refining and vacuum degassing are common but not mandatory.
Q960E is a different metallurgical problem, because strength and toughness must be balanced at a level where any segregation or coarse inclusion becomes a crack initiation site. Mills use a low-carbon microalloyed design, often with boron, together with secondary refining and vacuum degassing, and hold phosphorus to about 0.020 percent or below and sulphur to about 0.010 percent or below. Quenching is followed by tempering inside a narrow window, and furnace temperature uniformity plus plate flatness control become quality critical.
Mechanical Properties Compared
Typical specification values for the two grades are summarised below. Property guarantees change with thickness, so the mill certificate for the actual plate should always be checked.
| Property | Q690E | Q960E |
|---|---|---|
| Minimum yield strength, ReH | 690 MPa | 960 MPa |
| Tensile strength, Rm | 770 to 940 MPa | 980 to 1150 MPa |
| Elongation after fracture, A | 14 percent minimum | 10 percent minimum |
| Charpy V-notch energy at -40 C | 34 J minimum | 34 J minimum |
| Delivery condition | Thermo-mechanical or quenched and tempered | Quenched and tempered |
| Weldability | Good with routine low-hydrogen practice | Requires qualified procedure, preheat and heat input control |
Thickness and Size Capability
Q690E is widely available as plate from roughly 3 mm to 100 mm, and heavy sections and welded beams in the same grade are common. Because two production routes exist, buyers can often choose between thermo-mechanically controlled rolled plate with lower internal stress and quenched and tempered plate with tighter strength scatter.
Q960E is supplied mainly as quenched and tempered plate, most often in the 5 mm to 60 mm range, with heavier gauges available on special order and subject to property verification. Width and length options are narrower than for Q690E, and flatness tolerance is tighter because the grade is used in fatigue-loaded structures.
Welding and Fabrication
Q690E is welded with routine low-hydrogen procedures: clean joint preparation, controlled ambient conditions and consumables matched to the strength class. Preheat is usually modest and can be low or omitted on thin sections when the carbon equivalent and joint restraint allow. Heat input is kept inside a qualified range and interpass temperature is monitored so that the heat affected zone does not soften.
Q960E demands a qualified welding procedure specification, preheat typically in the 150 C to 200 C range, controlled heat input and a strict interpass limit. Matching consumables in the 960 MPa class are not always available, so undermatching filler metal, combined with joint detailing that places the weld in a lower stress region, is common practice. Inspection requirements and any post-weld heat treatment should be agreed before fabrication starts.
Where Each Grade Is Used
Q690E: wind tower sections, mining hydraulic supports, port and shipyard cranes, excavator and concrete pump booms, bridge components, heavy vehicle chassis, lifting and storage equipment.
Q960E: large mobile crane booms, columns and transfer structures in ultra-high-rise buildings, heavy forming press frames, offshore lifting appliances, and specialised lightweight structural components.
In many projects the two grades are combined: Q960E for the small number of highly stressed members where section size governs the design, and Q690E for secondary members, connections and the bulk of the structure. That mixture keeps overall cost and welding effort under control while still delivering the weight saving where it matters.
Cost and Supply Reality
Q960E carries a substantial price premium because of secondary refining, tight process windows, lower yield of first-grade product and additional testing. Domestic quotations have run at roughly two to two and a half times the price of Q690E, and lead times are longer because fewer mills produce the grade and orders are often grouped into a heat treatment campaign. Q690E, by contrast, is a commodity product with many qualified suppliers, short lead times and a wide stock of standard sizes.
How to Choose Between Them
Start from the governing design case. If the structure is strength governed, weight critical or space critical, and the value of the payload or floor area saved is large relative to fabrication cost, Q960E is the logical choice. If the design is stiffness governed or cost governed, Q690E will almost always be the better commercial answer, because the extra 270 MPa cannot be exploited without revisiting fatigue, buckling and connection design. As a rule of thumb, welded fabrication cost and defect risk rise faster than material savings as yield strength increases, so Q960E should be used in as few members as possible.
Frequently Asked Questions
Q: Which grade is stronger, Q960E or Q690E?
Q960E is stronger by design. Its minimum yield strength is 960 MPa against 690 MPa for Q690E, and its tensile range is correspondingly higher. Both are E-class steels tested for impact toughness at -40 C, so the difference lies in strength rather than in toughness.
Q: Is Q960E covered by GB/T 1591?
No. GB/T 1591-2018 covers high-strength low-alloy structural steels up to the Q690 class. The 960 MPa class is specified in GB/T 28909-2012, and for export work the equivalent grade is EN 10025-6 S960QL.
Q: Can Q960E and Q690E be welded to each other?
Yes, dissimilar joints are common, but they need a qualified procedure that satisfies the more demanding of the two base metals. Preheat and heat input are set by the Q960E side, while the filler metal is usually selected for the Q690E strength level to keep the joint ductile.
Q: What does the E suffix mean?
The E suffix is a toughness class rather than a strength class. It certifies a minimum Charpy V-notch energy at a test temperature of -40 C. Grades carrying D, C or B suffixes are tested at -20 C, 0 C and +20 C respectively.
Q: Why is Q960E more expensive than Q690E?
Higher alloy and cleanliness requirements, vacuum degassing, narrow quenching and tempering windows, lower first-grade yield and extra testing all add cost. Limited production capacity and smaller order volumes push the price higher still.
Q: Which grade suits wind power towers?
Most tower and foundation components are designed in the Q355 to Q690 range, where Q690E offers a good balance of strength, weldability and cost. Q960E is reserved for specialised high-load components such as lifting yokes and large crane structures.