What Is S690QL Steel Plate?
S690QL is a quenched and tempered (Q&T) high-strength structural steel defined in EN 10025-6, the European standard that covers flat products of high yield strength structural steels supplied in the quenched and tempered condition. The designation encodes the essential specification data: S for structural steel, 690 for the minimum specified yield strength in MPa, and QL for the quenched and tempered delivery condition with impact toughness verified at -40 °C. In the European numbering system the same grade carries the material number 1.8928.
Because the plate is quenched and tempered rather than merely normalized, the steel develops a fine tempered martensitic or bainitic microstructure. That structure produces a yield-to-tensile ratio far higher than ordinary structural steel while still providing the toughness needed to resist brittle fracture in cold service. This is why S690QL dominates weight-critical designs in cranes, mining equipment, bridges and offshore structures.
S690QL Equivalent Grades Across Standards
Global projects rarely reference one standard only, so buyers regularly ask which designation is equivalent to S690QL. The table summarises the grades most frequently quoted as equivalents. All of them are approximate: chemistry limits, impact test temperatures and inspection rules differ slightly from standard to standard, so every substitution should be checked against the governing project specification before the plate is ordered.
| Standard | Grade | Notes |
|---|---|---|
| EN 10025-6 | S690QL (1.8928) | Reference grade; Q&T delivery; impact tested at -40 °C |
| ASTM A514 / A709 | A514 Grade Q; A709 Grade 100 | Approximate equivalent for quenched and tempered plate |
| GB/T 16270 | Q690E | Chinese Q&T high strength structural steel, -40 °C impact |
| ISO 4950-2 | E690 | International designation, minimum yield 690 MPa |
| DIN 17102 (former) | TStE 690 V | Historical German designation, superseded by EN 10025-6 |
| AFNOR (former) | E690T | Historical French designation for the same strength class |
| Old European EN | FeE690VKT | Superseded designation, replaced by the S690QL symbol |
| Swedish standard SS | 2625 | Historical Nordic designation of the same grade family |
Chemical Composition and Carbon Equivalent
The values below are ladle analysis limits for S690QL (1.8928) in accordance with the EN 10025-6 specification. Carbon is capped at 0.20 % and the carbon equivalent value at 0.83, a combination selected so that the heat affected zone of a weld stays hard enough for strength but resistant to hydrogen cracking.
| Element | Max % | Element | Max % |
|---|---|---|---|
| C | 0.20 | Mo | 0.70 |
| Si | 0.80 | V | 0.12 |
| Mn | 1.70 | N | 0.015 |
| P | 0.020 | Nb | 0.060 |
| S | 0.010 | Ti | 0.050 |
| Ni | 2.00 | Cu | 0.50 |
| Cr | 1.50 | Zr | 0.15 |
| B | 0.005 | CEV | 0.83 |
Mechanical Properties of S690QL
Tensile and yield requirements fall as plate thickness rises, because thicker sections cool more slowly during quenching and therefore temper to a slightly lower strength level.
| Nominal thickness (mm) | 3-50 | 50-100 | 100-150 |
|---|---|---|---|
| Minimum yield strength ReH (MPa) | 690 | 650 | 630 |
| Tensile strength Rm (MPa) | 770-940 | 760-930 | 710-900 |
| Minimum elongation, Lo = 5.65√So (%) | 14 | 14 | 14 |
| Impact energy, longitudinal, 0 °C (J) | 50 | 50 | 50 |
| Impact energy, longitudinal, -20 °C (J) | 40 | 40 | 40 |
| Impact energy, longitudinal, -40 °C (J) | 30 | 30 | 30 |
Applications and Equivalent Grade Selection
Heavy transport: trailer frames, transport platforms and special purpose vehicles, where high strength reduces tare weight and raises payload.
Construction: load bearing structures, columns and beams that allow leaner sections without loss of safety.
Machine building: frames and support structures for heavy machinery exposed to dynamic loads.
Lifting equipment: crane booms, jibs and other load carrying components that benefit from a high strength to weight ratio.
Offshore and mining: structural nodes, platforms and earthmoving equipment working in cold and corrosive environments.
Substitution is a technical decision, not a commercial shortcut. Work through the following points before confirming an alternative grade:
Required yield and tensile strength at the actual plate thickness, not just at nominal thickness.
Impact test temperature and minimum energy demanded by the design code; a -20 °C grade should not be used where -40 °C toughness is specified.
Welding and fabrication conditions, including carbon equivalent, preheat requirements and available filler metals.
Governing design codes such as EN, ASTM or GB, and whether the code permits an equivalent grade at all.
Approval requirements of the project authority, classification society or end user.
Frequently Asked Questions
Q: What is the equivalent material to S690QL?
The closest equivalents are ASTM A514 Grade Q, also designated ASTM A709 Grade 100, GB/T 16270 Q690E, ISO 4950-2 E690 and the former German grade TStE 690 V. All are approximate and must be verified against the project specification.
Q: What does the QL suffix mean?
Q indicates the quenched and tempered delivery condition, and L indicates that impact toughness is verified at -40 °C.
Q: What is the difference between S690Q and S690QL?
S690Q is impact tested down to -20 °C with a minimum longitudinal energy of 40 J, while S690QL is tested down to -40 °C with a minimum of 30 J, which suits colder service conditions.
Q: What is the carbon equivalent limit of S690QL?
The maximum carbon equivalent value is 0.83, which supports controlled welding with suitable heat input and, where required, preheating.
Q: Can S700MC be substituted for S690QL?
Only after engineering review. S700MC is a thermomechanically rolled fine grain steel under EN 10149-2 with different toughness, thickness range and welding rules, so it is not a direct equivalent.
Q: Which thickness range is normally available?
S690QL is commonly rolled from 3 mm up to 150 mm, with mechanical properties specified in three thickness bands as shown above.
