S690QL
1.8928
High-yield-strength, fine-grain alloy structural steel, quenched and tempered · EN 10025-6:2019+A1:2022 — technical delivery conditions for quenched-and-tempered high-yield-strength flat products · EN 10025-1 — general technical delivery conditions where applicable
S690QL is a weldable quenched-and-tempered structural steel for weight-efficient, highly loaded fabrications. Its designation guarantees a nominal minimum yield strength of 690 MPa only through 50 mm thickness and longitudinal Charpy V-notch energy of at least 30 J at −40 °C. Properties, weldability and processing limits are strongly dependent on thickness, actual heat chemistry and preservation of the producer’s Q&T condition.
- 690 MPa for 3–50 mmMinimum yield strength · Reduces to 650 MPa above 50–100 mm and 630 MPa above 100–200 mm.
- QL: 30 J minimum at −40 °CLow-temperature quality · Standard verification is normally on longitudinal Charpy V-notch specimens.
- 3–200 mmStandard thickness range · Availability outside a producer’s normal dimensional program must be confirmed; material beyond the standard range is not automatically EN 10025-6 S690QL.
- Quenched and temperedDelivery condition · Subsequent heating can reduce strength or toughness by over-tempering or changing the microstructure.
- 0.65–0.83%Maximum standard CEV · Thickness-dependent limits; actual certified values are normally more useful for welding calculations.
- High load capacity at reduced section weightPrimary benefit · Stiffness, buckling, fatigue, joint design and fabrication constraints may prevent proportional thickness reduction.
Overview
- Designation system
- EN 10027 steel name and numerical designation systems
- Product forms
- Hot-rolled flat products, Plate and wide flat, Hot-rolled strip and plate/sheet cut from wide strip, subject to the applicable dimensional standard
- Condition
- Quenched and tempered (Q), Direct quenched after rolling and tempered, permitted as equivalent to conventional quenching and tempering
- Density
- 7850 kg/m³ (Typical engineering value for low-alloy structural steel; not a grade-specific EN 10025-6 acceptance requirement.)
What the designation means and what it covers
| Element | Meaning |
|---|---|
| S | Structural steel. |
| 690 | Specified minimum room-temperature yield strength in MPa for nominal thickness up to and including 50 mm. |
| Q | Supplied in the quenched-and-tempered condition. |
| L | Quality with specified impact properties at temperatures not lower than −40 °C. |
EN 10025-6 defines S690QL as an alloy special steel and applies to hot-rolled flat products. The designation alone should not be applied to structural hollow sections, forgings, castings, bars or pressure-purpose plate; those product forms require their own governing specifications even if a similar strength level or name is used.
The required properties apply in the delivered Q&T condition. Direct quenching immediately after hot rolling followed by tempering is accepted by the standard as equivalent to conventional reheating, quenching and tempering. The manufacturing route and detailed alloy design remain producer-controlled, provided all specification requirements are met.
Standard chemical controls
| Element | Maximum, mass % | Metallurgical relevance |
|---|---|---|
| C | 0.20 | Strength and hardenability; a major factor in hydrogen-cracking sensitivity. |
| Si | 0.80 | Deoxidation and strength; controlled-Si supply may require a special order agreement for galvanizing. |
| Mn | 1.70 | Strength, hardenability and toughness control. |
| P | 0.020 | Restricted for toughness and weld integrity. |
| S | 0.010 | Restricted for toughness and through-thickness quality. |
| N | 0.015 | Must be adequately bound by aluminium or other nitrogen-binding elements. |
| B | 0.005 | May provide strong hardenability effects at very low additions. |
| Cr | 1.50 | Hardenability and strength. |
| Cu | 0.50 | Residual or deliberate alloy contribution. |
| Mo | 0.70 | Hardenability and tempering response. |
| Nb | 0.06 | Grain refinement and precipitation effects. |
| Ni | 4.00 | Hardenability and low-temperature toughness; the broad standard maximum is not a typical target analysis. |
| Ti | 0.05 | Nitrogen binding and grain control. |
| V | 0.12 | Precipitation strengthening and grain control. |
| Zr | 0.15 | Optional grain-control/nitrogen-binding addition. |
These are specification maxima for heat analysis, not a typical composition. Producers usually use substantially narrower proprietary chemistry. Product-analysis limits differ and apply only when product analysis is specified.
The steel must be fully killed, fine grained and contain sufficient nitrogen-binding elements. The standard gives a usual guideline of at least 0.020% total aluminium and an Al:N ratio of at least 2:1 when other effective nitrogen binders are absent. Applicable nitrogen-binding elements and their contents are reported in the inspection document.
| Nominal thickness t | Maximum CEV |
|---|---|
| 3 ≤ t ≤ 50 mm | 0.65% |
| 50 < t ≤ 100 mm | 0.77% |
| 100 < t ≤ 200 mm | 0.83% |
The permitted standard envelope becomes relatively high in thick plate. Welding calculations should use the actual certified heat analysis and the producer’s recommendations rather than assuming the specification maximum represents the supplied material.
Mechanical requirements in the delivered condition
| Nominal thickness t | Minimum yield strength ReH | Tensile strength Rm | Minimum elongation A |
|---|---|---|---|
| 3 ≤ t ≤ 50 mm | 690 MPa | 770–940 MPa | 14% |
| 50 < t ≤ 100 mm | 650 MPa | 760–930 MPa | 14% |
| 100 < t ≤ 200 mm | 630 MPa | 710–900 MPa | 14% |
Elongation is based on proportional gauge length L0 = 5.65√S0. Nominal product thickness controls the applicable strength band.
The number “690” is not a universal yield-strength guarantee at every thickness. Using 690 MPa for plate thicker than 50 mm without checking the applicable table would overstate the specified strength.
| Test temperature | Longitudinal minimum | Transverse minimum when specifically agreed |
|---|---|---|
| 0 °C | 50 J | 35 J |
| −20 °C | 40 J | 30 J |
| −40 °C | 30 J | 27 J |
Routine QL verification is normally longitudinal at −40 °C. Transverse testing or another listed test temperature must be specified at ordering when required. Project fracture-control rules may demand substantially more than the basic grade minimum.
Specified Charpy energy establishes product-quality acceptance under the defined test conditions; it is not directly a fracture-toughness value, permissible service temperature or welded-joint guarantee. Plate thickness, stress state, detail category, strain rate, weld quality and residual stress must be considered under the applicable design and execution rules.
Welding and thermal processing
S690QL is intended to be weldable, but it requires more disciplined welding engineering than conventional S355 structural steel. Procedure qualification should address both hydrogen-assisted cold cracking and loss of HAZ strength or toughness. Preheat, interpass temperature, heat input and cooling time should be established from the actual heat chemistry, plate and joint thickness, restraint, consumable hydrogen level, ambient conditions and producer guidance, using EN 1011-2 or the governing fabrication code.
| Control | Practical significance |
|---|---|
| Actual heat analysis | Use certificate values to calculate CEV/CET or other parameters required by the welding method; do not base preheat solely on the grade name. |
| Hydrogen control | Use appropriately low-hydrogen consumables, dry storage and handling, and clean, dry joint surfaces. |
| Heat input and t8/5 | Excessive heat can over-temper or soften the HAZ; overly rapid cooling can create hard zones and increase cracking risk. |
| Consumable strength | Matching or overmatching filler is not automatically required in every joint. Selection must satisfy joint design, toughness and procedure qualification. |
| Restraint and sequence | High restraint, thick attachments and poor sequencing increase residual stress and cold-cracking risk. |
| Inspection timing | Where delayed hydrogen cracking is credible, the inspection plan should provide an appropriate delay before final NDT. |
The standard advises that stress relieving should remain at least 30 °C below the original tempering temperature and normally not exceed one hour. Because the original tempering temperature is usually not stated in advance, the steel producer should be consulted. Higher temperatures or longer holding times require prior agreement on the mechanical properties after treatment.
Uncontrolled post-weld heat treatment, hot forming or extensive flame heating can invalidate the delivered properties. A component cannot be assumed still to meet S690QL merely because the starting plate was certified to that grade.
Cutting, forming and machining
| Operation | Guidance |
|---|---|
| Thermal cutting | Suitable processes can be used, but edge hardness and cracking risk increase with thickness, alloy content, low plate temperature and rapid cooling. Producer-specific preheating and cooling recommendations should be followed. |
| Cold forming | Possible with larger forces, greater springback and larger radii than lower-strength structural steel. Surface condition and cut-edge quality become increasingly important. |
| Machining | Conventional machining is possible with rigid equipment, stable fixturing and tools selected for high-strength low-alloy plate. |
| Flame straightening | Only use controlled procedures. Local strength or toughness can be reduced if the thermal cycle over-tempers the steel. |
| Hot forming | Generally requires producer consultation and subsequent property verification because heating can destroy the original Q&T condition. |
| Applicable thickness | Bend-axis orientation | Recommended minimum inside radius |
|---|---|---|
| 3–16 mm | Axis transverse to rolling direction | 3t |
| 3–16 mm | Axis parallel to rolling direction | 4t |
These are informative recommendations, not guaranteed bend-test acceptance criteria. Confirm producer limits for thicker plate, narrow bends, difficult edge conditions or high cyclic duty.
Design and application implications
S690QL is used where high static strength can reduce section size and deadweight, including crane and lifting structures, mobile equipment, conveying systems, bridges, gates and other highly loaded welded fabrications. The potential benefit is greatest where strength and self-weight govern.
A direct thickness reduction in proportion to yield strength is rarely justified. Elastic modulus is essentially unchanged from ordinary structural steel, so deflection, vibration and elastic buckling may still govern. Welded-detail fatigue resistance is controlled strongly by geometry, notch severity, residual stress and execution quality and does not increase in proportion to base-metal yield strength. Thin high-strength details can also become more sensitive to local instability, distortion, misalignment and fabrication defects.
S690QL is a structural grade, not an abrasion-resistant plate grade and not a pressure-vessel grade. High yield strength alone does not establish wear performance, pressure-code acceptance or suitability for sour, cryogenic, elevated-temperature or fire service.
Specifying and purchasing S690QL
| Item | What should be stated or checked |
|---|---|
| Standard and grade | EN 10025-6:2019+A1:2022, S690QL or 1.8928, including the required national adoption where contractually relevant. |
| Product and dimensions | Product form, nominal dimensions, dimensional standard and required tolerance class; EN 10029 is commonly applicable to discrete plate. |
| Inspection document | Specify the required EN 10204 document type. Type 3.1 is commonly requested for traceable structural plate but should not be assumed unless ordered or required by the project. |
| Impact testing | Confirm QL testing at −40 °C, specimen orientation and whether transverse tests, higher energy or heat-treatment-unit testing are required. |
| Chemistry | Request product analysis if needed and ensure the certificate reports enough chemistry for the intended welding calculation. |
| Internal soundness | Specify EN 10160 ultrasonic acceptance class where lamination control is required; UT requirements should not be assumed from the grade alone. |
| Through-thickness properties | Specify EN 10164 Z-quality where welded details impose significant through-thickness strain or lamellar-tearing risk. |
| Surface condition | State the required EN 10163 class/subclass and any project limits on repaired areas or surface discontinuities. |
| Fabrication requirements | Communicate intended welding, bending, stress relieving, galvanizing or unusual thermal cycles before purchase. |
| Traceability | Maintain plate identity through nesting, cutting and fabrication and reconcile markings with the inspection certificate. |
Substitution should be assessed against the complete product specification, not only nominal yield strength. Product form, thickness, toughness orientation and temperature, chemistry, CEV, delivery condition, testing frequency, dimensional tolerances, NDT, certification and approved welding procedures can all prevent substitution between superficially similar 690 MPa grades.
Sources
- BS EN 10025-6:2019+A1:2022 — Hot rolled products of structural steels, Part 6British Standards Institution
- DIN EN 10025-6:2023-06 — German adoption of EN 10025-6:2019+A1:2022DIN Media
- EN 10025-6:2019+A1:2022 — Standard previewCEN reproduction via iTeh Standards
- High Strength Steel and Execution Guide, Publication P432Steel Construction Institute
- DILLIMAX 690 — High-strength fine-grained structural steel, quenched and temperedDillinger
- Properties and processing of DILLIMAX high-strength steelsDillinger
- Strenx products’ compliance with standardsSSAB
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