What Is S690QL Steel?
Chemical Composition, Mechanical Properties,
and EN 10025-6 Explained

What Is S690QL Steel?

S690QL (European material number 1.8928) is a high-strength quenched and tempered structural steel standardised under EN 10025-6. It sits near the upper end of the commercially weldable structural steel yield-strength range, delivering a guaranteed minimum yield strength of 690 MPa while retaining the toughness and weldability that safety-critical structural applications require.

The steel belongs to the family of fine-grained, thermomechanically controlled or quenched-and-tempered steels. Unlike conventional carbon steels that rely mainly on carbon for strength, S690QL achieves its performance through a precisely controlled multi-element alloying chemistry — kept low in carbon for weldability — activated by an industrial quenching and tempering heat treatment cycle.

The practical result is that structural designers can build significantly lighter and more efficient structures without sacrificing load-bearing capacity. For mobile machinery such as cranes and mining excavators, weight saving directly translates to greater payload and lower fuel consumption. For fixed infrastructure — offshore platforms, bridges, wind tower flanges — slimmer sections reduce material cost per unit of structural strength.

Understanding the Designation: S · 690 · Q · L

Each character in "S690QL" encodes a precise piece of technical information critical for correct specification and procurement:

EN 10025-6: The Governing Standard

EN 10025 is the European harmonised standard for hot-rolled products of structural steels, published by CEN and adopted nationally by DIN (Germany), BSI (UK), AFNOR (France), and UNI (Italy). Part 6 covers all high yield strength Q+T grades — including S690QL.

All S690QL forgings from Jiangsu Liangyi are manufactured and certified against EN 10025-6, with EN 10204 3.1 Material Test Certificates issued for every order. EN 10204 3.1 means properties were verified by the manufacturer's own accredited laboratory. EN 10204 3.2 certification — which adds co-sign-off by a customer-nominated independent third-party inspection body — is also available upon request for orders that require it.

Chemical Composition per EN 10025-6

S690QL (1.8928) is specified as maximum permitted limits for each alloying element. The low carbon ceiling is the foundational design decision — it is what keeps this ultra-high-strength grade weldable in structural fabrication.

Mechanical Properties by Section Thickness

EN 10025-6 specifies mechanical properties as a function of product thickness, because hardenability — the ability of the Q+T cycle to develop full strength across the section — decreases as section size increases.

Indicative values per EN 10025-6:2004 for S690QL (1.8928). Always verify against the current standard edition and the specific material test certificate for each heat.

Quench & Temper: Why Heat Treatment Defines Everything

The "Q" in S690QL is not cosmetic — it is the manufacturing process that creates the steel's mechanical performance. S690QL cannot approach its target properties through normalising or thermomechanical rolling alone. The full quenching and tempering cycle is mandatory and must be precisely controlled for every individual piece.

International Equivalents of S690QL (1.8928)

S690QL has no perfectly interchangeable equivalent in every global standard. Differences in chemistry limits, thickness ranges, and test methods mean all comparisons are approximate. Always verify the exact specification for your project. The most commonly cross-referenced near-equivalents:

S690QL vs Other High-Strength Structural Grades

S690QL sits on the EN 10025-6 yield-strength ladder between S550QL and S890Q. Each step up delivers weight savings but imposes increasingly demanding fabrication requirements and narrowing material availability:

S690QL represents the optimal balance point for most heavy engineering applications. Above S690QL, weldability constraints narrow significantly and certified material availability thins at competitive lead times. Below it, the weight and cost advantages of HSLA steel are not fully realised.

Why Forged S690QL Outperforms Rolled Plate

Most engineers first encounter S690QL as flat plate. For complex geometry, large cross-sections, or components requiring stringent fatigue and impact performance, forged S690QL delivers measurable advantages that plate cannot match.

1. Grain Flow Alignment

In rolled plate, grain structure is elongated along the rolling direction but essentially random in the transverse and through-thickness planes. In an open die forging, progressive deformation can be directed so that grain flow follows the contour of the finished component — tensile stresses and fatigue cycles act along the grain flow, exactly as the designer intended.

2. Homogeneity in Large Sections

The forging process — working material under high compressive stress across multiple reduction passes — breaks down casting porosity, closes internal voids, refines grain structure, and homogenises chemistry from centre to surface. The result is significantly more consistent mechanical properties across large cross-sections than plate of equivalent thickness.

3. Size Range Unavailable from Plate Mills

S690QL plate is typically available up to approximately 100–150 mm thickness. Jiangsu Liangyi produces S690QL forgings covering a far wider dimensional envelope:

This dimensional range opens S690QL to applications — large-diameter hydraulic cylinder barrels, heavy structural flanges, crane mast sections, and thick-wall pressure vessel nozzles — that plate cannot deliver. For full shape options, tolerances, and lead times, see Jiangsu Liangyi's custom S690QL open die forgings, seamless rolled rings, bars and discs.

Industrial Applications of S690QL Forged Steel

S690QL is the grade of choice wherever high structural efficiency, low-temperature toughness, and weldability must coexist in the same component:

Cranes and Lifting Equipment

Crane OEMs were among the earliest industrial adopters of 690 MPa structural steel. A crane boom built in S690QL versus S355 achieves the same structural capacity at roughly half the weight — directly increasing net lifting capacity, reducing counterweight requirement, lowering ground pressure, and cutting transportation costs across the machine's operating life.

Mining and Construction Machinery

Excavator arms, bucket edges, drilling mast structures, and haul truck body frames operate under severe repeated impact loading in abrasive, cold environments. S690QL's combination of high strength, retained toughness at sub-zero temperatures, and manageable welding procedure makes it the dominant structural steel choice in this equipment category across European, Australian, and North American markets.

Offshore Oil & Gas and Wind Energy

Offshore jacket structures, monopile foundations, and wind tower transition piece flanges all require S690QL or equivalent grades. The low-temperature impact sub-grade (QL) is mandatory for North Sea, Baltic, and Arctic deployments where service temperatures fall regularly to −20°C to −40°C.

Hydraulic Cylinders and Pressure Vessels

High-pressure hydraulic cylinder barrels, accumulator shells, and pressure vessel nozzle forgings in S690QL allow thinner wall sections for equivalent pressure ratings, reducing material cost and machining time. The combination of forgeable chemistry and high post-heat-treatment strength makes S690QL particularly well suited to this demanding application family.

Weldability and Fabrication Guidance

S690QL is a weldable structural steel, but its CEV up to 0.83 and high strength level mean hydrogen cold cracking is a genuine risk if correct welding procedures are not specified and followed. Treating S690QL like standard S355 will result in weld defects.

Sourcing S690QL Forged Parts: Specification Checklist

A complete specification eliminates ambiguity and ensures the forging manufacturer can deliver exactly what the project requires:

Jiangsu Liangyi Co., Limited manufactures S690QL forgings across all shapes and dimensions listed above, with a complete in-house production chain from EAF/ESR steel melting through precision open die forging, controlled Q+T heat treatment, and optional CNC precision machining — all under ISO 9001:2015 certification. To discuss your project requirements and receive a free quote within 24 hours, visit the S690QL (1.8928) forged steel parts page.

S690QL Steel — FAQs