S690QL vs S355
S355 is the world's most widely used structural steel; S690QL is a quenched and tempered high-strength grade offering almost twice the yield strength. The right choice depends on your project's load, weight and cost priorities.
Two Different Steel Classes
Both materials are structural steel; they are not two grades doing the same job, but two separate categories designed for different needs. The most fundamental difference between them is yield strength and production method.
S355 (EN 10025-2) is a general-purpose structural steel with a minimum yield strength of 355 MPa. It is produced normalized or thermomechanically rolled; being a cheap, easily sourced and very easily welded material, it is the standard for buildings, hangars, roofing and general construction.
S690QL (EN 10025-6) falls into the high-strength class with a minimum yield strength of 690 MPa. It is produced quenched and tempered (quenched & tempered, Q+T); thanks to its high strength, it carries the same load with thinner sections. It stands out in weight-critical applications such as cranes, construction machinery, dump bodies and bridges.
In short: S355 means low cost and easy processability, while S690QL means high strength and light weight. The right decision is made according to your project's dominant criterion.
S690QL vs S355 Big Comparison Table
A side-by-side comparison of the standard, mechanical and practical properties of the two grades. The rows where S690QL provides a clear advantage are highlighted:
| Property | S355 (S355J2) | S690QL |
|---|---|---|
| Standard | EN 10025-2 | EN 10025-6 |
| Min. Yield Strength (ReH) | 355 MPa | 690 MPa |
| Tensile Strength (Rm) | 470 – 630 MPa | 770 – 940 MPa |
| Production Method | Normalized / Thermomechanical | Quench + Temper (Q+T) |
| Elongation at Fracture (A) | ≥ 22 % | ≥ 14 % |
| Impact Toughness (Charpy V) | ≥ 27 J at −20°C | ≥ 30 J at −40°C |
| Hardness (typical) | ~160 HBW | 235 – 280 HBW |
| Weldability | Very easy (preheat usually not required) | Good (low hydrogen + preheat) |
| Weight Advantage | Reference | ~30–40% lighter section |
| Typical Use | Buildings, hangars, roofing, general construction | Cranes, construction machinery, dump bodies, bridges, ships |
| Price / kg Trend | Low (reference) | High (due to alloying + heat treatment) |
Note: The values are reference figures for thicknesses ≤ 50 mm and vary with thickness. For S355, the J2 sub-grade (−20°C impact guarantee) is taken as the basis; the JR/J0 grades have a different impact temperature.
When S355, When S690QL?
The choice becomes clear according to your project's dominant criterion. The guide below summarizes typical situations:
Choose S355
- Standard building and roof construction
- Projects where cost is the top priority
- Cases where thick sections are not a problem
- Designs governed by stiffness (deflection)
- Warehouses, hangars, racking and general fabrication
- Series production requiring easy, fast welding
Choose S690QL
- Crane booms, lifting and machinery chassis
- Mobile structures where weight is critical
- When payload / carrying capacity matters
- Structures requiring low-temperature (−40°C) toughness
- Dump bodies, bridges, ships and offshore
- Material saving target with thinner sections
Weight Saving: A Numerical Example
S690QL's most concrete advantage is weight saving. In a design where yield strength is the governing factor, using S690QL instead of S355 can reduce section thickness by about 30–40%. Below is an example of a plate that is equivalent in terms of strength:
| Parameter | S355 | S690QL |
|---|---|---|
| Required thickness (strength-equivalent) | 20 mm | 12 mm |
| Plate volume | 0.180 m³ | 0.108 m³ |
| Plate weight (≈7.85 g/cm³) | ≈ 1,413 kg | ≈ 848 kg |
| Weight saving | Reference | ≈ 40% (565 kg) |
| Weld groove volume (trend) | Reference | ~50% less |
Note: The example is for a scenario where yield strength is the governing factor and is for reference. When stiffness (deflection), buckling or fatigue governs, thickness cannot be reduced in the same proportion; the actual section must always be verified by project calculation.
This saving does not stop at steel tonnage: a lighter structure means lower transport cost, less weld consumption and, on mobile equipment, higher payload. You can quickly test your thickness selection with our weight calculator.
Welding & Processing Differences
The main differences in processing the two materials stem from S690QL's high-strength class:
- Welding: S355 can be welded in most cases without preheat and with little care. S690QL, on the other hand, requires low-hydrogen methods, controlled heat input and, depending on thickness, preheat (typically 100–200°C).
- Filler metal: Standard consumables are sufficient for S355. For S690QL, a matching-strength or deliberately slightly undermatched filler is selected.
- Bending: S355 bends easily at small radii. For S690QL the minimum inner bending radius is larger and the bending direction should be chosen perpendicular to the rolling direction.
- Cutting: Both materials can be cut by laser, plasma and oxy-fuel; S690QL is more sensitive to post-cut heat effects in thick sections.
S690QL vs S355 Frequently Asked Questions
How many times stronger is S690QL than S355?
In terms of yield strength, S690QL guarantees a minimum of 690 MPa while S355 guarantees a minimum of 355 MPa. This means S690QL has roughly 1.94 times (almost twice) the yield strength of S355.
A similar upper-level difference also exists in tensile strength (470–630 MPa for S355, 770–940 MPa for S690QL). However, stiffness (modulus of elasticity) is approximately the same for both steels; that is, being "stronger" does not reduce deflection, it only increases the load it can carry.
Can S690QL be used instead of S355?
Technically, yes. Because S690QL has higher strength it can be used in place of S355 and usually carries the same load with a thinner section.
However, in low-stress, cost-driven projects it may not be economical. Also, since design criteria such as stiffness (deflection) are independent of yield strength, it is not always possible to reduce thickness in proportion to strength. The decision must always be based on project calculation.
Which is cheaper, S355 or S690QL?
Per kilogram, S355 is clearly cheaper; S690QL has a higher price per kg because of its alloying, heat treatment (quenching + tempering) and tight quality control.
On the other hand, when less material is used with S690QL the total steel tonnage, weld volume and transport drop. For this reason, on weight-critical projects the total cost can break even or even turn in favour of S690QL. For a fair comparison, the basis should be the cost per finished part, not the price per kg.
How much weight saving do you get by using S690QL?
In designs where strength is the governing factor, switching from S355 to S690QL can typically reduce section thickness by about 30–40%; this provides a similar proportion of weight saving.
For example, on a plate where roughly 12 mm S690QL is used instead of 20 mm S355 in terms of strength, the weight drops by about 40%. When stiffness or fatigue governs, this ratio decreases; the actual saving varies by project.
Let's Choose the Right Steel for Your Project Together
Is S355 or S690QL right for you? Our technical team is ready to help with material selection, weight optimization and pricing. Both grades are delivered ex-stock, including cutting and bending.