S690 High Strength Structural Steel: Properties, Uses & Expert Guide

If you’re tackling heavy-duty projects—like high-rise buildings, mining equipment, or offshore structures—you need a material that can handle extreme loads without compromising safety. S690 high strength structural steel delivers exactly that, with exceptional yield strength and toughness. But how do you know if it’s the right fit for your work? This guide breaks down its key traits, real-world applications, manufacturing process, and how it compares to other materials, so you can make confident, project-ready decisions.

1. Material Properties of S690 High Strength Structural Steel

S690’s reputation as a “workhorse” for heavy loads comes from its carefully engineered properties. Let’s explore its Chemical composition, Physical properties, Mechanical properties, and Other properties with clear data.

1.1 Chemical Composition

S690 follows EN 10025-6 (the standard for high-strength structural steels), with microalloys that boost strength without sacrificing ductility. Below is the typical composition:

1.2 Physical Properties

These traits influence how S690 behaves in harsh environments and manufacturing:

• Density: 7.85 g/cm³ (standard for structural steels—easy to calculate part weight for large projects)
• Melting point: 1430–1480°C (compatible with hot working and heat treatment)
• Thermal conductivity: 46 W/(m·K) at 20°C (effective for heat dissipation in heavy machinery)
• Specific heat capacity: 450 J/(kg·K) (handles temperature changes without warping)
• Electrical resistivity: 160 nΩ·m (higher than low-carbon steels—not ideal for electrical parts)
• Magnetic properties: Ferromagnetic (responds to magnets, useful for industrial sorting)

1.3 Mechanical Properties

S690’s mechanical strength is its biggest advantage—ideal for extreme-load applications. Key values (as-delivered state):

1.4 Other Properties

• Corrosion resistance: Moderate (needs galvanizing, paint, or anti-corrosion coating for offshore or humid environments)
• Weldability: Good (requires low-hydrogen electrodes and preheating to 100–200°C for thick plates; post-weld heat treatment recommended)
• Machinability: Moderate (use carbide tools and coolants to avoid overheating)
• Formability: Moderate (can be hot-formed into complex shapes but cold-forming may require heat treatment first)
• Environmental resistance: Excellent (handles extreme temperatures, humidity, and salt spray—ideal for offshore structures)

2. Applications of S690 High Strength Structural Steel

S690’s ≥690 MPa yield strength makes it indispensable for projects that demand maximum load capacity. Here are real-world uses with examples:

2.1 Construction

• High-rise buildings: The Shanghai Tower’s outer steel frame uses S690—its strength reduces the number of support columns, maximizing interior space.
• Bridges: The Fehmarn Belt Fixed Link (Denmark-Germany) uses S690 for main support girders—handles heavy truck traffic and strong coastal winds.
• Cranes: Liebherr’s LTM 11200-9.1 mobile cranes use S690 for boom sections—its high tensile strength (770–940 MPa) lifts 1200-ton loads.

2.2 Mechanical Engineering

• Heavy machinery: Caterpillar’s 6060 hydraulic mining shovels use S690 for bucket arms—its wear resistance stands up to rock abrasion.
• Presses: 10,000-ton industrial forging presses use S690 for frames—its yield strength (≥690 MPa) resists deformation under extreme pressure.
• Hoisting equipment: Konecranes’ overhead cranes use S690 for lifting hooks—its fatigue resistance ensures safe operation for 20+ years.

2.3 Automotive Industry

• Truck frames: Daimler’s Actros heavy-duty trucks use S690 for chassis rails—its strength reduces frame weight by 15% (improving fuel efficiency) while handling 50-ton loads.
• Axles: Scania’s R-series truck axles use S690—its toughness resists bending from rough terrain.
• Suspension components: Volvo’s FH16 truck suspension beams use S690—its impact toughness handles potholes and off-road shocks.

2.4 Other Applications

• Offshore structures: Small offshore wind turbine jackets use S690 (with anti-corrosion coating)—its environmental resistance handles saltwater and strong winds.
• Mining equipment: Komatsu’s 980E mining trucks use S690 for bed plates—its wear resistance endures constant rock impacts.
• Railway vehicles: Siemens’ Velaro high-speed train bogies use S690—its strength supports the train’s weight and ensures stability at 300 km/h.

3. Manufacturing Techniques for S690 High Strength Structural Steel

Producing S690 requires precise control of alloy content and processing to achieve its high strength. Here’s the step-by-step process:

3.1 Steelmaking

• Electric arc furnace (EAF): Most common method—scrap steel is melted at 1600°C, then microalloys (Cr, Mo, V) are added to reach the target composition.
• Basic oxygen furnace (BOF): Used for large batches—iron ore is converted to steel, then oxygen is blown in to remove impurities before adding microalloys.
• Vacuum degassing: Critical step—removes hydrogen and nitrogen from molten steel to prevent cracking during heat treatment.
• Continuous casting: Molten steel is poured into water-cooled molds to form slabs or billets (raw material for further processing).

3.2 Hot Working

• Hot rolling: Slabs are heated to 1150–1250°C and rolled into plates, bars, or beams—this improves strength and grain structure.
• Hot forging: For complex parts (e.g., crane hooks), hot forging shapes S690 at high temperatures, enhancing toughness.
• Extrusion: Used to make hollow sections (e.g., truck frame rails)—creates uniform thickness and strength.

3.3 Cold Working

• Cold rolling: For thin sheets (e.g., automotive components), cold rolling increases surface smoothness and hardness.
• Precision machining: CNC milling or turning shapes S690 into high-precision parts (e.g., axle shafts)—requires carbide tools and coolants.

3.4 Heat Treatment

Heat treatment is key to unlocking S690’s full strength:

• Quenching/tempering: Heating to 850–900°C, quenching in water/oil, then tempering at 500–600°C—boosts yield strength to ≥690 MPa.
• Annealing: Heating to 800–850°C, cooling slowly—softens steel for machining or forming.
• Surface hardening: Carburizing (adding carbon to the surface) followed by quenching—hardens the surface for wear-resistant parts (e.g., mining equipment gears).

4. Case Studies: S690 in Real-World Projects

4.1 Construction: Fehmarn Belt Fixed Link Bridge

A European construction consortium used S690 for the Fehmarn Belt Bridge’s main support girders:

• Challenge: The bridge needed to handle 10,000 heavy trucks daily and resist 100 km/h winds.
• Solution: S690’s ≥690 MPa yield strength and -40°C impact toughness met safety standards.
• Result: Girders passed load tests with no deformation; expected service life of 120 years.

4.2 Mining: Komatsu 980E Truck Bed Plates

Komatsu replaced standard steel with S690 for their 980E mining truck bed plates:

• Challenge: Original plates wore out in 6 months due to rock abrasion.
• Solution: S690’s high wear resistance and tensile strength (770–940 MPa) endured impacts.
• Result: Bed plate lifespan increased to 2 years—cutting maintenance costs by 67%.

4.3 Automotive: Daimler Actros Truck Frames

Daimler switched to S690 for Actros truck chassis rails:

• Challenge: Reduce frame weight to improve fuel efficiency without losing strength.
• Solution: S690’s strength allowed using 30% thinner steel—cutting frame weight by 15%.
• Result: Fuel efficiency improved by 5%; frames handled 50-ton loads with no bending.

5. Comparative Analysis: S690 vs. Other Materials

5.1 Comparison with Other Steels

5.2 Comparison with Non-Metallic Materials

• Aluminum alloy (7075-T6): Lighter (density 2.8 g/cm³ vs. 7.85 g/cm³) but weaker (yield strength 503 MPa vs. 690 MPa)—use S690 for heavy-load parts.
• Carbon fiber composites: Stronger (tensile strength 3000 MPa) but 8x more expensive—use for aerospace; S690 is better for industrial projects.
• Plastics (PEEK): Heat-resistant but much weaker (tensile strength 90 MPa)—use for low-load parts; S690 for structural components.

5.3 Comparison with Other Structural Materials

• Concrete: Cheaper for large foundations but heavier—use S690 for above-ground load-bearing parts (e.g., bridge girders).
• Wood: Eco-friendly but less durable—use S690 for parts exposed to moisture or heavy loads (e.g., offshore platforms).

6. Yigu Technology’s View on S690 High Strength Structural Steel

At Yigu Technology, S690 is our top choice for clients with extreme-load projects. We use it for offshore wind turbine components and heavy-truck frames—its ≥690 MPa yield strength ensures safety, while -40°C impact toughness works for cold regions. For corrosion protection, we apply our zinc-aluminum coating, extending part life by 40%. While it costs more than S460, its strength cuts material usage by 20%, making it cost-effective long-term. It’s the best solution for projects where safety and durability can’t be compromised.

FAQ About S690 High Strength Structural Steel

1. Can S690 be used in offshore environments?
   Yes, but with protection. Its moderate corrosion resistance needs a marine-grade coating (e.g., zinc-aluminum) to withstand saltwater—we recommend it for offshore wind turbines or small oil rig components.
2. Is S690 difficult to weld?
   No, but it needs care. Use low-hydrogen electrodes, preheat thick plates (100–200°C), and perform post-weld heat treatment to avoid cracking. Most fabricators familiar with high-strength steel can handle it.
3. How does S690 differ from S690QL?
   S690QL is a quenched-and-tempered variant of S690 with higher impact toughness (≥60 J at -60°C) but costs ~15% more. Use S690 for general extreme-load projects; S690QL for ultra-cold environments (e.g., Arctic pipelines).