S700 high strength structural steel is a high-performance, low-alloy steel that represents a significant advancement in structural materials. Defined by its minimum yield strength of 700 MPa and tensile strength of 700-800 MPa, it is approximately twice as strong as standard structural steels like S355. This exceptional strength is achieved through a carefully controlled low-carbon chemistry and specialized thermomechanical processing, which results in a fine-grained microstructure. This combination allows S700 to provide the strength needed for heavy loads and long spans while maintaining the weldability and formability required for practical fabrication. For industries seeking to reduce weight, increase load capacity, and improve structural efficiency, S700 offers a proven and cost-effective solution.
Introduction
For decades, the structural steel industry has relied on a hierarchy of grades, with S355 and S460 serving as the standards for most construction and heavy equipment. However, as structures become larger and more complex, and as industries push for greater efficiency, the limitations of these grades become apparent. To achieve the required strength, designers often have to use very thick, heavy sections, which increase material costs, transportation expenses, and foundation loads. S700 was developed to overcome this. By using advanced metallurgy, it achieves a yield strength nearly double that of S355, allowing engineers to use thinner, lighter sections without sacrificing load-bearing capacity. This makes it an essential material for modern, weight-sensitive applications in construction, automotive, and heavy machinery.
What Are the Key Properties of S700?
The performance of S700 is defined by its optimized chemical composition and the mechanical properties achieved through advanced processing.
Chemical Composition
The chemistry of S700 is designed to achieve high strength while maintaining good weldability and toughness.
| Element | Content Range (%) | Its Role in Performance |
|---|---|---|
| Carbon (C) | 0.10 – 0.20 | Low enough for excellent weldability, high enough for strength. |
| Manganese (Mn) | 1.20 – 1.60 | The primary strengthening element, boosting tensile and yield strength. |
| Silicon (Si) | 0.20 – 0.50 | Acts as a deoxidizer and stabilizes mechanical properties. |
| Chromium (Cr) | 0.10 – 0.30 | Enhances corrosion resistance and hardenability. |
| Molybdenum (Mo) | 0.10 – 0.20 | Improves high-temperature strength. |
| Vanadium (V) | 0.05 – 0.10 | Refines grain structure, increasing strength and toughness. |
| Phosphorus (P) | ≤ 0.03 | Minimized to prevent cold brittleness. |
| Sulfur (S) | ≤ 0.03 | Controlled to maintain toughness and weldability. |
Mechanical and Physical Properties
These properties make S700 suitable for high-stress, weight-sensitive structural applications.
| Property | Value Range | Why It Matters |
|---|---|---|
| Yield Strength | 550 – 650 MPa | Twice the strength of S355 (355 MPa), allowing for much thinner sections. |
| Tensile Strength | 700 – 800 MPa | Provides a strong safety margin against failure. |
| Elongation | 15 – 20% | Maintains good ductility for forming and bending. |
| Impact Toughness | 60 – 80 J/cm² at -40°C | Remains tough in cold climates, outperforming many higher-strength steels. |
| Fatigue Strength | 350 – 450 MPa | Withstands repeated stress, critical for dynamic applications. |
| Hardness | 150 – 220 HB | Balances strength with good machinability and weldability. |
| Density | 7.85 g/cm³ | Standard for steel, simplifying design calculations. |
- Weldability: It has good weldability. For thin sections (under 15mm), no preheating is required. For thicker sections, a preheat of 150-200°C is recommended.
- Formability: It has good formability and can be cold bent up to 90° for 10mm thick plates, allowing for complex shapes without hot forming.
Where Is S700 Used in the Real World?
S700 is used in applications where high strength and weight reduction are critical.
Construction and Infrastructure
S700 is used for long-span bridges, high-rise buildings, and heavy industrial structures.
- Case Study: A construction firm used S460 for a 120-meter span highway bridge but faced weight-related transportation delays.
- They switched to S700 beams.
- The higher strength allowed for 18% lighter beams .
- Trucks could carry 2 beams per trip instead of 1, cutting transportation costs by $40,000 .
- Construction was sped up by 3 weeks .
Automotive and Heavy Machinery
S700 is used for electric vehicle (EV) chassis, heavy-duty truck frames, and crane booms.
- Case Study: An automotive manufacturer used S460 for EV chassis. The chassis weight of 500 kg was limiting battery range, and welding time was slowing production.
- They switched to S700 .
- The higher strength allowed for 20% thinner components , reducing chassis weight to 420 kg (a 16% reduction).
- This improved EV range by 12 km per charge .
- S700’s good weldability reduced welding time by 15% , increasing production capacity by 10% .
- Despite a 15% higher material cost, the weight reduction saved $30 per EV , and faster production saved $50,000 monthly , totaling $720,000 in annual savings .
Heavy Equipment and Marine
S700 is used for excavator arms, crane booms, and offshore platform frames.
- Excavator arms made from S700 are 15% lighter , improving machine maneuverability.
- Crane booms can achieve 80-meter spans without extra weight.
How Is S700 Manufactured?
The manufacturing process for S700 is designed to create a fine-grained, high-strength microstructure.
Steelmaking and Rolling
- Steelmaking: It is typically made in an Electric Arc Furnace (EAF) or Basic Oxygen Furnace (BOF) , with precise control of carbon, manganese, and microalloys like vanadium.
- Thermomechanical Rolling: This is the key process. The steel is hot rolled at carefully controlled temperatures to refine the grain structure, which is the primary source of its high strength.
- Quenching and Tempering: For the highest strength grades, a quenching and tempering heat treatment is used. The steel is heated to 880-920°C, rapidly cooled (quenched), and then reheated to 550-600°C (tempered) to balance strength and toughness.
Forming and Finishing
- Cold Bending: S700 can be cold bent up to 90° for plates up to 10mm thick, allowing for complex shapes without hot forming.
- Welding: Standard MIG, TIG, and arc welding methods are used. For thick sections, preheating to 150-200°C is recommended.
- Corrosion Protection: For outdoor applications, hot-dip galvanizing or epoxy painting is applied to protect against corrosion.
S700 vs. Other Structural Steels
Comparing S700 to other materials helps clarify its value for high-strength, weight-sensitive applications.
| Material | Yield Strength | Impact Toughness (-40°C) | Relative Cost | Best For |
|---|---|---|---|---|
| S700 | 550 – 650 MPa | 60 – 80 J/cm² | Medium-High | Weight-sensitive, high-load structures |
| S690 | 550 – 650 MPa | 40 – 60 J/cm² | Slightly Lower | High-strength applications with less cold-toughness requirement |
| S460 | 345 – 460 MPa | 50 – 70 J/cm² | 70% | General high-strength structures |
| S355 | 235 – 355 MPa | 40 – 60 J/cm² | 55% | Standard structural applications |
| Aluminum (6061) | 276 MPa | 10 – 15 J/cm² | 3x Higher | Lightweight, non-structural parts |
Key Takeaway: S700 offers a unique combination of ultra-high strength, good weldability, and excellent low-temperature toughness. It is significantly stronger than S355 and S460, allowing for substantial weight reductions. While it is more expensive than these grades, the savings in material weight, transportation, and assembly often offset the higher material cost. For applications where strength and weight are critical, S700 provides the best balance of performance and value.
Conclusion
S700 high strength structural steel is a high-performance material engineered for the most demanding structural applications. Its exceptional yield strength, combined with good weldability, formability, and low-temperature toughness, makes it the ideal choice for weight-sensitive projects such as long-span bridges, EV chassis, and heavy equipment. For engineers seeking to design lighter, more efficient, and more sustainable structures, S700 offers a proven and cost-effective solution.
FAQ About S700 High Strength Structural Steel
Can S700 be welded without preheating?
For thin sections (under 15mm), standard welding methods can be used without preheating. For thicker sections, or for welding in cold ambient conditions, preheating to 150-200°C is recommended to prevent hydrogen-induced cracking. Using low-hydrogen welding electrodes is also important.
Is S700 suitable for cold climates?
Yes. Its guaranteed impact toughness of 60-80 J/cm² at -40°C makes it well-suited for cold climates. It outperforms many other high-strength steels, such as S690, in low-temperature toughness, making it an excellent choice for Arctic or northern construction projects.
What is the main advantage of using S700 over S460?
The main advantage is weight reduction. S700’s higher yield strength (550-650 MPa vs. 345-460 MPa) allows for the use of 15-25% thinner sections to carry the same load. This reduces material weight, lowers transportation costs, and can simplify assembly. While S700 has a higher material cost per ton, the overall project cost can be lower due to these weight savings.
Discuss Your Projects with Yigu Rapid Prototyping
At Yigu Rapid Prototyping, we have extensive experience supplying and processing S700 high strength structural steel for demanding applications. We understand that for weight-sensitive projects, material selection is critical. We supply S700 in plates, beams, and custom-cut shapes, with full mill test certificates. Our team can provide guidance on welding procedures, forming, and corrosion protection to ensure your project meets its performance and efficiency goals. Whether you are designing an EV chassis, a long-span bridge, or a heavy-duty crane, we are here to help. Contact us today to discuss your project requirements.