What is a High-Strength Bolt
author: www.qishine.com
2026-04-02
In critical sectors such as heavy machinery, steel structure construction, bridges, wind power, and rail transportation, high-strength bolts play an irreplaceable role as key connecting components. As a company long engaged in the production and supply of high-strength fasteners, we understand that while a single bolt may be small, it is crucial to structural safety and the service life of engineering projects.
I. What is a High-Strength Bolt?
High-strength bolts generally refer to bolts with a property class of 8.8 or higher. These bolts undergo heat treatment (quenching and tempering) to achieve high tensile and yield strength. According to international standards, common property classes include:
High-strength bolts generally refer to bolts with a property class of 8.8 or higher. These bolts undergo heat treatment (quenching and tempering) to achieve high tensile and yield strength. According to international standards, common property classes include:
Class 8.8: Tensile strength approx. 800 MPa, yield strength approx. 640 MPa
Class 10.9: Tensile strength approx. 1000 MPa, yield strength approx. 900 MPa
Class 12.9: Tensile strength approx. 1200 MPa, yield strength approx. 1080 MPa
Class 10.9: Tensile strength approx. 1000 MPa, yield strength approx. 900 MPa
Class 12.9: Tensile strength approx. 1200 MPa, yield strength approx. 1080 MPa
In engineering practice, high-strength bolts are characterized not only by material strength but also by the emphasis on preload control and connection method. Unlike ordinary bolts that rely on shear resistance, high-strength bolts typically function by applying precise preload, generating significant frictional resistance between connected plates to transfer loads. This connection method is known as a friction-type connection and is the core reason for their widespread use in steel structures.
High Strength Bolt: Performance grade 8.8 and above
II. Advantages and Disadvantages of High-Strength Bolts
✅ Advantages
1. High Load-Bearing Capacity
High-strength bolts can withstand greater tensile and shear forces, making them suitable for high-stress and heavy-load applications.
✅ Advantages
1. High Load-Bearing Capacity
High-strength bolts can withstand greater tensile and shear forces, making them suitable for high-stress and heavy-load applications.
2. High Connection Rigidity and Excellent Fatigue Resistance
The friction-type connection formed by preload effectively resists dynamic loads and fatigue, reducing the risk of loosening.
The friction-type connection formed by preload effectively resists dynamic loads and fatigue, reducing the risk of loosening.
3. Convenient Construction and High Efficiency
Compared to welding or riveting, bolted connections are highly adaptable to construction environments, offer fast installation, and are particularly suitable for on-site assembly.
Compared to welding or riveting, bolted connections are highly adaptable to construction environments, offer fast installation, and are particularly suitable for on-site assembly.
4. Removable and Easy to Maintain
For structures requiring inspection, replacement, or disassembly, bolted connections offer irreplaceable maintainability.
For structures requiring inspection, replacement, or disassembly, bolted connections offer irreplaceable maintainability.
5. Controllable Quality and High Standardization
High-strength bolt production strictly adheres to ISO, GB, ASTM, and other standards, ensuring stable quality and strong traceability.
High-strength bolt production strictly adheres to ISO, GB, ASTM, and other standards, ensuring stable quality and strong traceability.
❌ Disadvantages
1. High Requirements for Construction Techniques
Controlling preload (using methods such as torque control, turn-of-nut, tensioning, etc.) directly affects connection quality. Improper operation can lead to insufficient preload or over-tightening.
1. High Requirements for Construction Techniques
Controlling preload (using methods such as torque control, turn-of-nut, tensioning, etc.) directly affects connection quality. Improper operation can lead to insufficient preload or over-tightening.
2. Sensitivity to Contact Surface Conditions
Friction-type connections require clean contact surfaces free of oil, grease, and loose rust, achieving a specific friction coefficient. This adds to surface treatment costs.
Friction-type connections require clean contact surfaces free of oil, grease, and loose rust, achieving a specific friction coefficient. This adds to surface treatment costs.
3. Higher Material Cost
High-strength bolts often use alloy steel (e.g., 40Cr, 35CrMo, 42CrMo), duplex stainless steel (e.g., 2205, 2507), or special alloys (e.g., Incoloy 800, Incoloy 625, Monel 400), and undergo rigorous heat treatment, making them more expensive than ordinary bolts.
High-strength bolts often use alloy steel (e.g., 40Cr, 35CrMo, 42CrMo), duplex stainless steel (e.g., 2205, 2507), or special alloys (e.g., Incoloy 800, Incoloy 625, Monel 400), and undergo rigorous heat treatment, making them more expensive than ordinary bolts.
4. Risk of Delayed Fracture
In environments susceptible to hydrogen embrittlement or stress corrosion, if material or process controls are inadequate, there is a potential risk of delayed cracking.
In environments susceptible to hydrogen embrittlement or stress corrosion, if material or process controls are inadequate, there is a potential risk of delayed cracking.
III. Typical Applications of High-Strength Bolts
1. Steel Structure Buildings
In large steel structure systems such as high-rise buildings, stadiums, and convention centers, high-strength bolts are core connectors for main beams, columns, and gusset plates, often appearing as heavy hex head high-strength bolts or twist-off type high-strength bolts.
1. Steel Structure Buildings
In large steel structure systems such as high-rise buildings, stadiums, and convention centers, high-strength bolts are core connectors for main beams, columns, and gusset plates, often appearing as heavy hex head high-strength bolts or twist-off type high-strength bolts.
2. Bridge Engineering
Applications like railway bridges, highway bridges, and cross-sea bridges demand extremely high connection reliability. High-strength bolts are used in critical areas such as main trusses, gusset plates, and bearing connections, providing excellent fatigue resistance and long-term stability.
Applications like railway bridges, highway bridges, and cross-sea bridges demand extremely high connection reliability. High-strength bolts are used in critical areas such as main trusses, gusset plates, and bearing connections, providing excellent fatigue resistance and long-term stability.
3. Wind Power & New Energy
Sectors like wind turbine towers, blade connections, and photovoltaic supports extensively use Class 10.9 and higher high-strength bolts. These applications demand superior corrosion resistance and anti-loosening capabilities under alternating loads and harsh environments.
Sectors like wind turbine towers, blade connections, and photovoltaic supports extensively use Class 10.9 and higher high-strength bolts. These applications demand superior corrosion resistance and anti-loosening capabilities under alternating loads and harsh environments.
4. Rail Transit & Vehicle Manufacturing
Components such as bogies, couplers, and body connections in high-speed trains, subways, and heavy-haul vehicles widely utilize high-strength bolts to ensure operational safety.
Components such as bogies, couplers, and body connections in high-speed trains, subways, and heavy-haul vehicles widely utilize high-strength bolts to ensure operational safety.
5. Heavy Machinery & Mining Equipment
Equipment like excavators, crushers, and presses operate under high vibration and impact conditions, where high-strength bolts are essential for structural integrity.
Equipment like excavators, crushers, and presses operate under high vibration and impact conditions, where high-strength bolts are essential for structural integrity.
Conclusion
A high-strength bolt is not merely a "high-strength" fastener; it represents a systematic connection solution integrating material science, heat treatment processes, precision manufacturing, construction techniques, and quality control. What it carries is not just load, but the foundation of engineering safety.
A high-strength bolt is not merely a "high-strength" fastener; it represents a systematic connection solution integrating material science, heat treatment processes, precision manufacturing, construction techniques, and quality control. What it carries is not just load, but the foundation of engineering safety.
As a fastener supplier, we understand that selecting the correct bolt is only the first step; using it correctly is the key. In practical projects, we recommend users choose the appropriate property class and surface treatment (such as hot-dip galvanizing, Dacromet, zinc-aluminum coating, etc.) based on operating conditions, and strictly adhere to specifications for construction and torque management.
A single bolt connects safety and carries trust. We hope this article helps you gain a more comprehensive and in-depth understanding of high-strength bolts, providing a valuable reference for your project selection and application.
Qishine is ideal choice for EPC companies and project contractors.
Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15960259563
+86 15985833169
Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15960259563
+86 15985833169
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