High‑strength Flange Bolts: Applications and Manufacturing Process

Features: Integrated flange on the bolt head, eliminating the need for separate washers. It provides larger bearing area and better anti‑vibration and anti‑loosening performance compared with ordinary hex bolts. Materials are generally alloy steels such as 40Cr, SCM435 and 42CrMo. Main domestic standards: GB/T5789, GB/T16674.
1. Main Applications

1. Automotive industry: Chassis, engine brackets, gearboxes, suspension systems and other key connecting parts.

2. Mechanical equipment: Heavy‑duty machinery, hydraulic equipment, gearboxes and machine tool assemblies.

3. Construction & steel structure: Steel frame connections, tower equipment and large‑scale support structures.

4. Power & energy: Wind turbine components, power transmission equipment and pipeline flange connections.

5. Railway & transportation: Locomotive and vehicle parts, high‑speed rail auxiliary structures.

2. Manufacturing Process

1. Raw material selection: High‑strength alloy steel wire rods are selected, with surface inspection and dimensional testing.

2. Wire drawing: The wire rod is drawn to the required diameter to remove surface oxide scale.

3. Cold forging: Cold‑heading forming to forge the bolt head and integrated flange, forming the basic shape of the bolt.

4. Thread rolling: Roll threads on the shank to obtain precise external threads.

5. Heat treatment: Quenching and tempering to achieve mechanical properties of grade 8.8, 10.9 or 12.9. This step is critical for high‑strength performance.

6. Surface treatment: Zinc‑plating, dacromet, phosphating or blackening for corrosion resistance.

7. Inspection & testing: Hardness test, tensile load test, dimensional inspection and visual inspection.

8. Sorting & packaging: Qualified products are sorted and packed for delivery.

Standards for Hexagon Flange Bolts

🇨🇳 Chinese GB Standards

1. GB/T 5789 — Hexagon flange bolts, heavy series, product grade B（加大系列B级六角法兰螺栓，高强度常用）

2. GB/T 5790 — Hexagon flange bolts with reduced shank, heavy series, product grade B（加大系列细杆法兰螺栓）

3. GB/T 16674.1 — Hexagon bolts with flange, small series, product grade A（小系列粗牙六角法兰螺栓，汽车行业用量最大）

4. GB/T 16674.2 — Hexagon bolts with flange with metric fine pitch thread, small series（小系列细牙六角法兰螺栓）

🌍 International & European Standards

1. ISO 4162 — Hexagon bolts with flange, small series（对应GB/T16674.1）

2. ISO 15072 — Hexagon bolts with flange, fine pitch thread, small series（细牙版本，对应GB/T16674.2）

3. DIN 6921 — Hexagon flange bolts (German standard, widely used in Europe)

4. DIN 6922 — Hexagon flange bolts with reduced shank

5. JIS B1189 — Japanese standard for hexagon flange bolts
💡 Note: DIN 6923 is the standard for flange nuts (not bolts).
🇺🇸 American Standards

• ASME B18.2.3.4M — Metric hex flange screws (US metric series)