2H heavy black hexagon nuts are fasteners designed for high-strength connection scenarios. They are made of alloy steel through a special process, and the surface is blackened to form an oxidized protective layer. The “2H” in its name represents the 10.9 strength grade in accordance with ISO 898-2 standard. It belongs to the category of ultra-high-strength fasteners and is widely used in industrial fields that bear extreme loads.
1. Key parameter indicators
|
Material |
42CrMo/SCM440 alloy steel |
|
Heat Treatment |
Quenching + tempering (hardness HRC 39-44) |
|
Tensile Strength |
≥ 1220 MPa |
|
Yield Strength |
≥ 1100 MPa |
|
Guaranteed Load |
≥ 1176 MPa |
|
Nominal Diameter |
M12 – M64 (commonly used M16 – M36) |
|
Width Across Flats |
19 – 85 mm (according to ISO 4032 standard) |
|
Height |
11 – 52 mm |
|
Surface Treatment |
Black film thickness: 8 – 15 μm |
|
Salt Spray Test |
72 h no red rust |
|
Friction Coefficient |
0.10 – 0.18 |
|
M24 Torque Value |
850 – 1050 N·m |
|
Preload Coefficient |
0.2 (special gasket required) |
2. Application scenarios
a .Heavy equipment field:
① Engineering machinery slewing bearing connection (excavator, shield machine)
② Wind power tower flange fastening
③ Hydraulic press frame assembly
b .Transportation industry:
① High-speed rail bogie suspension system
② Heavy truck chassis beam connection
③ Ship engine base fixing
c. Energy infrastructure projects:
① UHV transmission tower node reinforcement
② Oil drilling equipment explosion-proof connection
③ Nuclear power plant reactor pressure vessel sealing
3. Precautions for use
a. Installation specifications:
① A calibrated hydraulic torque wrench must be used
② A cross-symmetrical tightening sequence is used (it is recommended to load to the target torque in 3 times)
③ It is forbidden to use impact pneumatic tools for direct installation
b. Matching requirements:
① A 10.9 grade blackened bolt is required (the hardness difference should be controlled within HRC 4)
② The flange surface contact must reach Ra3.2 surface roughness
③ HRC 45-50 grade hardened gaskets are recommended
c. Environmental restrictions:
① Long-term use temperature range: -50℃~+150℃
② Anti-corrosion treatment is required for environments with chloride ion concentrations >500ppm
③ The inspection cycle should be shortened in acid-base environments (pH<4 or >10)
d. Maintenance points:
① Torque re-inspection every 500 working hours
② Perform penetrant testing every quarter in coastal areas
③ After disassembly, the threads need to be thoroughly cleaned and re-coated with molybdenum disulfide lubricant
5. Performance advantage analysis
a. Super strong load-bearing capacity:
Compared with ordinary 8.8 grade nuts, the tensile strength is increased by 50%, and it can withstand alternating loads for up to 10⁷ cycles
b. Environmental adaptability:
Black layer + penetrating oil composite protection system, achieving IP65 protection level
c. Anti-loosening characteristics:
With fine thread design, the preload retention rate under vibration environment is > 90%
d. Economic performance:
The service life is 3-5 times longer than that of galvanized products, and the full-cycle maintenance cost is reduced by 40%
This product series is developing in the direction of functional integration and status monitoring, meeting the intelligent needs of key fasteners in the era of Industry 4.0.
