The High Tensile Hex Bolt is an indispensable structural fastener designed for heavy-duty industrial machinery, structural steel fabrication, automotive engineering, and power infrastructure. Engineered from high-grade medium carbon steel and alloy steel (40Cr, 35CrMo, 42CrMo), these fasteners undergo precision quenching and tempering heat treatment to achieve superior yield strength, shear resistance, and fatigue durability according to global ISO standards.
Technical Specifications of High Tensile Hex Bolt
High tensile property classes (Grade 8.8, 10.9, and 12.9) specify extreme load-bearing thresholds. Grade 8.8 delivers a minimum tensile strength of 800 N/mm², Grade 10.9 reaches 1000 N/mm², while Grade 12.9 achieves up to 1200 N/mm² for critical structural connections requiring zero deformation under heavy stress.
| Property Rating | Core Material Grade | Tensile Strength (Min) | Yield Strength (Min) | Hardness (HRC / HV) |
|---|---|---|---|---|
| Class 8.8 | Medium Carbon Steel (45#) / 40Cr Steel | 800 N/mm² (800 MPa) | 640 N/mm² (640 MPa) | 22 – 32 HRC |
| Class 10.9 | Alloy Steel (40Cr / 35CrMo / 42CrMo) | 1000 N/mm² (1000 MPa) | 900 N/mm² (900 MPa) | 32 – 39 HRC |
| Class 12.9 | High Alloy Steel (35CrMo / 42CrMo) | 1200 N/mm² (1200 MPa) | 1080 N/mm² (1080 MPa) | 39 – 44 HRC |
Heat Treatment and Manufacturing Process for High Tensile Hex Bolt
At our manufacturing plant in Handan, China, high-tensile hex bolts undergo a rigorous cold-heading and thermal processing sequence to eliminate internal stresses and optimize metallurgical grain structure:
- Precision Cold Forging: High-speed cold-heading formers shape the hexagonal head, bevels, and shank with high dimensional repeatability and clear head stamps (e.g., 8.8, 10.9, 12.9).
- Continuous Mesh-Belt Heat Treatment: Bolts pass through computer-controlled mesh-belt furnaces for quenching in specialized oil and controlled tempering, achieving exact target hardness.
- Precision Thread Rolling: Threads are rolled post heat treatment (or pre-heat treatment per spec) to form smooth, pitch-perfect metric 6g or imperial 2A/3A threads that resist thread stripping under extreme torque.
- Surface Coating & Anti-Corrosion: Options include Black Oxide with rust-inhibiting oil coating, Electro-Galvanizing, Dacromet, or Geomet coating to prevent hydrogen embrittlement.
Heavy Duty Applications of High Tensile Hex Bolt
Due to their high yield strength and tensile endurance, Grade 8.8, 10.9, and 12.9 hex bolts are widely specified in load-critical projects globally:
- Steel Framing & Bridge Construction: Securing structural steel beams, girders, and heavy column flanges under dynamic vibration loads.
- Heavy Machinery & Automotive Industry: Assembly of engine blocks, hydraulic pumps, gearboxes, and crane chassis.
- Wind Energy & Power Substation Infrastructure: Anchoring power transmission equipment, tower brackets, and substation hardware systems.
Strict Quality Testing for High Tensile Hex Bolt
Handan YiHao Fastener implements rigorous Quality Control (QC) standards for every export lot. Testing procedures include Rockwell/Vickers hardness testing, wedge tensile load verification, magnetic particle inspection (MPI) for micro-cracks, and thread pitch gauge checks.
All export shipments are carefully packed in 25kg reinforced inner cartons, stacked on ISPM 15 compliant fumigated wooden pallets, and securely wrapped in stretch film to prevent corrosion during ocean transport.
Request Factory Direct Pricing for High Tensile Hex Bolts
Looking for a trusted manufacturer in Handan, China for Grade 8.8, 10.9, or 12.9 high tensile hex bolts? Contact Handan YiHao Fastener today for technical datasheets, full thread/partial thread specifications, assembly sets (bolt + nut + washer), and direct bulk factory quotes.
