How to test HV 10.9 DIN6914 EN14399-4 ?

Testing grade 10.9 HV DIN 6914 bolts involves a three-pronged approach: verifying dimensional accuracy, confirming mechanical properties, and ensuring proper surface treatment. Since the old DIN 6914 standard has been largely replaced by the European EN 14399-4, testing now typically follows this newer specification .

Here is a checklist of the key tests required:

📐 Dimensional Inspection

· Basic Dimensions: Verify critical geometries like the shank diameter (h12 tolerance for M12-M24) and head width (conforming to ISO 4014, Class A) .
· Thread Quality: Check threads with GO and NOGO gauges (tolerance class 6g). The bolt also features a short thread length to keep the thread out of the shear plane .

🔬 Mechanical Testing

· Tensile & Yield: Confirm minimum tensile strength of 1000 MPa and yield strength of 900 MPa .
· Hardness: Verify the specified range of 32-39 HRC (Rockwell C) .
· Ductility & Toughness: Ensure minimum 9% elongation after break, and for sizes ≥M16, perform Charpy impact tests (min. 27 J at -20°C) .

🛡 Surface & Embrittlement Tests

· Coating Check: Measure coating thickness (e.g., min. 50μm for hot-dip galvanizing) and verify lubricant for consistent friction .
· Hydrogen Embrittlement Relief: Verify post-plating baking was performed .
· Decarburization: Use metallographic methods (microindentation per ASTM F2328) to ensure surface carbon wasn't depleted during heat treatment .

💡 Crucial Requirements for HV System Bolts

· System HV Compliance: DIN 6914 bolts are part of the "System HV" assembly. For a valid preloaded connection, they must be tested and used with specific mating parts—namely HV nuts (DIN 6915/EN 14399-4) and hardened washers (DIN 6916/EN 14399-6) from the same manufacturer .
· Suitability for Preloading: The entire assembly must pass the preloading suitability test defined in EN 14399-2 to ensure it can achieve the required clamp load without galling or stripping .