I. Check the markings and color:
Markings: Carbon steel bolts are marked with their grade (e.g., 8.8, 10.9), stainless steel with A2-70, etc.
Color: Zinc-plated bolts are white/blue-white, Dacromet bolts are gray/silver-white, and hot-dip galvanized bolts are dark gray.
Note: Blurred markings or abnormal colors (e.g., yellowing galvanized bolts) may indicate a problem.
II. Test with tools:
Hardness test: Use a Rockwell hardness tester to measure the surface hardness (e.g., 8.8 grade is approximately 25-32 HRC).
Chemical analysis: Use a spectrometer to detect the content of elements such as carbon and manganese.
Metallographic examination: Use a microscope to check if the microstructure is uniform.
III. Quick self-inspection techniques:
Listen to the sound: High-strength bolts produce a crisp sound when dropped.
Scratch test: High-strength bolts are more difficult to scratch with hard tools.
Observe the luster: Tempered bolts have a colored luster under sunlight.
IV. Professional Testing
Tensile Test: Measures tensile strength.
Salt Spray Test: Measures corrosion resistance.
Non-destructive Testing: X-ray inspection for internal defects.
