Fastener defect troubleshooting
Twelve failure modes that put screws, nuts and bolts on hold — what you see, what proves it, and what stops it happening again.
Each entry separates the symptom from the confirming test, because most disputes between a fastener plant and its subcontractor are really disagreements about measurement. Root causes are ordered by how often they turn out to be the answer, not by how interesting they are.
Defect index
Scroll the table sideways on a narrow screen.
| Defect | Family | Process stage | Standards commonly cited | Grades most affected |
|---|---|---|---|---|
| Hydrogen embrittlement — delayed fracture after plating | Zinc plating | Zinc Plating Cr3+ | ISO 4042, ISO 15330-1, ASTM B850, ASTM F1940, ISO 898-1, ISO 10683 | SCM435, SCM440, SWCH10B33, SUP9 |
| Decarburization — surface carbon loss after heat treatment | Heat treatment | Heat Treatment | ISO 898-1, ISO 3887, ASTM E1077, ISO 6507-1, ASTM E384 | S45C, SCM435, SCM440, SUP9, SK85 (SK5) |
| Quench cracking | Heat treatment | Heat Treatment | ISO 9934-1, ASTM E1444, ISO 3452-1, ASTM E165, ISO 898-1 | S45C, SCM440, SK85 (SK5), SUJ2, SKS3 |
| Soft spots and incomplete hardening | Heat treatment | Heat Treatment | ISO 898-1, ISO 6508-1, ASTM E18, ISO 6507-1, ISO 642 | S45C, SWCH10B21, SWCH10B33, SCM435 |
| Distortion after heat treatment — bend, ovality, pitch drift | Dimensional | Heat Treatment | ISO 4759-1, ISO 965-1, ISO 1502, ISO 898-1, ASTM F606 | S45C, SCM435, SUP9, SWCH10B21 |
| Low hardness after tempering | Heat treatment | Heat Treatment | ISO 898-1, ISO 6508-1, ASTM E18, ISO 6507-1, ASTM F606 | SCM435, SCM440, SWCH10B21, S45C |
| Over-tempering — strength lost in the tempering stage | Heat treatment | Heat Treatment | ISO 898-1, ISO 6508-1, ISO 6507-1, ASTM E384 | SCM435, SCM440, SUP9, SUJ2 |
| White rust on zinc-plated parts | Zinc plating | Zinc Plating Cr3+ | ASTM B633, ISO 2081, ISO 4042, ISO 9227, ASTM B117, ISO 3497 | SWCH10B21, S20C, S45C |
| Early red rust on plated fasteners | Zinc plating | Zinc Plating Cr3+ | ASTM B633, ISO 4042, ISO 9227, ASTM B117, ISO 3497, ASTM B568 | SWCH10B21, S45C, SCM435 |
| Blistering of the zinc coating | Zinc plating | Zinc Plating Cr3+ | ASTM B571, ISO 2819, ASTM B633, ISO 2081, ISO 4042 | S45C, SCM435, SWCH10B33, SUS420J2 |
| Poor phosphate adhesion — coating rubs off, paint lifts | Phosphate coating | Phosphate Coating | DIN 50942, ISO 9717, MIL-DTL-16232, ISO 2409, ASTM D3359, TT-C-490 | S45C, SWCH10B21, SCM435, SUP9 |
| Thread gauge failure after plating | Dimensional | Zinc Plating Cr3+ | ISO 4042, ISO 965-1, ISO 1502, ASTM F1941, ASTM B633, ISO 3497 | SWCH10B21, SCM435, S45C |
Guidance based on published standards and general fastener metallurgy. Values are typical ranges that depend on the part, the material and the governing specification — the customer drawing and the applicable standard always prevail. This page does not replace a qualified failure analysis of your own parts.
Every defect, grouped by family
Heat treatment
Zinc plating
Dimensional
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