Small fasteners — screws, nuts and pins — for farm machinery, hardened to resist wear in heavy-duty use.
Agricultural machinery fasteners live in wet soil, fertiliser and abrasive dust, and get re-torqued in a field by whoever is nearest with a wrench. Two things decide their life: abrasive wear on the hardware that touches the ground, and corrosion from ammonium- and chloride-bearing residues on everything else. Neither is solved by a higher property class — they are solved by the right hardness band and a coating system that survives a wet crevice.
| Property class | 8.8 / 10.9 · wear parts to a hardness band, not a class |
|---|---|
| Hardness | 30–50 HRC · ground-engaging parts 42–52 HRC |
| Materials | S45C · SCM435 · SWCH10B33 · SUP9 |
| Coating system | Zn + Cr3+ + sealer · zinc phosphate + oil |
| Coating thickness | 8–15 µm Zn |
| Salt spray (NSS) | 240–500 h NSS |
| De-embrittlement bake | ≥ 320 HV or class ≥ 10.9 → ISO 4042 bake |
| Inspection methods | ISO 6508 · ISO 3497 · ISO 9227 |
Farm machinery drawings often mix a structural bolt and a wear part on the same sheet. Tell us which is which — the hardness band that makes a share bolt last will make a structural bolt brittle.
Plough bolts, tine bolts and share fixings run in soil that behaves like a grinding paste. The head shape wears away until there is no drive left and the joint cannot be undone without cutting it out. Through-hardened heads hold their form far longer, but hardness taken to the top of the range with no toughness left turns a wear problem into a brittle fracture problem — which is why the band matters more than the maximum.
Ammonium nitrate, urea and manure residues are aggressive, and they collect in the crevice between the nut face and the joint where they stay wet long after the outside has dried. Zinc is consumed rapidly in that crevice while the exposed surface still looks acceptable, so a fastener can be most of the way through when nothing on the outside says so.
Field machinery hits things. A fastener hardened to the top of its band with a marginal temper fails as a brittle break rather than yielding and holding. Tempering to the specified band — not to the top of the hardness range — is what leaves enough ductility to absorb an impact, and it is the single most common specification mistake on wear parts.
Implements vibrate over rough ground for entire working days. Joints re-torqued in a workshop with a torque wrench are re-torqued in a field by feel, so the practical defence is a finish that gives a consistent torque–tension relationship: repeatable feel then corresponds to a repeatable clamp load. An inconsistent coating turns every field service into a new preload.
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Yes. Through-hardening and quench-and-temper of small steel fasteners is our core process, and the useful range for ground-engaging wear parts is generally 42–52 HRC depending on grade and section. What we need is your hardness band and the measurement location. A part hardened at the top of the range wears well but takes impact badly, so the band matters more than the maximum.
No coating ignores ammonium and chloride residues; some systems simply last longer. Greater zinc thickness plus a sealer or top-coat generally moves the salt-spray result from around 72–120 h to around 240–480 h to first white and red corrosion, and zinc phosphate with oil is used where the part is painted afterwards or where oil retention matters. The real gain in the field comes from removing the wet crevice, which is a design change rather than a coating change.
No. We are a subcontract heat-treatment and finishing works. Screws, nuts, bolts, washers, pins and springs come to us from the manufacturer or the buyer, and we return them processed, in lots, with a test report per lot.
The bands on this page are typical industry values, not a guarantee for any specific part. The governing drawing, customer specification and standard always take precedence, and every value is confirmed against your part before production. V.S. Heat Treatment operates under ISO 9001:2015; no other certification or sector approval is claimed.
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