IS 4994:1996 is the Indian Standard (BIS) for electroplated coatings of zinc on iron and steel - specification. This standard specifies the requirements for electroplated zinc coatings applied to iron and steel to provide protection against corrosion. It classifies coatings based on thickness and service conditions, and outlines necessary pre-treatments, post-treatments (like hydrogen embrittlement relief and chromate conversion), and testing procedures.
Specifies the requirements for electroplated zinc coatings on iron and steel articles for corrosion protection.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Highest Thickness Grade (Severe Service) | Class 1 (Fe/Zn 25) - 25 µm minimum | Service Condition 4 (SC 4) - 25 µm minimum | ASTM B633-19 |
| Moderate Service Thickness | Class 2 (Fe/Zn 12) - 12 µm minimum | Code 12 (Zn 12) - 12 µm minimum local thickness | ISO 2081:2018 |
| Mild Service Thickness | Class 4 (Fe/Zn 5) - 5 µm minimum | Service Condition 1 (SC 1) - 5 µm minimum | ASTM B633-19 |
| Corrosion Test Method | Neutral Salt Spray Test (as per IS 5527 & IS 6013) | Neutral Salt Spray (NSS) Test (as per ISO 9227) | ISO 2081:2018 |
| Legacy Passivation (Cr6+) | Specifies 'Chromate conversion coatings'. | Type II (Coloured chromate), Type III (Clear chromate) | ASTM B633-19 |
| Modern Passivation (Cr6+-free) | Not defined in the 1996 version. | Types A, B, C, D, E, F specifying different trivalent passivates and sealants. | ISO 2081:2018 |
| Hydrogen Embrittlement Relief | Heat treatment at 190-220°C for 2-4 hours is recommended for hardened parts. | Baking at 190-220°C for a minimum of 4 hours is mandatory for parts with UTS ≥ 1000 MPa. | ISO 2081:2018 |