Din 50961 Fe Zn 8b
Appearance: A brilliant blue surface with a metallic sheen and subtle rainbow iridescence. It is the most visually attractive of all chromate finishes. Corrosion Resistance (Red Rust): According to the standard, Fe Zn 8b must withstand 72 hours in the neutral salt spray test (NSS) before red rust appears (when using Cr(III) based passivations). Electrical Conductivity: The blue film is very thin (approx. 0.1–0.5 µm). Unlike yellow or olive passivations, Fe Zn 8b offers relatively low contact resistance, making it ideal for threaded connections that require electrical grounding (e.g., automotive chassis bolts, electronic enclosures). Weldability: Due to its thin, conductive layer, blue passivated zinc is preferred over thicker coatings for resistance spot welding.
Important Warning: Historically, "b" passivation used hexavalent chromium (Cr VI). Due to EU RoHS and ELV directives, most modern Fe Zn 8b coatings use trivalent chromium (Cr III). The corrosion resistance is similar, but the color is slightly less iridescent. Always clarify with your plater if hex-free is mandatory.
While you still see DIN 50961 on drawings, it has been technically superseded by DIN EN ISO 2081 (Metallic and other inorganic coatings – Electroplated coatings of zinc with supplementary treatments). din 50961 fe zn 8b
Conversion Table:
| Old DIN 50961 | New ISO 2081 | Notes | | :--- | :--- | :--- | | Fe Zn 8b | Fe/Zn 8 / B (or Fe/Zn 8 / C) | "B" = Blue, "C" = Cr(III) | | Fe Zn 12c | Fe/Zn 12 / D | "D" = Yellow Cr(VI) replaced by Cr(III) yellow. | Appearance: A brilliant blue surface with a metallic
Advice for engineers: Continue to use "DIN 50961 Fe Zn 8b" on internal drawings if your supply chain understands it. However, for new designs, switch to ISO 2081: Fe/Zn 8 / T2 (where T2 = trivalent blue passivation).
Modern enforcement of EU Directive 2000/53/EC (End-of-Life Vehicles) and REACH restricts hexavalent chromium (Cr(VI)) in passivation layers. Traditional "type b" blue chromate often contained Cr(VI). automotive chassis bolts
Today, compliant DIN 50961 Fe Zn 8b coatings must use trivalent chromium (Cr(III)) passivation. However, Cr(III) blue passivates are:
Recommendation: If your supply chain requires full RoHS/REACH compliance, explicitly specify "tCr blue passivation (trivalent)" alongside DIN 50961 Fe Zn 8b.
