Din 50961 Fe Zn 8b May 2026

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.

If you are exporting to Europe or supplying the automotive industry (e.g., VW, BMW, Mercedes), note the following:

Reality: The "8" refers to the minimum local thickness on significant surfaces. Average thickness is typically higher (9–12 µm), and edges may be thicker due to current concentration.

| Designation Part | Meaning | | :--- | :--- | | DIN 50961 | German Standard for Zinc Electroplating | | Fe | Base Metal: Steel/Iron | | Zn | Coating: Zinc | | 8 | Thickness: min. 8 µm | | b | Finish: Blue/Clear Chromate (Trivalent) | din 50961 fe zn 8b

A common question is: How long will DIN 50961 Fe Zn 8b last in salt spray testing?

According to DIN 50961, the corrosion resistance for a blue-passivated zinc coating (type b) is significantly lower than yellow or olive-drab passivation. Under neutral salt spray testing (NSS per ISO 9227):

| Passivation Type (Code) | Time to White Rust (Zinc Corrosion) | Time to Red Rust (Steel Corrosion) | |------------------------|--------------------------------------|--------------------------------------| | Blue (b) | 6 – 12 hours | 48 – 72 hours | | Yellow (c) | 48 – 96 hours | 120 – 200 hours | | Olive-drab (d) | 120+ hours | 200+ hours |

Key takeaway: Fe Zn 8b offers low to moderate corrosion protection. It is suitable for indoor environments or dry assemblies, not for exposed outdoor or marine applications. Appearance: A brilliant blue surface with a metallic

This is the German standard (Deutsches Institut für Normung) titled "Electroplated coatings on iron and steel; Part 1: Zinc coatings".

In the world of mechanical engineering and corrosion protection, surface codes are the silent guardians of longevity. One of the most frequently specified, yet often misunderstood, codes on European technical drawings is DIN 50961 Fe Zn 8b.

If you have ever seen this notation on a blueprint for automotive fasteners, hydraulic fittings, or stamped steel parts, you know it dictates a specific type of zinc electroplating. But what does each character mean? What is the difference between "8" and "12"? And crucially, what does the lowercase "b" signify for your application?

This article dissects DIN 50961 Fe Zn 8b from every angle—chemical, metallurgical, and practical. By the end, you will know exactly when to specify this coating, how to inspect it, and what alternatives to consider. Electrical Conductivity: The blue film is very thin (approx

DIN 50961 is replaced by DIN EN ISO 2081:2018. The equivalent designation for Fe Zn 8b is:

ISO 2081 – Fe/Zn 8 – Cr(blue) (or simply "Fe/Zn 8, blue passivation")

However, ISO 2081 no longer ties specific corrosion resistance to color; you must specify required hours to white/red rust separately (e.g., "≥12 h to white rust").