Chromium-Free Dacromet: Standards and Alternatives

Summary: “Chromium-free Dacromet” is a trade description, not one coating specification. This guide explains the chromium terminology, compares ASTM, ISO and Chinese standards, and shows what must match before another zinc-flake coating can replace GEOMET.

The short answer

“Chromium-free Dacromet” usually means a zinc-flake coating developed without the hexavalent chromium used in traditional DACROMET. It does not name a specific product. Depending on the supplier, it may refer to GEOMET, another proprietary coating system or a domestic formulation.

Before buying it, establish three points: what form of chromium is excluded, which basecoat and topcoat will be applied, and which performance standard the finished fastener must meet. If the drawing names GEOMET, a different zinc-flake coating is a substitution and needs the drawing owner’s approval.

Why chromium was removed

DACROMET® began as a trade name. In China, “Dacromet” is also commonly used for the wider family of non-electrolytic zinc-aluminum-flake coatings. Dacromet and Zinc-Flake Coatings for High-Strength Fasteners explains how this coating type differs from electroplated zinc.

Traditional DACROMET formulations used chromic-acid chemistry and contained hexavalent chromium, written Cr(VI) or Cr6+.^[1]

Occupational exposure to Cr(VI)-contaminated mist, dust or fumes can cause cancer, respiratory illness, skin damage, and possible kidney or liver damage.^[2]

Workers handling coating solutions, mist and dust face the greatest exposure risk. A cured fastener does not create the same exposure as an open treatment bath, but residual Cr(VI) still matters for product compliance and end-of-life processing.

Suppliers began using terms such as “environment-friendly Dacromet” for replacement coatings. The wording is not standardized, so the quotation needs the exact chromium statement and coating name.

Separate the technology, product and standard

Level	What it identifies	Examples
Technology	The broad coating method	Non-electrolytic zinc-flake or zinc-aluminum-flake coating
Proprietary product	A manufacturer’s coating chemistry and system	GEOMET®, DELTA-PROTEKT®, Zintek®, Magni®
Specification	Classification, testing and acceptance requirements	ASTM F3393, ISO 10683, GB/T 5267.2, an OEM specification

A Chinese coating and GEOMET can use the same zinc-flake technology while remaining different products. State the product name and governing standard separately.

Cr(VI)-free and chromium-free are different claims

Supplier wording	What it means	What it does not tell you
Cr(VI)-free	Hexavalent chromium is excluded	Whether Cr(III) or another chromium form is present
Chromium-free / chrome-free	No form of chromium is intentionally used	Corrosion, friction, brand identity or customer approval
Environment-friendly Dacromet	The supplier is claiming an environmental improvement	Which substances are excluded and how the claim was checked
ASTM B117 tested	The coating was exposed in a salt-spray chamber	The test duration, pass/fail criterion or full coating specification

Specify Cr(VI)-free when the requirement concerns hexavalent chromium. Specify no intentionally added chromium or a total-chromium limit when every form of chromium must be excluded. Add the test method and acceptance limit when laboratory verification is required.

The current U.S. fastener standard

ASTM F3393-24 covers non-electrolytically applied zinc-flake systems on threaded fasteners at least 0.250 inch or M6 in nominal diameter.^[3]

The supplied coating system must be free of hexavalent chromium. Both water-based and solvent-based systems are permitted. ASTM F3393 defines coating classes and performance requirements and accepts any qualified coating brand.

ASTM F3393 replaced ASTM F1136/F1136M, F2833 and F3019/F3019M, which ASTM lists as withdrawn in 2025.^{[3] [4]} Older drawings may still refer to those numbers, so the applicable revision should be confirmed before quoting.

Total-chromium status and OEM approval require separate documentation. ASTM B117 specifies a salt-spray test method; it does not define a coating system.

How ASTM, ISO and Chinese standards differ

What does flZn/nc/480h mean?

flznnc480h is flZn/nc/480h written without separators. It is an ISO 10683-style zinc-flake designation:^{[5] [15]}

flZn identifies a non-electrolytically applied zinc-flake coating system;
nc means the system is free of hexavalent chromium, not necessarily every form of chromium;
480h requires no visible base-metal corrosion (red rust) after a 480-hour neutral salt spray test.

It does not identify GEOMET or any other coating brand. It also leaves open the topcoat, lubricant and friction requirements. Those details belong in the full ordering designation, together with the governing standard and edition. The 480 hours are a laboratory test requirement, not a claim of 480 hours of outdoor service life.^{[14] [15]}

Document	Main scope	Cr(VI)-free requirement
ASTM F3393-24	Zinc-flake systems on threaded fasteners at least 1/4 inch or M6	Required for the supplied coating system^[3]
ISO 10683:2018	Non-electrolytic zinc-flake systems on fasteners	Covers systems with or without Cr(VI)^[5]
GB/T 5267.2-2021	Chinese fastener coating standard, modified from ISO 10683	Covers systems with or without Cr(VI)^[6]
GB/T 26110-2025	Broader Chinese technical specification for zinc-aluminum coatings	State the chromium restriction separately^[7]

For fasteners, GB/T 5267.2 is the more specific Chinese document. It is a modified adoption of ISO 10683, not an identical copy. ASTM F3393 has a different classification system and an explicit Cr(VI)-free requirement.

Where GB/T 26110-2025 fits

GB/T 26110-2025 took effect on July 1, 2026 and replaced the 2010 edition. It is a general technical specification for zinc-aluminum coatings; GB/T 5267.2 remains the fastener-specific standard.^[7]

GB/T 26110 is a recommended national standard. A drawing or purchase order can make it part of the contract.^[8] Quote the coating name and chromium requirement alongside the standard.

Is GEOMET the U.S. standard?

No. GEOMET is a proprietary coating family, not the name of the U.S. standard. It appears in many industrial and OEM specifications, but ASTM F3393 also allows other zinc-flake systems that meet the specified class.^{[3] [9]}

Other proprietary systems include:

Dörken DELTA-PROTEKT KL 120 with VH 321 GZ, which Dörken identifies as a Cr(VI)-free system approved to GM’s GMW14671 Type H;^[10]
MKS Atotech Zintek ONE HP, an inorganic silver zinc-flake basecoat that Atotech identifies as Cr(VI)-free;^[11]
Magni 565 Black, which Magni describes as a chrome-free duplex fastener coating; the 565 family also appears against multiple customer specifications in Magni's OEM listings.^[12]

Each supplier has its own basecoats, topcoats and approved applicators.

NOF describes GEOMET as waterborne and chromium-free.^[13] Its individual products are compared in What Is GEOMET? 321, 360, 430, 500 and 720 Explained.

Can a Chinese chromium-free coating replace GEOMET?

Yes, when the drawing permits an equivalent coating and the proposed system meets every specified requirement. No, when the drawing names a GEOMET product or an approved-material list that does not include the proposed coating.

Requirement on the drawing or contract	Substitution decision
A named GEOMET grade	Use that grade unless the drawing owner approves the change
An OEM approved-material list	Use a listed coating and applicator, or complete the OEM qualification process
“GEOMET or approved equivalent”	Submit the alternative through the stated approval process
A Cr(VI) restriction plus measurable coating performance, with no named brand	A Chinese-made coating or another alternative can qualify if it meets every requirement
Only matching ASTM B117 hours	Not enough; friction, thickness, pretreatment and other requirements still need to match

A complete comparison covers corrosion, coefficient of friction, thickness, thread fit, pretreatment, color, chemical resistance and applicator approval. Neutral salt spray is an accelerated laboratory test, not a prediction of service life.^[14]

What to put on the RFQ

Do not put only “environment-friendly Dacromet” on the order. State:

the governing standard and edition;
the chromium restriction and any required test method;
the basecoat, topcoat or integral lubricant;
coating thickness or mass;
corrosion test, duration and pass/fail point;
friction or torque/clamp-force requirement;
thread and recess acceptance criteria;
pretreatment restrictions for high-strength parts;
required certificates and lot test reports;
whether substitutions require written authorization.

Tie the coating name, build, standard and performance class to the same quoted system; “environment-friendly” alone is not a usable specification.

Catalog note: these products are listed with Dacromet finishes. Confirm their chromium status on the quotation.

References

From the Catalog

Dacromet Coated Button Head Socket Cap Screw Alloy Steel 35CrMo UNC ASME B18.3 View Product

Dacromet Grade 12.9 Hexagon Socket Cap Screws M16/M18/M20/M27 Alloy Steel Bolts DIN 912 Gb70.1 Compliant View Product

High Strength 35CrMo Alloy Steel Wedge Lock Washer Dacromet DIN25201 Double Fold Self-Locking Design View Product

Chromium-Free Dacromet: Standards, Alternatives and Selection