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Surface treatments

Description

ArcelorMittal's range of hot and cold rolled, coated and uncoated steels can be delivered with different types of surface treatments. Surface treatments protect the material from corrosion and/or improve its in-use properties.

Oils are one such treatment. They are generally applied electrostatically. Dry lubes are lubricants which appear dry at ambient temperature and liquefy when heated during the drawing process. There is also a range of surface treatment products that react chemically with the coating to provide the desired properties. Surface treatments are applied by spraying or roll-coating, followed by removal of excess product in some cases.

Mechanical properties

Protective oils are the most commonly used treatment. They provide temporary protection from corrosion until secondary processing of the material. A number of high quality oils called pre-lubes (pre-lubricants) provide excellent lubricating properties in addition to corrosion protection. They are used to draw certain parts without re-oiling blanks.
When even more exacting drawing performance is required, ArcelorMittal can offer several surface treatments for zinc coatings: prephosphating for electrogalvanized steels, NIT for electrogalvanized and hot-dip galvanized sheet, L-Treatment for Galvannealed. These are very thin surface treatments. They are detected by analysis of the chemical surface elements and are systematically associated with protective oil or a pre-lube.

In the specific case of Zinc Magnesium coatins, Alkaline activation is suggested to optimize adhesive bonding properties.

Recommendations

Forming

The different surface treatments improve drawing by reducing the friction coefficients of coated and uncoated steel. At the top end of the range (NIT, L-Treatment, Pre-phosphating, dry lube) stick slip phenomena are also reduced, thus lowering the risk of seizure and fracture.

Comparison of the friction coefficients of Extragal® with and without NIT and comparison of a pre-phosphated electro-galvanised steel with Extragal® + NIT

Comparison of the friction coefficients of Extragal® with and without NIT and comparison of a pre-phosphated electro-galvanised steel with Extragal® + NIT

NIT, L-Treatment and dry lube also contribute to ensuring very uniform tribologic behaviour even for parts requiring very light oiling. In some cases, they can limit zinc abrasion, reducing the re-work rate and cleaning frequency in drawn visible parts.

Joining / painting process

Surface treatments have a very minor effect on surface electrical resistance. Therefore, they have very little impact on the welding process.
However, they do have a considerable effect on surface chemistry. Their compatibility with the adhesive bonding and painting processes specific to individual users must therefore be verified.

In the case of Zagnelis coatings, Alkaline activation is specifically designed to ensure excellent behaviour of the coating with all kinds of adhesives.

ArcelorMittal's team of experts can offer guidance on the most suitable choice of surface treatment.

Sizes available / options

The choice of surface treatment depends on the substrate and on the intended application and effects. The process conditions (drawing, assembly, painting, etc.) should be considered when making a choice. Size options also depend on the substrate.
ArcelorMittal's technical teams can help you select the best surface treatment for your application.

Surface treatment Electrogalvanized Extragal® / Ultragal® Galvannealed Jetgal® Zagnelis® Surface Zagnelis® Protect Uncoated cold rolled Uncoated hot rolled
Protective oil/Pre-lubes I* I* I* I I* I I I
Pre-phosphating I*     D        
L-Treatment     I*          
NIT I* I*   I        
Dry lubes I I         I I
Alkaline activation         I* I    

I: Industrial
D: Under development
* Available in visible part quality

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