What designation do you use to define your steel?
Remember that the designation of materials can be summarised in 5 characteristics, defined by the reference UNI EN standards:
- Quality grade:
This is a code to which the chemical and mechanical limits of the steel are associated. It establishes the steel’s aptitude for machining.
- Quantity of surface coating:
This indicates the quantity of coating in g/m2 (on hot galvanised steel for example) or in microns (on electro-galvanised steel) and the type of coating (galvanised, aluminised, etc.).
Remember that the only reliable way to evaluate the quantity of coating is defined in the applicable standard.
- Aspect or superficial quality:
This indicates the condition of the surface (for example, a type A surface allows imperfections that the type B surface does not). It does not define characteristics such as the brilliance or opacity of the surface, nor does it give any guarantee about use of the product for cosmetic purposes.
- Surface finish:
In cold rolled steel this identifies a range of roughness (for example a surface with an “m” finish has a range of roughness of between 0.6 and 1.9 microns, which is very broad for those who require cosmetic properties on the finished product). In coated steels, this indicates the structure of the “spangles” (typically we speak of the “M” surface which has a micro-spangle structure ranging from invisible (zero spangle) to clearly visible spangles, although no dimensional limits are defined).
- Protective surface treatment:
This indicates the type of surface protection which is applied to protect the steel temporarily (for 3 months after shipping, if the product is stored in a suitable environment) against oxidation and/or to support future treatments (such as painting).
In the case of pickled hot and cold rolled sheets, the products are supplied with an oiling treatment, unless the customer expressly requests otherwise.
Remember that if you don’t want your material oiled, the product will not be guaranteed against oxidation.
With coated products (for example hot galvanised steel), the treatment is normally “C” (passivating chemical); this is a product that helps the material to develop a condition of surface passivation, which helps it to self-protect against oxidation.
Remember that slight coloration from the passivating agent (usually a light shade of green) does not affect the material’s use, and is covered by the applicable regulations.
- For hot rolled black or pickled steel sheets, consider points 1 and 5.
- For cold rolled steel, points 1, 3, 4, 5.
- For hot dip galvanised or aluminised steel, and cold electro-coated steel, points 1, 2, 3, 4, 5.
To designate the appropriate material, (particularly where there are restrictive characteristics not fulfilled by the simple designation of the steel (where we talk about brilliance, for example), it’s important to know how the steel is going to be used, but most importantly which machining and/or treatment it might be subjected to, such as:
- zinc coating
If you have important, specific requirements for your machining processes and for the use of your product, always tell your supplier. This allows you to find the right material, and avoid wasting time, or extra costs.
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