Corrosive Resistance: Normal Spangle versus Minimized Spangle
The corrosive resistance of galvanized coils and sheet is basically determined by the thickness of its coating. The thicker the zinc coat, the longer the service life of the galvanized product - under the same environmental conditions. In most atmospheres, zinc coating provides highly durable protection, since zinc corrodes about 25 times slower plain steel. Galvanization offers far greater resistance to corrosion than any other alternative system of protection.
CSN provides galvanized steel to various different surface finish standards, such as normal spangle galvanized sheet (CZ-NL), minimum spangle galvanized sheet (CZ-MI) and extra-smooth galvanized sheet; the chosen finish being dependent on the material's intended use. (It should be noted that the coating finish does not change its protective properties - since corrosive resistance only varies with the thickness of the coating, and once again to emphasize, not the finish.) The graph shows the results of internal tests carried out by CSN, as well as trials conducted by users of galvanized sheet steel in markets such as home appliances, automotive and civil construction.
As you can see in the graph below, where the weight of the applied coating is the same, so too is the service life whether it has normal spangle (CS-NL) or minimized spangle (CZ-MI) finish (based on time taken to reach 5% corrosion).
Weathering steel A particular type of structural steel that needs no protection against atmospheric corrosion (such as painting), weathering steel is also known in Brazil as “aço patinável” (or patina-bound steel).
The steel gets its name from its high resistance to atmospheric corrosion. It is a low alloy -steel, which includes very small amounts of copper, chromium, nickel and phosphorus.
While the steel remains open to the elements, a thin protective layer of oxide forms on its surface, but it has distinctly different characteristics when compared with common rust. In Portuguese this special rust is called “patina”, because of its aged/textured appearance, hence the name “patina-bound” steel. It is generated by alternate cycles of wetting (rain, dew, etc.) and drying (sun, wind, etc).
CSN started producing these types of steel in Brazil in 1960, when it started producing COR TENTM steel. Having undergone several stages of development, CSN now has a family of "patina-bound" steels, called CSN COR.
The CSN COR family includes two types of steel: CSN COR 420 (mid mechanical strength) and CSN COR 500 (high mechanical strength). These steels can be used in the most variable of weather conditions, offering good performance, with or without painting. In addition, these materials can be welded, cut and cold formed with relative ease.
Welding As with conventional structural steels, such as ASTM A36, the "patina-bound" steels CSN COR 420 and CSN COR 500 are also easy to weld. Since they are corrosion resistant steels, the welding electrode used should have the same characteristics. These steels are particularly well suited to electrical resistance welding in the production of tubing and structural profiles.
Painting The same paint intended for regular structural steel may also be applied to "patina-bound" steels. The application of paint will at least double the service life of the steel.
Painting "patina-bound" steel is recommended where it is to be used in very severe atmospheric conditions.
Preparation for painting is by mechanical or blast cleaning, just the same as with regular structural steels. Paint should not be applied on top of any oxide .
Main applications of CSN COR
Bridges, viaducts, walkways;
Commercial and residential buildings;
Industrial; agricultural and commercial warehousing;
INAL employee working in the laboratory 