1.How corrosion resistant is an untreated bare board?
Intrinsic Characteristics: Cold-rolled steel sheets are made of carbon steel, which readily reacts with oxygen and water in the air at room temperature, causing rust.
Relative Advantages: Compared to hot-rolled sheets of the same composition, cold-rolled sheets actually exhibit better corrosion resistance. This is because a key process in cold rolling-bright annealing-forms a very thin and dense oxide film on the steel surface, which effectively isolates the steel from air and moisture, providing basic protection. Furthermore, precisely controlling the trace alloying elements such as chromium, nickel, and copper in the steel can further enhance its intrinsic corrosion resistance to some extent.
2.What are the functions of the zinc coating?
Physical isolation: Separates the steel from the corrosive environment.
Electrochemical protection (sacrificial anode): Even if the coating is damaged and the steel is exposed, zinc, being more chemically reactive than iron, will preferentially "sacrifice" itself to protect the steel substrate. Therefore, the lifespan of galvanized cold-rolled steel sheets can be 15-30 times that of ordinary steel sheets. With advanced finishing processes, the corrosion resistance of galvanized sheets can be further significantly improved.
3.How corrosion resistant is special weathering steel?
There is also a special type of cold-rolled product, such as ArcelorMittal's Indaten® series, which, by adding alloying elements such as copper, chromium, and phosphorus, allows it to form a dense oxide layer (commonly known as a "rust layer" or "passivation layer") that is firmly bonded to the substrate in the natural environment. This rust layer effectively prevents the internal metal from continuing to corrode, thus allowing for "bare" use without the need for coating.
4.What are the reasons for the poor corrosion resistance of bare cold-rolled steel sheets?
It rusts very easily and requires immediate processing or rust prevention.
5.What are the reasons for the superior corrosion resistance of special weather-resistant cold-rolled steel sheets?
A dense, protective rust layer is formed through alloy composition, eliminating the need for painting.