Mild environment (low humidity, low pollution)
In areas with mild climates, such as inland regions with low humidity and less industrial pollution, Q355NHA usually takes 6 - 12 months for the rust layer to stabilize. In the early stage (1 - 3 months), the surface will form a thin, uneven rust layer. As time goes by, the rust layer gradually thickens and becomes dense. By 6 - 12 months, a stable, dense, and uniform reddish - brown rust layer is formed, which can effectively prevent further corrosion of the internal steel.Harsh environment (high humidity, high pollution)
In harsh environments like coastal areas (with high salt spray content in the air) or industrial areas (with high levels of sulfur dioxide and other corrosive gases), the corrosion rate of Q355NHA is accelerated. Generally, it takes 3 - 6 months for the rust layer to stabilize. The high humidity and rich corrosive media in the environment make the chemical reaction on the steel surface faster, and the rust layer can quickly develop into a stable protective layer.
If Q355NHA undergoes pre - weathering treatment (such as artificial simulation of natural corrosion environment in the factory to accelerate rust layer formation), the rust layer can be stabilized before leaving the factory. The factory can control the environmental conditions (such as temperature, humidity, and the composition of the corrosive medium), so that the steel surface forms a stable rust layer in 2 - 4 weeks. After installation and use, there is no need for a long - term natural weathering process, and it can directly play a protective role.
If a protective coating (such as a transparent anti - rust coating) is applied on the surface of Q355NHA, the formation and stabilization of the rust layer will be affected. The coating can isolate the steel from the external environment, slowing down the corrosion rate. If the coating is intact, the rust layer formation is very slow. Only when the coating is damaged and the steel is exposed to the environment will the rust layer start to form, and the stabilization time will depend on the local environment (refer to the natural weathering time above).
