Corrosion resistance of S235 steel in different environments

S235 steel is a common low-alloy structural steel whose main components are carbon, manganese and trace elements and complies with European standard EN10025-2. Compared with other steel materials, S235JR has a lower strength grade (yield strength of 235MPa), good weldability and plasticity, but relatively weak corrosion resistance. The following is a detailed analysis of the corrosion resistance of S235 steel in different environments.

1. Atmospheric environment
In the atmospheric environment, the corrosion resistance of S235 steel is affected by many factors, especially the chloride content. In areas close to the ocean or other sources of chloride pollution, the corrosion effect of chloride on stainless steel is particularly significant. Water vapor and pollutants in the atmosphere can form a protective film on the surface of steel to slow down the corrosion process. However, in areas with high humidity or heavy pollution, the rate of corrosion may be accelerated.

2.Soil environment
The corrosion resistance of S235 steel in soil environments depends on the type and composition of the soil. According to experimental studies, the corrosion behavior of S235 steel in three typical soil environments is as follows:
a. Near neutral yellow brown soil
In this environment, S235 steel mainly undergoes uneven general corrosion and local pitting corrosion. The corrosion products are mainly composed of Fe2O3 and FeOOH, with a loose outer layer structure and a dense inner layer structure.
b.Alkaline saline-alkali soil
In alkaline saline-alkali soil, a structurally complete corrosion product layer is formed on the surface of S235 steel, which inhibits the oxygen consumption reaction of the cathode and results in the lowest corrosion rate.
c.Acidic red soil
The higher concentration of H+ in acidic red soil promotes the cathode hydrogen evolution reaction and the generation of cracks, resulting in the highest corrosion rate. In the later stage of corrosion, a dense Fe3O4 internal rust layer forms on the surface of S235 steel, so the corrosion rate when corroded for 15 days is greater than that when corroded for 30 days.

3. Water environment
a.Sea water environment
In seawater environment, the corrosion resistance of S235 steel is relatively weak. Salt and other impurities in seawater accelerate the corrosion process. In order to improve the corrosion resistance of S235 steel in seawater, surface treatment methods such as coating or galvanizing can be used.
b. Freshwater environment
In fresh water, S235 steel has relatively good corrosion resistance. However, prolonged exposure to water sources containing chloride ions (such as swimming pool water) may still cause corrosion.

4. Temperature and humidity environment
Temperature and humidity also have a significant impact on the corrosion resistance of S235 steel. High temperature and high humidity environments accelerate the corrosion process, especially in conditions containing corrosive media. Therefore, in environments with high temperatures and high humidity, S235 steel requires additional protective measures.

In summary, there are significant differences in the corrosion resistance of S235 steel in different environments. In the atmospheric environment, its corrosion resistance is affected by the chloride content; in the soil environment, its corrosion resistance depends on the soil type and composition; in the water environment, the seawater environment is unfavorable to its corrosion resistance, and the freshwater environment is relatively good; temperature and humidity will also have an impact on the corrosion resistance. In order to improve the corrosion resistance of S235 steel, surface treatment methods such as coating and galvanizing can be used, and additional protective measures can be taken in specific environments.

S235