Why does ferritic steel corrode when left unprotected in the natural environment?

Ferritic steel corrodes when left unprotected in the natural environment primarily due to its high iron content and the absence of alloying elements that enhance corrosion resistance. In the presence of moisture and oxygen, ferritic steel undergoes oxidation, leading to the formation of rust. This process is accelerated in environments with contaminants such as salts or acids, which can break down protective oxide layers and promote further corrosion. Without protective coatings or treatments, the steel is vulnerable to environmental factors that lead to deterioration over time.