420F stainless steel offers good corrosion resistance in mildly corrosive environments such as fresh water, atmospheric conditions, and mild chemicals. Its high chromium content (12-14%) provides a protective oxide layer on the surface of the material, preventing rust and corrosion.

However, 420F steel may not be suitable for use in highly corrosive environments, such as those containing acids or salt water, as it may experience pitting corrosion. Additionally, its high sulfur content may result in lower resistance to certain types of corrosion, such as intergranular corrosion. 

Overall, the corrosion resistance of 420F steel is suitable for many common applications, but it is important to consider the specific environment in which the material will be used to ensure it is appropriate for the intended purpose.