There aren't enough details disclosed to offer any specific advice. The JIS G3114 standard consists of several different carbon steels that are all classified as "atmospheric corrosion resistant." The corrosive environment you are trying to protect against is not specified either. Depending on the specific environment, several means of corrosion protection may be applicable. Barrier coatings or metal alloying are used to protect against atmospheric corrosion. The three main coating types used are organic coatings, inorganic zinc-rich coatings, and metallic (for example, galvanized) coatings. The selection of the coating is a function of the expected severity of the environment, the corrosivity of the environment, the expected lifetime of the structure, and the possibility of re-coating as a maintenance activity. Applications in or near marine environments can be especially problematic. I would suggest that you talk to a coating supplier about your application to get specific recommendations.