We have studied on flattening structural and engineering metallic materials such as pure iron and stainless steels on an atomic scale by using electrochemical techniques in order to elongate the initial period of material life before generating corrosion products. We demonstrate a step-terrace structure on whole surface of large particle over 100 nm and the maximum wide region of the step-terrace structure was 400 nm, which included the widest terrace width larger than 15 nm by electrochemical reduction of air-formed oxidation film and then passivation. We found the flattening technique by the electrochemical methods was available for not only a sputter-deposit film of 304 stainless steel but also a bulk material of 430 stainless steel.