Tin plate is a steel plate formed by electroplating tin coating on the surface of cold rolled sheet. Chrome-plated iron is treated with electrolytic chromic acid. In addition, there are coated irons for can-making in which the surface of chromium-plated iron is coated with resin films such as PET and PP. These products are not only used in container materials such as food cans and beverage cans, but are also widely used in electronic components and other fields.