Iron can be said to be the most valuable metallic element for mankind. In terms of availability and price, it is the most common metal compared to other metals. In Japan, during the Industrial Revolution, iron was once referred to as “king of industry”. Iron is the best metal element in many respects, as in everyday life, knives and other cutlery, as well as industrial machinery, are almost all made from iron, and iron is also heat-treated to increase its hardness.