Iron, as a steel material with diverse properties achieved by adding carbon and other elements, is the most fundamental metallic material in manufacturing. Due to its excellent strength, toughness, workability, and cost performance, it is indispensable in all industrial sectors, including automobiles, construction, machinery, and infrastructure. Processing methods are also diverse, including casting where molten iron is poured into molds, forging where it is heated and hammered into shape, and rolling where it is extended by rollers, in addition to plastic working, cutting, welding, heat treatment, and surface treatment, which are widely used. By optimizing alloy components and heat treatment conditions, materials ranging from high-tensile steel to stainless steel and tool steel are developed and utilized according to required performance.