How does adding carbon to iron change its physical properties?

Adding carbon to iron significantly alters its physical properties, primarily increasing its hardness and strength. Pure iron is soft and not very useful for engineering purposes. However, when small amounts of carbon are added, it forms steel, a much stronger material. The carbon can exist in solid solution within the iron's crystal structure or as iron carbide (cementite). The amount of carbon directly influences the resulting properties; for instance, steel with 0.77 percent carbon transforms into a microstructure called pearlite, which is considerably harder than pure iron. This versatility in properties, achieved by varying carbon content, makes iron-carbon alloys, like steel, essential in engineering.123