Sword construction and metallurgy are complex and involved. There were undoubtedly a multitude of methods and techniques to the craft over the centuries. The final purpose of each was to create a strong, light blade capable of holding a good edge. The quality of steel in Medieval swords could vary from weapon to weapon. It depended a great deal on its heat treatment.
Steel is iron with a higher carbon content and is much stronger.
Steel was made from selected iron ore by repeating heating in a hot charcoal fire. The raw metal was worked by hammer into a bar. A sword might be constructed from several separate pieces of iron and steel, each carefully hammered on. Separate bars were also sometimes then added for edges. This made the steel hard but also brittle.