iron
鐡 centers on the metal iron, often used for its strength and durability.
鐡 is a variant form of 鐵 (iron). The left side 金 indicates metal, while the right side is a complex phonetic component that historically contributed the sound. The exact development of the right side is uncertain.
The left side 金 (metal) tells you this is a metal. The right side looks like a heavy, sturdy structure, like a piece of iron equipment.
For テツ, imagine a heavy iron anvil that makes a sharp 'tets' sound when struck: tets -> テツ.