iron
鉄 centers on the metal iron, a strong, hard material used for tools and construction.
鉄 is the modern simplified form of 鐵. The older form combines 金 (metal) with a phonetic component that contributed the sound. The modern 失 shape is a simplification and should not be treated as the original historical component.
The left side 金 means metal, and the right side 失 looks like a person losing something. Imagine losing a piece of iron metal: 鉄 is iron.
For テツ, picture a heavy iron weight that makes a loud 'tets' sound when it drops: tets -> テツ, and the iron clangs on the floor.
iron (Fe)
railroad; railway; rail transport
subway; metro; underground (railway)
iron plate; steel plate
steel
electric railway
national railway
gun; firearm
iron and steel
steel frame; steel beam; steel girder
rebar; (iron) reinforcing bar; reinforcing steel
private railway
iron manufacture
made of iron
iron rod; iron bar; iron club
ironworking; ironworker
railway bridge; iron bridge
iron ore
municipal subway
ironworks; steelworks
pig iron
non-ferrous metal