Iron vs Steel: What's the Real Difference?

Drop a cast iron pan and it might crack in two. Drop a steel knife and it just bounces. Yet both are more than ninety percent iron. The difference is a tiny pinch of one ingredient, just a few grams in a kilogram bar, and that pinch changed the world. In this video we zoom inside the metal to see how carbon atoms jam iron's sliding rows, why too much carbon makes cast iron brittle, and how a blast furnace turns rusty rock into metal. Plus Tutankhamun's dagger from space, Bessemer's trick that made steel cheap, why the Eiffel Tower isn't steel, how blacksmiths and Japanese swordsmiths control hardness with water and clay, and the invisible shield that keeps stainless steel from rusting. 0:00 Same metal, different behavior 0:46 Inside pure iron 1:13 Carbon: the secret ingredient 1:43 Cast iron and the sweet spot 2:22 Iron from the sky 2:48 The Iron Age 3:31 Rock to metal: the blast furnace 4:10 Bessemer makes steel cheap 4:47 The Eiffel Tower isn't steel 5:17 Quenching and tempering 6:10 The secret of the katana 6:58 Why stainless steel doesn't rust 7:38 Harry Brearley and the Statue of Liberty 8:05 Try this at home Sources: Britannica on steel, cast iron, wrought iron, the blast furnace, the Bessemer process, tempering, the Iron Age and the Japanese sword; Comelli et al., Meteoritics & Planetary Science (2016) on Tutankhamun's meteoritic iron dagger; Société d'Exploitation de la Tour Eiffel; worldsteel "World Steel in Figures"; British Stainless Steel Association on chromium oxide passivation, Harry Brearley (1913) and magnetic properties of stainless steel; US National Park Service on the Statue of Liberty restoration (1984–86); Steel Recycling Institute. Nuts & Whys explains the hidden reasons behind everyday things, with animations that show you how they really work. Subscribe for a new explainer every week. #steel #howthingswork #engineering