This image taken from Raw to Ready: Komatsu demonstrates that if you make things out of pure iron, they’re going to be way too soft: swords will bend, train tracks will sag under their own weight. Zooming into over one million times magnification, it’s easy to see why iron has trouble holding its shape. Its atoms are naturally aligned in neat, organized rows and layers. When two forces push on different sides and cause the atoms to move by one another -- essentially skipping over from one to another – it’s how a metal deforms. This is where carbon in coal makes a big difference. Adding carbon to iron changes its crystal structure and its makes the valleys between atoms deeper, so that when one atom moves over to the next, it’s more energy for it to overcome.