Durability gets treated like a single number, as if you could just look at a spec sheet and know how long a part will last. In practice, it's a combination of factors: carbon content, heat treatment, surface finish, and how the part is actually used. Carbon steel happens to give engineers a lot of control over all four, which is a big reason it's stayed the default material for so many mechanical parts. Carbon as a hardness dial The basic relationship is simple enough: more carbon generally means more hardness and wear resistance, up to a point. A high carbon steel sheet resists scratching, denting, and abrasion far better than mild steel, which is exactly why it ends up in tools, blades, and load-bearing components that see constant friction. The tradeoff is ductility — push carbon content too high without proper heat treatment and you get a part that's hard but prone to cracking under shock loads. This is where annealed carbon steel comes into the picture. Annealin...