Steel is one of the most important materials in the modern world: a strong, durable metal made by combining iron with small amounts of carbon. Steel is much harder and tougher than pure iron, which makes it perfect for building everything from skyscrapers and bridges to cars, ships, and surgical tools.

The process of making steel involves heating iron to extremely high temperatures (over 2,500 degrees Fahrenheit) and carefully controlling how much carbon gets mixed in. Too little carbon and you just have iron; too much and the metal becomes brittle like cast iron. Getting the balance right creates steel's signature strength and flexibility.

Steel transformed civilization when people figured out how to make it efficiently in the 1850s. Suddenly, engineers could build taller buildings, longer bridges, and faster railroads. The steel frame of the Empire State Building, completed in 1931, still stands strong today. Modern steel comes in many varieties: stainless steel resists rust, tool steel stays sharp for cutting, and structural steel holds up buildings.

The word also describes a quality of toughness and determination. When someone has nerves of steel, they stay calm under pressure. To steel yourself means to gather your courage and prepare mentally for something difficult, like steeling yourself before a challenging presentation.