Alloyed steels, steel combined with other elements to increase their hardness and strength, are the hardest known metals. Maraging steel, a heat-treated steel, is one of the strongest steel alloys.
All steel is a combination of iron and carbon, making it an alloy, which is any metal made of two or more elements heated together. All steels are an alloy but not all steel is alloy steel. Alloy steel requires iron, carbon and an additional third element to be called alloy steel. As well as increasing hardness, the process of alloying steel can increase its strength, toughness, resistance to corrosion and wear, hardness, and hot hardness.