Answer:
Steel is mostly iron, but has between 0.25% and 2% carbon. Other metals can be added to steel to give it particular properties:
Chromium - improves durability and prevents rust (stainless steel).
Nickel - increases durability and resistance to heat and acids.
Manganese - increases strength and resistance to wear.
Molybdenum - increases strength and resistance to heat.
Tungsten - retains hardness at high temperatures.
Vanadium - increases strength and springiness.